worldgen: sober palettes and connected industrial galleries for alpha21

README.md

@@ -15,11 +15,26 @@ infrastructures qui permettront progressivement d'ouvrir de nouveaux continents.
 Ce dépôt démarre la nouvelle base Fabric. La [vision complète](docs/vision.md)
 conserve les intentions ; le [backlog](docs/backlog.md) suit les
 tickets. Les systèmes d’économie, de progression collective et les dimensions
-décrits dans la vision ne sont pas encore implémentés. **L’alpha.20 est publiée** : elle reprend
+décrits dans la vision ne sont pas encore implémentés. **L’alpha.21 est construite et
-l’architecture des bâtiments, leurs palettes, les blocs sculptés et les raccords
+vérifiée** : palettes sobres, couvertures portées, petits quartiers reliés et
-des vitres. Les villes, infrastructures et réseaux gardent leurs implantations.
+premières galeries industrielles. Voir [le catalogue alpha.21](docs/architecture-alpha21.md),
-Voir le [catalogue illustré](docs/architecture-alpha20.md) et l’état du canal
+[les essais alpha.21](docs/testing-alpha21.md)
-packwiz dans [Distribution](docs/packwiz.md).
+et l’état du canal packwiz dans [Distribution](docs/packwiz.md).
+
+## Alpha.21 — matériaux, quartiers et traversées
+
+La ville revient à la pierre lisse, pierre, briques de pierre, andésite et chêne.
+Le tuf accompagne surtout les chemins et les sous-sols. Les toits et ornements
+sont raccordés à leurs appuis ; les pièces gardent leurs aménagements. La ville
+recherche des petits quartiers séparés par du terrain naturel, avec des chemins
+vers le cœur. Les lieux patrimoniaux recherchent davantage de raccords.
+
+L’option expérimentale ajoute une recherche de galeries industrielles : chaussée
+cinq blocs, deux trottoirs, salles et escaliers de surface. Les placements sur
+pente sont assouplis et les destinations isolées sont prioritaires pour les chemins.
+Créer un **nouveau monde Sanctuary** pour ce générateur21. Les anciens mondes
+conservent leur génération. Les vérifications et coordonnées du
+témoin sont consignées dans [les essais](docs/testing-alpha21.md).
 
 ## Alpha.20 — identité des bâtiments
 
@@ -443,7 +458,7 @@ sera une mise à jour explicite, avec vérification des API et des sauvegardes.
 | Fabric API | 0.160.0+26.3 |
 | Fabric Loom | 1.17.20 |
 | Gradle Wrapper | 9.5.1, distribution vérifiée par SHA-256 |
-| Sanctuary / pack | 0.1.0-alpha.19 |
+| Sanctuary / pack | 0.1.0-alpha.21 |
 
 Java 25 et Python 3.11 ou plus récent sont nécessaires. Le script pack utilise
 uniquement la bibliothèque standard et repère aussi une installation Python
@@ -472,7 +487,7 @@ décrits dans [Validation](docs/testing.md).
 
 Résultats :
 
-- `mods/sanctuary/build/libs/sanctuary-0.1.0-alpha.19.jar` : mod à installer avec
+- `mods/sanctuary/build/libs/sanctuary-0.1.0-alpha.21.jar` : mod à installer avec
   Fabric API sur la version Minecraft indiquée.
 - `build/packwiz/` : pack de développement complet, avec le mod construit et
   l'index vérifié. Voir [Installation packwiz](packwiz/README.md).

docs/architecture-alpha21.md

@@ -0,0 +1,24 @@
+# Alpha.21 — palettes et couvertures
+
+La ville revient à une base commune : pierre lisse, pierre, briques de pierre,
+andésite et chêne. Les façades, seuils, corniches et verrières gardent leurs
+formes ; les pièces conservent leurs fonctions et leur circulation. La serre
+emploie le bouleau comme bois propre. Le tuf accompagne les routes et les
+parties souterraines.
+
+![Modèles des bâtiments alpha.21](images/architecture-alpha21-overview.png)
+
+Ces vues sont calculées depuis les blocs produits par les renderers21 et les
+modèles/textures de Minecraft 26.3-pre-2. Elles montrent des variantes choisies,
+sans terrain, éclairage ni végétation de la partie. Ce ne sont pas des captures
+du client et elles ne prouvent pas les raccords avec le relief.
+
+Les couvertures de l’atelier, du dépôt, de la serre, du relais radio et du refuge
+reposent sur des murs ou charpentes. L’ancien plafond opaque sous leur nouvelle
+couverture est retiré. Les vérifications contrôlent aussi les petits appuis des
+excavations, piscines, rampes de garage et ornements.
+
+![Coupe des couvertures](images/architecture-alpha21-roofs.png)
+
+La seconde planche coupe volontairement les murs pour voir les dessous des toits.
+Les détails de validation et la graine d’essai sont dans [le protocole](testing-alpha21.md).

docs/backlog.md

@@ -779,6 +779,38 @@ en briques de pierre. Ajouter des blocs sculptés et du relief architectural.
 **État : livré en alpha.20 ; code, artefacts et même instance Prism vérifiés.** Voir
 [le contrat et les essais alpha.20](testing-alpha20.md).
 
+### WG-24 — Palettes sobres, toits portés et galeries — alpha.21
+
+**Branche :** `codex/palettes-reseaux-alpha21`.
+
+Reprendre les extérieurs sans changer les plans intérieurs approuvés : smooth
+stone, stone brick, stone, andésite et chêne dominants en ville ; un bois cohérent
+par bâtiment unique et tuf surtout au sol et sous terre. Corriger les toits
+suspendus et les anciens plafonds superposés, avec appuis vérifiables.
+
+Étendre la ville par au plus deux petits quartiers séparés de terrain naturel,
+reliés par des chemins praticables ; rapprocher les destinations patrimoniales
+par un graphe de chemins. Ajouter des galeries industrielles abandonnées :
+chaussée de cinq blocs, deux trottoirs, quelques grandes salles et deux accès
+par escaliers depuis la surface, en respectant les eaux et structures existantes.
+
+Ajouter des fronts rocheux et de petits filons intacts dans les galeries et
+leurs salles de maintenance : ressources vanilla réellement minables, sans
+régénération de butin ni remplacement des blocs déjà extraits. Fournir un MRpack
+pour l’essai séparé demandé.
+
+Assouplir les refus de placement : admettre les pentes, des volumes partiellement
+enfouis et des appuis adaptés ; rechercher des détours et prioriser les lieux
+isolés pour les chemins. Garder une ville fragmentée sans socle géant.
+
+Nouvelle génération21 réservée aux nouveaux mondes ; tous les codecs et rendus
+20 et antérieurs restent disponibles. Tailles512/724/1024, Moyen par défaut ;
+option expérimentale enregistrée. Aucun monde personnel modifié. Vérifier les
+pièces natives, accès, connexions, supports, création/réouverture, ancien monde20,
+puis livrer le pack stable21 et synchroniser la même instance Prism.
+
+**État : implémenté et vérifié ; MRpack fourni, publication et synchronisation en cours.**
+
 ## Réserve de thèmes futurs
 
 Ces thèmes servent à retrouver la vision, pas à demander leur implémentation immédiate. On en extrait un ticket seulement lorsqu'il devient utile au prochain incrément jouable.

docs/testing-alpha21.md

@@ -0,0 +1,138 @@
+# Alpha.21 — contrat et vérification
+
+Ticket WG-24, branche `codex/palettes-reseaux-alpha21`.
+Minecraft 26.3-pre-2, Fabric Loader 0.19.5, Fabric API 0.160.0+26.3,
+Java 25. Les dépendances restent celles de l’alpha.20.
+
+## Résultat recherché
+
+La ville reprend une palette de pierre lisse, pierre, briques de pierre,
+andésite et chêne. Les plans intérieurs sont conservés ; les corrections
+portent sur les matériaux, les appuis et les couvertures. Chaque infrastructure
+emploie un bois cohérent. Le tuf reste surtout au sol et dans les sous-sols.
+
+La ville peut accueillir deux petits quartiers supplémentaires reliés à son
+cœur, avec du terrain naturel entre eux. La réserve centrale existante n’est
+pas agrandie. Les infrastructures reçoivent davantage de chemins entre des
+entrées réelles. Les recherches respectent des budgets de colonnes et refusent
+un quartier si sa liaison entière ne peut pas être construite.
+
+Les galeries industrielles expérimentales ont cinq blocs de chaussée et un
+trottoir de chaque côté, des salles de maintenance et deux accès par escaliers.
+Le plan est recherché après les structures précédentes et évite leurs volumes,
+l’hydrologie. Un tablier continu peut franchir une cavité entre ses appuis ;
+les travées sans appuis complets sont limitées à 34 blocs, avec des piliers
+locaux d’au plus 16 blocs et deux couches de roche intacte sous les appuis. Chaque tronçon a une pièce native
+locale ; aucun démarrage de structure ne charge toute l’île.
+
+## Sauvegardes et comparaison
+
+Créer un **nouveau monde Sanctuary**, taille **Moyen**, graine **0**, avec
+**Structures expérimentales** activées. Petit 512, Moyen 724 et Grand 1024 restent
+les tailles proposées par le bouton natif **Personnaliser**.
+
+Le nouveau codec est `sanctuary:island_v21`. Les codecs et pièces 20 et
+antérieurs restent disponibles, sans modifier leurs rendus. Le journal 21
+réutilise le schéma de persistance existant avec une génération distincte ;
+les ouvertures entre versions incompatibles sont refusées. Aucune conversion
+ni rénovation automatique des mondes précédents n’est effectuée.
+
+Pour comparer sans les infrastructures, créer un autre monde avec l’option
+expérimentale désactivée. Une sauvegarde 21 nécessite le binaire 21 ou un futur
+binaire compatible ; elle ne se rétrograde pas en remplaçant simplement le JAR.
+
+## Compatibilité vérifiée
+
+373 fichiers de production historiques sont identiques au commit de publication
+20 (`0edac29`). Le preset caché `sanctuary_v20` est une copie exacte de son
+ancien preset public. Création et réouverture natives de la génération 20 donnent
+les mêmes plans, structures, appuis, accès et coffres que les rapports publiés.
+La comparaison ignore seulement l’identifiant du processus, le chemin du monde
+et deux nouveaux compteurs de détail ajoutés à l’oracle de connexion des tests.
+
+## Galeries vérifiées dans Minecraft
+
+Moyen, graine 0 : 23 modules dont deux accès et une salle, sur un axe de 340 blocs.
+Les entrées sont `-135 253 -178` et `-135 249 162` ; chaussée à Y 216. La portée
+sans appuis complets la plus longue du témoin est 17 blocs. Le plan emploie
+8 686 colonnes de bruit, avec un budget maximal de 12 000 ; cette recherche prend
+environ 11 secondes sur la machine de développement, hors reste du monde.
+
+La création et la réouverture dans deux JVM distinctes passent : 34 chunks
+FULL, 57 635 blocs vérifiés, mêmes pièces natives, mêmes coffres différés et
+modification témoin conservée. L’oracle de collision de Minecraft vérifie un
+corps de 0,6×1,8 bloc, 74 cibles et 520 pas entre les deux portiques ; il utilise
+les vrais escaliers et les demi-marches des trottoirs.
+
+Une alcôve d’excavation inachevée ouvre le parement de la salle sur une paroi
+irrégulière de tuf, pierre et deepslate. Certains tronçons exposent de petits
+filons ordinaires. Le témoin contient cinq minerais de charbon, dix-neuf de
+fer, cinq de redstone, un de diamant et un d’émeraude ajoutés dans ces fronts.
+Cuivre, or et lapis font aussi partie des variantes possibles. Ce sont des
+blocs finis, sans mécanisme de réapparition après minage. Ces quantités excluent
+les minerais naturels de l’île et ne constituent pas une garantie par graine.
+
+## Autres vérifications
+
+La création et la réouverture natives de la ville passent. Le témoin possède
+un cœur et deux quartiers reliés, 65 pièces de rue, trois immeubles de logements,
+un hôtel, une bibliothèque, un jardin et une place. La réserve centrale n’est
+pas étendue. Les deux nouveaux chemins sont longs de 51 et 38 cellules. Une
+expansion de test distincte est également vérifiée ; aucune expansion personnelle
+n’est activée.
+
+La piscine couverte, le garage, la salle d’expansion, leurs accès et les égouts
+restent présents. Les contrôles natifs vérifient les bassins et sorties après
+exécution observée de la simulation des fluides.
+
+Les quatorze types de lieux patrimoniaux apparaissent sur Moyen, graine 0,
+avec douze liaisons et 127 segments. Leur création native passe : 141 pièces,
+91 271 blocs, 140 chunks FULL et quatorze coffres différés. Les trois réseaux
+oubliés sont également parcourus. Les chemins rejoignent deux entrées de ville.
+L’observatoire et le quai du vide restent isolés sur ce témoin : leurs chemins
+n’ont pas trouvé de tracé admissible dans le budget. La commande `/sanctuary structures` indique leurs entrées ; aucun raccord
+construit complet n’est revendiqué.
+
+Les smokes des renderers, plans, pièces enregistrées et raccords passent.
+La réouverture des lieux patrimoniaux conserve également le plan, les pièces,
+les coffres et la modification témoin. L’option expérimentale désactivée passe :
+elle ne publie aucun module de galerie. `check build assemblePack` passe, avec les huit GameTests généraux. Le
+MRpack, son index et le JAR embarqué sont vérifiés ; la publication et la
+synchronisation restent à consigner.
+
+Les chemins de quartier regroupent leurs pentes à l’intérieur de rectangles ;
+leurs frontières et raccords sont des paliers plats. Les structures restent
+conditionnées par le terrain admissible, dans un budget borné. La traversée
+industrielle ne relie pas encore tous les réseaux souterrains historiques.
+
+Les vues de modèles éventuelles ne remplacent pas une inspection dans le client.
+Aucune validation Windows native ni charge multijoueur n’est revendiquée.
+
+
+## Reproduire les contrôles
+
+Depuis ce dépôt, avec Java 25, les mondes de test restent sous `mods/sanctuary/build/`.
+Pour chaque scénario, exécuter la création puis sa réouverture avant tout autre
+scénario qui nettoie ce monde de développement :
+
+```sh
+./gradlew :sanctuary:runGameTest -PsanctuaryTransit21Tests=true -PsanctuaryResourceSurvey=off -PsanctuaryDensityMaps=false --max-workers=1
+./gradlew :sanctuary:runGameTest -PsanctuaryTransit21Tests=true -PsanctuaryExpansionReload=true -PsanctuaryResourceSurvey=off -PsanctuaryDensityMaps=false --max-workers=1
+```
+
+Remplacer `sanctuaryTransit21Tests` par `sanctuaryLostCity21Tests` pour la ville
+ou `sanctuaryHeritage21Tests` pour les infrastructures. Le cas OFF ajoute
+`-PsanctuaryExperimentalStructures=false` à une création du scénario transit.
+Les rapports de cette livraison sont conservés localement dans
+`build/alpha21-evidence/`. `./gradlew check build assemblePack` constitue la
+vérification complète avant export.
+
+## Artefacts vérifiés
+
+MRpack : `Sanctuary-0.1.0-alpha.21.mrpack`. Son JAR est identique au JAR du build.
+Les versions et hashes de l’index packwiz sont contrôlés, ainsi que le ZIP
+d’amorçage Prism. SHA-256 du JAR :
+
+```text
+e528e42d99f9e1ea221f780ea089b49b42a1a4e9e24e4ddd001d045183202c21
+```

gradle.properties

@@ -8,6 +8,6 @@ loader_version=0.19.5
 loom_version=1.17.20
 fabric_api_version=0.160.0+26.3
 
-mod_version=0.1.0-alpha.20
+mod_version=0.1.0-alpha.21
-pack_version=0.1.0-alpha.20
+pack_version=0.1.0-alpha.21
 maven_group=fr.koka.sanctuary

mods/sanctuary/build.gradle

@@ -40,7 +40,10 @@ tasks.named('runGameTest') {
     systemProperty('sanctuary.test.unified', providers.gradleProperty('sanctuaryUnifiedTests').getOrElse('true'))
     systemProperty('sanctuary.test.diameter', providers.gradleProperty('sanctuaryTestDiameter').getOrElse('724'))
     systemProperty('sanctuary.test.generation', providers.gradleProperty('sanctuaryTestGeneration').getOrElse(
-        providers.gradleProperty('sanctuaryLostCityTests').map { it.toBoolean() }.getOrElse(false) ? '14' : providers.gradleProperty('sanctuaryLostCity15Tests').map { it.toBoolean() }.getOrElse(false) ? '15' : providers.gradleProperty('sanctuaryLostCity16Tests').map { it.toBoolean() }.getOrElse(false) ? '16' : providers.gradleProperty('sanctuaryRuins17Tests').map { it.toBoolean() }.getOrElse(false) ? '17' : providers.gradleProperty('sanctuaryHeritage19Tests').map { it.toBoolean() }.getOrElse(false) ? '19' : '20'))
+        providers.gradleProperty('sanctuaryLostCityTests').map { it.toBoolean() }.getOrElse(false) ? '14' : providers.gradleProperty('sanctuaryLostCity15Tests').map { it.toBoolean() }.getOrElse(false) ? '15' : providers.gradleProperty('sanctuaryLostCity16Tests').map { it.toBoolean() }.getOrElse(false) ? '16' : providers.gradleProperty('sanctuaryRuins17Tests').map { it.toBoolean() }.getOrElse(false) ? '17' : providers.gradleProperty('sanctuaryHeritage19Tests').map { it.toBoolean() }.getOrElse(false) ? '19' : (providers.gradleProperty('sanctuaryHeritage20Tests').map { it.toBoolean() }.getOrElse(false) || providers.gradleProperty('sanctuaryLostCity20Tests').map { it.toBoolean() }.getOrElse(false)) ? '20' : '21'))
+    systemProperty('sanctuary.test.heritage21', providers.gradleProperty('sanctuaryHeritage21Tests').getOrElse('false'))
+    systemProperty('sanctuary.test.lostCity21', providers.gradleProperty('sanctuaryLostCity21Tests').getOrElse('false'))
+    systemProperty('sanctuary.test.transit21', providers.gradleProperty('sanctuaryTransit21Tests').getOrElse('false'))
     systemProperty('sanctuary.test.expansion', providers.gradleProperty('sanctuaryExpansionTests').getOrElse('false'))
     systemProperty('sanctuary.test.expansionReload', providers.gradleProperty('sanctuaryExpansionReload').getOrElse('false'))
     systemProperty('sanctuary.test.lostCity', providers.gradleProperty('sanctuaryLostCityTests').getOrElse('false'))
@@ -76,12 +79,18 @@ tasks.named('processGametestResources') {
     inputs.property('lostCity20', lostCity20)
     def heritage20 = providers.gradleProperty('sanctuaryHeritage20Tests').map { it.toBoolean() }.getOrElse(false)
     inputs.property('heritage20', heritage20)
+    def heritage21 = providers.gradleProperty('sanctuaryHeritage21Tests').map { it.toBoolean() }.getOrElse(false)
+    inputs.property('heritage21', heritage21)
+    def lostCity21 = providers.gradleProperty('sanctuaryLostCity21Tests').map { it.toBoolean() }.getOrElse(false)
+    inputs.property('lostCity21', lostCity21)
+    def transit21 = providers.gradleProperty('sanctuaryTransit21Tests').map { it.toBoolean() }.getOrElse(false)
+    inputs.property('transit21', transit21)
     def heritage19 = providers.gradleProperty('sanctuaryHeritage19Tests').map { it.toBoolean() }.getOrElse(false)
     inputs.property('heritage19', heritage19)
     def voidReuse = providers.gradleProperty('sanctuaryVoidReuseTests').map { it.toBoolean() }.getOrElse(false)
     inputs.property('voidReuse', voidReuse)
     filesMatching('fabric.mod.json') {
-        expand(gametest_entrypoint: lostCity20 ? 'fr.koka.sanctuary.gametest.LostCity20WorldGameTests' : heritage20 ? 'fr.koka.sanctuary.gametest.Heritage20WorldGameTests' : heritage19 ? 'fr.koka.sanctuary.gametest.Heritage19WorldGameTests' : ruins17 ? 'fr.koka.sanctuary.gametest.Ruins17WorldGameTests' : voidReuse ? 'fr.koka.sanctuary.gametest.ExpansionVoidReuseGameTests' : lostCity16 ? 'fr.koka.sanctuary.gametest.LostCity16WorldGameTests' : lostCity15 ? 'fr.koka.sanctuary.gametest.LostCity15WorldGameTests' : lostCity ? 'fr.koka.sanctuary.gametest.LostCityWorldGameTests' : expansion ? 'fr.koka.sanctuary.gametest.ExpansionWorldGameTests' : benchmark
+        expand(gametest_entrypoint: transit21 ? 'fr.koka.sanctuary.gametest.Transit21WorldGameTests' : lostCity21 ? 'fr.koka.sanctuary.gametest.LostCity21WorldGameTests' : heritage21 ? 'fr.koka.sanctuary.gametest.Heritage21WorldGameTests' : lostCity20 ? 'fr.koka.sanctuary.gametest.LostCity20WorldGameTests' : heritage20 ? 'fr.koka.sanctuary.gametest.Heritage20WorldGameTests' : heritage19 ? 'fr.koka.sanctuary.gametest.Heritage19WorldGameTests' : ruins17 ? 'fr.koka.sanctuary.gametest.Ruins17WorldGameTests' : voidReuse ? 'fr.koka.sanctuary.gametest.ExpansionVoidReuseGameTests' : lostCity16 ? 'fr.koka.sanctuary.gametest.LostCity16WorldGameTests' : lostCity15 ? 'fr.koka.sanctuary.gametest.LostCity15WorldGameTests' : lostCity ? 'fr.koka.sanctuary.gametest.LostCityWorldGameTests' : expansion ? 'fr.koka.sanctuary.gametest.ExpansionWorldGameTests' : benchmark
             ? 'fr.koka.sanctuary.gametest.WorldgenPerformanceGameTests'
             : unified ? 'fr.koka.sanctuary.gametest.UnifiedWorldGameTests'
             : 'fr.koka.sanctuary.gametest.SanctuaryWorldGameTests')
@@ -468,3 +477,34 @@ tasks.named('lostCitySurface20Smoke') {
     if (providers.gradleProperty('sanctuaryArchitecturePreview').isPresent())
         systemProperty('sanctuary.city20.exteriorPreview', rootProject.layout.buildDirectory.file('alpha20-preview/exterior.json').get().asFile.absolutePath)
 }
+
+// Generation21 keeps published20 renderers immutable.
+[
+    heritage21RendererSmoke: 'heritage.HeritageRenderer21Smoke',
+    heritage21PieceSmoke: 'heritage.HeritagePiece21Smoke',
+    heritage21PlannerSmoke: 'heritage.HeritagePlanner21Smoke',
+    lostCity21PlannerSmoke: 'city.LostCityPlanner21Smoke',
+    lostCitySurface21Smoke: 'city.LostCitySurface21Smoke',
+    lostCityInteriors21Smoke: 'city.LostCityInteriors21Smoke',
+    transit21Smoke: 'transit.Transit21Smoke'
+].each { name, harness ->
+    def smoke = tasks.register(name, JavaExec) {
+        group = 'verification'
+        dependsOn('testClasses')
+        classpath = sourceSets.test.runtimeClasspath
+        mainClass = "fr.koka.sanctuary.worldgen.${harness}"
+    }
+    tasks.named('check') { dependsOn(smoke) }
+}
+tasks.named('heritage21RendererSmoke') {
+    if (providers.gradleProperty('sanctuaryArchitecturePreview').isPresent())
+        systemProperty('sanctuary.test.heritage21.export', rootProject.layout.buildDirectory.dir('alpha21-preview/heritage').get().asFile.absolutePath)
+}
+tasks.named('lostCityInteriors21Smoke') {
+    if (providers.gradleProperty('sanctuaryArchitecturePreview').isPresent())
+        systemProperty('sanctuary.city21.preview', rootProject.layout.buildDirectory.file('alpha21-preview/city.json').get().asFile.absolutePath)
+}
+tasks.named('lostCitySurface21Smoke') {
+    if (providers.gradleProperty('sanctuaryArchitecturePreview').isPresent())
+        systemProperty('sanctuary.city21.exteriorPreview', rootProject.layout.buildDirectory.file('alpha21-preview/exterior.json').get().asFile.absolutePath)
+}

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Heritage21WorldGameTests.java

@@ -0,0 +1,554 @@
+package fr.koka.sanctuary.gametest;
+
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import fr.koka.sanctuary.worldgen.heritage.HeritagePiece21;
+import fr.koka.sanctuary.worldgen.heritage.HeritagePlan19;
+import fr.koka.sanctuary.worldgen.heritage.HeritageRenderer21;
+import fr.koka.sanctuary.worldgen.heritage.HeritageStructures19;
+import fr.koka.sanctuary.worldgen.ruins.RuinsPiece20;
+import fr.koka.sanctuary.worldgen.ruins.RuinsPlan17;
+import fr.koka.sanctuary.worldgen.ruins.RuinsRenderer20;
+import fr.koka.sanctuary.worldgen.ruins.RuinsStructures17;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.HexFormat;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Predicate;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.core.HolderSet;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.item.Item;
+import net.minecraft.world.item.Items;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.DoorBlock;
+import net.minecraft.world.level.block.TrapDoorBlock;
+import net.minecraft.world.level.block.entity.RandomizableContainerBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.levelgen.structure.StructureStart;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceSerializationContext;
+import net.minecraft.world.level.storage.LevelResource;
+import net.minecraft.world.level.storage.loot.LootParams;
+import net.minecraft.world.level.storage.loot.LootTable;
+import net.minecraft.world.level.storage.loot.parameters.LootContextParams;
+import net.minecraft.world.level.storage.loot.parameters.LootContextParamSets;
+import net.minecraft.world.phys.AABB;
+import net.minecraft.world.phys.Vec3;
+
+/** Native creation/reload proof confined to a disposable generation21 starter island. */
+public final class Heritage21WorldGameTests {
+    private static final Direction[] HORIZONTAL = {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST};
+    @GameTest(maxTicks = 12000)
+    public void heritagePersistsWithRealDestinations(GameTestHelper helper) {
+        helper.assertTrue(helper.getLevel().getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator,
+            "The heritage proof requires a Sanctuary generator");
+        var generator = (SanctuaryChunkGenerator) helper.getLevel().getChunkSource().getGenerator();
+        helper.assertTrue(generator.rootGeneration() == 21, "Use a fresh generation21 test world; do not convert an old save");
+        new Scenario(helper, generator, Boolean.getBoolean("sanctuary.test.expansionReload")).advance();
+    }
+    private static final class Scenario {
+        final GameTestHelper helper;
+        final ServerLevel level;
+        final SanctuaryChunkGenerator generator;
+        final HeritagePlan19 plan;
+        final boolean reload;
+        final Map<String, Object> report = new LinkedHashMap<>();
+        final List<ChunkPos> chunks = new ArrayList<>();
+        final List<StructureStart> starts = new ArrayList<>();
+        final List<StructureStart> ruinsStarts = new ArrayList<>();
+        JsonObject previous;
+        BlockPos gold;
+        int nextChunk;
+        boolean prepared;
+        Scenario(GameTestHelper helper, SanctuaryChunkGenerator generator, boolean reload) {
+            this.helper = helper; this.level = helper.getLevel(); this.generator = generator; this.reload = reload;
+            this.plan = generator.heritagePlan19();
+            report.put("seed", level.getSeed()); report.put("size", generator.initialDiameter());
+            report.put("process_id", ProcessHandle.current().pid()); report.put("world_directory", world(level).toString());
+            report.put("experimental_structures", generator.experimentalStructures());
+            report.put("structures_enabled", level.structureManager().shouldGenerateStructures());
+            report.put("scope", "Native local starts, saved sites and routes, player-sized entrances, supports and unopened chests on the starter island. "
+                + "All14 tool tables are sampled separately without consuming a saved chest. Door states are restored after traversal. "
+                + "No personal save or expansion is opened; one disposable outer-wall edit is checked in a second JVM. "
+                + "Missing rails are intentional; this proof checks walking and saved rail shapes, not an uninterrupted minecart journey.");
+        }
+        void advance() {
+            try {
+                if (!prepared) { report.put("stage", "prepare"); prepare(); prepared = true; if (plan.isEmpty()) { finishDisabled(); return; } }
+                if (nextChunk < chunks.size()) {
+                    report.put("stage", "load_full_chunks"); var pos = chunks.get(nextChunk++);
+                    helper.assertTrue(level.getChunk(pos.x(), pos.z(), ChunkStatus.FULL, true) instanceof LevelChunk,
+                        "Heritage footprint must reach native FULL: " + pos);
+                    if (nextChunk % 20 == 0) SanctuaryMod.LOGGER.info("Heritage21 loaded {}/{} footprint chunks", nextChunk, chunks.size());
+                    helper.runAtTickTime(helper.getTick() + 1, this::advance); return;
+                }
+                report.put("stage", "verify_native_geometry"); verifyPlaced(); report.put("passed", true);
+                if (!reload) {
+                    helper.assertTrue(gold != null && level.getBlockState(gold).isCollisionShapeFullBlock(level, gold), "Gold witness must replace a solid wall away from circulation");
+                    level.setBlock(gold, Blocks.GOLD_BLOCK.defaultBlockState(), 3); report.put("gold_witness", coords(gold));
+                    helper.assertTrue(level.getServer().saveEverything(true, true, true), "Flush native starts, unopened loot and the wall edit");
+                    report.put("world_flushed_before_shutdown", true);
+                } else {
+                    helper.assertTrue(level.getBlockState(gold).is(Blocks.GOLD_BLOCK), "Reload replaced the player's wall edit");
+                    report.put("gold_witness", coords(gold)); report.put("gold_witness_preserved", true);
+                }
+                write(level, report, reload); helper.succeed();
+            } catch (Exception failure) {
+                report.put("passed", false); report.put("failure", failure.toString());
+                try { write(level, report, reload); } catch (IOException ignored) { }
+                throw new IllegalStateException("Heritage21 native " + (reload ? "reload" : "creation") + " failed", failure);
+            }
+        }
+        void prepare() throws IOException {
+            var ops = RegistryOps.create(JsonOps.INSTANCE, level.registryAccess());
+            var encoded = ChunkGenerator.CODEC.encodeStart(ops, generator).getOrThrow();
+            var decoded = ChunkGenerator.CODEC.parse(ops, encoded).getOrThrow();
+            helper.assertTrue(decoded instanceof SanctuaryChunkGenerator copy && copy.rootGeneration() == 21
+                && copy.experimentalStructures() == generator.experimentalStructures(), "Generation21 codec lost its experimental switch");
+            report.put("generator_codec", encoded); report.put("plan_sha256", planHash(plan));
+            report.put("planned_sites", plan.sites().stream().map(site -> Map.of("id", site.id(), "kind", site.kind().name(),
+                "entry", coords(HeritagePiece21.locator(site)), "floor_y", site.floorY(), "foundation_depth", site.foundationDepth(), "footings", site.supports().size())).toList());
+            report.put("planned_links", plan.links().stream().map(link -> Map.of("id", link.id(), "from", link.fromId(), "to", link.toId(), "kind", link.kind().name(), "length", link.path().size(), "path", pathCoords(link))).toList());
+            report.put("planning_samples", plan.samples()); report.put("planning_columns", plan.columns()); report.put("planning_diagnostics", plan.diagnostics());
+            helper.assertTrue(plan.samples() <= HeritagePlan19.MAX_SAMPLES && plan.columns() <= HeritagePlan19.MAX_COLUMNS, "Heritage planning exceeded its budget");
+            verifyLootTables(helper, report);
+            if (reload) {
+                previous = JsonParser.parseString(Files.readString(proof(level))).getAsJsonObject();
+                helper.assertTrue(previous.get("passed").getAsBoolean() && previous.get("world_flushed_before_shutdown").getAsBoolean(), "Reload needs a successful flushed creation proof");
+                helper.assertTrue(previous.get("process_id").getAsLong() != ProcessHandle.current().pid(), "Reload must use a second JVM");
+                helper.assertTrue(previous.get("seed").getAsLong() == level.getSeed() && previous.get("size").getAsInt() == generator.initialDiameter()
+                    && previous.get("world_directory").getAsString().equals(world(level).toString()), "Reload selected another world");
+                helper.assertTrue(previous.get("generator_codec").equals(encoded) && previous.get("plan_sha256").getAsString().equals(planHash(plan)), "Saved settings or planned identities changed on reload");
+                if (previous.has("gold_witness")) gold = readPos(previous.getAsJsonArray("gold_witness"));
+            }
+            if (!generator.experimentalStructures() || !level.structureManager().shouldGenerateStructures()) {
+                helper.assertTrue(plan.isEmpty() && plan.segments().isEmpty() && plan.links().isEmpty(), "Disabled generation published heritage geometry"); return;
+            }
+            helper.assertTrue(!plan.isEmpty(), "Enabled reference island has no heritage site");
+            report.put("present_site_kinds", plan.sites().stream().map(s -> s.kind().name()).distinct().sorted().toList());
+            report.put("missing_site_kinds", java.util.Arrays.stream(HeritagePlan19.Kind.values()).filter(k -> plan.sites().stream().noneMatch(s -> s.kind() == k)).map(Enum::name).toList());
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(HeritageStructures19.KEY);
+            var origins = new HashSet<ChunkPos>(); var uniqueChunks = new HashSet<ChunkPos>();
+            plan.sites().forEach(s -> origins.add(new ChunkPos(s.startChunkX(), s.startChunkZ())));
+            plan.segments().forEach(s -> origins.add(new ChunkPos(s.startChunkX(), s.startChunkZ())));
+            for (var origin : origins.stream().sorted(Comparator.comparingInt(ChunkPos::x).thenComparingInt(ChunkPos::z)).toList()) {
+                var chunk = level.getChunk(origin.x(), origin.z(), ChunkStatus.STRUCTURE_STARTS, true);
+                var start = chunk.getStartForStructure(structure.value());
+                helper.assertTrue(start != null && start.isValid(), "Accepted site/route has no native start at " + origin); starts.add(start);
+                for (var piece : start.getPieces()) {
+                    helper.assertTrue(piece instanceof HeritagePiece21, "Heritage loaded a foreign piece type");
+                    var box = piece.getBoundingBox();
+                    helper.assertTrue(Math.abs((long) (box.minX() >> 4) - origin.x()) <= 7 && Math.abs((long) (box.maxX() >> 4) - origin.x()) <= 7
+                        && Math.abs((long) (box.minZ() >> 4) - origin.z()) <= 7 && Math.abs((long) (box.maxZ() >> 4) - origin.z()) <= 7, "Native start references a distant route endpoint");
+                    box.intersectingChunks().forEach(uniqueChunks::add);
+                }
+            }
+            for (var site : plan.sites()) uniqueChunks.add(ChunkPos.containing(HeritagePiece21.locator(site)));
+            for (var link : plan.links()) for (var point : link.path()) uniqueChunks.add(new ChunkPos(point.x() >> 4, point.z() >> 4));
+            helper.assertTrue(uniqueChunks.size() <= 1024, "Bounded proof footprint exceeds1024 chunks");
+            var ruins = generator.ruinsPlan17();
+            report.put("ruins_plan_sha256", hash(ruins.networks().toString()));
+            if (reload) helper.assertTrue(previous.get("ruins_plan_sha256").getAsString().equals(hash(ruins.networks().toString())), "Reload changed forgotten room planning");
+            helper.assertTrue(!ruins.isEmpty(), "Reference20 must demonstrate native experimental room architecture");
+            var ruinsType = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(RuinsStructures17.KEY);
+            var ruinsOrigins = new HashSet<ChunkPos>();
+            for (var network : ruins.networks()) {
+                var origin = new ChunkPos(network.startChunkX(), network.startChunkZ()); if (!ruinsOrigins.add(origin)) continue;
+                var nativeStart = level.getChunk(origin.x(), origin.z(), ChunkStatus.STRUCTURE_STARTS, true).getStartForStructure(ruinsType.value());
+                helper.assertTrue(nativeStart != null && nativeStart.isValid(), "Missing native20 forgotten network: " + network.id());
+                ruinsStarts.add(nativeStart);
+                for (var piece : nativeStart.getPieces()) {
+                    helper.assertTrue(piece instanceof RuinsPiece20, "Generation21 loaded a historical forgotten piece");
+                    piece.getBoundingBox().intersectingChunks().forEach(uniqueChunks::add);
+                }
+            }
+            chunks.addAll(uniqueChunks.stream().sorted(Comparator.comparingInt(ChunkPos::x).thenComparingInt(ChunkPos::z)).toList());
+        }
+        void finishDisabled() throws IOException {
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(HeritageStructures19.KEY);
+            var start = level.getChunk(0, 0, ChunkStatus.STRUCTURE_STARTS, true).getStartForStructure(structure.value());
+            helper.assertTrue(start == null || !start.isValid(), "Disabled heritage emitted a native start");
+            helper.assertTrue(generator.findNearestMapStructure(level, HolderSet.direct(structure), new BlockPos(0, 250, 0), 100, false) == null, "Disabled heritage is locatable");
+            report.put("empty_plan_verified", true); report.put("passed", true);
+            if (!reload) { helper.assertTrue(level.getServer().saveEverything(true, true, true), "Save disabled experiment setting"); report.put("world_flushed_before_shutdown", true); }
+            write(level, report, reload); helper.succeed();
+        }
+        void verifyPlaced() {
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(HeritageStructures19.KEY);
+            var context = StructurePieceSerializationContext.fromLevel(level); var summaries = new ArrayList<Map<String, Object>>();
+            int blocks = 0, chests = 0, pieces = 0, supports = 0;
+            var connections = NativeConnections20.Stats.empty();
+            for (var start : starts) {
+                var origin = start.getChunkPos(); var saved = start.createTag(context, origin); String nativeHash = hash(saved.toString());
+                var copy = StructureStart.loadStaticStart(context, saved, level.getSeed());
+                helper.assertTrue(copy != null && copy.isValid() && copy.createTag(context, origin).equals(saved), "Native start failed an exact NBT roundtrip");
+                var expectedPayloads = new HashSet<net.minecraft.nbt.CompoundTag>();
+                plan.sites().stream().filter(s -> s.startChunkX() == origin.x() && s.startChunkZ() == origin.z()).forEach(s -> expectedPayloads.add(HeritagePiece21.encodeSite(s)));
+                plan.segments().stream().filter(s -> s.startChunkX() == origin.x() && s.startChunkZ() == origin.z()).forEach(s -> expectedPayloads.add(HeritagePiece21.encodeSegment(s)));
+                var actualPayloads = new HashSet<net.minecraft.nbt.CompoundTag>();
+                if (reload) {
+                    JsonObject prior = null;
+                    for (var value : previous.getAsJsonArray("starts")) { var item = value.getAsJsonObject(); var at = item.getAsJsonArray("start_chunk"); if (at.get(0).getAsInt() == origin.x() && at.get(1).getAsInt() == origin.z()) prior = item; }
+                    helper.assertTrue(prior != null && prior.get("native_start_sha256").getAsString().equals(nativeHash), "Reload changed saved geometry or native reference count");
+                }
+                var loot = new ArrayList<Map<String, Object>>();
+                for (var value : start.getPieces()) {
+                    var piece = (HeritagePiece21) value; pieces++;
+                    var tag = piece.createTag(context); var restored = new HeritagePiece21(context, tag);
+                    helper.assertTrue(restored.createTag(context).equals(tag), "Saved piece parameters changed on native load");
+                    actualPayloads.add(tag.getCompound("SanctuaryHeritage").orElseThrow());
+                    var corrupt = tag.copy(); corrupt.getCompound("SanctuaryHeritage").orElseThrow().putInt("Schema", 22);
+                    boolean rejected = false; try { new HeritagePiece21(context, corrupt); } catch (IllegalArgumentException expected) { rejected = true; }
+                    helper.assertTrue(rejected, "Unknown schema must fail closed");
+                    piece.getBoundingBox().intersectingChunks().forEach(at -> helper.assertTrue(level.getChunk(at.x(), at.z(), ChunkStatus.FULL, true)
+                        .getReferencesForStructure(structure.value()).contains(origin.pack()), "FULL chunk lost its native structure reference"));
+                    var expected = rendered(piece); blocks += expected.blocks().size();
+                    for (var entry : expected.blocks().entrySet()) {
+                        var at = entry.getKey(); var wanted = entry.getValue(); helper.assertTrue(piece.getBoundingBox().isInside(at), "Renderer escaped saved bounds");
+                        if (reload && at.equals(gold)) continue;
+                        helper.assertTrue(level.getBlockState(at).is(wanted.getBlock()), "Clipping or decoration changed heritage at " + at + ": expected " + wanted + " got " + level.getBlockState(at));
+                        helper.assertTrue(!wanted.is(Blocks.SPAWNER), "Heritage must not create spawners");
+                    }
+                    connections = connections.add(NativeConnections20.verify(helper, expected.blocks(), reload ? Set.of(gold) : Set.of()));
+                    if (piece.isSite()) {
+                        supports += verifySiteBearing(helper, generator, plan, piece.site());
+                        if (!reload && gold == null) {
+                            gold = expected.blocks().entrySet().stream().filter(e -> isOuterWall(piece.site(), e.getKey()) && e.getValue().isCollisionShapeFullBlock(level, e.getKey()))
+                                .map(Map.Entry::getKey).sorted(Comparator.<BlockPos>comparingInt(p -> p.getY()).thenComparingInt(p -> p.getX()).thenComparingInt(p -> p.getZ())).findFirst().orElse(null);
+                        }
+                    } else for (var cell : piece.segment().cells()) { supports++; assertRock(helper, new BlockPos(cell.x(), cell.minY() - 1, cell.z())); }
+                    for (var chest : expected.chests()) {
+                        helper.assertTrue(level.getBlockEntity(chest.position()) instanceof RandomizableContainerBlockEntity, "Deferred chest is missing");
+                        var entity = (RandomizableContainerBlockEntity) level.getBlockEntity(chest.position());
+                        helper.assertTrue(entity.getLootTable() != null && entity.getLootTable().equals(chest.table()) && entity.getLootTableSeed() == chest.seed(), "Deferred loot table/seed was lost or consumed");
+                        if (piece.isSite()) helper.assertTrue(chest.table().equals(lootKey(piece.site().kind())), "Site uses another kind's tool table");
+                        loot.add(Map.of("position", coords(chest.position()), "table", chest.table().identifier().toString(), "seed", chest.seed())); chests++;
+                    }
+                }
+                helper.assertTrue(actualPayloads.equals(expectedPayloads) && start.getPieces().size() == expectedPayloads.size(), "Native start lost or duplicated planned pieces");
+                summaries.add(Map.of("start_chunk", List.of(origin.x(), origin.z()), "native_start_sha256", nativeHash, "pieces", start.getPieces().size(), "unopened_chests", loot));
+            }
+            report.put("connected_blocks", connections);
+            helper.assertTrue(connections.panes() > 0 && connections.stairs() > 0 && connections.nativeOracles() > 0,
+                "Reference20 needs real panes/stairs validated by vanilla neighbor rules");
+            if (level.getSeed() == 0 && generator.initialDiameter() == 724)
+                helper.assertTrue(connections.crossChunkPaneLinks() > 0, "Reference20 must demonstrate a real pane join across a chunk boundary");
+            verifyRuins();
+            report.put("starts", summaries); report.put("native_pieces", pieces); report.put("native_blocks_checked", blocks);
+            report.put("full_chunks_checked", chunks.size()); report.put("rock_supports_checked", supports); report.put("unopened_deferred_chests", chests);
+            report.put("stage", "verify_site_routes"); var sites = new ArrayList<Map<String, Object>>(); for (var site : plan.sites()) sites.add(verifyAccess(helper, site)); report.put("native_sites", sites);
+            report.put("stage", "verify_read_only_landings");
+            report.put("read_only_landmarks", verifyReadOnlyLandings(helper, generator, plan));
+            report.put("stage", "verify_island_routes"); report.put("native_links", verifyLinks(helper, plan));
+            int greatestSpan = plan.links().stream().mapToInt(Heritage21WorldGameTests::routeSpan).max().orElse(0);
+            report.put("greatest_single_route_span", greatestSpan);
+            var reachedIds = new HashSet<String>(); plan.links().forEach(l -> { reachedIds.add(l.fromId()); reachedIds.add(l.toId()); });
+            report.put("connected_destination_ids", reachedIds.stream().sorted().toList());
+            report.put("isolated_destination_ids", plan.sites().stream().map(HeritagePlan19.Site::id).filter(id -> !reachedIds.contains(id)).toList());
+            report.put("connected_city_arrivals", plan.landmarks().stream().filter(l -> l.kind() == HeritagePlan19.LandmarkKind.CITY && reachedIds.contains(l.id())).map(HeritagePlan19.Landmark::id).toList());
+            var located = generator.findNearestMapStructure(level, HolderSet.direct(structure), new BlockPos(0, 250, 0), 100, false);
+            helper.assertTrue(located != null && located.getSecond().is(HeritageStructures19.KEY) && plan.sites().stream().anyMatch(s -> HeritagePiece21.locator(s).equals(located.getFirst())), "Locate must lead to a real exterior site entry");
+            report.put("locate", coords(located.getFirst()));
+        }
+        void verifyRuins() {
+            var context = StructurePieceSerializationContext.fromLevel(level);
+            var registry = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(RuinsStructures17.KEY);
+            var summaries = new ArrayList<Map<String, Object>>(); int count = 0, blockCount = 0, lootCount = 0;
+            var connections = NativeConnections20.Stats.empty();
+            for (var start : ruinsStarts) {
+                var origin = start.getChunkPos(); var saved = start.createTag(context, origin); var digest = hash(saved.toString());
+                var loaded = StructureStart.loadStaticStart(context, saved, level.getSeed());
+                helper.assertTrue(loaded != null && loaded.createTag(context, origin).equals(saved), "Forgotten20 native start NBT changed");
+                var expectedRooms = generator.ruinsPlan17().networks().stream().filter(n -> n.startChunkX() == origin.x() && n.startChunkZ() == origin.z()).flatMap(n -> n.rooms().stream()).toList();
+                var actualRooms = start.getPieces().stream().map(RuinsPiece20.class::cast).map(RuinsPiece20::room).toList();
+                helper.assertTrue(expectedRooms.size() == actualRooms.size() && new HashSet<>(expectedRooms).equals(new HashSet<>(actualRooms)), "Forgotten20 native rooms differ from plan");
+                if (reload) {
+                    JsonObject prior = null;
+                    for (var value : previous.getAsJsonArray("ruins_starts")) { var item = value.getAsJsonObject(); var at = item.getAsJsonArray("start_chunk"); if (at.get(0).getAsInt() == origin.x() && at.get(1).getAsInt() == origin.z()) prior = item; }
+                    helper.assertTrue(prior != null && prior.get("native_start_sha256").getAsString().equals(digest), "Forgotten20 native start changed on a second JVM load");
+                }
+                for (var raw : start.getPieces()) {
+                    var piece = (RuinsPiece20) raw; var room = piece.room(); count++;
+                    var tag = piece.createTag(context); var roundtrip = new RuinsPiece20(context, tag);
+                    helper.assertTrue(roundtrip.room().equals(room) && roundtrip.createTag(context).equals(tag), "Forgotten20 piece lost saved parameters");
+                    piece.getBoundingBox().intersectingChunks().forEach(at -> helper.assertTrue(level.getChunk(at.x(), at.z(), ChunkStatus.FULL, true).getReferencesForStructure(registry.value()).contains(origin.pack()), "Forgotten20 chunk lost native references"));
+                    var expected = rendered(room); blockCount += expected.blocks().size();
+                    for (var entry : expected.blocks().entrySet()) {
+                        helper.assertTrue(piece.getBoundingBox().isInside(entry.getKey()), "Forgotten20 renderer escaped saved bounds");
+                        helper.assertTrue(level.getBlockState(entry.getKey()).is(entry.getValue().getBlock()), "Forgotten20 native geometry changed at " + entry.getKey());
+                    }
+                    connections = connections.add(NativeConnections20.verify(helper, expected.blocks(), Set.of()));
+                    for (var support : room.supports()) assertRock(helper, new BlockPos(support.x(), support.minY() - 1, support.z()));
+                    for (var chest : expected.chests()) {
+                        helper.assertTrue(level.getBlockEntity(chest.position()) instanceof RandomizableContainerBlockEntity, "Forgotten20 missing deferred chest");
+                        var entity = (RandomizableContainerBlockEntity) level.getBlockEntity(chest.position());
+                        helper.assertTrue(chest.table().equals(entity.getLootTable()) && chest.seed() == entity.getLootTableSeed(), "Forgotten20 consumed/changed saved loot"); lootCount++;
+                    }
+                }
+                summaries.add(Map.of("start_chunk", List.of(origin.x(), origin.z()), "native_start_sha256", digest, "pieces", start.getPieces().size()));
+            }
+            report.put("ruins_starts", summaries); report.put("ruins_native_pieces", count); report.put("ruins_native_blocks_checked", blockCount);
+            report.put("ruins_unopened_deferred_chests", lootCount); report.put("ruins_connections", connections);
+            report.put("ruins_access", generator.ruinsPlan17().networks().stream().map(n -> verifyAccess(helper, n)).toList());
+        }
+    }
+    private record Chest(BlockPos position, ResourceKey<LootTable> table, long seed) {}
+    private record Rendered(Map<BlockPos, BlockState> blocks, List<Chest> chests) {}
+    private static Rendered rendered(HeritagePiece21 piece) {
+        var blocks = new HashMap<BlockPos, BlockState>(); var chests = new ArrayList<Chest>();
+        int x0 = piece.isSite() ? piece.site().minX() : piece.segment().minX();
+        int y0 = piece.isSite() ? piece.site().floorY() : piece.segment().minY();
+        int z0 = piece.isSite() ? piece.site().minZ() : piece.segment().minZ();
+        var writer = new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState state) { blocks.put(new BlockPos(x0 + x, y0 + y, z0 + z), state); }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+                var at = new BlockPos(x0 + x, y0 + y, z0 + z); blocks.put(at, Blocks.CHEST.defaultBlockState()); chests.add(new Chest(at, table, RandomSource.create(seed).nextLong()));
+            }
+        };
+        if (piece.isSite()) HeritageRenderer21.render(piece.site(), writer); else HeritageRenderer21.renderSegment(piece.segment(), writer);
+        return new Rendered(blocks, chests);
+    }
+    private static Rendered rendered(RuinsPlan17.Room room) {
+        var blocks = new HashMap<BlockPos, BlockState>(); var chests = new ArrayList<Chest>();
+        RuinsRenderer20.render(room, new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState state) { blocks.put(at(room, x, y, z), state); }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+                var position = at(room, x, y, z); blocks.put(position, Blocks.CHEST.defaultBlockState()); chests.add(new Chest(position, table, RandomSource.create(seed).nextLong()));
+            }
+        });
+        return new Rendered(blocks, chests);
+    }
+    private static Map<String, Object> verifyAccess(GameTestHelper helper, RuinsPlan17.Network network) {
+        var level = helper.getLevel(); var access = network.rooms().stream().filter(r -> r.kind() == RuinsPlan17.Kind.ACCESS).findFirst().orElseThrow();
+        var hatches = new HashMap<BlockPos, BlockState>();
+        rendered(access).blocks().forEach((at, state) -> { if (state.is(Blocks.DARK_OAK_TRAPDOOR)) hatches.put(at, level.getBlockState(at)); });
+        helper.assertTrue(hatches.size() == 1, "Each network must have one usable wooden surface hatch");
+        hatches.forEach((at, state) -> {
+            helper.assertTrue(state.is(Blocks.DARK_OAK_TRAPDOOR) && state.canSurvive(level, at), "Surface hatch is missing its native support");
+            level.setBlock(at, state.setValue(BlockStateProperties.OPEN, true), 2);
+        });
+        try {
+            Predicate<BlockPos> inside = pos -> network.rooms().stream().anyMatch(r -> r.contains(pos.getX(), pos.getY(), pos.getZ()));
+            var start = RuinsPiece20.locator(access); var reached = walk(helper, start, inside);
+            int targets = 0;
+            for (var room : network.rooms()) for (var target : RuinsRenderer20.targets(room)) {
+                var point = at(room, target.x(), target.y(), target.z());
+                helper.assertTrue(reached.contains(point), "Native network " + network.id() + " cannot reach " + room.kind() + "/" + target.name() + " at " + point);
+                targets++;
+            }
+            for (var hatch : hatches.keySet()) helper.assertTrue(reached.contains(hatch), "Surface approach cannot enter its ladder shaft");
+            return Map.of("id", network.id(), "family", network.family().name(), "rooms", network.rooms().size(),
+                "entrance", coords(start), "walkable_targets", targets, "standing_cells", reached.size());
+        } finally { hatches.forEach((at, state) -> level.setBlock(at, state, 2)); }
+    }
+    private static BlockPos at(RuinsPlan17.Room room, int x, int y, int z) { return new BlockPos(room.minX() + x, room.minY() + y, room.minZ() + z); }
+    private static boolean isOuterWall(HeritagePlan19.Site site, BlockPos pos) {
+        return pos.getY() >= site.floorY() + 2 && pos.getY() <= site.floorY() + 3
+            && (pos.getX() == site.minX() + 2 || pos.getX() == site.maxX() - 2 || pos.getZ() == site.minZ() + 2 || pos.getZ() == site.maxZ() - 2)
+            && Math.abs(pos.getX() - site.entry().x()) + Math.abs(pos.getZ() - site.entry().z()) > 6;
+    }
+    private static Map<String, Object> verifyAccess(GameTestHelper helper, HeritagePlan19.Site site) {
+        var level = helper.getLevel(); var expected = rendered(new HeritagePiece21(site)); var doors = new HashMap<BlockPos, BlockState>();
+        expected.blocks().forEach((at, state) -> {
+            if ((state.getBlock() instanceof DoorBlock || state.getBlock() instanceof TrapDoorBlock) && state.hasProperty(BlockStateProperties.OPEN)) doors.put(at, level.getBlockState(at));
+        });
+        doors.forEach((at, state) -> level.setBlock(at, state.setValue(BlockStateProperties.OPEN, true), 2));
+        try {
+            var entry = HeritagePiece21.locator(site);
+            Predicate<BlockPos> inside = p -> p.equals(entry) || p.getX() >= site.minX() && p.getX() <= site.maxX()
+                && p.getZ() >= site.minZ() && p.getZ() <= site.maxZ() && p.getY() >= site.floorY() - 4 && p.getY() < site.maxY();
+            var reached = walk(helper, entry, inside); int targets = 0;
+            for (var target : HeritageRenderer21.targets(site)) {
+                var at = new BlockPos(site.minX() + target.x(), site.floorY() + target.y(), site.minZ() + target.z());
+                helper.assertTrue(reached.contains(at), "Site " + site.id() + " cannot reach " + target.name() + " at " + at); targets++;
+            }
+            return Map.of("id", site.id(), "kind", site.kind().name(), "entry", coords(entry), "standing_cells", reached.size(), "walkable_targets", targets);
+        } finally { doors.forEach((at, state) -> level.setBlock(at, state, 2)); }
+    }
+    private static List<Map<String, Object>> verifyLinks(GameTestHelper helper, HeritagePlan19 plan) {
+        helper.assertTrue(!plan.links().isEmpty(), "Reference island needs a real route between accepted destinations");
+        var entries = new HashMap<String, HeritagePlan19.Entry>(); plan.sites().forEach(s -> entries.put(s.id(), s.entry())); plan.landmarks().forEach(s -> entries.put(s.id(), s.entry()));
+        var cells = new HashMap<Long, HeritagePlan19.Cell>(); plan.segments().forEach(s -> s.cells().forEach(c -> cells.put(column(c.x(), c.z()), c)));
+        var result = new ArrayList<Map<String, Object>>();
+        for (var link : plan.links()) {
+            var from = entries.get(link.fromId()); var to = entries.get(link.toId());
+            helper.assertTrue(from != null && to != null, "Route points to an absent destination");
+            var first = link.path().getFirst(); var last = link.path().getLast();
+            helper.assertTrue(first.x() == from.x() && first.z() == from.z() && first.floorY() + 1 == from.y()
+                && last.x() == to.x() && last.z() == to.z() && last.floorY() + 1 == to.y(), "Route does not meet its real entrances");
+            int present = 0, missing = 0;
+            for (int i = 0; i < link.path().size(); i++) {
+                var point = link.path().get(i); var at = new BlockPos(point.x(), point.floorY() + 1, point.z());
+                helper.assertTrue(standable(helper.getLevel(), at), "Ballast route " + link.id() + " is blocked at " + at);
+                if (i > 0) { var prior = link.path().get(i - 1); if (point.floorY() > prior.floorY()) helper.assertTrue(clearBody(helper.getLevel(), new BlockPos(prior.x(), prior.floorY() + 2, prior.z())), "Route slope cannot be climbed by a player"); }
+                var cell = cells.get(column(point.x(), point.z()));
+                if (cell != null && cell.rail() != HeritagePlan19.Rail.NONE) {
+                    var actual = helper.getLevel().getBlockState(at);
+                    if (cell.railPresent()) {
+                        helper.assertTrue(actual.is(Blocks.RAIL), "Saved existing rail disappeared");
+                        helper.assertTrue(actual.getValue(BlockStateProperties.RAIL_SHAPE).name().equals(cell.rail().name()), "Native rail update changed the intended slope or curve at " + at); present++;
+                    } else { helper.assertTrue(!actual.is(Blocks.RAIL), "An intentionally missing rail regenerated"); missing++; }
+                }
+            }
+            int spanX = link.path().stream().mapToInt(HeritagePlan19.Point::x).max().orElseThrow() - link.path().stream().mapToInt(HeritagePlan19.Point::x).min().orElseThrow();
+            int spanZ = link.path().stream().mapToInt(HeritagePlan19.Point::z).max().orElseThrow() - link.path().stream().mapToInt(HeritagePlan19.Point::z).min().orElseThrow();
+            result.add(Map.of("id", link.id(), "from", link.fromId(), "to", link.toId(), "kind", link.kind().name(), "length", link.path().size(),
+                "span_x", spanX, "span_z", spanZ, "existing_rails", present, "deliberately_missing_rails", missing, "path", pathCoords(link)));
+        }
+        return result;
+    }
+    private static int routeSpan(HeritagePlan19.Link link) {
+        int spanX = link.path().stream().mapToInt(HeritagePlan19.Point::x).max().orElseThrow()
+            - link.path().stream().mapToInt(HeritagePlan19.Point::x).min().orElseThrow();
+        int spanZ = link.path().stream().mapToInt(HeritagePlan19.Point::z).max().orElseThrow()
+            - link.path().stream().mapToInt(HeritagePlan19.Point::z).min().orElseThrow();
+        return Math.max(spanX, spanZ);
+    }
+    private static List<List<Integer>> pathCoords(HeritagePlan19.Link link) {
+        return link.path().stream().map(point -> List.of(point.x(), point.floorY(), point.z())).toList();
+    }
+    private static int verifySiteBearing(GameTestHelper helper, SanctuaryChunkGenerator generator, HeritagePlan19 plan, HeritagePlan19.Site site) {
+        int checked = 0;
+        // The planner certifies a nine-point bearing grid, either directly below its slab or below a saved short footing.
+        for (int dx : new int[] {1, 8, 15}) for (int dz : new int[] {1, 8, 15}) {
+            int x = site.minX() + dx, z = site.minZ() + dz;
+            var support = site.supports().stream().filter(s -> s.x() == x && s.z() == z).findFirst();
+            int bottom = support.map(HeritagePlan19.Support::minY).orElse(site.minY());
+            for (int below = 1; below <= 2; below++) {
+                var at = new BlockPos(x, bottom - below, z); assertRock(helper, at);
+                helper.assertTrue(plan.protects(at.getX(), at.getY(), at.getZ()) && generator.protectsCityDecoration(at),
+                    "Site's certified bearing layer is not published in the decoration mask: " + site.id() + " at " + at);
+                helper.assertTrue(!plan.contains(at.getX(), at.getY(), at.getZ()), "Original bearing rock became a writable heritage volume: " + at);
+                checked++;
+            }
+        }
+        return checked;
+    }
+    private static List<Map<String, Object>> verifyReadOnlyLandings(GameTestHelper helper, SanctuaryChunkGenerator generator, HeritagePlan19 plan) {
+        var used = new HashSet<String>(); plan.links().forEach(link -> { used.add(link.fromId()); used.add(link.toId()); });
+        var result = new ArrayList<Map<String, Object>>();
+        for (var landmark : plan.landmarks()) if (used.contains(landmark.id())) {
+            var e = landmark.entry(); int checked = 0;
+            for (int side = -1; side <= 1; side++) {
+                int x = e.x() + ((e.facing() & 1) == 0 ? side : 0), z = e.z() + ((e.facing() & 1) == 1 ? side : 0);
+                for (int y = e.y() - 2; y <= e.y() + 2; y++) {
+                    var at = new BlockPos(x, y, z);
+                    helper.assertTrue(plan.protects(x, y, z) && generator.protectsCityDecoration(at), "Read-only arrival lost its decoration mask: " + landmark.id() + " at " + at);
+                    helper.assertTrue(!plan.contains(x, y, z), "Heritage gained write ownership of a historical arrival: " + landmark.id() + " at " + at);
+                    if (y == e.y() - 1) assertRock(helper, at);
+                    if (y >= e.y()) helper.assertTrue(helper.getLevel().getBlockState(at).isAir(), "Decoration obstructed a certified historical arrival: " + at);
+                    checked++;
+                }
+            }
+            result.add(Map.of("id", landmark.id(), "entry", List.of(e.x(), e.y(), e.z()), "read_only_cells", checked));
+        }
+        return result;
+    }
+    private static void assertRock(GameTestHelper helper, BlockPos at) {
+        helper.assertTrue(helper.getLevel().getBlockState(at).isSolid() && helper.getLevel().getFluidState(at).isEmpty(), "Lost original rock bearing at " + at);
+    }
+    private static void verifyLootTables(GameTestHelper helper, Map<String, Object> report) {
+        var result = new ArrayList<Map<String, Object>>(); var level = helper.getLevel();
+        var params = new LootParams.Builder(level).withParameter(LootContextParams.ORIGIN, new Vec3(0, 160, 0)).create(LootContextParamSets.CHEST);
+        for (var kind : HeritagePlan19.Kind.values()) {
+            var table = level.getServer().reloadableRegistries().getLootTable(lootKey(kind));
+            helper.assertTrue(table != LootTable.EMPTY, "Heritage tool table did not load: " + kind);
+            for (long seed : new long[] {0, 42, -1}) helper.assertTrue(table.getRandomItems(params, seed).stream().anyMatch(stack -> stack.is(tool(kind))), "Tool table is empty or lacks its expected primary tool: " + kind);
+            result.add(Map.of("kind", kind.name(), "table", lootKey(kind).identifier().toString(), "sampled_seeds", List.of(0, 42, -1)));
+        }
+        report.put("tool_tables_sampled_separately", result);
+    }
+    private static ResourceKey<LootTable> lootKey(HeritagePlan19.Kind kind) { return ResourceKey.create(Registries.LOOT_TABLE, SanctuaryMod.id("chests/heritage19/" + kind.name().toLowerCase(Locale.ROOT))); }
+    private static Item tool(HeritagePlan19.Kind kind) {
+        return switch (kind) {
+            case OBSERVATORY -> Items.SPYGLASS;
+            case POST_OFFICE, EXPEDITION_OFFICE, RADIO_RELAY -> Items.COMPASS;
+            case SUBSTATION, IMPOSSIBLE_SERVICE -> Items.CLOCK;
+            case FREIGHT_STATION -> Items.MINECART;
+            case COMMUNAL_DEPOT -> Items.IRON_AXE;
+            case RAIL_WORKSHOP -> Items.IRON_PICKAXE;
+            case PUMP_STATION -> Items.BUCKET;
+            case GREENHOUSE -> Items.IRON_HOE;
+            case VOID_DOCK -> Items.LEAD;
+            case PHOTO_CLUB -> Items.BOOK;
+            case CONSTRUCTION_REFUGE -> Items.IRON_SHOVEL;
+        };
+    }
+    private static Set<BlockPos> walk(GameTestHelper helper, BlockPos start, Predicate<BlockPos> inside) {
+        var level = helper.getLevel(); helper.assertTrue(inside.test(start) && standable(level, start), "Blocked or unsupported exterior entrance: " + start);
+        var seen = new HashSet<BlockPos>(); var queue = new ArrayDeque<BlockPos>(); seen.add(start); queue.add(start);
+        while (!queue.isEmpty()) {
+            var pos = queue.removeFirst();
+            for (var direction : HORIZONTAL) for (int dy = -1; dy <= 1; dy++) {
+                var next = pos.relative(direction).offset(0, dy, 0);
+                if (!inside.test(next) || dy > 0 && !clearBody(level, pos.above())) continue;
+                if (standable(level, next) && seen.add(next)) queue.add(next);
+            }
+            for (int dy : new int[] {-1, 1}) {
+                var next = pos.offset(0, dy, 0); if (!inside.test(next)) continue;
+                if ((level.getBlockState(pos).is(Blocks.LADDER) || level.getBlockState(next).is(Blocks.LADDER) || level.getBlockState(pos.below()).is(Blocks.LADDER))
+                        && standable(level, next) && seen.add(next)) queue.add(next);
+            }
+            helper.assertTrue(seen.size() <= 50_000, "Native site traversal escaped its bounds");
+        }
+        return seen;
+    }
+    private static boolean standable(ServerLevel level, BlockPos pos) {
+        if (!clearBody(level, pos)) return false;
+        if (level.getBlockState(pos).is(Blocks.LADDER) || level.getBlockState(pos.below()).is(Blocks.LADDER)) return true;
+        var below = pos.below(); return level.getBlockState(below).getCollisionShape(level, below).toAabbs().stream()
+            .anyMatch(b -> b.maxY >= .5 && b.minX <= .5 && b.maxX >= .5 && b.minZ <= .5 && b.maxZ >= .5);
+    }
+    private static boolean clearBody(ServerLevel level, BlockPos pos) {
+        var body = new AABB(pos.getX() + .2, pos.getY(), pos.getZ() + .2, pos.getX() + .8, pos.getY() + 1.8, pos.getZ() + .8);
+        for (var at : new BlockPos[] {pos, pos.above()}) {
+            if (!level.getFluidState(at).isEmpty()) return false;
+            for (var shape : level.getBlockState(at).getCollisionShape(level, at).toAabbs()) if (shape.move(at.getX(), at.getY(), at.getZ()).intersects(body)) return false;
+        }
+        return true;
+    }
+    private static long column(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+    private static List<Integer> coords(BlockPos pos) { return List.of(pos.getX(), pos.getY(), pos.getZ()); }
+    private static BlockPos readPos(com.google.gson.JsonArray value) { return new BlockPos(value.get(0).getAsInt(), value.get(1).getAsInt(), value.get(2).getAsInt()); }
+    private static Path world(ServerLevel level) { return level.getServer().getWorldPath(LevelResource.ROOT).toAbsolutePath().normalize(); }
+    private static Path proof(ServerLevel level) { return world(level).resolve("heritage21-create-proof.json"); }
+    private static String planHash(HeritagePlan19 plan) { return hash(plan.sites().toString() + plan.landmarks() + plan.links() + plan.segments()); }
+    private static void write(ServerLevel level, Map<String, Object> report, boolean reload) throws IOException {
+        var path = Path.of("diagnostics", "heritage21-" + (reload ? "reload" : "create") + ".json"); Files.createDirectories(path.getParent());
+        var value = new GsonBuilder().setPrettyPrinting().create().toJson(report) + "\n"; Files.writeString(path, value); if (!reload) Files.writeString(proof(level), value);
+    }
+    private static String hash(String value) {
+        try { return HexFormat.of().formatHex(MessageDigest.getInstance("SHA-256").digest(value.getBytes(StandardCharsets.UTF_8))); }
+        catch (NoSuchAlgorithmException impossible) { throw new AssertionError(impossible); }
+    }
+}

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/PopulationDiagnostics.java

@@ -211,7 +211,7 @@ public final class PopulationDiagnostics {
 
         void prepare() throws IOException {
             boolean heritage = level.getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator sanctuary
-                && (sanctuary.rootGeneration() == 19 || sanctuary.rootGeneration() == 20) && sanctuary.experimentalStructures();
+                && (sanctuary.rootGeneration() == 19 || sanctuary.rootGeneration() == 20 || sanctuary.rootGeneration() == 21) && sanctuary.experimentalStructures();
             // Generation19 explicitly prospects destinations across the root island before publishing them.
             // A consulted hydrology region is a bounded immutable plan, not a loaded/generated chunk.
             // Historical generators retain their original near-spawn contract.

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Transit21WorldGameTests.java

@@ -0,0 +1,453 @@
+package fr.koka.sanctuary.gametest;
+
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import com.mojang.serialization.JsonOps;
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import fr.koka.sanctuary.worldgen.transit.TransitPiece21;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21;
+import fr.koka.sanctuary.worldgen.transit.TransitRenderer21;
+import fr.koka.sanctuary.worldgen.transit.TransitStructures21;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.HexFormat;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Predicate;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.core.HolderSet;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.RegistryOps;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.StairBlock;
+import net.minecraft.world.level.block.entity.RandomizableContainerBlockEntity;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.levelgen.structure.StructureStart;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceSerializationContext;
+import net.minecraft.world.level.storage.LevelResource;
+import net.minecraft.world.level.storage.loot.LootTable;
+import net.minecraft.world.phys.AABB;
+
+/** Opt-in native proof confined to the new generation21 starter island in a disposable development world. */
+public final class Transit21WorldGameTests {
+    private static final Direction[] HORIZONTAL = {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST};
+
+    @GameTest(maxTicks = 12000)
+    public void industrialTransitPersistsNatively(GameTestHelper helper) {
+        helper.assertTrue(helper.getLevel().getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator,
+            "The industrial-transits proof requires a Sanctuary generator");
+        var generator = (SanctuaryChunkGenerator) helper.getLevel().getChunkSource().getGenerator();
+        helper.assertTrue(generator.rootGeneration() == 21, "Use a fresh generation21 test world; do not convert old saves");
+        new Scenario(helper, generator, Boolean.getBoolean("sanctuary.test.expansionReload")).advance();
+    }
+
+    private static final class Scenario {
+        final GameTestHelper helper;
+        final ServerLevel level;
+        final SanctuaryChunkGenerator generator;
+        final TransitPlan21 plan;
+        final boolean reload;
+        final Map<String, Object> report = new LinkedHashMap<>();
+        final List<ChunkPos> chunks = new ArrayList<>();
+        final List<StructureStart> starts = new ArrayList<>();
+        final Map<BlockPos, BlockState> allGeometry = new HashMap<>();
+        JsonObject previous;
+        BlockPos gold;
+        int nextChunk;
+        boolean prepared;
+
+        Scenario(GameTestHelper helper, SanctuaryChunkGenerator generator, boolean reload) {
+            this.helper = helper; this.level = helper.getLevel(); this.generator = generator; this.reload = reload;
+            this.plan = generator.transitPlan21();
+            report.put("seed", level.getSeed()); report.put("size", generator.initialDiameter());
+            report.put("process_id", ProcessHandle.current().pid()); report.put("world_directory", world(level).toString());
+            report.put("experimental_structures", generator.experimentalStructures());
+            report.put("structures_enabled", level.structureManager().shouldGenerateStructures());
+            report.put("planning_diagnostic", plan.diagnostic());
+            report.put("scope", "Native starts, references, geometry, rock bearings, unopened loot and a player-sized stair walk between two surface gates. "
+                + "No expansion is created and no personal save is opened. A single outer-wall gold edit in this disposable world "
+                + "is saved and checked in a second JVM. Traversal remains inside the modules and certified portico approaches; underground one-block rises need real correctly oriented stairs. Only the certified natural portico approaches permit an ordinary one-block jump. No flight, ladder or external terrain shortcut is allowed. No fluid simulation is claimed.");
+        }
+        void advance() {
+            try {
+                if (!prepared) {
+                    prepare(); prepared = true;
+                    if (plan.isEmpty()) { finishDisabled(); return; }
+                }
+                if (nextChunk < chunks.size()) {
+                    var pos = chunks.get(nextChunk++);
+                    var loaded = level.getChunk(pos.x(), pos.z(), ChunkStatus.FULL, true);
+                    helper.assertTrue(loaded instanceof LevelChunk, "Every room footprint must reach native FULL: " + pos);
+                    if (nextChunk % 10 == 0) SanctuaryMod.LOGGER.info("Industrial transit21: loaded {}/{} footprint chunks", nextChunk, chunks.size());
+                    helper.runAtTickTime(helper.getTick() + 1, this::advance); return;
+                }
+                verifyPlaced();
+                report.put("passed", true);
+                if (!reload) {
+                    helper.assertTrue(gold != null && level.getBlockState(gold).isCollisionShapeFullBlock(level, gold),
+                        "Gameplay witness must replace a solid outer wall away from every doorway");
+                    level.setBlock(gold, Blocks.GOLD_BLOCK.defaultBlockState(), 3);
+                    report.put("gold_witness", coords(gold));
+                    helper.assertTrue(level.getServer().saveEverything(true, true, true), "Flush native structures, deferred loot and the gold edit");
+                    report.put("world_flushed_before_shutdown", true);
+                } else {
+                    helper.assertTrue(level.getBlockState(gold).is(Blocks.GOLD_BLOCK), "Reload replaced the existing wall edit");
+                    report.put("gold_witness", coords(gold)); report.put("gold_witness_preserved", true);
+                }
+                write(level, report, reload); helper.succeed();
+            } catch (Exception failure) {
+                report.put("passed", false); report.put("failure", failure.toString());
+                try { write(level, report, reload); } catch (IOException ignored) { }
+                throw new IllegalStateException("Industrial transit21 native " + (reload ? "reload" : "creation") + " failed", failure);
+            }
+        }
+        void prepare() throws IOException {
+            var ops = RegistryOps.create(JsonOps.INSTANCE, level.registryAccess());
+            var encoded = ChunkGenerator.CODEC.encodeStart(ops, generator).getOrThrow();
+            var decoded = ChunkGenerator.CODEC.parse(ops, encoded).getOrThrow();
+            helper.assertTrue(decoded instanceof SanctuaryChunkGenerator copy && copy.rootGeneration() == 21
+                && copy.experimentalStructures() == generator.experimentalStructures(), "The generation21 codec must preserve its experimental switch");
+            report.put("generator_codec", encoded); report.put("plan_sha256", planHash(plan)); report.put("planning_samples", plan.samples());
+            helper.assertTrue(plan.samples() <= TransitPlan21.MAX_SAMPLES, "Transit planning exceeded its budget");
+            if (reload) {
+                previous = JsonParser.parseString(Files.readString(proof(level))).getAsJsonObject();
+                helper.assertTrue(previous.get("passed").getAsBoolean() && previous.get("world_flushed_before_shutdown").getAsBoolean(),
+                    "Reload requires the successful, flushed creation proof");
+                helper.assertTrue(previous.get("process_id").getAsLong() != ProcessHandle.current().pid(), "Reload must run in a separate JVM");
+                helper.assertTrue(previous.get("seed").getAsLong() == level.getSeed()
+                    && previous.get("size").getAsInt() == generator.initialDiameter()
+                    && previous.get("world_directory").getAsString().equals(world(level).toString()), "Reload used another world, seed or size");
+                helper.assertTrue(previous.get("generator_codec").equals(encoded) && previous.get("plan_sha256").getAsString().equals(planHash(plan)),
+                    "Saved switch or planned generation21 room identities changed on reload");
+                if (previous.has("gold_witness")) gold = readPos(previous.getAsJsonArray("gold_witness"));
+            }
+            boolean enabled = generator.experimentalStructures() && level.structureManager().shouldGenerateStructures();
+            if (!enabled) {
+                helper.assertTrue(plan.isEmpty(), "Experimental=false or generateStructures=false must publish no industrial transit");
+                return;
+            }
+            helper.assertTrue(!plan.isEmpty(), "Enabled reference island has no experimental network");
+            helper.assertTrue(plan.modules().stream().filter(m -> m.kind() == TransitPlan21.Kind.ACCESS).count() == 2,
+                "A through-route needs two independent saved surface stairs");
+            int spanX = plan.modules().stream().mapToInt(TransitPlan21.Module::maxX).max().orElseThrow()
+                - plan.modules().stream().mapToInt(TransitPlan21.Module::minX).min().orElseThrow() + 1;
+            int spanZ = plan.modules().stream().mapToInt(TransitPlan21.Module::maxZ).max().orElseThrow()
+                - plan.modules().stream().mapToInt(TransitPlan21.Module::minZ).min().orElseThrow() + 1;
+            report.put("span_x", spanX); report.put("span_z", spanZ);
+            helper.assertTrue(Math.max(spanX, spanZ) >= generator.initialDiameter() * .4,
+                "The native transit reference must cross at least40% of the island's nominal diameter");
+            report.put("modules", plan.modules().size());
+            report.put("halls", plan.modules().stream().filter(m -> m.kind() == TransitPlan21.Kind.HALL).count());
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(TransitStructures21.KEY);
+            var origins = new HashSet<Long>(); var uniqueChunks = new HashSet<ChunkPos>();
+            for (var network : plan.modules()) {
+                long origin = new ChunkPos(network.startChunkX(), network.startChunkZ()).pack();
+                if (!origins.add(origin)) continue;
+                var chunk = level.getChunk(network.startChunkX(), network.startChunkZ(), ChunkStatus.STRUCTURE_STARTS, true);
+                var start = chunk.getStartForStructure(structure.value());
+                helper.assertTrue(start != null && start.isValid(), "Accepted experimental network has no native start: " + network.kind() + " at " + network.centerX() + "," + network.centerZ());
+                starts.add(start);
+                for (var piece : start.getPieces()) {
+                    helper.assertTrue(piece instanceof TransitPiece21, "Industrial transit loaded a foreign or historical piece type");
+                    piece.getBoundingBox().intersectingChunks().forEach(at -> {
+                        helper.assertTrue(Math.abs(at.x() - network.startChunkX()) <= 7 && Math.abs(at.z() - network.startChunkZ()) <= 7,
+                            "Transit native start exceeds its local reference range");
+                        uniqueChunks.add(at);
+                    });
+                }
+            }
+            helper.assertTrue(uniqueChunks.size() <= 256, "The bounded root-only proof unexpectedly covers more than256 chunks");
+            chunks.addAll(uniqueChunks.stream().sorted(java.util.Comparator.comparingInt(ChunkPos::x).thenComparingInt(ChunkPos::z)).toList());
+        }
+        void finishDisabled() throws IOException {
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(TransitStructures21.KEY);
+            var chunk = level.getChunk(0, 0, ChunkStatus.STRUCTURE_STARTS, true);
+            var start = chunk.getStartForStructure(structure.value());
+            helper.assertTrue(start == null || !start.isValid(), "Disabled experimental generation emitted a native start");
+            var located = generator.findNearestMapStructure(level, HolderSet.direct(structure), new BlockPos(0, 250, 0), 100, false);
+            helper.assertTrue(located == null, "Disabled experimental structures must not be located or prepared");
+            report.put("empty_plan_verified", true); report.put("passed", true);
+            if (!reload) {
+                helper.assertTrue(level.getServer().saveEverything(true, true, true), "Save the disabled experiment setting");
+                report.put("world_flushed_before_shutdown", true);
+            }
+            write(level, report, reload); helper.succeed();
+        }
+        void verifyPlaced() {
+            var structure = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(TransitStructures21.KEY);
+            var context = StructurePieceSerializationContext.fromLevel(level);
+            var sites = new ArrayList<Map<String, Object>>();
+            var modules = new ArrayList<Map<String, Object>>();
+            int blocks = 0, supports = 0, chests = 0, pieces = 0;
+            var bearingMasks = new HashMap<TransitPlan21.Module, Integer>();
+            for (var start : starts) {
+                var origin = start.getChunkPos(); var saved = start.createTag(context, origin);
+                var copy = StructureStart.loadStaticStart(context, saved, level.getSeed());
+                helper.assertTrue(copy != null && copy.isValid() && copy.createTag(context, origin).equals(saved), "The native start changed on an NBT roundtrip");
+                var expectedRooms = plan.modulesForChunk(origin.x(), origin.z());
+                var actualRooms = start.getPieces().stream().map(TransitPiece21.class::cast).map(TransitPiece21::module).toList();
+                helper.assertTrue(actualRooms.size() == expectedRooms.size() && new HashSet<>(actualRooms).equals(new HashSet<>(expectedRooms)),
+                    "Native start did not persist every planned room exactly once");
+                String nativeHash = hash(saved.toString());
+                if (reload) {
+                    JsonObject prior = null;
+                    for (var value : previous.getAsJsonArray("starts")) {
+                        var site = value.getAsJsonObject(); var at = site.getAsJsonArray("start_chunk");
+                        if (at.get(0).getAsInt() == origin.x() && at.get(1).getAsInt() == origin.z()) prior = site;
+                    }
+                    helper.assertTrue(prior != null && prior.get("native_start_sha256").getAsString().equals(nativeHash),
+                        "Reload altered native room parameters, supports or reference count");
+                }
+                var loot = new ArrayList<Map<String, Object>>();
+                for (var piece : start.getPieces()) {
+                    var roomPiece = (TransitPiece21) piece; var room = roomPiece.module(); pieces++;
+                    piece.getBoundingBox().intersectingChunks().forEach(at -> {
+                        var full = level.getChunk(at.x(), at.z(), ChunkStatus.FULL, true);
+                        helper.assertTrue(full.getReferencesForStructure(structure.value()).contains(origin.pack()), "A saved FULL chunk lost the native structure reference");
+                    });
+                    var roomTag = roomPiece.createTag(context);
+                    var roundtrip = new TransitPiece21(context, roomTag);
+                    helper.assertTrue(roundtrip.module().equals(room) && roundtrip.createTag(context).equals(roomTag), "The native room failed its exact saved-field roundtrip");
+                    var corrupt = roomTag.copy(); var payload = corrupt.getCompound("SanctuaryModule").orElseThrow(); payload.putInt("Schema", 99);
+                    boolean rejected = false;
+                    try { new TransitPiece21(context, corrupt); } catch (IllegalArgumentException expected) { rejected = true; }
+                    helper.assertTrue(rejected, "An unknown generation21 piece schema must be refused");
+                    var expected = rendered(room); blocks += expected.blocks().size();
+                    expected.blocks().forEach((at, state) -> helper.assertTrue(allGeometry.putIfAbsent(at, state) == null,
+                        "Two saved transit modules paint the same position: " + at));
+                    modules.add(Map.of("kind", room.kind().name(), "min", List.of(room.minX(), room.minY(), room.minZ()),
+                        "max", List.of(room.maxX(), room.maxY(), room.maxZ()), "floor_y", room.floorY(),
+                        "surface_y", room.surfaceY(), "openings", room.openings(), "supports", room.supports().size(),
+                        "start_chunk", List.of(room.startChunkX(), room.startChunkZ())));
+                    for (var entry : expected.blocks().entrySet()) {
+                        var at = entry.getKey(); var wanted = entry.getValue();
+                        helper.assertTrue(TransitPiece21.bounds(room).isInside(at), "Renderer escaped its saved room/support bounds");
+                        helper.assertTrue(plan.protects(at.getX(), at.getY(), at.getZ()) && generator.protectsCityDecoration(at),
+                            "Transit construction/cleared air is missing its published decoration protection at " + at);
+                        if (reload && at.equals(gold)) continue;
+                        helper.assertTrue(level.getBlockState(at).is(wanted.getBlock()),
+                            "Native clipping or later decoration changed " + room.kind() + " at " + at + ": expected " + wanted + " got " + level.getBlockState(at));
+                        helper.assertTrue(!level.getBlockState(at).is(Blocks.SPAWNER), "Experimental architecture must not create a spawner");
+                    }
+                    supports += verifyBearings(helper, generator, room, bearingMasks);
+                    for (var entry : expected.blocks().entrySet()) if (entry.getValue().is(Blocks.LANTERN)) {
+                        var at = entry.getKey(); var state = level.getBlockState(at);
+                        helper.assertTrue(state.canSurvive(level, at) && level.getBlockState(at.above()).isFaceSturdy(level, at.above(), Direction.DOWN),
+                            "Transit lamp lost its complete ceiling bearing at " + at);
+                    }
+                    for (var chest : expected.chests()) {
+                        helper.assertTrue(level.getBlockEntity(chest.position()) instanceof RandomizableContainerBlockEntity, "Deferred native chest block entity is missing");
+                        var entity = (RandomizableContainerBlockEntity) level.getBlockEntity(chest.position());
+                        helper.assertTrue(chest.table().equals(entity.getLootTable()) && entity.getLootTableSeed() == chest.seed(),
+                            "Native chest loot must remain deferred with its exact table and seed");
+                        loot.add(Map.of("position", coords(chest.position()), "table", chest.table().identifier().toString(), "seed", chest.seed())); chests++;
+                    }
+                    if (!reload && gold == null && room.kind() != TransitPlan21.Kind.ACCESS && room.kind() != TransitPlan21.Kind.JUNCTION)
+                        gold = new BlockPos(room.minX(), room.floorY() + 1, room.minZ() + 1);
+                }
+                sites.add(Map.of("start_chunk", List.of(origin.x(), origin.z()), "native_start_sha256", nativeHash,
+                    "pieces", start.getPieces().size(), "unopened_chests", loot));
+            }
+            report.put("module_coordinates", modules);
+            report.put("starts", sites);
+            int weakSpan = 0, longestSpan = 0;
+            for (var room : plan.modules()) {
+                weakSpan = bearingMasks.get(room) == 15 ? 0 : weakSpan + 1;
+                longestSpan = Math.max(longestSpan, weakSpan);
+                helper.assertTrue(weakSpan <= 2, "Native deck spans more than 34 blocks without distributed rock bearings");
+            }
+            report.put("longest_span_without_full_bearings", longestSpan * 17);
+            var ores = new java.util.TreeMap<String, Integer>();
+            allGeometry.values().forEach(state -> {
+                var id = net.minecraft.core.registries.BuiltInRegistries.BLOCK.getKey(state.getBlock()).toString();
+                if (id.endsWith("_ore")) ores.merge(id, 1, Integer::sum);
+            });
+            report.put("finite_exposed_ores", ores);
+            var traversal = verifyAccess(helper, plan);
+            report.put("native_connections", NativeConnections20.verify(helper, allGeometry,
+                reload && gold != null ? Set.of(gold) : Set.of()));
+            report.put("module_coordinates", modules);
+            var located = generator.findNearestMapStructure(level, HolderSet.direct(structure), new BlockPos(0, 250, 0), 100, false);
+            helper.assertTrue(located != null && located.getSecond().is(TransitStructures21.KEY), "Native locate cannot find a saved industrial transit");
+            helper.assertTrue(plan.modules().stream().filter(r -> r.kind() == TransitPlan21.Kind.ACCESS)
+                .anyMatch(r -> TransitPiece21.locator(r).equals(located.getFirst())), "Locate must lead to a surface entrance rather than an underground floor");
+            report.put("starts", sites); report.put("native_pieces", pieces); report.put("native_blocks_checked", blocks);
+            report.put("full_chunks_checked", chunks.size()); report.put("rock_supports_checked", supports);
+            report.put("unopened_deferred_chests", chests); report.put("native_routes", traversal); report.put("locate", coords(located.getFirst()));
+        }
+    }
+    private record Chest(BlockPos position, ResourceKey<LootTable> table, long seed) {}
+    private record Rendered(Map<BlockPos, BlockState> blocks, List<Chest> chests) {}
+    private static Rendered rendered(TransitPlan21.Module room) {
+        var blocks = new HashMap<BlockPos, BlockState>(); var chests = new ArrayList<Chest>();
+        TransitRenderer21.render(room, new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState state) { blocks.put(at(room, x, y, z), state); }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+                var position = at(room, x, y, z); blocks.put(position, Blocks.CHEST.defaultBlockState()); chests.add(new Chest(position, table, RandomSource.create(seed).nextLong()));
+            }
+        });
+        return new Rendered(blocks, chests);
+    }
+    private static int verifyBearings(GameTestHelper helper, SanctuaryChunkGenerator generator, TransitPlan21.Module room, Map<TransitPlan21.Module, Integer> masks) {
+        var level = helper.getLevel(); int checked = 0, quarters = 0;
+        for (int z = room.minZ();; z = Math.min(z + 4, room.maxZ())) {
+            for (int x = room.minX();; x = Math.min(x + 4, room.maxX())) {
+                int anchor = room.minY() - 1;
+                for (var support : room.supports()) if (support.x() == x && support.z() == z) anchor = support.minY() - 1;
+                var bearing = new BlockPos(x, anchor, z);
+                boolean supported = level.getBlockState(bearing).isSolid() && level.getFluidState(bearing).isEmpty()
+                    && level.getBlockState(bearing.below()).isSolid() && level.getFluidState(bearing.below()).isEmpty();
+                if (supported) {
+                quarters |= 1 << ((x < room.centerX() ? 0 : 1) + (z < room.centerZ() ? 0 : 2));
+                for (int dy = 0; dy >= -1; dy--) {
+                    var at = new BlockPos(x, anchor + dy, z);
+                    helper.assertTrue(level.getBlockState(at).isSolid() && level.getFluidState(at).isEmpty(),
+                        "Transit bearing grid lost one of its two untouched rock layers at " + at);
+                    helper.assertTrue(generator.protectsCityDecoration(at), "A certified transit rock dependency is unprotected at " + at);
+                    checked++;
+                }
+                }
+                if (x == room.maxX()) break;
+            }
+            if (z == room.maxZ()) break;
+        }
+        helper.assertTrue(room.kind() == TransitPlan21.Kind.GALLERY || room.kind() == TransitPlan21.Kind.JUNCTION || quarters == 15, "The continuous deck lost its distributed rock bearings");
+        masks.put(room, quarters);
+        return checked;
+    }
+    private static Map<String, Object> verifyAccess(GameTestHelper helper, TransitPlan21 plan) {
+        var level = helper.getLevel();
+        var accesses = plan.modules().stream().filter(m -> m.kind() == TransitPlan21.Kind.ACCESS).toList();
+        helper.assertTrue(accesses.size() == 2, "Native transit requires exactly two surface gates");
+        Predicate<BlockPos> inside = pos -> plan.contains(pos.getX(), pos.getY(), pos.getZ())
+            || accesses.stream().anyMatch(m -> pos.getX() >= m.centerX() - 2 && pos.getX() <= m.centerX() + 2
+                && pos.getZ() >= m.minZ() - 3 && pos.getZ() < m.minZ()
+                && pos.getY() >= m.surfaceY() && pos.getY() <= m.surfaceY() + 2);
+        var start = TransitPiece21.locator(accesses.getFirst());
+        Predicate<BlockPos> naturalApproach = pos -> accesses.stream().anyMatch(m ->
+            pos.getX() >= m.centerX() - 2 && pos.getX() <= m.centerX() + 2
+                && pos.getZ() >= m.minZ() - 3 && pos.getZ() < m.minZ()
+                && pos.getY() >= m.surfaceY() && pos.getY() <= m.surfaceY() + 2);
+        var reached = walk(helper, start, inside, naturalApproach); int targets = 0;
+        var arrivals = new ArrayList<Map<String, Object>>();
+        for (var module : plan.modules()) for (var target : TransitRenderer21.targets(module)) {
+            var point = at(module, target.x(), target.y(), target.z());
+            helper.assertTrue(reached.containsKey(Foot.at(point)), "Native transit cannot walk from its first portico to "
+                + module.kind() + "/" + target.name() + " at " + point);
+            targets++;
+        }
+        for (var access : accesses) {
+            var gate = TransitPiece21.locator(access);
+            helper.assertTrue(reached.containsKey(Foot.at(gate)), "The second independent surface gate is not connected by real stairs");
+            int approaches = 0;
+            for (int x = access.centerX() - 2; x <= access.centerX() + 2; x++) for (int z = access.minZ() - 3; z < access.minZ(); z++) {
+                var high = new BlockPos(x, access.surfaceY() + 1, z);
+                var low = high.below(); var position = standable(level, high) ? high : low;
+                helper.assertTrue(standable(level, position) && reached.containsKey(Foot.at(position)),
+                    "The certified natural approach no longer joins its portico at " + position);
+                helper.assertTrue(level.getBlockState(position.below()).isSolid()
+                    && level.getFluidState(position.below()).isEmpty(), "A surface arrival is suspended above air or water");
+                approaches++;
+            }
+            arrivals.add(Map.of("gate", coords(gate), "roadway", coords(at(access, 8, 2, 8)),
+                "rise", access.surfaceY() - access.floorY(), "steps_from_first_gate", reached.get(Foot.at(gate)),
+                "natural_approach_cells", approaches));
+        }
+        return Map.of("surface_accesses", arrivals, "walkable_targets", targets, "standing_cells", reached.size(),
+            "surface_to_surface_steps", reached.get(Foot.at(TransitPiece21.locator(accesses.getLast()))),
+            "traversal_policy", "0.6 by1.8 native collision volume, half-block sidewalk steps; underground rises require a real forward-facing stair; natural portico approaches alone permit a normal one-block jump; no vertical moves");
+    }
+    /** Half-block standing elevations retain real sidewalk slabs without pretending an integer cell can hover over them. */
+    private record Foot(int x, int halfY, int z) {
+        static Foot at(BlockPos pos) { return new Foot(pos.getX(), pos.getY() * 2, pos.getZ()); }
+        double y() { return halfY / 2.0; }
+        BlockPos block() { return new BlockPos(x, Math.floorDiv(halfY, 2), z); }
+        BlockPos bearing() { return new BlockPos(x, Math.floorDiv(halfY - 1, 2), z); }
+        Foot rise(int halves) { return new Foot(x, halfY + halves, z); }
+        Foot move(Direction direction, int halves) { return new Foot(x + direction.getStepX(), halfY + halves, z + direction.getStepZ()); }
+    }
+    private static Map<Foot, Integer> walk(GameTestHelper helper, BlockPos start, Predicate<BlockPos> inside, Predicate<BlockPos> naturalApproach) {
+        var level = helper.getLevel(); var first = Foot.at(start);
+        helper.assertTrue(inside.test(start) && standable(level, first), "Blocked native surface portico: " + start);
+        var seen = new HashMap<Foot, Integer>(); var queue = new ArrayDeque<Foot>(); seen.put(first, 0); queue.add(first);
+        while (!queue.isEmpty()) {
+            var pos = queue.removeFirst();
+            for (var direction : HORIZONTAL) for (int dy = -2; dy <= 2; dy++) {
+                var next = pos.move(direction, dy);
+                if (!inside.test(next.block()) || seen.containsKey(next)) continue;
+                boolean ordinaryThreshold = naturalApproach.test(pos.block()) || naturalApproach.test(next.block());
+                // Native step height is enough for a half slab; a full block needs the two treads of a stair.
+                if (dy > 0 && (!clearBody(level, pos.rise(dy))
+                    || dy == 2 && !ordinaryThreshold && !ascendingStair(level, next.bearing(), direction))) continue;
+                if (dy < 0 && (!clearBody(level, next.rise(-dy))
+                    || dy == -2 && !ordinaryThreshold && !ascendingStair(level, pos.bearing(), direction.getOpposite()))) continue;
+                if (standable(level, next)) { seen.put(next, seen.get(pos) + 1); queue.add(next); }
+            }
+            helper.assertTrue(seen.size() <= 120_000, "Native transit traversal exceeded its bounded room volumes");
+        }
+        return seen;
+    }
+    private static boolean ascendingStair(ServerLevel level, BlockPos pos, Direction direction) {
+        var state = level.getBlockState(pos);
+        return state.getBlock() instanceof StairBlock
+            && state.getValue(BlockStateProperties.HORIZONTAL_FACING) == direction
+            && state.getValue(BlockStateProperties.HALF) == net.minecraft.world.level.block.state.properties.Half.BOTTOM;
+    }
+    private static boolean standable(ServerLevel level, BlockPos pos) { return standable(level, Foot.at(pos)); }
+    private static boolean standable(ServerLevel level, Foot pos) {
+        if (!clearBody(level, pos)) return false;
+        var below = pos.bearing(); double top = pos.y() - below.getY();
+        return level.getBlockState(below).getCollisionShape(level, below).toAabbs().stream()
+            .anyMatch(b -> Math.abs(b.maxY - top) < .0001 && b.minX <= .5 && b.maxX >= .5 && b.minZ <= .5 && b.maxZ >= .5);
+    }
+    private static boolean clearBody(ServerLevel level, Foot pos) {
+        var body = new AABB(pos.x() + .2, pos.y(), pos.z() + .2, pos.x() + .8, pos.y() + 1.8, pos.z() + .8);
+        for (int y = (int) Math.floor(pos.y()); y <= (int) Math.floor(pos.y() + 1.8 - .0001); y++) {
+            var at = new BlockPos(pos.x(), y, pos.z());
+            if (!level.getFluidState(at).isEmpty()) return false;
+            for (var shape : level.getBlockState(at).getCollisionShape(level, at).toAabbs())
+                if (shape.move(at.getX(), at.getY(), at.getZ()).intersects(body)) return false;
+        }
+        return true;
+    }
+    private static BlockPos at(TransitPlan21.Module room, int x, int y, int z) { return new BlockPos(room.minX() + x, room.minY() + y, room.minZ() + z); }
+    private static List<Integer> coords(BlockPos pos) { return List.of(pos.getX(), pos.getY(), pos.getZ()); }
+    private static BlockPos readPos(com.google.gson.JsonArray value) { return new BlockPos(value.get(0).getAsInt(), value.get(1).getAsInt(), value.get(2).getAsInt()); }
+    private static Path world(ServerLevel level) { return level.getServer().getWorldPath(LevelResource.ROOT).toAbsolutePath().normalize(); }
+    private static Path proof(ServerLevel level) { return world(level).resolve("transit21-create-proof.json"); }
+    private static String planHash(TransitPlan21 plan) { return hash(plan.modules().toString()); }
+    private static void write(ServerLevel level, Map<String, Object> report, boolean reload) throws IOException {
+        var path = Path.of("diagnostics", "transit21-" + (reload ? "reload" : "create") + ".json"); Files.createDirectories(path.getParent());
+        var value = new GsonBuilder().setPrettyPrinting().create().toJson(report) + "\n";
+        Files.writeString(path, value);
+        if (!reload) Files.writeString(proof(level), value);
+    }
+    private static String hash(String value) {
+        try { return HexFormat.of().formatHex(MessageDigest.getInstance("SHA-256").digest(value.getBytes(StandardCharsets.UTF_8))); }
+        catch (NoSuchAlgorithmException impossible) { throw new AssertionError(impossible); }
+    }
+}

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/UnifiedWorldSettingsDiagnostics.java

@@ -52,7 +52,10 @@ final class UnifiedWorldSettingsDiagnostics {
         helper.assertTrue(historical19.overworld() instanceof SanctuaryChunkGenerator old && old.rootGeneration() == 19
                 && old.source().generation() == 19 && old.experimentalStructures(), "Historical19 keeps its original renderer and world settings");
         var generator = (SanctuaryChunkGenerator) standard.overworld();
-        helper.assertTrue(generator.rootGeneration() == 20 && generator.source().generation() == 20 && generator.experimentalStructures(), "The public preset uses generation20 with its new-world option");
+        var historical20 = presets.getOrThrow(ResourceKey.create(Registries.WORLD_PRESET, SanctuaryMod.id("sanctuary_v20")));
+        helper.assertTrue(historical20.value().createWorldDimensions().overworld() instanceof SanctuaryChunkGenerator old && old.rootGeneration() == 20
+                && old.source().generation() == 20 && old.experimentalStructures(), "Historical20 keeps its original architecture");
+        helper.assertTrue(generator.rootGeneration() == 21 && generator.source().generation() == 21 && generator.experimentalStructures(), "The public preset uses generation21 with its new-world option");
         helper.assertTrue(generator.initialDiameter() == 724, "The public preset defaults to Medium / 724 blocks");
         for (var tag : List.of(WorldPresetTags.NORMAL, WorldPresetTags.EXTENDED)) {
             var visible = presets.getOrThrow(tag).stream().map(holder -> holder.getRegisteredName())
@@ -62,11 +65,11 @@ final class UnifiedWorldSettingsDiagnostics {
         }
 
         var ops = RegistryOps.create(JsonOps.INSTANCE, access);
-        var activeCodec = generator.rootGeneration() == 20 ? SanctuaryChunkGenerator.ARCHITECTURE20_CODEC : generator.rootGeneration() == 19 ? SanctuaryChunkGenerator.HERITAGE19_CODEC : generator.rootGeneration() == 17 ? SanctuaryChunkGenerator.RUINS17_CODEC : generator.rootGeneration() == 16 ? SanctuaryChunkGenerator.CITY16_CODEC : generator.rootGeneration() == 15 ? SanctuaryChunkGenerator.CITY15_CODEC : generator.rootGeneration() == 14 ? SanctuaryChunkGenerator.CITY_CODEC : SanctuaryChunkGenerator.CODEC;
+        var activeCodec = generator.rootGeneration() == 21 ? SanctuaryChunkGenerator.NETWORK21_CODEC : generator.rootGeneration() == 20 ? SanctuaryChunkGenerator.ARCHITECTURE20_CODEC : generator.rootGeneration() == 19 ? SanctuaryChunkGenerator.HERITAGE19_CODEC : generator.rootGeneration() == 17 ? SanctuaryChunkGenerator.RUINS17_CODEC : generator.rootGeneration() == 16 ? SanctuaryChunkGenerator.CITY16_CODEC : generator.rootGeneration() == 15 ? SanctuaryChunkGenerator.CITY15_CODEC : generator.rootGeneration() == 14 ? SanctuaryChunkGenerator.CITY_CODEC : SanctuaryChunkGenerator.CODEC;
         var serialized = activeCodec.codec().encodeStart(ops, generator).getOrThrow().getAsJsonObject();
         serialized.remove("experimental_structures");
         helper.assertTrue(activeCodec.codec().parse(ops, serialized).getOrThrow().experimentalStructures(),
-            "Generation20 omitted experimental option defaults to enabled");
+            "Generation21 omitted experimental option defaults to enabled");
         helper.assertTrue(!((SanctuaryChunkGenerator) historical16.overworld()).withExperimentalStructures(true).experimentalStructures(),
             "The new-world switch cannot activate experimental generation in a historical16 generator");
         serialized.remove("initial_diameter");

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/mixin/SanctuaryGameTestServerMixin.java

@@ -21,7 +21,7 @@ public abstract class SanctuaryGameTestServerMixin {
     // generation test's deadline before its IO/workers can complete. This is test-only pacing.
     @Inject(method = "waitUntilNextTick", at = @At("RETURN"))
     private void sanctuary$paceExpansionWorkers(CallbackInfo ci) {
-        if (Boolean.getBoolean("sanctuary.test.heritage20") || Boolean.getBoolean("sanctuary.test.lostCity20")
+        if ((Boolean.getBoolean("sanctuary.test.heritage20") || Boolean.getBoolean("sanctuary.test.heritage21") || Boolean.getBoolean("sanctuary.test.lostCity21") || Boolean.getBoolean("sanctuary.test.transit21")) || Boolean.getBoolean("sanctuary.test.lostCity20")
                 || Boolean.getBoolean("sanctuary.test.heritage19") || Boolean.getBoolean("sanctuary.test.ruins17") || Boolean.getBoolean("sanctuary.test.expansion") || Boolean.getBoolean("sanctuary.test.lostCity")
                 || Boolean.getBoolean("sanctuary.test.lostCity16") || Boolean.getBoolean("sanctuary.test.lostCity15") || Boolean.getBoolean("sanctuary.test.voidReuse")) {
             long until = System.nanoTime() + 20_000_000L;
@@ -47,9 +47,9 @@ public abstract class SanctuaryGameTestServerMixin {
         "Lnet/minecraft/world/level/levelgen/presets/WorldPresets;FLAT_ALL_DIMENSIONS:Lnet/minecraft/resources/ResourceKey;"))
     private static ResourceKey<WorldPreset> sanctuary$selectActualPreset() {
         if (Boolean.getBoolean("sanctuary.test.unified")) {
-            int generation = Integer.getInteger("sanctuary.test.generation", 20);
+            int generation = Integer.getInteger("sanctuary.test.generation", 21);
-            if (generation != 13 && generation != 14 && generation != 15 && generation != 16 && generation != 17 && generation != 19 && generation != 20) throw new IllegalArgumentException("Unsupported test generation");
+            if (generation != 13 && generation != 14 && generation != 15 && generation != 16 && generation != 17 && generation != 19 && generation != 20 && generation != 21) throw new IllegalArgumentException("Unsupported test generation");
-            return ResourceKey.create(Registries.WORLD_PRESET, SanctuaryMod.id(generation == 20 ? "sanctuary" : "sanctuary_v" + generation));
+            return ResourceKey.create(Registries.WORLD_PRESET, SanctuaryMod.id(generation == 21 ? "sanctuary" : "sanctuary_v" + generation));
         }
         if (Boolean.getBoolean("sanctuary.test.expansion")) return ResourceKey.create(Registries.WORLD_PRESET, SanctuaryMod.id("expansion_lab"));
         int players = Integer.getInteger("sanctuary.test.players", 10);

mods/sanctuary/src/main/java/fr/koka/sanctuary/SanctuaryMod.java

@@ -65,6 +65,9 @@ public final class SanctuaryMod implements ModInitializer {
         Registry.register(BuiltInRegistries.BIOME_SOURCE, id("island_v19"), SanctuaryBiomeSource.HERITAGE19_CODEC);
         Registry.register(BuiltInRegistries.CHUNK_GENERATOR, id("island_v20"), SanctuaryChunkGenerator.ARCHITECTURE20_CODEC);
         Registry.register(BuiltInRegistries.BIOME_SOURCE, id("island_v20"), SanctuaryBiomeSource.ARCHITECTURE20_CODEC);
+        Registry.register(BuiltInRegistries.CHUNK_GENERATOR, id("island_v21"), SanctuaryChunkGenerator.NETWORK21_CODEC);
+        Registry.register(BuiltInRegistries.BIOME_SOURCE, id("island_v21"), SanctuaryBiomeSource.NETWORK21_CODEC);
+        fr.koka.sanctuary.worldgen.transit.TransitStructures21.register();
         fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.register();
         fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.register();
         Registry.register(BuiltInRegistries.DENSITY_FUNCTION_TYPE, id("population_island"), PopulationIslandDensity.CODEC);

mods/sanctuary/src/main/java/fr/koka/sanctuary/client/SanctuaryWorldOptionsScreen.java

@@ -51,11 +51,11 @@ public final class SanctuaryWorldOptionsScreen extends Screen {
         contents.addChild(sizeButton);
         diameterHint = contents.addChild(new MultiLineTextWidget(diameterHint(), font)
                 .setMaxWidth(310).setCentered(true));
-        if (generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20) {
+        if (generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21) {
             contents.addChild(CycleButton.builder((Boolean enabled) -> enabled ? CommonComponents.OPTION_ON : CommonComponents.OPTION_OFF, experimental)
                 .withValues(true, false).create(0, 0, 280, 20, Component.translatable("sanctuary.world_options.experimental"),
                     (button, value) -> experimental = value));
-            contents.addChild(new MultiLineTextWidget(Component.translatable((generator.rootGeneration() == 19 || generator.rootGeneration() == 20) ? "sanctuary.world_options.heritage_hint" : "sanctuary.world_options.experimental_hint"), font)
+            contents.addChild(new MultiLineTextWidget(Component.translatable((generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? "sanctuary.world_options.heritage_hint" : "sanctuary.world_options.experimental_hint"), font)
                 .setMaxWidth(310).setCentered(true));
         }
         layout.addToContents(contents);

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/ExpansionChunkGenerator.java

@@ -123,6 +123,7 @@ public class ExpansionChunkGenerator extends ChunkGenerator {
         fr.koka.sanctuary.worldgen.city.LostCityStructures.generate(this, registries, state, structures, chunk, templates, dimension);
         fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.generate(this, registries, state, structures, chunk, templates, dimension);
         fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.generate(this, registries, state, structures, chunk, templates, dimension);
+        fr.koka.sanctuary.worldgen.transit.TransitStructures21.generate(this, registries, state, structures, chunk, templates, dimension);
         ExpansionStructures.generate(this, registries, state, structures, chunk, templates, dimension);
     }
     @Override public void spawnOriginalMobs(WorldGenRegion region) {

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/ExpansionIsland.java

@@ -41,7 +41,7 @@ public record ExpansionIsland(String id, String parent, String direction, String
         if (!((spatialGeneration(generation) ? DIAMETERS : LEGACY_DIAMETERS).contains(diameter) || (id.equals("sanctuary") && (diameter == 724 || (generation == 13 || spatialGeneration(generation)) && diameter == 1024)))) throw new IllegalArgumentException("Unsupported nominal diameter");
         if (Math.abs((long) centerX) > 100_000 || Math.abs((long) centerZ) > 100_000 || (centerX & 15) != 0 || (centerZ & 15) != 0) throw new IllegalArgumentException("Invalid island centre");
         if (!List.of("reserved", "ready").contains(status) || (generation != GENERATION && !spatialGeneration(generation) && !(generation == 13 && id.equals("sanctuary")))) throw new IllegalArgumentException("Unsupported island state or generation");
-        if (climate.equals("lost_city") && (!spatialGeneration(generation) || id.equals("sanctuary"))) throw new IllegalArgumentException("Lost City requires a generation 14, 15, 16, 17, 19 or 20 expansion");
+        if (climate.equals("lost_city") && (!spatialGeneration(generation) || id.equals("sanctuary"))) throw new IllegalArgumentException("Lost City requires a generation 14, 15, 16, 17, 19, 20 or 21 expansion");
         if (reuseToken == null || !reuseToken.isEmpty() && (!spatialGeneration(generation) || id.equals("sanctuary") || !reuseToken.matches("[0-9a-f]{64}")))
             throw new IllegalArgumentException("Invalid void reuse certificate token");
     }
@@ -53,7 +53,7 @@ public record ExpansionIsland(String id, String parent, String direction, String
         return new ExpansionIsland("sanctuary", "sanctuary", "north", "temperate", diameter, 0, 0, seed, "natural", "ready", generation);
     }
 
-    public static boolean spatialGeneration(int generation) { return generation == 14 || generation == 15 || generation == 16 || generation == 17 || generation == 19 || generation == 20; }
+    public static boolean spatialGeneration(int generation) { return generation == 14 || generation == 15 || generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21; }
     public boolean origin() { return id.equals("sanctuary"); }
     public double referenceDiameter() { return origin() && diameter == 724 ? Math.sqrt(2) * 512 : 512; }
     public double horizontalScale() { return origin() ? 1.0 : diameter / referenceDiameter(); }

mods/sanctuary/src/main/java/fr/koka/sanctuary/mixin/UnifiedDecorationProtectionMixin.java

@@ -26,7 +26,8 @@ public abstract class UnifiedDecorationProtectionMixin {
         if (owner == null || destination == null || !owner.id().equals(destination.id())
                 || !fr.koka.sanctuary.worldgen.city.LostCityStructures.isPlacing()
                     && !fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.isPlacing()
-                    && !fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.isPlacing() && generator.protectsCityDecoration(pos))
+                    && !fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.isPlacing()
+                    && !fr.koka.sanctuary.worldgen.transit.TransitStructures21.isPlacing() && generator.protectsCityDecoration(pos))
             callback.setReturnValue(false);
     }
 
@@ -41,7 +42,7 @@ public abstract class UnifiedDecorationProtectionMixin {
         if (state.is(Blocks.SUGAR_CANE)) return;
         // Generation16 reserves its architectural volume before decoration. Only its own
         // native pieces may replace water there; published generations retain the old rule.
-        if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20)
+        if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21)
                 && fr.koka.sanctuary.worldgen.city.LostCityStructures.isPlacing()
                 && generator.protectsCityDecoration(pos)) return;
         if (generator.protectsDecoration(pos) && !region.getBlockState(pos).equals(state)) {

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/SanctuaryBiomeSource.java

@@ -50,6 +50,10 @@ public final class SanctuaryBiomeSource extends ExpansionBiomeSource {
         Biome.CODEC.listOf().fieldOf("biomes").forGetter(source -> source.allBiomes)
     ).apply(i, biomes -> new SanctuaryBiomeSource(biomes, 20)));
 
+    public static final MapCodec<SanctuaryBiomeSource> NETWORK21_CODEC = RecordCodecBuilder.mapCodec(i -> i.group(
+        Biome.CODEC.listOf().fieldOf("biomes").forGetter(source -> source.allBiomes)
+    ).apply(i, biomes -> new SanctuaryBiomeSource(biomes, 21)));
+
     private final List<Holder<Biome>> allBiomes;
     private final PopulationIslandBiomeSource population;
     private final boolean cities;
@@ -83,7 +87,7 @@ public final class SanctuaryBiomeSource extends ExpansionBiomeSource {
         cityPlans = java.util.Map.copyOf(plans);
     }
 
-    @Override protected MapCodec<SanctuaryBiomeSource> codec() { return generation == 20 ? ARCHITECTURE20_CODEC : generation == 19 ? HERITAGE19_CODEC : generation == 17 ? RUINS17_CODEC : generation == 16 ? CITY16_CODEC : generation == 15 ? CITY15_CODEC : cities ? CITY_CODEC : CODEC; }
+    @Override protected MapCodec<SanctuaryBiomeSource> codec() { return generation == 21 ? NETWORK21_CODEC : generation == 20 ? ARCHITECTURE20_CODEC : generation == 19 ? HERITAGE19_CODEC : generation == 17 ? RUINS17_CODEC : generation == 16 ? CITY16_CODEC : generation == 15 ? CITY15_CODEC : cities ? CITY_CODEC : CODEC; }
 
     @Override public BiomeResolver createResolver(Climate.Sampler sampler) {
         BiomeResolver woodlands = population.createResolver(sampler);

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/SanctuaryChunkGenerator.java

@@ -57,11 +57,25 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         Codec.BOOL.optionalFieldOf("experimental_structures", true).forGetter(SanctuaryChunkGenerator::experimentalStructures)
     ).apply(i, (source, diameter, experimental) -> new SanctuaryChunkGenerator(source, diameter, 20, experimental)));
 
+    public static final MapCodec<SanctuaryChunkGenerator> NETWORK21_CODEC = RecordCodecBuilder.mapCodec(i -> i.group(
+        SanctuaryBiomeSource.NETWORK21_CODEC.fieldOf("biome_source").forGetter(SanctuaryChunkGenerator::source),
+        DIAMETER_CODEC.optionalFieldOf("initial_diameter", 724).forGetter(SanctuaryChunkGenerator::initialDiameter),
+        Codec.BOOL.optionalFieldOf("experimental_structures", true).forGetter(SanctuaryChunkGenerator::experimentalStructures)
+    ).apply(i, (source, diameter, experimental) -> new SanctuaryChunkGenerator(source, diameter, 21, experimental)));
+
     private final boolean experimentalStructures;
     private volatile fr.koka.sanctuary.worldgen.ruins.RuinsPlan17 ruinsPlan17 = fr.koka.sanctuary.worldgen.ruins.RuinsPlan17.EMPTY;
     private boolean ruinsPrepared;
     private volatile fr.koka.sanctuary.worldgen.heritage.HeritagePlan19 heritagePlan19 = fr.koka.sanctuary.worldgen.heritage.HeritagePlan19.EMPTY;
     private boolean heritagePrepared;
+    private final java.util.Map<ExpansionIsland, fr.koka.sanctuary.worldgen.city.LostCityPlanner21.Result> cityPlacements21 = new java.util.concurrent.ConcurrentHashMap<>();
+    private volatile fr.koka.sanctuary.worldgen.transit.TransitPlan21 transitPlan21 = fr.koka.sanctuary.worldgen.transit.TransitPlan21.EMPTY;
+    private boolean transitPrepared;
+    public fr.koka.sanctuary.worldgen.transit.TransitPlan21 transitPlan21() { return transitPlan21; }
+    public fr.koka.sanctuary.worldgen.city.LostCityPlanner21.Result cityPlacement21(ExpansionIsland island) {
+        lostCityPlan(island);
+        return cityPlacements21.get(cityIdentity(island));
+    }
     private volatile Context originContext;
     private final int generation;
     private net.minecraft.world.level.LevelHeightAccessor heightAccessor;
@@ -97,12 +111,12 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
     }
     private SanctuaryChunkGenerator(SanctuaryBiomeSource source, int initialDiameter, int generation, boolean experimental) {
         super(source, initialDiameter, true);
-        this.experimentalStructures = (generation == 17 || generation == 19 || generation == 20) && experimental;
+        this.experimentalStructures = (generation == 17 || generation == 19 || generation == 20 || generation == 21) && experimental;
         this.generation = generation;
         if (generation != source.generation()) throw new IllegalArgumentException("Sanctuary generator and biome source versions must agree");
     }
     @Override public SanctuaryBiomeSource source() { return (SanctuaryBiomeSource) super.source(); }
-    @Override protected MapCodec<SanctuaryChunkGenerator> codec() { return generation == 20 ? ARCHITECTURE20_CODEC : generation == 19 ? HERITAGE19_CODEC : generation == 17 ? RUINS17_CODEC : generation == 16 ? CITY16_CODEC : generation == 15 ? CITY15_CODEC : generation == 14 ? CITY_CODEC : CODEC; }
+    @Override protected MapCodec<SanctuaryChunkGenerator> codec() { return generation == 21 ? NETWORK21_CODEC : generation == 20 ? ARCHITECTURE20_CODEC : generation == 19 ? HERITAGE19_CODEC : generation == 17 ? RUINS17_CODEC : generation == 16 ? CITY16_CODEC : generation == 15 ? CITY15_CODEC : generation == 14 ? CITY_CODEC : CODEC; }
     public SanctuaryChunkGenerator withInitialDiameter(int diameter) {
         return new SanctuaryChunkGenerator(source().copy(), diameter, generation, experimentalStructures);
     }
@@ -113,8 +127,9 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
     public fr.koka.sanctuary.worldgen.ruins.RuinsPlan17 ruinsPlan17() { return ruinsPlan17; }
     public fr.koka.sanctuary.worldgen.heritage.HeritagePlan19 heritagePlan19() { return heritagePlan19; }
     public boolean intersectsExperimentalStructures(int minX, int minY, int minZ, int maxX, int maxY, int maxZ) {
-        return (generation == 17 || generation == 19 || generation == 20) && ruinsPlan17.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ)
+        return (generation == 17 || generation == 19 || generation == 20 || generation == 21) && ruinsPlan17.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ)
-            || (generation == 19 || generation == 20) && heritagePlan19.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ);
+            || (generation == 19 || generation == 20 || generation == 21) && heritagePlan19.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ)
+            || generation == 21 && transitPlan21.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ);
     }
     public IslandCapacity capacity() {
         return switch (initialDiameter()) {
@@ -151,12 +166,14 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         prepareCities(islands);
         prepareRuins(islands);
         prepareHeritage(islands);
+        prepareTransit(islands);
     }
     @Override public void setIslands(List<ExpansionIsland> islands) {
         // Complete and publish city geometry before workers can observe the new owner list.
         prepareCities(islands);
         prepareRuins(islands);
         prepareHeritage(islands);
+        prepareTransit(islands);
         super.setIslands(islands);
     }
     private void prepareCities(List<ExpansionIsland> islands) {
@@ -167,7 +184,7 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             source().setCityPlans(java.util.Map.of());
             return;
         }
-        if ((generation == 16 || generation == 17 || generation == 19 || generation == 20) && !cityStructuresEnabled) {
+        if ((generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21) && !cityStructuresEnabled) {
             cityProtection16 = fr.koka.sanctuary.worldgen.city.LostCityProtection16.EMPTY;
             activeCityPlans = java.util.Map.of();
             source().setCityPlans(java.util.Map.of());
@@ -183,7 +200,7 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             }
             cityProtection15 = protection.build();
         }
-        if (generation == 16 || generation == 17 || generation == 19 || generation == 20) {
+        if (generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21) {
             var protection = new fr.koka.sanctuary.worldgen.city.LostCityProtection16.Builder();
             for (var island : islands) {
                 protection.add(published.get(island.id()), undergroundPlan16(island));
@@ -198,7 +215,7 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         source().setCityPlans(published);
     }
     private void prepareRuins(List<ExpansionIsland> islands) {
-        if ((generation != 17 && generation != 19 && generation != 20) || !experimentalStructures || !cityStructuresEnabled || ruinsPrepared) return;
+        if ((generation != 17 && generation != 19 && generation != 20 && generation != 21) || !experimentalStructures || !cityStructuresEnabled || ruinsPrepared) return;
         var root = islands.stream().filter(ExpansionIsland::origin).findFirst().orElseThrow();
         var terrain = context(root);
         var sampled = new fr.koka.sanctuary.worldgen.ruins.RuinsTerrain17(root, terrain.generator(), terrain.random(),
@@ -211,9 +228,23 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             root.seed(), plan.networks().size(), plan.samples(), sampled.columnsUsed(), (System.nanoTime() - start) / 1_000_000);
     }
     private void prepareHeritage(List<ExpansionIsland> islands) {
-        if ((generation != 19 && generation != 20) || !experimentalStructures || !cityStructuresEnabled || heritagePrepared) return;
+        if ((generation != 19 && generation != 20 && generation != 21) || !experimentalStructures || !cityStructuresEnabled || heritagePrepared) return;
         var root = islands.stream().filter(ExpansionIsland::origin).findFirst().orElseThrow();
         var terrain = context(root);
+        if (generation == 21) {
+            var sampled = new fr.koka.sanctuary.worldgen.heritage.HeritageTerrain21(root, terrain.generator(), terrain.random(),
+                heightAccessor, pos -> protectsDecoration(pos) || cityProtection16.contains(pos.getX(), pos.getY(), pos.getZ())
+                    || ruinsPlan17.protects(pos.getX(), pos.getY(), pos.getZ()));
+            long start = System.nanoTime();
+            sampled.discoverLandmarks(lostCityPlan(root), ruinsPlan17);
+            var plan = fr.koka.sanctuary.worldgen.heritage.HeritagePlanner21.plan(root.seed(), root.centerX(), root.centerZ(), root.diameter(), sampled);
+            heritagePlan19 = plan;
+            heritagePrepared = true;
+            SanctuaryMod.LOGGER.info("Heritage21 seed {}: {} sites, {} routes, {} segments, {} probes, {} native columns in {} ms; {}",
+                root.seed(), plan.sites().size(), plan.links().size(), plan.segments().size(), plan.samples(), sampled.columnsUsed(),
+                (System.nanoTime() - start) / 1_000_000, plan.diagnostics());
+            return;
+        }
         var sampled = new fr.koka.sanctuary.worldgen.heritage.HeritageTerrain19(root, terrain.generator(), terrain.random(),
             heightAccessor, pos -> protectsDecoration(pos) || cityProtection16.contains(pos.getX(), pos.getY(), pos.getZ())
                 || ruinsPlan17.protects(pos.getX(), pos.getY(), pos.getZ()));
@@ -226,6 +257,19 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             root.seed(), plan.sites().size(), plan.links().size(), plan.segments().size(), plan.samples(), sampled.columnsUsed(),
             (System.nanoTime() - start) / 1_000_000, plan.diagnostics());
     }
+    private void prepareTransit(List<ExpansionIsland> islands) {
+        if (generation != 21 || !experimentalStructures || !cityStructuresEnabled || transitPrepared) return;
+        var root = islands.stream().filter(ExpansionIsland::origin).findFirst().orElseThrow();
+        var terrain = context(root);
+        var sampled = new fr.koka.sanctuary.worldgen.transit.TransitTerrain21(root, terrain.generator(), terrain.random(),
+            heightAccessor, pos -> protectsDecoration(pos) || cityProtection16.contains(pos.getX(), pos.getY(), pos.getZ())
+                || ruinsPlan17.protects(pos.getX(), pos.getY(), pos.getZ()) || heritagePlan19.protects(pos.getX(), pos.getY(), pos.getZ()));
+        long start = System.nanoTime();
+        transitPlan21 = fr.koka.sanctuary.worldgen.transit.TransitPlanner21.plan(root.seed(), root.centerX(), root.centerZ(), root.diameter(), sampled);
+        transitPrepared = true;
+        SanctuaryMod.LOGGER.info("Transit21 seed {}: {} modules, {} probes, {} columns in {} ms; {}", root.seed(),
+            transitPlan21.modules().size(), transitPlan21.samples(), sampled.columnsUsed(), (System.nanoTime() - start) / 1_000_000, transitPlan21.diagnostic());
+    }
     private static ExpansionIsland cityIdentity(ExpansionIsland island) {
         // State and receipt do not change the terrain geometry used by a cached plan.
         var ready = island.status().equals("ready") ? island : island.ready();
@@ -236,6 +280,7 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         var key = cityIdentity(island);
         if (source().islands().stream().noneMatch(saved -> cityIdentity(saved).equals(key))) {
             cityPlans.remove(key);
+            cityPlacements21.remove(key);
             undergroundPlans.remove(key);
             undergroundPlans16.remove(key);
             citySupports.remove(key);
@@ -251,6 +296,39 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         return cityPlans.computeIfAbsent(cityIdentity(island), ignored -> {
             long start = System.nanoTime();
             var terrain = context(island);
+            if (generation == 21) {
+                var sampled = new fr.koka.sanctuary.worldgen.city.LostCityTerrain21(island, terrain.generator(), terrain.random(),
+                    heightAccessor, pos -> island.origin() && protectsDecoration(pos));
+                var placement = fr.koka.sanctuary.worldgen.city.LostCityPlanner21.plan(island.seed(), island.centerX(), island.centerZ(),
+                    island.diameter(), island.origin(), sampled);
+                var surface = placement.surface();
+                cityPlacements21.put(cityIdentity(island), placement);
+                citySupports16.put(cityIdentity(island), placement.supports());
+                if (placement.reservation() != null) cityReservations16.put(cityIdentity(island), placement.reservation());
+                var supports = new fr.koka.sanctuary.worldgen.city.LostCityProtection16.Builder();
+                for (var support : placement.supports()) supports.addViaductSupport(support);
+                if (placement.reservation() != null) supports.addReservation(placement.reservation());
+                var extraDistricts = surface.districts().stream()
+                    .filter(d -> !placement.core().surface().districts().contains(d)).toList();
+                supports.add(new fr.koka.sanctuary.worldgen.city.LostCityPlan(extraDistricts),
+                    new fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Plan(List.of(), 0));
+                var supportMask = supports.build();
+                var underground = fr.koka.sanctuary.worldgen.city.LostCityUnderground16.plan(island.seed(), placement.core().surface(),
+                    new fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Terrain() {
+                        @Override public boolean solid(int x, int y, int z) { return sampled.solid(x, y, z); }
+                        @Override public boolean owns(int x, int z) { return sampled.owns(x, z); }
+                        @Override public boolean exteriorAir(int x, int y, int z, int dx, int dz) { return sampled.exteriorAir(x, y, z, dx, dz); }
+                        @Override public boolean protectedAt(int x, int y, int z) {
+                            return supportMask.contains(x, y, z) || sampled.protectedAt(x, y, z);
+                        }
+                    });
+                undergroundPlans16.put(cityIdentity(island), underground);
+                SanctuaryMod.LOGGER.info("Lost City21 {} seed {}: {} city districts, {} underground networks, {} noise columns in {} ms",
+                    island.id(), island.seed(), surface.districts().size(), underground.networks().size(), sampled.columnsUsed(),
+                    (System.nanoTime() - start) / 1_000_000);
+                SanctuaryMod.LOGGER.info("City21 extensions: {}", placement.diagnostics());
+                return surface;
+            }
             if (generation == 16 || generation == 17 || generation == 19 || generation == 20) {
                 var sampled = new fr.koka.sanctuary.worldgen.city.LostCityTerrain16(island, terrain.generator(), terrain.random(),
                     heightAccessor, pos -> island.origin() && protectsDecoration(pos));
@@ -322,9 +400,10 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         });
     }
     public boolean protectsCityDecoration(net.minecraft.core.BlockPos pos) {
-        if (generation == 16 || generation == 17 || generation == 19 || generation == 20) return cityProtection16.contains(pos.getX(), pos.getY(), pos.getZ())
+        if (generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21) return cityProtection16.contains(pos.getX(), pos.getY(), pos.getZ())
-            || (generation == 17 || generation == 19 || generation == 20) && ruinsPlan17.protects(pos.getX(), pos.getY(), pos.getZ())
+            || (generation == 17 || generation == 19 || generation == 20 || generation == 21) && ruinsPlan17.protects(pos.getX(), pos.getY(), pos.getZ())
-            || (generation == 19 || generation == 20) && heritagePlan19.protects(pos.getX(), pos.getY(), pos.getZ());
+            || (generation == 19 || generation == 20 || generation == 21) && heritagePlan19.protects(pos.getX(), pos.getY(), pos.getZ())
+            || generation == 21 && transitPlan21.protects(pos.getX(), pos.getY(), pos.getZ());
         if (generation == 15) return cityProtection15.contains(pos.getX(), pos.getY(), pos.getZ());
         if (generation != 14) return false;
         var island = islandAt(pos.getX(), pos.getZ());
@@ -346,20 +425,20 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
         return citySupports.getOrDefault(cityIdentity(island), List.of());
     }
     public boolean intersectsCityConstruction16(int minX, int minY, int minZ, int maxX, int maxY, int maxZ) {
-        return (generation == 16 || generation == 17 || generation == 19 || generation == 20) && cityProtection16.intersects(minX, minY, minZ, maxX, maxY, maxZ);
+        return (generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21) && cityProtection16.intersects(minX, minY, minZ, maxX, maxY, maxZ);
     }
     public fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Plan undergroundPlan16(ExpansionIsland island) {
-        if (generation != 16 && generation != 17 && generation != 19 && generation != 20) return new fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Plan(List.of(), 0);
+        if (generation != 16 && generation != 17 && generation != 19 && generation != 20 && generation != 21) return new fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Plan(List.of(), 0);
         lostCityPlan(island);
         return undergroundPlans16.getOrDefault(cityIdentity(island), new fr.koka.sanctuary.worldgen.city.LostCityUnderground16.Plan(List.of(), 0));
     }
     public List<LostCityPlanner16.Support> citySupports16(ExpansionIsland island) {
-        if (generation != 16 && generation != 17 && generation != 19 && generation != 20) return List.of();
+        if (generation != 16 && generation != 17 && generation != 19 && generation != 20 && generation != 21) return List.of();
         lostCityPlan(island);
         return citySupports16.getOrDefault(cityIdentity(island), List.of());
     }
     public LostCityPlanner16.Fallback cityReservation16(ExpansionIsland island) {
-        if (generation != 16 && generation != 17 && generation != 19 && generation != 20) return null;
+        if (generation != 16 && generation != 17 && generation != 19 && generation != 20 && generation != 21) return null;
         lostCityPlan(island);
         return cityReservations16.get(cityIdentity(island));
     }
@@ -371,10 +450,12 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             net.minecraft.core.BlockPos origin, int radius, boolean skipReferenced) {
         if (structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.city.LostCityStructures.KEY))
             return fr.koka.sanctuary.worldgen.city.LostCityStructures.findNearest(level, structures, origin, radius, skipReferenced);
-        if ((generation == 17 || generation == 19 || generation == 20) && structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.KEY))
+        if ((generation == 17 || generation == 19 || generation == 20 || generation == 21) && structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.KEY))
             return fr.koka.sanctuary.worldgen.ruins.RuinsStructures17.findNearest(level, structures, origin, radius, skipReferenced);
-        if ((generation == 19 || generation == 20) && structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.KEY))
+        if ((generation == 19 || generation == 20 || generation == 21) && structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.KEY))
             return fr.koka.sanctuary.worldgen.heritage.HeritageStructures19.findNearest(level, structures, origin, radius, skipReferenced);
+        if (generation == 21 && structures.size() == 1 && structures.get(0).is(fr.koka.sanctuary.worldgen.transit.TransitStructures21.KEY))
+            return fr.koka.sanctuary.worldgen.transit.TransitStructures21.findNearest(level, structures, origin, radius, skipReferenced);
         return super.findNearestMapStructure(level, structures, origin, radius, skipReferenced);
     }
     @Override protected Context context(ExpansionIsland island) {
@@ -402,7 +483,7 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
     @Override protected void afterTerrain(ExpansionIsland island, ChunkAccess chunk) {
         // Root water/lava are already applied by the Population hook on the named delegate.
         if (!island.origin()) super.afterTerrain(island, chunk);
-        if ((generation == 16 || generation == 17 || generation == 19 || generation == 20) && cityStructuresEnabled) {
+        if ((generation == 16 || generation == 17 || generation == 19 || generation == 20 || generation == 21) && cityStructuresEnabled) {
             var reserved = cityReservations16.get(cityIdentity(island));
             if (reserved != null) {
                 var mutable = new net.minecraft.core.BlockPos.MutableBlockPos();

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityInteriors21.java

@@ -0,0 +1,767 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Kind;
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Parcel;
+import java.util.ArrayList;
+import fr.koka.sanctuary.worldgen.detail.ConnectedBlocks20;
+import java.util.List;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.Rotation;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BedPart;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.block.state.properties.DoorHingeSide;
+import net.minecraft.world.level.block.state.properties.DoubleBlockHalf;
+import net.minecraft.world.level.block.state.properties.SlabType;
+import net.minecraft.world.level.storage.loot.BuiltInLootTables;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** Complete generation-21 buildings. Published renderers deliberately never call this renderer.
+ * A north-facing plan is rotated once; all positions remain relative to the saved parcel. */
+public final class LostCityInteriors21 {
+    private static final BlockState AIR = Blocks.AIR.defaultBlockState();
+    private static final BlockState STONE = Blocks.STONE.defaultBlockState();
+    private static final BlockState SMOOTH = Blocks.SMOOTH_STONE.defaultBlockState();
+    private static final BlockState WOOD = Blocks.OAK_PLANKS.defaultBlockState();
+    private static final BlockState TILE = Blocks.POLISHED_ANDESITE.defaultBlockState();
+    private static final int STOREY = 5;
+
+    private LostCityInteriors21() {}
+
+    /** Reachable standing positions, in the same rotated local coordinates as BlockWriter. */
+    public record Room(String name, int x, int y, int z) {}
+
+    /** Local, already rotated enclosure including the floor, full ceiling, four walls and door. */
+    public record Bathroom(String name, int minX, int minY, int minZ, int maxX, int maxY, int maxZ,
+                           int doorX, int doorY, int doorZ) {}
+
+    private record Area(int left, int front, int right, int back) {}
+
+    /** Adjacent storeys always change plan; the saved parcel seed chooses which plan comes first. */
+    public static int layout(Parcel parcel, int floor) {
+        validate(parcel);
+        if (floor < 0 || floor >= parcel.floors()) throw new IllegalArgumentException("Invalid interior floor");
+        return (int) ((parcel.seed() ^ (parcel.seed() >>> 32)) & 1L) ^ (floor & 1);
+    }
+
+    private static Area rear(Parcel p, int floor, boolean east) {
+        boolean wide = layout(p, floor) == 1;
+        return east ? new Area(wide ? 10 : 11, wide ? 10 : 11, 14, 14)
+            : new Area(2, wide ? 10 : 11, wide ? 6 : 5, 14);
+    }
+
+    private static int frontWall(Parcel p, int floor) { return layout(p, floor) == 0 ? 7 : 8; }
+
+    private static String frontUse(Parcel p, int floor) {
+        int variant = layout(p, floor);
+        return switch (p.kind()) {
+            case APARTMENT -> variant == 0 ? "kitchen_dining" : "studio_bedroom";
+            case HOTEL -> floor == 0 ? "reception" : "guest_suite";
+            case LIBRARY -> variant == 0 ? "book_stacks" : "periodicals_reading";
+            case RESTAURANT -> variant == 0 ? "dining_room" : "kitchen";
+            case BARRACKS -> variant == 0 ? "dormitory" : "duty_office";
+            case HALL -> floor == 0 ? "ticket_office" : "administration";
+            default -> throw new IllegalArgumentException("Not an interior kind");
+        };
+    }
+
+    private static String rearUse(Parcel p, int floor, boolean east) {
+        int variant = layout(p, floor);
+        return switch (p.kind()) {
+            case APARTMENT -> east ? "bathroom" : variant == 0 ? "bedroom" : "kitchen_dining";
+            case HOTEL -> floor == 0 ? east ? "laundry" : "lounge"
+                : variant == 0 ? east ? "guest_room" : "bedroom" : east ? "bathroom" : "guest_lounge";
+            case LIBRARY -> variant == 0 ? east ? "archive" : "reading_room" : east ? "bathroom" : "catalogue_office";
+            case RESTAURANT -> variant == 0 ? east ? "kitchen" : "washrooms" : east ? "pantry" : "dining_room";
+            case BARRACKS -> east ? "equipment_store" : variant == 0 ? "washrooms" : "officer_bedroom";
+            case HALL -> variant == 0 ? east ? "bathroom" : "meeting_room" : east ? "meeting_room" : "archive";
+            default -> throw new IllegalArgumentException("Not an interior kind");
+        };
+    }
+
+    public static void render(Parcel parcel, LostCityRenderer.BlockWriter output) {
+        validate(parcel);
+        var connected = ConnectedBlocks20.buffer(output);
+        new Building(parcel, connected).render();
+        connected.flush();
+    }
+
+    /** These describe actual rooms and services, not decorative labels placed in the world. */
+    public static List<Room> rooms(Parcel parcel) {
+        validate(parcel);
+        List<Room> result = new ArrayList<>();
+        add(result, parcel, "street_entrance", 8, 1, 0);
+        add(result, parcel, "vestibule", 8, 1, 3);
+        for (int floor = 0; floor < parcel.floors(); floor++) {
+            int y = floor * STOREY + 1;
+            String prefix = "floor_" + floor + "/";
+            add(result, parcel, prefix + "corridor", 8, y, 8);
+            add(result, parcel, prefix + "stair_landing", 4, y, 8);
+            add(result, parcel, prefix + frontUse(parcel, floor), 11, y, 6);
+            if (parcel.kind() == Kind.HALL && floor < 2) {
+                if (floor == 0) {
+                    add(result, parcel, prefix + "auditorium", 8, y, 11);
+                    add(result, parcel, prefix + "stage", 9, y + 1, 13);
+                } else add(result, parcel, prefix + "gallery", 8, y, 10);
+            } else {
+                Area west = rear(parcel, floor, false), east = rear(parcel, floor, true);
+                add(result, parcel, prefix + rearUse(parcel, floor, false), west.right(), y, 11);
+                add(result, parcel, prefix + rearUse(parcel, floor, true), east.left(), y, 11);
+            }
+        }
+        for (var bath : bathroomPlans(parcel)) {
+            int targetZ = bath.southDoor() ? bath.z1() - 1 : bath.z0() + 1;
+            add(result, parcel, bath.name(), bath.doorX(), bath.floor() * STOREY + 1, targetZ);
+        }
+        add(result, parcel, "roof", 8, parcel.floors() * STOREY + 1, 8);
+        switch (parcel.kind()) {
+            case HOTEL -> add(result, parcel, "roof_laundry_pavilion", 10, parcel.floors() * STOREY + 1, 5);
+            case APARTMENT -> add(result, parcel, "roof_residents_terrace", 8, parcel.floors() * STOREY + 1, 10);
+            case LIBRARY -> add(result, parcel, "roof_reading_terrace", 11, parcel.floors() * STOREY + 1, 10);
+            case RESTAURANT -> add(result, parcel, "roof_dining_terrace", 11, parcel.floors() * STOREY + 1, 8);
+            case BARRACKS -> add(result, parcel, "roof_service_stair", 4, parcel.floors() * STOREY + 1, 8);
+            default -> { }
+        }
+        return List.copyOf(result);
+    }
+
+    private record BathPlan(String name, int floor, int x0, int z0, int x1, int z1, int doorX, boolean southDoor) {}
+
+    private static List<BathPlan> bathroomPlans(Parcel p) {
+        List<BathPlan> result = new ArrayList<>();
+        for (int floor = 0; floor < p.floors(); floor++) {
+            if (p.kind() == Kind.HOTEL && floor > 0)
+                result.add(new BathPlan("floor_" + floor + "/suite_bathroom", floor, 10, 1, 15, 4, 12, true));
+            if (p.kind() == Kind.HALL && floor < 2) continue;
+            for (boolean east : new boolean[]{false, true}) {
+                String use = rearUse(p, floor, east);
+                if (!use.equals("bathroom") && !use.equals("washrooms")) continue;
+                Area room = rear(p, floor, east);
+                result.add(new BathPlan("floor_" + floor + "/" + (east ? "east" : "west") + "_bathroom_interior",
+                    floor, room.left() - 1, 12, room.right() + 1, 15, east ? 12 : 4, false));
+            }
+        }
+        return List.copyOf(result);
+    }
+
+    public static List<Bathroom> bathrooms(Parcel p) {
+        validate(p);
+        List<Bathroom> result = new ArrayList<>();
+        for (var b : bathroomPlans(p)) {
+            int x0 = rx(b.x0(), b.z0(), p.facing()), z0 = rz(b.x0(), b.z0(), p.facing());
+            int x1 = rx(b.x1(), b.z1(), p.facing()), z1 = rz(b.x1(), b.z1(), p.facing());
+            int doorZ = b.southDoor() ? b.z1() : b.z0();
+            result.add(new Bathroom(b.name(), Math.min(x0, x1), b.floor() * STOREY, Math.min(z0, z1),
+                Math.max(x0, x1), b.floor() * STOREY + 4, Math.max(z0, z1), rx(b.doorX(), doorZ, p.facing()),
+                b.floor() * STOREY + 1, rz(b.doorX(), doorZ, p.facing())));
+        }
+        return List.copyOf(result);
+    }
+
+    private static void validate(Parcel p) {
+        if (!p.kind().building() || p.width() != 17 || p.depth() != 17 || p.floors() < 2)
+            throw new IllegalArgumentException("Generation-21 interiors require a 17x17 building with 2..5 floors");
+    }
+
+    private static void add(List<Room> result, Parcel p, String name, int x, int y, int z) {
+        result.add(new Room(name, rx(x, z, p.facing()), y, rz(x, z, p.facing())));
+    }
+    private static int rx(int x, int z, int facing) {
+        return switch (facing) { case 0 -> x; case 1 -> 16 - z; case 2 -> 16 - x; default -> z; };
+    }
+    private static int rz(int x, int z, int facing) {
+        return switch (facing) { case 0 -> z; case 1 -> x; case 2 -> 16 - z; default -> 16 - x; };
+    }
+
+    private static final class Building {
+        final Parcel p;
+        final LostCityRenderer.BlockWriter output;
+        final Rotation rotation;
+        Building(Parcel p, LostCityRenderer.BlockWriter output) {
+            this.p = p;
+            this.output = output;
+            rotation = switch (p.facing()) {
+                case 0 -> Rotation.NONE; case 1 -> Rotation.CLOCKWISE_90;
+                case 2 -> Rotation.CLOCKWISE_180; default -> Rotation.COUNTERCLOCKWISE_90;
+            };
+        }
+        void set(int x, int y, int z, BlockState state) {
+            output.set(rx(x, z, p.facing()), y, rz(x, z, p.facing()), state.rotate(rotation));
+        }
+        void set(int x, int y, int z, Block block) { set(x, y, z, block.defaultBlockState()); }
+        void box(int x0, int y0, int z0, int x1, int y1, int z1, BlockState state) {
+            for (int x = x0; x <= x1; x++) for (int z = z0; z <= z1; z++)
+                for (int y = y0; y <= y1; y++) set(x, y, z, state);
+        }
+        BlockState facing(Block block, Direction direction) {
+            return block.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, direction);
+        }
+        BlockState brick(int x, int y, int z) { return LostCityPalette.masonry(p.seed(), x, y, z); }
+        BlockState weatheredBrick(int x, int y, int z) {
+            // Weathering follows a few masonry joints, never private room partitions.
+            int weather = roll(x, y, z, 12);
+            return (weather == 0 ? Blocks.MOSSY_STONE_BRICKS : weather < 3
+                ? Blocks.CRACKED_STONE_BRICKS : Blocks.STONE_BRICKS).defaultBlockState();
+        }
+        int roll(int x, int y, int z, int bound) { return LostCityPalette.roll(p.seed(), x, y, z, bound); }
+
+        void render() {
+            int roof = p.floors() * STOREY;
+            box(0, -p.foundationDepth(), 0, 16, -1, 16, Blocks.STONE_BRICKS.defaultBlockState());
+            box(0, 0, 0, 16, 0, 16, SMOOTH);
+            box(0, 1, 0, 16, roof + 4, 16, AIR);
+            shell(roof);
+            architecturalEnvelope(roof);
+            for (int floor = 0; floor < p.floors(); floor++) {
+                partitions(floor);
+                furnishings(floor);
+            }
+            stairs();
+            entrance();
+            roof(roof);
+            // Only one deferred loot table per building; empty furniture is not a resource vault.
+            int lootX = 6;
+            int lootZ = 6;
+            box(lootX, 2, lootZ, lootX, 3, lootZ, AIR);
+            ResourceKey<LootTable> table = switch (p.kind()) {
+                case LIBRARY, HALL -> BuiltInLootTables.VILLAGE_CARTOGRAPHER;
+                case RESTAURANT -> BuiltInLootTables.VILLAGE_BUTCHER;
+                case BARRACKS -> BuiltInLootTables.VILLAGE_FLETCHER;
+                default -> BuiltInLootTables.VILLAGE_PLAINS_HOUSE;
+            };
+            output.chest(rx(lootX, lootZ, p.facing()), 1, rz(lootX, lootZ, p.facing()), table,
+                p.seed() ^ 0x21c17a7eL ^ p.kind().ordinal());
+        }
+
+        void shell(int roof) {
+            for (int floor = 0; floor <= p.floors(); floor++) {
+                int base = floor * STOREY;
+                for (int x = 1; x <= 15; x++) for (int z = 1; z <= 15; z++)
+                    set(x, base, z, floor == p.floors() ? SMOOTH : floorMaterial(floor, x, z));
+                if (floor == p.floors()) continue;
+                // A pale ceiling and contrasting structural floor are separate layers.
+                box(2, base + 4, 2, 14, base + 4, 14,
+                    Blocks.SMOOTH_STONE_SLAB.defaultBlockState().setValue(BlockStateProperties.SLAB_TYPE, SlabType.TOP));
+                for (int y = 1; y <= 4; y++) for (int horizontal = 1; horizontal <= 15; horizontal++) {
+                    facade(horizontal, base + y, 1, horizontal, y, true);
+                    facade(horizontal, base + y, 15, horizontal, y, true);
+                    facade(1, base + y, horizontal, horizontal, y, false);
+                    facade(15, base + y, horizontal, horizontal, y, false);
+                }
+                // Floor bands remain intact even where windows have fallen out.
+                for (int n = 1; n <= 15; n++) {
+                    set(n, base, 1, SMOOTH); set(n, base, 15, SMOOTH);
+                    set(1, base, n, SMOOTH); set(15, base, n, SMOOTH);
+                }
+                if (p.kind() == Kind.HOTEL || p.kind() == Kind.LIBRARY) {
+                    for (int x : new int[]{3, 13}) for (int y = 0; y <= 4; y++) set(x, base + y, 0, SMOOTH);
+                }
+                if (p.kind() == Kind.APARTMENT) for (int x = 11; x <= 14; x++)
+                    set(x, base + 1, 0, Blocks.SMOOTH_STONE_SLAB);
+                if (p.kind() == Kind.RESTAURANT) box(10, base + 4, 0, 14, base + 4, 0,
+                    Blocks.OAK_SLAB.defaultBlockState());
+            }
+            if (p.kind() == Kind.HALL) {
+                // The auditorium spans two storeys; its upper level is a guarded gallery.
+                box(3, 4, 11, 13, 5, 14, AIR);
+                for (int x = 3; x <= 13; x++) set(x, 6, 11, rail(true));
+                for (int z = 12; z <= 14; z++) { set(3, 6, z, rail(false)); set(13, 6, z, rail(false)); }
+            }
+        }
+
+        BlockState floorMaterial(int floor, int x, int z) {
+            if (x == 1 || z == 1 || x == 15 || z == 15) return SMOOTH;
+            return switch (p.kind()) {
+                case LIBRARY -> (x <= 5 || z >= 10 ? Blocks.OAK_PLANKS : Blocks.SMOOTH_STONE).defaultBlockState();
+                case APARTMENT, HOTEL -> WOOD;
+                case RESTAURANT -> ((x / 3 + z / 3) & 1) == 0 ? SMOOTH : TILE;
+                case BARRACKS -> x <= 5 ? TILE : WOOD;
+                default -> x == 7 || x == 9 ? TILE : SMOOTH;
+            };
+        }
+
+        BlockState pier() {
+            return switch (p.kind()) {
+                case APARTMENT, LIBRARY -> Blocks.STRIPPED_OAK_LOG.defaultBlockState();
+                case HOTEL, RESTAURANT -> SMOOTH;
+                case BARRACKS -> Blocks.STONE_BRICKS.defaultBlockState();
+                default -> Blocks.CHISELED_STONE_BRICKS.defaultBlockState();
+            };
+        }
+
+        void facade(int x, int y, int z, int horizontal, int withinFloor, boolean eastWest) {
+            boolean column = horizontal == 1 || horizontal == 6 || horizontal == 10 || horizontal == 15;
+            boolean window = !column && (withinFloor == 2 || withinFloor == 3
+                || withinFloor == 1 && (p.kind() == Kind.LIBRARY || p.kind() == Kind.RESTAURANT || p.kind() == Kind.HALL));
+            if (column) set(x, y, z, pier());
+            else if (window) {
+                if (roll(x, y / 5, z, 17) != 0) set(x, y, z,
+                    p.kind() == Kind.BARRACKS ? rail(eastWest) : pane(eastWest));
+            } else set(x, y, z, withinFloor == 4 && horizontal % 5 == 0
+                ? weatheredBrick(x, y, z) : SMOOTH);
+        }
+
+        /** Volume belongs to its use: projected bays, clipped corners and distinct roof profiles. */
+        void architecturalEnvelope(int roof) {
+            for (int floor = 0; floor < p.floors(); floor++) {
+                int y = floor * STOREY;
+                // Project the floor plates as a continuous, one-block cornice inside the parcel.
+                for (int n = 1; n <= 15; n++) {
+                    set(n, y, 0, stairTrim(Direction.NORTH)); set(n, y, 16, stairTrim(Direction.SOUTH));
+                    set(0, y, n, stairTrim(Direction.WEST)); set(16, y, n, stairTrim(Direction.EAST));
+                }
+                switch (p.kind()) {
+                    case APARTMENT -> {
+                        // Bay windows increase the living room rather than drawing flat stripes on it.
+                        for (int z : new int[]{4, 5, 6, 11, 12, 13}) {
+                            set(16, y, z, Blocks.OAK_PLANKS);
+                            set(16, y + 1, z, Blocks.OAK_PLANKS);
+                            set(16, y + 2, z, Blocks.GLASS_PANE);
+                            set(16, y + 3, z, Blocks.GLASS_PANE);
+                            set(16, y + 4, z, Blocks.OAK_SLAB.defaultBlockState().setValue(BlockStateProperties.SLAB_TYPE, SlabType.TOP));
+                        }
+                        for (int z : new int[]{3, 7, 10, 14}) box(16, y + 1, z, 16, y + 4, z, pier());
+                        // Original wall remains the sill, with an open bay above it; privacy walls restore themselves later.
+                        for (int z : new int[]{4, 5, 6, 11, 12, 13}) box(15, y + 2, z, 15, y + 3, z, AIR);
+                        bevelFront(y);
+                    }
+                    case HOTEL -> {
+                        for (int x : new int[]{2, 5, 11, 14}) box(x, y + 1, 0, x, y + 4, 0, pier());
+                        for (int x : new int[]{3, 4, 12, 13}) set(x, y + 1, 0, Blocks.OAK_FENCE);
+                        box(2, y + 4, 0, 5, y + 4, 0, Blocks.OAK_PLANKS.defaultBlockState());
+                        box(11, y + 4, 0, 14, y + 4, 0, Blocks.OAK_PLANKS.defaultBlockState());
+                    }
+                    case LIBRARY -> {
+                        // Tall fins frame broad glazing and project beyond the reading rooms.
+                        for (int x : new int[]{2, 5, 11, 14}) box(x, y + 1, 0, x, y + 4, 0, Blocks.STRIPPED_OAK_LOG.defaultBlockState());
+                        for (int x : new int[]{3, 4, 12, 13}) {
+                            set(x, y + 4, 0, Blocks.OAK_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+                        }
+                        bevelFront(y);
+                    }
+                    case RESTAURANT -> {
+                        // Separate fascia and timber valance shelter the shop windows.
+                        for (int x = 10; x <= 14; x++) {
+                            set(x, y + 3, 0, Blocks.OAK_SLAB);
+                            set(x, y + 4, 0, Blocks.OAK_PLANKS);
+                        }
+                        for (int z : new int[]{3, 7, 11, 14}) set(16, y + 4, z, Blocks.ANDESITE);
+                    }
+                    case BARRACKS -> {
+                        for (int z : new int[]{2, 7, 12, 15}) box(0, y + 1, z, 0, y + 4, z, pier());
+                        for (int x : new int[]{2, 5, 11, 14}) box(x, y + 1, 0, x, y + 4, 0, Blocks.STONE_BRICKS.defaultBlockState());
+                        for (int x : new int[]{3, 4, 12, 13}) set(x, y + 1, 0, Blocks.CHISELED_STONE_BRICKS);
+                    }
+                    case HALL -> {
+                        for (int x : new int[]{2, 5, 11, 14}) box(x, y + 1, 0, x, y + 4, 0, pier());
+                        for (int x = 2; x <= 14; x++) set(x, y + 4, 0,
+                            Blocks.ANDESITE_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+                    }
+                    default -> throw new IllegalStateException();
+                }
+            }
+        }
+
+        BlockState stairTrim(Direction outward) {
+            Block block = Blocks.STONE_BRICK_STAIRS;
+            return facing(block, outward.getOpposite()).setValue(BlockStateProperties.HALF,
+                net.minecraft.world.level.block.state.properties.Half.TOP);
+        }
+
+        void bevelFront(int y) {
+            // Remove two rectangular corners and close them with actual stepped returns.
+            for (int x : new int[]{1, 15}) {
+                box(x, y, 1, x, y + 4, 1, AIR);
+                int adjacent = x == 1 ? 2 : 14;
+                box(adjacent, y + 1, 1, adjacent, y + 4, 1, pier());
+                box(x, y + 1, 2, x, y + 4, 2, pier());
+            }
+        }
+
+        void partitions(int floor) {
+            int y = floor * STOREY;
+            int front = frontWall(p, floor);
+            // The west stairwell, central corridor and vestibule are independent of furniture.
+            box(5, y + 1, 2, 5, y + 4, 9, SMOOTH);
+            door(5, y + 1, 8, Direction.WEST, false);
+            box(10, y + 1, 2, 10, y + 4, front, SMOOTH);
+            box(10, y + 1, front, 15, y + 4, front, SMOOTH);
+            door(10, y + 1, 6, Direction.EAST, false);
+            if (floor == 0) {
+                box(6, 1, 4, 9, 4, 4, SMOOTH);
+                door(8, 1, 4, Direction.SOUTH, false);
+            }
+            if (p.kind() == Kind.HALL && floor < 2) {
+                if (floor == 0) {
+                    box(2, 1, 10, 14, 4, 10, SMOOTH);
+                    door(7, 1, 10, Direction.SOUTH, true);
+                    door(8, 1, 10, Direction.SOUTH, false);
+                }
+            } else {
+                Area west = rear(p, floor, false), east = rear(p, floor, true);
+                box(1, y + 1, west.front() - 1, west.right() + 1, y + 4, west.front() - 1, SMOOTH);
+                box(west.right() + 1, y + 1, west.front() - 1, west.right() + 1, y + 4, 15, SMOOTH);
+                box(east.left() - 1, y + 1, east.front() - 1, 15, y + 4, east.front() - 1, SMOOTH);
+                box(east.left() - 1, y + 1, east.front() - 1, east.left() - 1, y + 4, 15, SMOOTH);
+                door(west.right() + 1, y + 1, 11, Direction.WEST, false);
+                door(east.left() - 1, y + 1, 11, Direction.EAST, false);
+            }
+            // A hanging lantern touches a full ceiling block, never the recessed underside of a top slab.
+            set(8, y + 4, 8, SMOOTH);
+            set(8, y + 3, 8, Blocks.LANTERN.defaultBlockState().setValue(BlockStateProperties.HANGING, true));
+            // Weathering stays on facades and roofs: it must not replace a privacy partition.
+        }
+
+        void furnishings(int floor) {
+            int y = floor * STOREY;
+            int variant = layout(p, floor);
+            switch (p.kind()) {
+                case APARTMENT -> {
+                    if (variant == 0) { kitchenFront(y); bedroom(floor, false); }
+                    else { frontBedroom(floor); kitchenRear(floor, false); }
+                }
+                case HOTEL -> {
+                    if (floor == 0) { reception(y); lounge(floor, false); laundry(floor); }
+                    else {
+                        anchoredBed(14, y + 1, frontWall(p, floor) - 2, Direction.SOUTH);
+                        set(11, y + 1, 5, Blocks.BARREL); set(11, y + 2, 5, Blocks.FLOWER_POT);
+                        if (variant == 0) { bedroom(floor, false); bedroom(floor, true); }
+                        else lounge(floor, false);
+                    }
+                }
+                case LIBRARY -> {
+                    if (variant == 0) {
+                        box(14, y + 1, 2, 14, y + 3, 6, Blocks.BOOKSHELF.defaultBlockState());
+                        box(12, y + 1, 2, 12, y + 2, 3, Blocks.BOOKSHELF.defaultBlockState());
+                        desk(12, y, 5, Direction.SOUTH);
+                        readingRoom(floor, false); archive(floor, true);
+                    } else {
+                        readingFront(y); readingRoom(floor, false);
+                        set(2, y + 1, 14, Blocks.CARTOGRAPHY_TABLE);
+                    }
+                }
+                case RESTAURANT -> {
+                    if (variant == 0) {
+                        table(13, y, 3); table(13, y, 5);
+                        set(11, y + 1, 2, Blocks.POTTED_DEAD_BUSH);
+                        kitchenRear(floor, true);
+                    } else {
+                        kitchenFront(y); diningRear(floor, false); pantry(floor, true);
+                    }
+                }
+                case BARRACKS -> {
+                    if (variant == 0) {
+                        anchoredBed(12, y + 1, 3, Direction.NORTH); anchoredBed(14, y + 1, 3, Direction.NORTH);
+                        set(11, y + 1, 2, Blocks.BARREL); set(11, y + 2, 2, Blocks.BARREL);
+                        seat(13, y + 1, 6, Direction.NORTH);
+                    } else { reception(y); bedroom(floor, false); }
+                    box(12, y + 1, 14, 14, y + 2, 14, Blocks.BARREL.defaultBlockState());
+                    set(14, y + 1, 11, Blocks.FLETCHING_TABLE);
+                    set(12, y + 1, 11, Blocks.GRINDSTONE.defaultBlockState()
+                        .setValue(BlockStateProperties.ATTACH_FACE,
+                            net.minecraft.world.level.block.state.properties.AttachFace.FLOOR));
+                }
+                case HALL -> {
+                    if (floor == 0 || floor > 1 && variant == 0) reception(y); else readingFront(y);
+                    if (floor == 0) auditorium();
+                    else if (floor >= 2) {
+                        if (variant == 0) readingRoom(floor, false);
+                        else { archive(floor, false); readingRoom(floor, true); }
+                    }
+                }
+                default -> throw new IllegalArgumentException("Not an interior kind");
+            }
+            for (var bath : bathroomPlans(p)) if (bath.floor() == floor) bathroom(bath);
+        }
+
+        void kitchenFront(int y) {
+            kitchenLine(y, 11, 2, Direction.SOUTH);
+            table(13, y, 5);
+        }
+
+        void kitchenRear(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            kitchenLine(y, room.left(), 14, Direction.NORTH);
+            if (east) {
+                set(14, y + 1, 11, SMOOTH); set(14, y + 2, 11, Blocks.FLOWER_POT);
+                set(12, y + 1, 11, Blocks.CRAFTING_TABLE);
+            } else table(room.left() + 2, y, 11);
+        }
+
+        void kitchenLine(int y, int left, int z, Direction face) {
+            set(left, y + 1, z, facing(Blocks.FURNACE, face));
+            set(left + 1, y + 1, z, Blocks.WATER_CAULDRON.defaultBlockState().setValue(BlockStateProperties.LEVEL_CAULDRON, 2));
+            set(left + 2, y + 1, z, facing(Blocks.SMOKER, face));
+            set(left + 3, y + 1, z, Blocks.BARREL);
+            box(left, y + 3, z, left + 3, y + 3, z, SMOOTH);
+            set(left + 2, y + 2, z, Blocks.IRON_TRAPDOOR);
+            for (int x = left; x <= left + 3; x++) set(x, y + 3, z, Blocks.SMOOTH_STONE);
+            for (int x = left; x <= left + 3; x++) set(x, y, z, (x & 1) == 0 ? SMOOTH : TILE);
+        }
+
+        void bedroom(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            anchoredBed(east ? room.right() - 1 : room.left() + 1, y + 1, 13, east ? Direction.EAST : Direction.WEST);
+            set(east ? room.right() : room.left(), y + 1, 11, Blocks.BARREL);
+            desk(east ? room.left() + 1 : room.right() - 1, y, 11, Direction.SOUTH);
+            set(east ? room.left() : room.right(), y + 1, 14, Blocks.BOOKSHELF);
+        }
+
+        void frontBedroom(int floor) {
+            int y = floor * STOREY;
+            anchoredBed(14, y + 1, 3, Direction.NORTH);
+            set(11, y + 1, 2, Blocks.BARREL); set(11, y + 2, 2, Blocks.FLOWER_POT);
+            desk(12, y, 5, Direction.SOUTH);
+        }
+
+        void bathroom(BathPlan bath) {
+            int y = bath.floor() * STOREY;
+            for (int x = bath.x0(); x <= bath.x1(); x++) for (int z = bath.z0(); z <= bath.z1(); z++) {
+                set(x, y, z, ((x + z) & 1) == 0 ? SMOOTH : TILE);
+                set(x, y + 4, z, SMOOTH);
+                boolean wall = x == bath.x0() || x == bath.x1() || z == bath.z0() || z == bath.z1();
+                for (int up = 1; up <= 3; up++) set(x, y + up, z, wall ? SMOOTH : AIR);
+            }
+            int doorZ = bath.southDoor() ? bath.z1() : bath.z0();
+            door(bath.doorX(), y + 1, doorZ, bath.southDoor() ? Direction.NORTH : Direction.SOUTH, false);
+            int fixtureZ = bath.southDoor() ? bath.z0() + 1 : bath.z1() - 1;
+            int toiletX = bath.southDoor() ? bath.x1() - 2 : bath.x0() + 1;
+            Direction view = bath.southDoor() ? Direction.SOUTH : Direction.EAST;
+            set(toiletX, y + 1, fixtureZ, seating(Blocks.POLISHED_ANDESITE_STAIRS, view));
+            set(toiletX, y + 2, fixtureZ, Blocks.IRON_TRAPDOOR);
+            set(bath.x1() - 1, y + 1, fixtureZ, Blocks.WATER_CAULDRON.defaultBlockState().setValue(BlockStateProperties.LEVEL_CAULDRON, 2));
+        }
+
+        void reception(int y) {
+            box(12, y + 1, 5, 14, y + 1, 5, Blocks.OAK_PLANKS.defaultBlockState());
+            set(13, y + 2, 5, Blocks.FLOWER_POT);
+            set(14, y + 1, 2, Blocks.BOOKSHELF); set(14, y + 2, 2, Blocks.BARREL);
+            desk(12, y, 3, Direction.SOUTH);
+            set(11, y + 1, 2, Blocks.POTTED_DEAD_BUSH);
+        }
+
+        void laundry(int floor) {
+            int y = floor * STOREY;
+            for (int z = 11; z <= 12; z++) set(14, y + 1, z, Blocks.WATER_CAULDRON.defaultBlockState()
+                .setValue(BlockStateProperties.LEVEL_CAULDRON, z == 11 ? 1 : 2));
+            box(12, y + 1, 14, 14, y + 1, 14, Blocks.BARREL.defaultBlockState());
+            // The rack stands on the storage counter; recessed rear glazing cannot carry it.
+            for (int x : new int[]{12, 14}) set(x, y + 2, 14, Blocks.OAK_PLANKS);
+            box(12, y + 3, 14, 14, y + 3, 14, Blocks.OAK_SLAB.defaultBlockState());
+            set(12, y + 1, 11, Blocks.LOOM);
+        }
+
+        void lounge(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            box(room.left(), y + 1, 14, room.left() + 2, y + 1, 14, seating(Blocks.OAK_STAIRS, Direction.NORTH));
+            desk(room.left() + 1, y, 11, Direction.SOUTH);
+            set(room.left(), y + 1, 12, Blocks.BOOKSHELF);
+        }
+
+        void readingRoom(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            desk(east ? room.left() + 1 : room.right() - 1, y, 11, Direction.SOUTH);
+            box(room.left(), y + 1, 14, room.right(), y + 2, 14, Blocks.BOOKSHELF.defaultBlockState());
+            set(east ? room.right() : room.left(), y + 1, 11, facing(Blocks.LECTERN, Direction.NORTH));
+        }
+
+        void readingFront(int y) {
+            desk(12, y, 3, Direction.SOUTH);
+            box(14, y + 1, 2, 14, y + 2, 5, Blocks.BOOKSHELF.defaultBlockState());
+            set(11, y + 1, 2, facing(Blocks.LECTERN, Direction.SOUTH));
+        }
+
+        void archive(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            box(room.left(), y + 1, 14, room.right(), y + 3, 14, Blocks.BOOKSHELF.defaultBlockState());
+            box(east ? room.right() : room.left(), y + 1, 11, east ? room.right() : room.left(), y + 2, 12, Blocks.BARREL.defaultBlockState());
+            set(room.left() + 1, y + 1, 12, facing(Blocks.LECTERN, Direction.NORTH));
+        }
+
+        void pantry(int floor, boolean east) {
+            int y = floor * STOREY;
+            Area room = rear(p, floor, east);
+            box(room.left(), y + 1, 14, room.right(), y + 2, 14, Blocks.BARREL.defaultBlockState());
+            set(room.right(), y + 1, 11, Blocks.CRAFTING_TABLE);
+            set(room.right(), y + 2, 11, Blocks.FLOWER_POT);
+        }
+
+        void diningRear(int floor, boolean east) {
+            Area room = rear(p, floor, east);
+            int y = floor * STOREY;
+            table(room.left() + 2, y, 12);
+            box(room.left(), y + 1, 14, room.right(), y + 1, 14, seating(Blocks.OAK_STAIRS, Direction.NORTH));
+        }
+
+        void auditorium() {
+            for (int x : new int[]{3, 4, 5, 11, 12, 13}) seat(x, 1, 11, Direction.SOUTH);
+            box(3, 1, 13, 13, 1, 14, WOOD);
+            set(8, 1, 12, facing(Blocks.OAK_STAIRS, Direction.SOUTH));
+            set(8, 2, 14, facing(Blocks.LECTERN, Direction.NORTH));
+            for (int x : new int[]{3, 13}) {
+                box(x, 2, 14, x, 3, 14, WOOD);
+                set(x, 4, 14, Blocks.STONE_BRICK_SLAB);
+            }
+        }
+
+        void stairs() {
+            for (int floor = 0; floor < p.floors(); floor++) {
+                int base = floor * STOREY;
+                for (int step = 1; step <= STOREY; step++) {
+                    int z = step + 2;
+                    box(2, base + step, z, 3, base + step + 3, z, AIR);
+                    for (int x = 2; x <= 3; x++) {
+                        // A one-block inclined spine joins successive treads physically, without
+                        // filling the headroom above the preceding storey's matching flight.
+                        set(x, base + step - 1, z, Blocks.STONE_BRICKS);
+                        set(x, base + step, z, facing(Blocks.STONE_BRICK_STAIRS, Direction.SOUTH));
+                    }
+                }
+                box(2, base + STOREY, 8, 4, base + STOREY, 9, TILE);
+                box(2, base + STOREY + 1, 8, 4, base + STOREY + 3, 9, AIR);
+            }
+            // This full-height side aisle joins every lower stair approach to its landing door.
+            for (int floor = 0; floor <= p.floors(); floor++) {
+                int y = floor * STOREY;
+                box(4, y + 1, 2, 4, y + 3, 9, AIR);
+            }
+        }
+
+        void entrance() {
+            for (int x : new int[]{6, 9}) box(x, 1, 0, x, 3, 0, SMOOTH);
+            box(6, 4, 0, 9, 4, 1, Blocks.STONE_BRICK_SLAB.defaultBlockState());
+            box(7, 0, 0, 8, 0, 3, TILE);
+            // Native SOUTH/RIGHT opens against the west jamb; SOUTH/LEFT against the east jamb.
+            door(7, 1, 1, Direction.SOUTH, true);
+            door(8, 1, 1, Direction.SOUTH, false);
+            set(4, 1, 0, Blocks.POTTED_DEAD_BUSH);
+            set(12, 1, 16, Blocks.COMPOSTER);
+        }
+
+        void roof(int y) {
+            // Clipped parapets and a heavy coping keep each accessible roof legible from below.
+            for (int n = 2; n <= 14; n++) {
+                set(n, y + 1, 1, Blocks.STONE_BRICKS); set(n, y + 1, 15, Blocks.STONE_BRICKS);
+                set(1, y + 1, n, Blocks.STONE_BRICKS); set(15, y + 1, n, Blocks.STONE_BRICKS);
+                set(n, y + 2, 1, Blocks.STONE_BRICK_SLAB); set(n, y + 2, 15, Blocks.STONE_BRICK_SLAB);
+                set(1, y + 2, n, Blocks.STONE_BRICK_SLAB); set(15, y + 2, n, Blocks.STONE_BRICK_SLAB);
+            }
+            switch (p.kind()) {
+                case APARTMENT -> {
+                    // Two small roof gardens and a timber portico leave the stair landing and central crossing free.
+                    roofPlanter(10, y, 4); roofPlanter(10, y, 12);
+                    for (int x : new int[]{6, 13}) box(x, y + 1, 14, x, y + 3, 14, Blocks.STRIPPED_OAK_LOG.defaultBlockState());
+                    box(6, y + 4, 14, 13, y + 4, 14, Blocks.OAK_SLAB.defaultBlockState());
+                    desk(8, y, 12, Direction.NORTH);
+                }
+                case HOTEL -> {
+                    roofRoom(y, 9, 3, 14, 7, Blocks.SMOOTH_STONE);
+                    door(9, y + 1, 5, Direction.EAST, false);
+                    set(12, y + 1, 4, Blocks.BARREL); set(13, y + 1, 4, Blocks.LOOM);
+                    box(11, y + 1, 12, 13, y + 1, 12, seating(Blocks.OAK_STAIRS, Direction.NORTH));
+                }
+                case LIBRARY -> {
+                    // One transparent cap above a hollow timber curb, open all the way to the stacks.
+                    // No opaque former roof plate or second glass floor remains under this canopy.
+                    for (int x = 10; x <= 13; x++) for (int z = 3; z <= 7; z++) {
+                        boolean edge = x == 10 || x == 13 || z == 3 || z == 7;
+                        set(x, y + 1, z, edge ? Blocks.STRIPPED_OAK_LOG.defaultBlockState() : AIR);
+                        set(x, y + 2, z, edge ? Blocks.OAK_SLAB : Blocks.GLASS);
+                    }
+                    box(11, y - 1, 4, 12, y + 1, 6, AIR);
+                    desk(11, y, 12, Direction.NORTH); set(14, y + 1, 12, Blocks.LECTERN);
+                }
+                case RESTAURANT -> {
+                    // A real dining terrace and rear kitchen extraction with full supporting columns.
+                    table(11, y, 6); table(11, y, 11);
+                    for (int z : new int[]{3, 14}) box(14, y + 1, z, 14, y + 3, z, Blocks.STRIPPED_OAK_LOG.defaultBlockState());
+                    box(14, y + 4, 3, 14, y + 4, 14, Blocks.OAK_PLANKS.defaultBlockState());
+                    box(6, y + 1, 14, 7, y + 3, 14, Blocks.STONE_BRICKS.defaultBlockState());
+                    set(6, y + 4, 14, Blocks.IRON_BARS); set(7, y + 4, 14, Blocks.IRON_BARS);
+                }
+                case BARRACKS -> {
+                    // Enclosed stair head gives the barracks a service tower, without hiding its usable exit.
+                    // The whole last flight sits inside the stair head: a front wall at z=6
+                    // would cross the headroom over its penultimate step.
+                    roofRoom(y, 1, 2, 5, 10, Blocks.SMOOTH_STONE);
+                    door(5, y + 1, 8, Direction.EAST, false);
+                    box(10, y + 1, 12, 13, y + 1, 14, Blocks.POLISHED_ANDESITE.defaultBlockState());
+                    set(11, y + 2, 13, Blocks.IRON_TRAPDOOR);
+                }
+                case HALL -> {
+                    for (int step = 0; step < 3; step++) {
+                        int edge = 2 + step * 2;
+                        box(edge, y + 1 + step, 1, 16 - edge, y + 1 + step, 2, Blocks.STONE_BRICKS.defaultBlockState());
+                    }
+                    for (int x : new int[]{6, 10}) set(x, y + 4, 2, Blocks.CHISELED_STONE_BRICKS);
+                    desk(11, y, 12, Direction.NORTH);
+                }
+                default -> throw new IllegalStateException();
+            }
+        }
+
+        void roofRoom(int y, int x0, int z0, int x1, int z1, Block wall) {
+            for (int x = x0; x <= x1; x++) for (int z = z0; z <= z1; z++) {
+                boolean edge = x == x0 || x == x1 || z == z0 || z == z1;
+                for (int up = 1; up <= 3; up++) set(x, y + up, z, edge ? wall.defaultBlockState() : AIR);
+                // A bottom slab touches the full-height walls immediately below it.
+                // A top slab here would float half a block above the pavilion.
+                set(x, y + 4, z, Blocks.STONE_BRICK_SLAB.defaultBlockState());
+            }
+        }
+        void roofPlanter(int x, int y, int z) {
+            for (int dx = 0; dx <= 3; dx++) set(x + dx, y + 1, z, Blocks.STONE_BRICKS);
+            set(x + 1, y + 1, z, Blocks.DIRT); set(x + 2, y + 1, z, Blocks.DIRT);
+            set(x + 1, y + 2, z, Blocks.OXEYE_DAISY); set(x + 2, y + 2, z, Blocks.CORNFLOWER);
+        }
+
+        void door(int x, int y, int z, Direction facing, boolean rightHinge) {
+            BlockState state = facing(Blocks.OAK_DOOR, facing)
+                .setValue(BlockStateProperties.DOOR_HINGE, rightHinge ? DoorHingeSide.RIGHT : DoorHingeSide.LEFT)
+                .setValue(BlockStateProperties.OPEN, false)
+                .setValue(BlockStateProperties.POWERED, false);
+            set(x, y, z, state.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF, DoubleBlockHalf.LOWER));
+            set(x, y + 1, z, state.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF, DoubleBlockHalf.UPPER));
+        }
+        void anchoredBed(int x, int y, int z, Direction facing) {
+            BlockState state = facing(Blocks.BED.white(), facing);
+            set(x, y, z, state.setValue(BlockStateProperties.BED_PART, BedPart.FOOT));
+            set(x + facing.getStepX(), y, z + facing.getStepZ(), state.setValue(BlockStateProperties.BED_PART, BedPart.HEAD));
+            int wallX = x + facing.getStepX() * 2, wallZ = z + facing.getStepZ() * 2;
+            Direction alongWall = facing.getClockWise();
+            for (int width = -1; width <= 1; width++) for (int up = 0; up <= 3; up++)
+                set(wallX + alongWall.getStepX() * width, y + up, wallZ + alongWall.getStepZ() * width, SMOOTH);
+        }
+        void table(int x, int y, int z) {
+            set(x, y + 1, z, Blocks.OAK_FENCE); set(x, y + 2, z, Blocks.OAK_PRESSURE_PLATE);
+            seat(x - 1, y + 1, z, Direction.EAST);
+            seat(x + 1, y + 1, z, Direction.WEST);
+        }
+        void desk(int x, int y, int z, Direction approachSide) {
+            set(x, y + 1, z, Blocks.OAK_FENCE); set(x, y + 2, z, Blocks.OAK_PRESSURE_PLATE);
+            seat(x + approachSide.getStepX(), y + 1, z + approachSide.getStepZ(), approachSide.getOpposite());
+        }
+        void seat(int x, int y, int z, Direction lookingToward) {
+            set(x, y, z, seating(Blocks.OAK_STAIRS, lookingToward));
+        }
+        BlockState seating(Block stair, Direction lookingToward) {
+            // Stair FACING points uphill, into its full-height back, opposite a seated player's view.
+            return facing(stair, lookingToward.getOpposite());
+        }
+        BlockState rail(boolean eastWest) { return connected(Blocks.IRON_BARS, eastWest); }
+        BlockState pane(boolean eastWest) { return connected(Blocks.GLASS_PANE, eastWest); }
+        BlockState connected(Block block, boolean eastWest) {
+            return block.defaultBlockState().setValue(BlockStateProperties.EAST, eastWest)
+                .setValue(BlockStateProperties.WEST, eastWest).setValue(BlockStateProperties.NORTH, !eastWest)
+                .setValue(BlockStateProperties.SOUTH, !eastWest);
+        }
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityPiece21.java

@@ -0,0 +1,92 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import java.util.Arrays;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.StructureManager;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.levelgen.structure.BoundingBox;
+import net.minecraft.world.level.levelgen.structure.StructurePiece;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceSerializationContext;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** Generation21 surface parcel. Its distinct native type preserves all published city renderers. */
+public final class LostCityPiece21 extends StructurePiece {
+    private static final int SCHEMA = 1;
+    private final LostCityPlan.Parcel parcel;
+
+    public LostCityPiece21(LostCityPlan.Parcel parcel) {
+        super(LostCityStructures.PIECE21, 0, bounds(parcel));
+        this.parcel = parcel;
+        setOrientation(null);
+    }
+
+    public LostCityPiece21(StructurePieceSerializationContext context, CompoundTag tag) {
+        super(LostCityStructures.PIECE21, tag);
+        if (tag.getInt("SanctuarySchema").orElseThrow() != SCHEMA)
+            throw new IllegalArgumentException("Unsupported Lost City piece schema");
+        parcel = new LostCityPlan.Parcel(LostCityPlan.Kind.valueOf(tag.getString("Kind").orElseThrow()),
+            tag.getInt("MinX").orElseThrow(), tag.getInt("MinZ").orElseThrow(),
+            tag.getInt("Width").orElseThrow(), tag.getInt("Depth").orElseThrow(),
+            tag.getInt("FloorY").orElseThrow(), tag.getInt("Floors").orElseThrow(),
+            tag.getInt("Facing").orElseThrow(), tag.getLong("ParcelSeed").orElseThrow(),
+            tag.getInt("FoundationDepth").orElseThrow(), tag.getIntArray("SurfaceHeights").orElseThrow());
+        if (!getBoundingBox().equals(bounds(parcel)))
+            throw new IllegalArgumentException("Lost City parcel disagrees with its saved native bounding box");
+        setOrientation(null);
+    }
+
+    public LostCityPlan.Parcel parcel() { return parcel; }
+
+    @Override public BlockPos getLocatorPosition() {
+        int x = parcel.width() / 2, z = parcel.depth() / 2;
+        return new BlockPos(parcel.minX() + x, parcel.surfaceY(x, z) + 1, parcel.minZ() + z);
+    }
+
+    @Override protected void addAdditionalSaveData(StructurePieceSerializationContext context, CompoundTag tag) {
+        tag.putInt("SanctuarySchema", SCHEMA);
+        tag.putString("Kind", parcel.kind().name());
+        tag.putInt("MinX", parcel.minX()); tag.putInt("MinZ", parcel.minZ());
+        tag.putInt("Width", parcel.width()); tag.putInt("Depth", parcel.depth());
+        tag.putInt("FloorY", parcel.floorY()); tag.putInt("Floors", parcel.floors());
+        tag.putInt("Facing", parcel.facing()); tag.putLong("ParcelSeed", parcel.seed());
+        tag.putInt("FoundationDepth", parcel.foundationDepth());
+        tag.putIntArray("SurfaceHeights", parcel.surfaceHeights());
+    }
+
+    @Override public void postProcess(WorldGenLevel level, StructureManager structures, ChunkGenerator generator,
+            RandomSource random, BoundingBox chunkClip, ChunkPos chunkPos, BlockPos pivot) {
+        LostCityStructures.placing(() -> render(parcel, new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState block) {
+                BlockPos pos = world(x, y, z);
+                if (getBoundingBox().isInside(pos) && chunkClip.isInside(pos))
+                    placeBlock(level, block, pos.getX(), pos.getY(), pos.getZ(), chunkClip);
+            }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> loot, long seed) {
+                BlockPos pos = world(x, y, z);
+                if (getBoundingBox().isInside(pos) && chunkClip.isInside(pos))
+                    createChest(level, chunkClip, RandomSource.create(seed), pos, loot, null);
+            }
+        }));
+    }
+
+    private static void render(LostCityPlan.Parcel parcel, LostCityRenderer.BlockWriter writer) {
+        LostCitySurface21.render(parcel, writer);
+    }
+
+    private BlockPos world(int x, int y, int z) {
+        return new BlockPos(parcel.minX() + x, parcel.floorY() + y, parcel.minZ() + z);
+    }
+
+    private static BoundingBox bounds(LostCityPlan.Parcel parcel) {
+        int low = Math.min(parcel.floorY(), Arrays.stream(parcel.surfaceHeights()).min().orElse(parcel.floorY()))
+            - parcel.foundationDepth();
+        int high = Math.max(parcel.maxY(), Arrays.stream(parcel.surfaceHeights()).max().orElse(parcel.floorY()) + 5);
+        return new BoundingBox(parcel.minX(), low, parcel.minZ(), parcel.maxX(), high, parcel.maxZ());
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityPlanner21.java

@@ -0,0 +1,248 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.*;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/** Preserve the certified compact16 core. At most two modest natural outlying blocks are admitted
+ * together with complete three-wide approaches; a failed route publishes neither its road nor its block. */
+public final class LostCityPlanner21 {
+    public static final int MAX_EXTRA_COLUMNS = 4_000, MAX_EXTRA_CHECKS = 220_000;
+    public static final int MAX_COLUMNS = LostCityPlanner16.MAX_COLUMNS + MAX_EXTRA_COLUMNS;
+    public static final int MAX_VOLUME_CHECKS = LostCityPlanner16.MAX_VOLUME_CHECKS + MAX_EXTRA_CHECKS;
+    private static final int[] DX = {0, 1, 0, -1}, DZ = {-1, 0, 1, 0};
+    private static final int INVALID = Integer.MIN_VALUE;
+    private LostCityPlanner21() {}
+    public record Point(int x, int floorY, int z) {}
+    public record Connection(int districtIndex, List<Point> path) { public Connection { path = List.copyOf(path); } }
+    public record Result(LostCityPlanner16.Result core, LostCityPlan surface,
+                         List<LostCityPlanner16.Support> supports, int columns, int volumeChecks,
+                         List<Connection> connections, Map<String, Integer> diagnostics) {
+        public Result {
+            supports = List.copyOf(supports); connections = List.copyOf(connections); diagnostics = Map.copyOf(diagnostics);
+            if (columns > MAX_COLUMNS || volumeChecks > MAX_VOLUME_CHECKS || connections.size() > 2)
+                throw new IllegalArgumentException("Generation21 city exceeded its bounded extension");
+        }
+        public LostCityPlanner16.Fallback reservation() { return core.reservation(); }
+    }
+    public static Result plan(long seed, int cx, int cz, int diameter, boolean origin, LostCityPlanner16.Terrain terrain) {
+        var core = LostCityPlanner16.plan(seed, cx, cz, diameter, origin, terrain);
+        var districts = new ArrayList<>(core.surface().districts()); var supports = new ArrayList<>(core.supports());
+        var links = new ArrayList<Connection>(); var probe = new Probe(terrain);
+        if (origin && !districts.isEmpty()) {
+            var center = districts.getFirst(); int mx = (center.minX() + center.maxX()) / 2, mz = (center.minZ() + center.maxZ()) / 2;
+            int first = (int) Long.remainderUnsigned(mix(seed ^ 0x21c175L), 4);
+            try {
+                for (int attempt = 0; attempt < 8 && links.size() < 2; attempt++) {
+                    int d = (first + attempt) & 3;
+                    int radius = Math.max(center.maxX() - center.minX(), center.maxZ() - center.minZ()) / 2 + (attempt < 4 ? 42 : 58);
+                    int x = mx + DX[d] * radius, z = mz + DZ[d] * radius;
+                    probe.reject("cluster-attempt");
+                    // The old one-lot natural solver already certifies foundations, ramps and short supported bridges.
+                    var mini = LostCityPlanner16.plan(mix(seed ^ attempt * 3191L ^ 0x2100L), x, z, 96, false, probe);
+                    if (mini.surface().isEmpty()) { probe.reject("no-natural-block"); continue; }
+                    var district = mini.surface().districts().getFirst();
+                    if (overlap(district, districts, 14)) { probe.reject("insufficient-natural-gap"); continue; }
+                    var all = new ArrayList<>(districts); all.add(district);
+                    var path = connect(seed ^ attempt, center, district, all, probe);
+                    if (path == null) { probe.reject("no-complete-approach"); continue; }
+                    var parcels = new ArrayList<>(district.parcels()); parcels.addAll(path.roads());
+                    District joined;
+                    try { joined = new District(district.startChunkX(), district.startChunkZ(), district.seed(), parcels); }
+                    catch (IllegalArgumentException tooWide) { probe.reject("native-reference-radius"); continue; }
+                    links.add(new Connection(districts.size(), path.path())); districts.add(joined); supports.addAll(mini.supports());
+                    probe.reject("connected-cluster");
+                }
+            } catch (Exhausted exhausted) { probe.reject("extension-budget"); }
+        }
+        return new Result(core, new LostCityPlan(districts), supports, core.columns() + probe.columns.size(),
+            core.volumeChecks() + probe.checks, links, probe.reasons);
+    }
+    private record Entry(int x, int y, int z, int facing) {}
+    private record XZ(int x, int z) { XZ move(int d, int n) { return new XZ(x + DX[d] * n, z + DZ[d] * n); } }
+    private record Pair(Entry a, Entry b) {}
+    private record Road(int x, int z, int floor, int foundation) {}
+    private record Footprint(int x, int z, int width, int depth) {}
+    private record Route(List<Point> path, List<Parcel> roads) {}
+    private static Route connect(long seed, District core, District extra, List<District> all, Probe probe) {
+        var pairs = new ArrayList<Pair>();
+        for (var a : entries(core, all)) for (var b : entries(extra, all)) pairs.add(new Pair(a, b));
+        pairs.sort(Comparator.comparingInt(p -> Math.abs(p.a.x - p.b.x) + Math.abs(p.a.z - p.b.z)));
+        for (var pair : pairs.stream().limit(6).toList()) {
+            var a = pair.a; var b = pair.b; var outA = new XZ(a.x, a.z).move(a.facing, 3); var outB = new XZ(b.x, b.z).move(b.facing, 3);
+            for (int variant = 0; variant < 4; variant++) {
+                var points = new ArrayList<XZ>(); points.add(new XZ(a.x, a.z)); line(points, outA);
+                if (variant == 0) line(points, new XZ(outB.x, outA.z));
+                else if (variant == 1) line(points, new XZ(outA.x, outB.z));
+                else if (variant == 2) { int mid = (outA.x + outB.x) / 2; line(points, new XZ(mid, outA.z)); line(points, new XZ(mid, outB.z)); }
+                else { int mid = (outA.z + outB.z) / 2; line(points, new XZ(outA.x, mid)); line(points, new XZ(outB.x, mid)); }
+                line(points, outB); line(points, new XZ(b.x, b.z));
+                if (points.size() > 192 || new java.util.HashSet<>(points).size() != points.size()) continue;
+                var route = profile(seed, points, a, b, all, probe); if (route != null) return route;
+            }
+        }
+        return null;
+    }
+    private static List<Entry> entries(District district, List<District> all) {
+        var result = new ArrayList<Entry>();
+        for (var p : district.parcels()) if (p.kind() == Kind.STREET && p.width() >= 3 && p.depth() >= 3) {
+            for (int d = 0; d < 4; d++) {
+                int lx = d == 1 ? p.width() - 1 : d == 3 ? 0 : p.width() / 2;
+                int lz = d == 2 ? p.depth() - 1 : d == 0 ? 0 : p.depth() / 2;
+                int x = p.minX() + lx, z = p.minZ() + lz, floor = p.surfaceY(lx, lz); boolean valid = true;
+                for (int side = -1; side <= 1; side++) {
+                    int px = x + DZ[d] * side, pz = z + DX[d] * side;
+                    if (existingFloor(px, pz, all) != floor || existingFloor(px + DX[d], pz + DZ[d], all) != INVALID) { valid = false; break; }
+                }
+                if (valid) result.add(new Entry(x, floor, z, d));
+            }
+        }
+        return result;
+    }
+    private static Route profile(long seed, List<XZ> path, Entry a, Entry b, List<District> all, Probe probe) {
+        int n = path.size(); int[] low = new int[n], high = new int[n], floor = new int[n];
+        // Partition the complete footprint before choosing elevations. Every partition boundary
+        // will be a level landing, so a renderer never needs a neighboring parcel to form a stair.
+        var footprintCells = new LinkedHashMap<Long, XZ>();
+        for (int i = 0; i < n; i++) for (var cell : strip(path, i))
+            if (existingFloor(cell.x, cell.z, all) == INVALID) footprintCells.putIfAbsent(key(cell.x, cell.z), cell);
+        var footprints = footprints(footprintCells);
+        var owner = new HashMap<Long, Integer>();
+        for (int i = 0; i < footprints.size(); i++) {
+            var f = footprints.get(i);
+            for (int z = f.z; z < f.z + f.depth; z++) for (int x = f.x; x < f.x + f.width; x++) owner.put(key(x, z), i);
+        }
+        int[] grade = new int[n];
+        for (int i = 1; i < n; i++) {
+            grade[i] = 1;
+            for (var aCell : strip(path, i - 1)) for (var bCell : strip(path, i)) {
+                int distance = Math.abs(aCell.x - bCell.x) + Math.abs(aCell.z - bCell.z);
+                if (distance == 0 || distance == 1 && !java.util.Objects.equals(
+                        owner.get(key(aCell.x, aCell.z)), owner.get(key(bCell.x, bCell.z)))) grade[i] = 0;
+            }
+        }
+        for (int i = 0; i < n; i++) {
+            low[i] = 176; high[i] = 350;
+            for (var p : strip(path, i)) {
+                int old = existingFloor(p.x, p.z, all);
+                if (old == -1) return null;
+                if (old != INVALID) { low[i] = Math.max(low[i], old); high[i] = Math.min(high[i], old); }
+                else {
+                    var g = probe.ground(p.x, p.z);
+                    if (!g.dry() || g.protectedTerrain() || g.solidDepth() < 3) return null;
+                    low[i] = Math.max(low[i], g.top() - 2); high[i] = Math.min(high[i], g.top() + 3);
+                }
+            }
+        }
+        low[0] = high[0] = a.y; low[n - 1] = high[n - 1] = b.y;
+        for (int i = 1; i < n; i++) { low[i] = Math.max(low[i], low[i - 1] - grade[i]); high[i] = Math.min(high[i], high[i - 1] + grade[i]); }
+        for (int i = n - 2; i >= 0; i--) { low[i] = Math.max(low[i], low[i + 1] - grade[i + 1]); high[i] = Math.min(high[i], high[i + 1] + grade[i + 1]); }
+        var cells = new LinkedHashMap<Long, Road>(); var result = new ArrayList<Point>();
+        for (int i = 0; i < n; i++) {
+            if (low[i] > high[i]) return null;
+            int min = i == 0 ? low[i] : Math.max(low[i], floor[i - 1] - grade[i]), max = i == 0 ? high[i] : Math.min(high[i], floor[i - 1] + grade[i]);
+            if (min > max) return null;
+            var p = path.get(i); floor[i] = Math.clamp(probe.ground(p.x, p.z).top(), min, max); result.add(new Point(p.x, floor[i], p.z));
+            for (var c : strip(path, i)) {
+                int old = existingFloor(c.x, c.z, all); if (old != INVALID) { if (old != floor[i]) return null; continue; }
+                var g = probe.ground(c.x, c.z); int foundation = Math.max(1, floor[i] - g.top() + 1), bottom = floor[i] - foundation;
+                if (!probe.solid(c.x, bottom, c.z) || !probe.solid(c.x, bottom - 1, c.z)) return null;
+                for (int y = bottom - 1; y <= floor[i] + 8; y++) if (probe.protectedAt(c.x, y, c.z)) return null;
+                var previous = cells.putIfAbsent(key(c.x, c.z), new Road(c.x, c.z, floor[i], foundation));
+                if (previous != null && previous.floor != floor[i]) return null;
+            }
+        }
+        // Bends may put nonconsecutive centerline strips next to each other. Their shared
+        // partition edge obeys the same level-landing contract, including existing town roads.
+        for (var cell : cells.values()) for (int d = 0; d < 4; d++) {
+            int nx = cell.x + DX[d], nz = cell.z + DZ[d];
+            var neighbor = cells.get(key(nx, nz));
+            if (neighbor != null && !owner.get(key(cell.x, cell.z)).equals(owner.get(key(nx, nz)))
+                    && neighbor.floor != cell.floor) return null;
+            int old = existingFloor(nx, nz, all);
+            if (old >= 0 && old != cell.floor) return null;
+        }
+        var parcels = new ArrayList<Parcel>();
+        for (var f : footprints) {
+            int foundation = 1;
+            for (int z = f.z; z < f.z + f.depth; z++) for (int x = f.x; x < f.x + f.width; x++)
+                foundation = Math.max(foundation, cells.get(key(x, z)).foundation);
+            int[] heights = new int[f.width * f.depth];
+            for (int z = f.z; z < f.z + f.depth; z++) for (int x = f.x; x < f.x + f.width; x++) {
+                var cell = cells.get(key(x, z)); int bottom = cell.floor - foundation;
+                // A rectangular parcel uses one foundation depth. Certify its deeper columns
+                // explicitly rather than extending another column's rock certificate sideways.
+                if (!probe.solid(x, bottom, z) || !probe.solid(x, bottom - 1, z)) return null;
+                for (int y = bottom - 1; y < cell.floor - cell.foundation - 1; y++)
+                    if (probe.protectedAt(x, y, z)) return null;
+                heights[(z - f.z) * f.width + x - f.x] = cell.floor;
+            }
+            parcels.add(new Parcel(Kind.STREET, f.x, f.z, f.width, f.depth, heights[0], 0, 0,
+                mix(seed ^ key(f.x, f.z)), foundation, heights));
+        }
+        return new Route(List.copyOf(result), List.copyOf(parcels));
+    }
+    /** Disjoint, completely occupied rectangles, each contained in a single native chunk. */
+    private static List<Footprint> footprints(Map<Long, XZ> cells) {
+        var remaining = new java.util.HashSet<>(cells.keySet()); var result = new ArrayList<Footprint>();
+        for (var at : cells.values().stream().sorted(Comparator.comparingInt(XZ::z).thenComparingInt(XZ::x)).toList()) {
+            if (!remaining.contains(key(at.x, at.z))) continue;
+            int width = 1, depth = 1;
+            while ((at.x + width >> 4) == (at.x >> 4) && remaining.contains(key(at.x + width, at.z))) width++;
+            while ((at.z + depth >> 4) == (at.z >> 4)) {
+                boolean complete = true;
+                for (int x = at.x; x < at.x + width; x++) complete &= remaining.contains(key(x, at.z + depth));
+                if (!complete) break;
+                depth++;
+            }
+            for (int z = at.z; z < at.z + depth; z++) for (int x = at.x; x < at.x + width; x++) remaining.remove(key(x, z));
+            result.add(new Footprint(at.x, at.z, width, depth));
+        }
+        return List.copyOf(result);
+    }
+    private static List<XZ> strip(List<XZ> points, int i) {
+        var p = points.get(i); var result = new java.util.LinkedHashSet<XZ>(); result.add(p);
+        for (int next : new int[]{i - 1, i + 1}) if (next >= 0 && next < points.size()) {
+            var q = points.get(next); int dx = Integer.signum(q.x - p.x), dz = Integer.signum(q.z - p.z);
+            result.add(new XZ(p.x + dz, p.z + dx)); result.add(new XZ(p.x - dz, p.z - dx));
+        }
+        return List.copyOf(result);
+    }
+    private static void line(List<XZ> points, XZ goal) {
+        var p = points.getLast(); while (p.x != goal.x) { p = new XZ(p.x + Integer.signum(goal.x - p.x), p.z); points.add(p); }
+        while (p.z != goal.z) { p = new XZ(p.x, p.z + Integer.signum(goal.z - p.z)); points.add(p); }
+    }
+    private static int existingFloor(int x, int z, List<District> all) {
+        for (var d : all) for (var p : d.parcels()) if (x >= p.minX() && x <= p.maxX() && z >= p.minZ() && z <= p.maxZ())
+            return p.kind() == Kind.STREET ? p.surfaceY(x - p.minX(), z - p.minZ()) : -1;
+        return INVALID;
+    }
+    private static boolean overlap(District candidate, List<District> all, int gap) {
+        for (var d : all) if (candidate.minX() <= d.maxX() + gap && candidate.maxX() >= d.minX() - gap
+                && candidate.minZ() <= d.maxZ() + gap && candidate.maxZ() >= d.minZ() - gap) return true;
+        return false;
+    }
+    private static final class Exhausted extends RuntimeException {}
+    private static final class Probe implements LostCityPlanner16.Terrain {
+        final LostCityPlanner16.Terrain source; final Map<Long, LostCityPlanner.Ground> columns = new HashMap<>();
+        final Map<String, Integer> reasons = new LinkedHashMap<>(); int checks;
+        Probe(LostCityPlanner16.Terrain source) { this.source = source; }
+        public boolean owns(int x, int z) { return source.owns(x, z); }
+        public LostCityPlanner.Ground ground(int x, int z) {
+            if (!owns(x, z)) return new LostCityPlanner.Ground(0, 0, false, true);
+            long key = key(x, z); var old = columns.get(key); if (old != null) return old;
+            if (columns.size() >= MAX_EXTRA_COLUMNS) throw new Exhausted();
+            var value = source.ground(x, z); columns.put(key, value); return value;
+        }
+        public boolean solid(int x, int y, int z) { count(); ground(x, z); return owns(x, z) && source.solid(x, y, z); }
+        public boolean protectedAt(int x, int y, int z) { count(); ground(x, z); return !owns(x, z) || source.protectedAt(x, y, z); }
+        void count() { if (checks >= MAX_EXTRA_CHECKS) throw new Exhausted(); checks++; }
+        void reject(String reason) { reasons.merge(reason, 1, Integer::sum); }
+    }
+    private static long key(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+    private static long mix(long v) { v = (v ^ v >>> 30) * 0xbf58476d1ce4e5b9L; v = (v ^ v >>> 27) * 0x94d049bb133111ebL; return v ^ v >>> 31; }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityStructure.java

@@ -29,17 +29,18 @@ public final class LostCityStructure extends Structure {
                     throw new IllegalStateException("Lost City district exceeds native structure reference range");
             }
             return Optional.of(new GenerationStub(LostCityStructures.locator(district), pieces -> {
-                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20) && generator.cityReservation16(island) != null)
+                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21) && generator.cityReservation16(island) != null
+                        && (generator.rootGeneration() != 21 || generator.cityPlacement21(island).core().surface().districts().contains(district)))
                     pieces.addPiece(new LostCityFoundationPiece16(generator.cityReservation16(island), district.seed()));
                 if (generator.rootGeneration() == 15) for (var support : generator.citySupports(island)) {
                     if (support.startChunkX() == district.startChunkX() && support.startChunkZ() == district.startChunkZ())
                         pieces.addPiece(new LostCitySupportPiece15(support));
                 }
-                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20)) for (var support : generator.citySupports16(island)) {
+                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21)) for (var support : generator.citySupports16(island)) {
                     if (support.startChunkX() == district.startChunkX() && support.startChunkZ() == district.startChunkZ())
                         pieces.addPiece(new LostCitySupportPiece16(support));
                 }
-                district.parcels().forEach(parcel -> pieces.addPiece(generator.rootGeneration() == 20 ? new LostCityPiece20(parcel) : (generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20) ? new LostCityPiece16(parcel) : generator.rootGeneration() == 15
+                district.parcels().forEach(parcel -> pieces.addPiece(generator.rootGeneration() == 21 ? new LostCityPiece21(parcel) : generator.rootGeneration() == 20 ? new LostCityPiece20(parcel) : (generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? new LostCityPiece16(parcel) : generator.rootGeneration() == 15
                     ? new LostCityPiece15(parcel) : new LostCityPiece(parcel)));
                 if (generator.rootGeneration() == 15) for (var network : generator.undergroundPlan(island).networks()) {
                     if (network.startChunkX() != district.startChunkX() || network.startChunkZ() != district.startChunkZ()) continue;
@@ -49,13 +50,13 @@ public final class LostCityStructure extends Structure {
                     network.modules().stream().filter(m -> m.kind() == LostCityUnderground15.Kind.ACCESS)
                         .forEach(m -> pieces.addPiece(new LostCityUndergroundPiece15(m)));
                 }
-                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20)) for (var network : generator.undergroundPlan16(island).networks()) {
+                if ((generator.rootGeneration() == 16 || generator.rootGeneration() == 17 || generator.rootGeneration() == 19 || generator.rootGeneration() == 20 || generator.rootGeneration() == 21)) for (var network : generator.undergroundPlan16(island).networks()) {
                     if (network.startChunkX() != district.startChunkX() || network.startChunkZ() != district.startChunkZ()) continue;
                     // Surface comes first, rooms/corridors next, shafts last so every entrance remains open.
                     network.modules().stream().filter(m -> m.kind() != LostCityUnderground16.Kind.ACCESS)
-                        .forEach(m -> pieces.addPiece(generator.rootGeneration() == 20 ? new LostCityUndergroundPiece20(m) : new LostCityUndergroundPiece16(m)));
+                        .forEach(m -> pieces.addPiece((generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? new LostCityUndergroundPiece20(m) : new LostCityUndergroundPiece16(m)));
                     network.modules().stream().filter(m -> m.kind() == LostCityUnderground16.Kind.ACCESS)
-                        .forEach(m -> pieces.addPiece(generator.rootGeneration() == 20 ? new LostCityUndergroundPiece20(m) : new LostCityUndergroundPiece16(m)));
+                        .forEach(m -> pieces.addPiece((generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? new LostCityUndergroundPiece20(m) : new LostCityUndergroundPiece16(m)));
                 }
             }));
         }

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityStructures.java

@@ -40,6 +40,8 @@ public final class LostCityStructures {
         BuiltInRegistries.STRUCTURE_PIECE, SanctuaryMod.id("lost_city_underground_v15"), LostCityUndergroundPiece15::new);
     public static final StructurePieceType SUPPORT15 = Registry.register(
         BuiltInRegistries.STRUCTURE_PIECE, SanctuaryMod.id("lost_city_support_v15"), LostCitySupportPiece15::new);
+    public static final StructurePieceType PIECE21 = Registry.register(BuiltInRegistries.STRUCTURE_PIECE,
+        SanctuaryMod.id("lost_city_parcel_v21"), LostCityPiece21::new);
     public static final StructurePieceType PIECE20 = Registry.register(
         BuiltInRegistries.STRUCTURE_PIECE, SanctuaryMod.id("lost_city_parcel_v20"), LostCityPiece20::new);
     public static final StructurePieceType PIECE16 = Registry.register(

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCitySurface21.java

@@ -0,0 +1,302 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.worldgen.detail.ConnectedBlocks20;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.Rotation;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.block.state.properties.Half;
+import net.minecraft.world.level.block.state.properties.SlabType;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** New surface architecture on the saved generation16 footprints. Published renderers remain immutable. */
+public final class LostCitySurface21 {
+    private static final Direction[] HORIZONTAL = {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST};
+    private LostCitySurface21() {}
+
+    public static void render(LostCityPlan.Parcel parcel, LostCityRenderer.BlockWriter output) {
+        if (parcel.kind().building()) { LostCityInteriors21.render(parcel, output); return; }
+        var connected = ConnectedBlocks20.buffer(output);
+        if (parcel.kind() == LostCityPlan.Kind.STREET || parcel.kind() == LostCityPlan.Kind.BRIDGE) {
+            road(parcel, connected);
+        } else {
+            new Exterior(parcel, connected).render();
+        }
+        connected.flush();
+    }
+
+    private static void road(LostCityPlan.Parcel p, LostCityRenderer.BlockWriter output) {
+        boolean alongX = p.width() > p.depth(), bridge = p.kind() == LostCityPlan.Kind.BRIDGE;
+        for (int z = 0; z < p.depth(); z++) for (int x = 0; x < p.width(); x++) {
+            int y = p.surfaceY(x, z) - p.floorY();
+            int across = alongX ? z : x, along = alongX ? x : z, breadth = alongX ? p.depth() : p.width();
+            boolean edge = across == 0 || across == breadth - 1;
+            // A legible curb and patterned shoulders, not per-block random pavement.
+            Block paving = edge ? Blocks.POLISHED_TUFF : across == 1 || across == breadth - 2
+                ? along % 4 == 0 ? Blocks.CHISELED_TUFF_BRICKS : Blocks.TUFF_BRICKS
+                : Blocks.POLISHED_ANDESITE;
+            if (!bridge) for (int down = 1; down <= p.foundationDepth(); down++)
+                output.set(x, y - down, z, Blocks.STONE_BRICKS.defaultBlockState());
+            output.set(x, y, z, paving.defaultBlockState());
+            for (int up = 1; up <= 8; up++) output.set(x, y + up, z, Blocks.AIR.defaultBlockState());
+            if (bridge && edge) {
+                // Posts grow from the existing deck only; the certified natural bearings are untouched.
+                output.set(x, y + 1, z, (along % 5 == 0 ? Blocks.CHISELED_TUFF_BRICKS : Blocks.IRON_BARS).defaultBlockState());
+                if (along % 5 == 0) output.set(x, y + 2, z, Blocks.TUFF_BRICK_SLAB.defaultBlockState());
+                continue;
+            }
+            for (var direction : HORIZONTAL) {
+                int nx = x + direction.getStepX(), nz = z + direction.getStepZ();
+                if (nx >= 0 && nx < p.width() && nz >= 0 && nz < p.depth()
+                        && p.surfaceY(nx, nz) == p.surfaceY(x, z) + 1) {
+                    output.set(x, y + 1, z, Blocks.TUFF_BRICK_STAIRS.defaultBlockState()
+                        .setValue(BlockStateProperties.HORIZONTAL_FACING, direction));
+                    break;
+                }
+            }
+        }
+    }
+
+    private static final class Exterior implements LostCityRenderer.BlockWriter {
+        final LostCityPlan.Parcel p;
+        final LostCityRenderer.BlockWriter output;
+        final Rotation turn;
+        Exterior(LostCityPlan.Parcel p, LostCityRenderer.BlockWriter output) {
+            this.p = p; this.output = output;
+            turn = switch (p.facing()) { case 1 -> Rotation.CLOCKWISE_90; case 2 -> Rotation.CLOCKWISE_180;
+                case 3 -> Rotation.COUNTERCLOCKWISE_90; default -> Rotation.NONE; };
+        }
+        int x(int x, int z) { return switch (p.facing()) { case 1 -> p.width() - 1 - z; case 2 -> p.width() - 1 - x; case 3 -> z; default -> x; }; }
+        int z(int x, int z) { return switch (p.facing()) { case 1 -> x; case 2 -> p.depth() - 1 - z; case 3 -> p.depth() - 1 - x; default -> z; }; }
+        @Override public void set(int x, int y, int z, BlockState state) {
+            output.set(x(x, z), y, z(x, z), palette(y, state).rotate(turn));
+        }
+        BlockState palette(int y, BlockState state) {
+            Block block = null;
+            if (state.is(Blocks.STONE) && y < 0) block = Blocks.STONE_BRICKS;
+            else if (state.is(Blocks.DARK_OAK_PLANKS)) block = Blocks.OAK_PLANKS;
+            else if (state.is(Blocks.DARK_OAK_FENCE)) block = Blocks.OAK_FENCE;
+            else if (state.is(Blocks.DARK_OAK_STAIRS)) block = Blocks.OAK_STAIRS;
+            else if (state.is(Blocks.DARK_OAK_SLAB)) block = Blocks.OAK_SLAB;
+            else if (state.is(Blocks.CALCITE)) block = Blocks.SMOOTH_STONE;
+            else if (y > 0) {
+                if (state.is(Blocks.TUFF_BRICKS)) block = Blocks.STONE_BRICKS;
+                else if (state.is(Blocks.CHISELED_TUFF_BRICKS) || state.is(Blocks.CHISELED_TUFF)) block = Blocks.CHISELED_STONE_BRICKS;
+                else if (state.is(Blocks.TUFF_BRICK_SLAB)) block = Blocks.STONE_BRICK_SLAB;
+                else if (state.is(Blocks.POLISHED_TUFF_SLAB)) block = Blocks.SMOOTH_STONE_SLAB;
+                else if (state.is(Blocks.TUFF_BRICK_STAIRS)) block = Blocks.STONE_BRICK_STAIRS;
+                else if (state.is(Blocks.POLISHED_TUFF)) block = Blocks.POLISHED_ANDESITE;
+            }
+            if (block == null) return state;
+            BlockState result = block.defaultBlockState();
+            for (var property : state.getProperties()) if (result.hasProperty(property)) result = copy(result, state, property);
+            return result;
+        }
+        <T extends Comparable<T>> BlockState copy(BlockState into, BlockState from,
+                net.minecraft.world.level.block.state.properties.Property<T> property) {
+            return into.setValue(property, from.getValue(property));
+        }
+        void set(int x, int y, int z, Block block) { set(x, y, z, block.defaultBlockState()); }
+        @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+            output.chest(x(x, z), y, z(x, z), table, seed ^ 0x21c17a7eL);
+        }
+        void box(int x0, int y0, int z0, int x1, int y1, int z1, Block block) {
+            for (int x = x0; x <= x1; x++) for (int z = z0; z <= z1; z++) for (int y = y0; y <= y1; y++) set(x, y, z, block);
+        }
+        void render() {
+            if (p.width() != 17 || p.depth() != 17) throw new IllegalArgumentException("Generation21 amenities require the certified 17x17 footprint");
+            // Keep the proven pool containment, excavation steps and garage ramps. All new ornament is
+            // composed before connection resolution, so clipping cannot split a rail or window design.
+            var north = new LostCityPlan.Parcel(p.kind(), p.minX(), p.minZ(), 17, 17, p.floorY(), p.floors(), 0,
+                p.seed(), p.foundationDepth(), p.surfaceHeights());
+            LostCitySurface16.render(north, new LostCityRenderer.BlockWriter() {
+                @Override public void set(int x, int y, int z, BlockState state) {
+                    Exterior.this.set(x, y, z, state);
+                }
+                @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) { Exterior.this.chest(x, y, z, table, seed); }
+            });
+            // The north threshold is a level promenade, shared by every admitted parcel.
+            for (int x = 0; x <= 16; x++) set(x, 0, 0, x % 4 == 0 ? Blocks.CHISELED_TUFF_BRICKS : Blocks.TUFF_BRICKS);
+            switch (p.kind()) {
+                case PARK -> park();
+                case PARK_GARDEN -> garden();
+                case PARK_PLAYGROUND -> playground();
+                case PARK_MEMORIAL -> memorial();
+                case PLAZA -> plaza();
+                case MARKET -> market();
+                case PARKING -> garage();
+                case POOL -> { if (p.foundationDepth() >= 8) pool(); else park(); }
+                case EXCAVATION -> { if (p.foundationDepth() >= 8) excavation(); else park(); }
+                default -> throw new IllegalArgumentException("Not an exterior amenity");
+            }
+        }
+        void paths() {
+            for (int n = 1; n <= 16; n++) for (int across = 7; across <= 9; across++) {
+                set(across, 0, n, across == 8 ? Blocks.POLISHED_TUFF : Blocks.TUFF_BRICKS);
+                set(n, 0, across, across == 8 ? Blocks.POLISHED_TUFF : Blocks.TUFF_BRICKS);
+            }
+        }
+        void bench(int x, int y, int z, int length, Direction view) {
+            for (int dx = 0; dx < length; dx++) set(x + dx, y, z, Blocks.OAK_STAIRS.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, view.getOpposite()));
+            set(x - 1, y, z, Blocks.TUFF_BRICK_SLAB); set(x + length, y, z, Blocks.TUFF_BRICK_SLAB);
+        }
+        void lamp(int x, int z) {
+            set(x, 1, z, Blocks.CHISELED_TUFF_BRICKS); box(x, 2, z, x, 3, z, Blocks.OAK_FENCE);
+            set(x, 4, z, Blocks.OAK_PLANKS); set(x, 5, z, Blocks.LANTERN);
+        }
+        void park() {
+            paths(); bench(10, 1, 3, 3, Direction.SOUTH); bench(10, 1, 11, 3, Direction.NORTH);
+            lamp(5, 11); lamp(11, 5);
+            // A small oak screen joins the existing trees without introducing another wood palette.
+            box(3, 1, 12, 3, 4, 12, Blocks.OAK_LOG);
+            for (int x = 2; x <= 4; x++) for (int z = 11; z <= 13; z++)
+                set(x, 5, z, Blocks.OAK_LEAVES.defaultBlockState().setValue(BlockStateProperties.PERSISTENT, true));
+            for (int z = 2; z <= 5; z++) set(6, 0, z, Blocks.POLISHED_ANDESITE);
+        }
+        void garden() {
+            paths();
+            // Four parterres have low carved kerbs, soil beds and a shared central promenade.
+            for (int x0 : new int[]{2, 10}) for (int z0 : new int[]{2, 10}) {
+                for (int n = 0; n < 5; n++) {
+                    set(x0 + n, 0, z0, Blocks.SMOOTH_STONE); set(x0 + n, 0, z0 + 4, Blocks.SMOOTH_STONE);
+                    set(x0, 0, z0 + n, Blocks.SMOOTH_STONE); set(x0 + 4, 0, z0 + n, Blocks.SMOOTH_STONE);
+                }
+                set(x0, 1, z0, Blocks.CHISELED_TUFF); set(x0 + 4, 1, z0 + 4, Blocks.CHISELED_TUFF);
+            }
+            bench(7, 1, 15, 3, Direction.NORTH);
+            // Pergola along the west planting bed, not across a circulation route.
+            for (int z : new int[]{2, 6}) box(1, 1, z, 1, 3, z, Blocks.STRIPPED_OAK_LOG);
+            box(1, 4, 2, 1, 4, 6, Blocks.OAK_SLAB); lamp(15, 8);
+        }
+        void playground() {
+            paths();
+            for (int x = 1; x <= 7; x++) { set(x, 0, 1, Blocks.OAK_PLANKS); set(x, 0, 7, Blocks.OAK_PLANKS); }
+            for (int z = 1; z <= 7; z++) { set(1, 0, z, Blocks.OAK_PLANKS); set(7, 0, z, Blocks.OAK_PLANKS); }
+            // The hanging seat's upper half meets the chain above; a bottom slab would leave a gap.
+            set(4, 2, 4, Blocks.OAK_SLAB.defaultBlockState().setValue(BlockStateProperties.SLAB_TYPE, SlabType.TOP));
+            // The last ascending step used to touch its neighbors only diagonally, over empty air.
+            set(12, 1, 10, Blocks.OAK_PLANKS);
+            // Braced climbing platform: low guards leave the three front steps open.
+            for (int x : new int[]{11, 13}) set(x, 4, 13, Blocks.OAK_FENCE);
+            set(12, 4, 13, Blocks.OAK_FENCE);
+            set(11, 4, 11, Blocks.OAK_FENCE); set(13, 4, 11, Blocks.OAK_FENCE);
+            bench(3, 1, 13, 3, Direction.NORTH); lamp(15, 3);
+        }
+        void plaza() {
+            for (int x = 1; x <= 15; x++) for (int z = 1; z <= 15; z++) {
+                int d = Math.max(Math.abs(x - 8), Math.abs(z - 8));
+                set(x, 0, z, d == 3 || d == 6 ? Blocks.POLISHED_ANDESITE : d == 4 || d == 7 ? Blocks.TUFF_BRICKS : Blocks.SMOOTH_STONE);
+            }
+            // Dry civic fountain: bevelled bowl, carved pedestal, projecting cap.
+            for (int x = 6; x <= 10; x++) for (int z = 6; z <= 10; z++) {
+                if (x != 6 && x != 10 && z != 6 && z != 10) continue;
+                boolean corner = (x == 6 || x == 10) && (z == 6 || z == 10);
+                set(x, 1, z, corner ? Blocks.CHISELED_TUFF_BRICKS : Blocks.TUFF_BRICK_SLAB);
+            }
+            set(8, 1, 8, Blocks.CHISELED_TUFF); set(8, 2, 8, Blocks.CHISELED_TUFF_BRICKS);
+            set(8, 3, 8, Blocks.POLISHED_TUFF_SLAB); lamp(2, 12); lamp(14, 4);
+        }
+        void memorial() {
+            // The memorial keeps its open central approach and gains stepped stone shoulders.
+            for (int x = 1; x <= 15; x++) for (int z = 1; z <= 15; z++)
+                set(x, 0, z, x == 5 || x == 11 || z == 5 || z == 11 ? Blocks.TUFF_BRICKS : Blocks.POLISHED_ANDESITE);
+            for (int x = 7; x <= 9; x++) {
+                set(x, 1, 7, Blocks.TUFF_BRICK_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+                set(x, 1, 9, Blocks.TUFF_BRICK_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.NORTH));
+            }
+            set(8, 2, 8, Blocks.CHISELED_TUFF); set(8, 3, 8, Blocks.CHISELED_TUFF_BRICKS);
+            set(8, 4, 8, Blocks.CHISELED_STONE_BRICKS); set(8, 5, 8, Blocks.SMOOTH_STONE_SLAB);
+            lamp(3, 8); lamp(13, 8);
+        }
+        void market() {
+            for (int x = 1; x <= 15; x++) for (int z = 1; z <= 15; z++)
+                set(x, 0, z, x >= 7 && x <= 9 || z >= 7 && z <= 9 ? Blocks.TUFF_BRICKS : Blocks.POLISHED_ANDESITE);
+            for (int x0 : new int[]{2, 11}) for (int z0 : new int[]{2, 11}) {
+                for (int x = x0; x <= x0 + 3; x++) for (int z = z0; z <= z0 + 2; z++)
+                    set(x, 4, z, Blocks.OAK_SLAB);
+                for (int x : new int[]{x0, x0 + 3}) {
+                    set(x, 1, z0, Blocks.CHISELED_TUFF_BRICKS);
+                    box(x, 2, z0, x, 3, z0, Blocks.STRIPPED_OAK_LOG);
+                }
+                // Only one roof layer: the former raised bottom slab was separated by half a block.
+                // Rear posts and a full-width beam make the canopy's load path visible from the stall.
+                for (int x : new int[]{x0, x0 + 3}) box(x, 2, z0 + 2, x, 3, z0 + 2, Blocks.STRIPPED_OAK_LOG);
+                box(x0, 3, z0, x0 + 3, 3, z0, Blocks.OAK_PLANKS);
+                box(x0, 3, z0 + 2, x0 + 3, 3, z0 + 2, Blocks.OAK_PLANKS);
+            }
+            // The shared chest replaces this stall's counter: a pot cannot sit on its recessed lid.
+            set(13, 2, 13, Blocks.AIR); set(12, 2, 13, Blocks.FLOWER_POT);
+            lamp(1, 8); lamp(15, 8);
+        }
+        void pool() {
+            // Each submerged tread bears on a masonry riser down to the basin floor;
+            // water between diagonal stairs is not a structural connection.
+            for (int step = 1; step <= 3; step++) for (int x = 7; x <= 9; x++)
+                for (int y = -3; y < -step; y++) set(x, y, step + 4, Blocks.SMOOTH_STONE);
+            for (int x = 3; x <= 13; x++) for (int z = 4; z <= 13; z++) {
+                if (x == 3 || x == 13 || z == 4 || z == 13) set(x, 0, z, Blocks.SMOOTH_STONE);
+            }
+            // Changing/showers canopy stands beside the deck; it never enters the sealed basin.
+            for (int x : new int[]{10, 15}) box(x, 1, 1, x, 3, 1, Blocks.STRIPPED_OAK_LOG);
+            for (int x : new int[]{10, 15}) box(x, 1, 3, x, 3, 3, Blocks.STRIPPED_OAK_LOG);
+            box(10, 3, 1, 15, 3, 1, Blocks.OAK_PLANKS);
+            box(10, 3, 3, 15, 3, 3, Blocks.OAK_PLANKS);
+            box(10, 4, 1, 15, 4, 3, Blocks.OAK_SLAB);
+            for (int x = 11; x <= 14; x++) set(x, 1, 1, Blocks.WATER_CAULDRON.defaultBlockState()
+                .setValue(BlockStateProperties.LEVEL_CAULDRON, 2));
+            set(15, 4, 2, Blocks.OAK_PLANKS); set(15, 5, 2, Blocks.LANTERN);
+            for (int z : new int[]{5, 9}) set(15, 1, z, Blocks.OAK_STAIRS.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.EAST));
+            box(2, 0, 14, 14, 0, 15, Blocks.TUFF_BRICKS);
+        }
+        void excavation() {
+            // Each descending stone step rests on a small riser down to the certified pit floor.
+            for (int step = 1; step <= 5; step++) for (int x = 7; x <= 9; x++)
+                for (int y = -4; y < -step; y++) set(x, y, step + 2, Blocks.STONE_BRICKS);
+            // Reinforced temporary footings and timber trestles stay out of the central descent.
+            for (int x : new int[]{4, 12}) {
+                box(x, -4, 11, x, -1, 11, Blocks.CHISELED_STONE_BRICKS);
+                set(x, 0, 11, Blocks.OAK_PLANKS);
+            }
+            box(3, 3, 13, 13, 3, 13, Blocks.STRIPPED_OAK_LOG);
+            for (int x : new int[]{3, 13}) box(x, -4, 13, x, 2, 13, Blocks.STONE_BRICKS);
+            // Replace the single beam with an open construction shelter, one canopy on grounded posts.
+            // All four trestles start on the excavated floor, not on the missing former ground plane.
+            for (int x : new int[]{3, 13}) box(x, -4, 10, x, 2, 10, Blocks.STONE_BRICKS);
+            box(3, 3, 10, 13, 3, 10, Blocks.STRIPPED_OAK_LOG);
+            for (int x : new int[]{3, 8, 13}) box(x, 3, 10, x, 3, 13, Blocks.OAK_PLANKS);
+            box(3, 4, 10, 13, 4, 13, Blocks.OAK_SLAB);
+            set(3, 4, 13, Blocks.OAK_PLANKS);
+            set(3, 5, 13, Blocks.LANTERN);
+            set(1, 1, 11, Blocks.GRINDSTONE); set(1, 1, 10, Blocks.CRAFTING_TABLE);
+        }
+        void garage() {
+            int base = p.foundationDepth() >= 8 ? -5 : 0;
+            // The ramp's five-wide masonry wedge joins every tread to the garage floor.
+            if (base < 0) for (int z = 0; z <= 4; z++) for (int x = 6; x <= 10; x++)
+                for (int y = base + 1; y < -z; y++) set(x, y, z, Blocks.STONE_BRICKS);
+            for (int x : new int[]{3, 13}) for (int z : new int[]{3, 13}) {
+                box(x, base + 1, z, x, base + 4, z, Blocks.POLISHED_ANDESITE);
+                set(x, base + 1, z, Blocks.CHISELED_TUFF_BRICKS);
+            }
+            for (int z = 6; z <= 15; z++) for (int x = 1; x <= 15; x++)
+                if (x <= 5 || x >= 11) set(x, base, z, z % 4 == 0 ? Blocks.SMOOTH_STONE : Blocks.POLISHED_ANDESITE);
+            // A ribbed structural fascia and ventilation blades make this an open modern garage.
+            for (int x = 0; x <= 16; x++) {
+                // The underground ramp cuts through this former ceiling strip: never paint it back.
+                if (base == 0 || x < 6 || x > 10)
+                    set(x, base + 5, 0, x % 4 == 0 ? Blocks.CHISELED_STONE_BRICKS : Blocks.SMOOTH_STONE);
+                if (x < 6 || x > 10) set(x, base + 3, 0, Blocks.IRON_TRAPDOOR.defaultBlockState()
+                    .setValue(BlockStateProperties.OPEN, true).setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.NORTH));
+            }
+            for (int x : new int[]{5, 11}) {
+                set(x, base + 4, 9, Blocks.SMOOTH_STONE);
+                set(x, base + 3, 9, Blocks.LANTERN.defaultBlockState().setValue(BlockStateProperties.HANGING, true));
+            }
+        }
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/city/LostCityTerrain21.java

@@ -0,0 +1,85 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.expansion.ExpansionIsland;
+import fr.koka.sanctuary.expansion.ExpansionTerrain;
+import fr.koka.sanctuary.worldgen.PopulationHydrologyRuntime;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Predicate;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.levelgen.NoiseBasedChunkGenerator;
+import net.minecraft.world.level.levelgen.RandomState;
+
+/** Generation21 bounded noise-column cache shared by surface and underground planning, never loaded chunks. */
+public final class LostCityTerrain21 implements LostCityUnderground16.Terrain, LostCityPlanner16.Terrain {
+    public static final int MAX_COLUMNS = 24_096;
+    private final ExpansionIsland island;
+    private final NoiseBasedChunkGenerator generator;
+    private final RandomState random;
+    private final LevelHeightAccessor height;
+    private final Predicate<BlockPos> protectedVolume;
+    private final Map<Long, NoiseColumn> columns = new HashMap<>();
+    private final BlockPos fluidCandidate;
+
+    public LostCityTerrain21(ExpansionIsland island, NoiseBasedChunkGenerator generator, RandomState random,
+            LevelHeightAccessor height, Predicate<BlockPos> protectedVolume) {
+        this.island = island; this.generator = generator; this.random = random;
+        this.height = height; this.protectedVolume = protectedVolume;
+        fluidCandidate = ExpansionTerrain.pocketCandidate(island);
+    }
+
+    private NoiseColumn column(int x, int z) {
+        if (!owns(x, z)) return null;
+        long key = ((long) x << 32) ^ (z & 0xffffffffL);
+        var cached = columns.get(key);
+        if (cached != null) return cached;
+        if (columns.size() >= MAX_COLUMNS) return null;
+        var result = generator.getBaseColumn(x, z, height, random);
+        columns.put(key, result);
+        return result;
+    }
+
+    public LostCityPlanner.Ground ground(int x, int z) {
+        var column = column(x, z);
+        if (column == null) return new LostCityPlanner.Ground(0, 0, false, true);
+        int top = 383;
+        while (top > 0 && column.getBlock(top).isAir()) top--;
+        int bottom = top;
+        while (bottom > 0 && top - bottom < 24 && column.getBlock(bottom).isSolid()
+                && column.getBlock(bottom).getFluidState().isEmpty()) bottom--;
+        boolean dry = column.getBlock(top).isSolid() && column.getBlock(top).getFluidState().isEmpty();
+        boolean water = island.origin() && top >= 168 && dry && top - bottom >= 6
+            && PopulationHydrologyRuntime.protects(generator, random, new BlockPos(x, top, z), 1, 30, 12);
+        return new LostCityPlanner.Ground(top, top - bottom, dry, water);
+    }
+
+    @Override public boolean solid(int x, int y, int z) {
+        if (y < 0 || y >= 384) return false;
+        var column = column(x, z);
+        return column != null && column.getBlock(y).isSolid() && column.getBlock(y).getFluidState().isEmpty();
+    }
+    @Override public boolean protectedAt(int x, int y, int z) {
+        if (y < 0 || y >= 384) return true;
+        var column = column(x, z);
+        if (column == null || !column.getBlock(y).getFluidState().isEmpty()) return true;
+        if (!island.origin() && island.relief().equals("volcano")
+                && Math.abs(x - fluidCandidate.getX()) <= 2 && Math.abs(z - fluidCandidate.getZ()) <= 2) return true;
+        return protectedVolume.test(new BlockPos(x, y, z));
+    }
+    @Override public boolean exteriorAir(int x, int y, int z, int dx, int dz) {
+        if (Math.abs(dx) + Math.abs(dz) != 1 || y < 1 || y >= 380 || !owns(x, z)) return false;
+        for (int distance = 0; distance <= 32; distance++) {
+            int px = x + dx * distance, pz = z + dz * distance;
+            if (!owns(px, pz)) return false; // Never infer exterior air in another present or future owner.
+            var sample = column(px, pz);
+            if (sample == null) return false;
+            for (int dy = -3; dy < 3; dy++) if (!sample.getBlock(y + dy).isAir()
+                    || protectedVolume.test(new BlockPos(px, y + dy, pz))) return false;
+        }
+        return true;
+    }
+    @Override public boolean owns(int x, int z) { return island.contains(x, z); }
+    public int columnsUsed() { return columns.size(); }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritageCommands19.java

@@ -19,7 +19,7 @@ public final class HeritageCommands19 {
                     var level = source.getLevel();
                     if (!Level.OVERWORLD.equals(level.dimension())
                             || !(level.getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator generator)
-                            || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20) || !generator.experimentalStructures()) {
+                            || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21) || !generator.experimentalStructures()) {
                         source.sendFailure(Component.translatable("sanctuary.heritage.unavailable"));
                         return 0;
                     }
@@ -28,6 +28,11 @@ public final class HeritageCommands19 {
                     for (var site : plan.sites()) source.sendSuccess(() -> Component.translatable("sanctuary.heritage.entry",
                         Component.translatable("sanctuary.heritage.kind." + site.kind().name().toLowerCase(Locale.ROOT)),
                         site.entry().x(), site.entry().y(), site.entry().z()), false);
+                    if (generator.rootGeneration() == 21) for (var module : generator.transitPlan21().modules()) {
+                        if (module.kind() != fr.koka.sanctuary.worldgen.transit.TransitPlan21.Kind.ACCESS) continue;
+                        var at = fr.koka.sanctuary.worldgen.transit.TransitPiece21.locator(module);
+                        source.sendSuccess(() -> Component.translatable("sanctuary.transit.entry", at.getX(), at.getY(), at.getZ()), false);
+                    }
                     return plan.sites().size();
                 }))));
     }

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritagePiece21.java

@@ -0,0 +1,185 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import java.util.ArrayList;
+import java.util.Set;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.nbt.Tag;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.StructureManager;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.levelgen.structure.BoundingBox;
+import net.minecraft.world.level.levelgen.structure.StructurePiece;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceSerializationContext;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** Self-contained schema21 geometry. Reload never needs the planner or a distant route destination. */
+public final class HeritagePiece21 extends StructurePiece {
+    private static final Set<String> SITE_KEYS = Set.of("Schema", "Type", "Id", "Kind", "MinX", "FloorY", "MinZ",
+        "Width", "Depth", "Height", "Facing", "Seed", "FoundationDepth", "Supports", "Entry");
+    private static final Set<String> ROUTE_KEYS = Set.of("Schema", "Type", "Id", "FromId", "ToId", "Kind",
+        "StartChunkX", "StartChunkZ", "Cells", "Seed");
+    private static final Set<String> SUPPORT_KEYS = Set.of("X", "MinY", "Z", "MaxY");
+    private static final Set<String> ENTRY_KEYS = Set.of("X", "Y", "Z", "Facing");
+    private static final Set<String> CELL_KEYS = Set.of("X", "FloorY", "Z", "FoundationDepth", "Rail", "RailPresent");
+    private final HeritagePlan19.Site site;
+    private final HeritagePlan19.Segment segment;
+
+    public HeritagePiece21(HeritagePlan19.Site site) {
+        super(HeritageStructures19.PIECE21, 0, bounds(site));
+        this.site = site; this.segment = null; setOrientation(null);
+    }
+    public HeritagePiece21(HeritagePlan19.Segment segment) {
+        super(HeritageStructures19.PIECE21, 0, bounds(segment));
+        this.site = null; this.segment = segment; setOrientation(null);
+    }
+    public HeritagePiece21(StructurePieceSerializationContext context, CompoundTag tag) {
+        super(HeritageStructures19.PIECE21, tag);
+        var payload = tag.getCompound("SanctuaryHeritage").orElseThrow(() -> new IllegalArgumentException("Missing saved heritage geometry"));
+        String type = string(payload, "Type");
+        if (type.equals("SITE")) { site = decodeSite(payload); segment = null; }
+        else if (type.equals("ROUTE")) { site = null; segment = decodeSegment(payload); }
+        else throw new IllegalArgumentException("Unknown heritage piece type");
+        if (!getBoundingBox().equals(isSite() ? bounds(site) : bounds(segment)))
+            throw new IllegalArgumentException("Heritage geometry disagrees with its saved native bounds");
+        setOrientation(null);
+    }
+    public boolean isSite() { return site != null; }
+    public HeritagePlan19.Site site() { if (site == null) throw new IllegalStateException("This heritage piece is a route"); return site; }
+    public HeritagePlan19.Segment segment() { if (segment == null) throw new IllegalStateException("This heritage piece is a site"); return segment; }
+    @Override public BlockPos getLocatorPosition() {
+        if (isSite()) return locator(site);
+        var cell = segment.cells().getFirst(); return new BlockPos(cell.x(), cell.floorY() + 1, cell.z());
+    }
+    public static BlockPos locator(HeritagePlan19.Site site) { return new BlockPos(site.entry().x(), site.entry().y(), site.entry().z()); }
+    @Override protected void addAdditionalSaveData(StructurePieceSerializationContext context, CompoundTag tag) {
+        tag.put("SanctuaryHeritage", isSite() ? encodeSite(site) : encodeSegment(segment));
+    }
+    public static CompoundTag encodeSite(HeritagePlan19.Site site) {
+        var tag = header("SITE", site.id(), site.kind().name(), site.seed());
+        tag.putInt("MinX", site.minX()); tag.putInt("FloorY", site.floorY()); tag.putInt("MinZ", site.minZ());
+        tag.putInt("Width", site.width()); tag.putInt("Depth", site.depth()); tag.putInt("Height", site.height());
+        tag.putInt("Facing", site.facing()); tag.putInt("FoundationDepth", site.foundationDepth());
+        var entry = new CompoundTag(); entry.putInt("X", site.entry().x()); entry.putInt("Y", site.entry().y());
+        entry.putInt("Z", site.entry().z()); entry.putInt("Facing", site.entry().facing()); tag.put("Entry", entry);
+        var supports = new ListTag();
+        for (var support : site.supports()) {
+            var value = new CompoundTag(); value.putInt("X", support.x()); value.putInt("MinY", support.minY());
+            value.putInt("Z", support.z()); value.putInt("MaxY", support.maxY()); supports.add(value);
+        }
+        tag.put("Supports", supports); return tag;
+    }
+    public static CompoundTag encodeSegment(HeritagePlan19.Segment segment) {
+        var tag = header("ROUTE", segment.id(), segment.kind().name(), segment.seed());
+        tag.putString("FromId", segment.fromId()); tag.putString("ToId", segment.toId());
+        tag.putInt("StartChunkX", segment.startChunkX()); tag.putInt("StartChunkZ", segment.startChunkZ());
+        var cells = new ListTag();
+        for (var cell : segment.cells()) {
+            var value = new CompoundTag(); value.putInt("X", cell.x()); value.putInt("FloorY", cell.floorY());
+            value.putInt("Z", cell.z()); value.putInt("FoundationDepth", cell.foundationDepth());
+            value.putString("Rail", cell.rail().name()); value.putBoolean("RailPresent", cell.railPresent()); cells.add(value);
+        }
+        tag.put("Cells", cells); return tag;
+    }
+    public static HeritagePlan19.Site decodeSite(CompoundTag tag) {
+        schema(tag, "SITE", SITE_KEYS);
+        var entry = compound(tag, "Entry", ENTRY_KEYS);
+        var saved = list(tag, "Supports", 9); var supports = new ArrayList<HeritagePlan19.Support>();
+        for (var value : saved) {
+            var support = element(value, SUPPORT_KEYS);
+            supports.add(new HeritagePlan19.Support(coordinate(support, "X"), integer(support, "MinY"),
+                coordinate(support, "Z"), integer(support, "MaxY")));
+        }
+        return new HeritagePlan19.Site(id(tag, "Id"), HeritagePlan19.Kind.valueOf(string(tag, "Kind")),
+            coordinate(tag, "MinX"), integer(tag, "FloorY"), coordinate(tag, "MinZ"), integer(tag, "Width"),
+            integer(tag, "Depth"), integer(tag, "Height"), integer(tag, "Facing"), seed(tag), integer(tag, "FoundationDepth"),
+            supports, new HeritagePlan19.Entry(coordinate(entry, "X"), integer(entry, "Y"), coordinate(entry, "Z"), integer(entry, "Facing")));
+    }
+    public static HeritagePlan19.Segment decodeSegment(CompoundTag tag) {
+        schema(tag, "ROUTE", ROUTE_KEYS);
+        var saved = list(tag, "Cells", 256); var cells = new ArrayList<HeritagePlan19.Cell>();
+        for (var value : saved) {
+            var cell = element(value, CELL_KEYS);
+            type(cell, "RailPresent", Tag.TAG_BYTE);
+            byte present = cell.getByte("RailPresent").orElseThrow();
+            if (present != 0 && present != 1) throw new IllegalArgumentException("Invalid saved rail presence");
+            cells.add(new HeritagePlan19.Cell(coordinate(cell, "X"), integer(cell, "FloorY"), coordinate(cell, "Z"),
+                integer(cell, "FoundationDepth"), HeritagePlan19.Rail.valueOf(string(cell, "Rail")), present == 1));
+        }
+        String from = id(tag, "FromId"), to = id(tag, "ToId");
+        var kind = HeritagePlan19.RouteKind.valueOf(string(tag, "Kind"));
+        if (from.equals(to) && kind != HeritagePlan19.RouteKind.PATH)
+            throw new IllegalArgumentException("Only a local pedestrian landing may join a destination to itself");
+        return new HeritagePlan19.Segment(id(tag, "Id"), from, to, kind,
+            integer(tag, "StartChunkX"), integer(tag, "StartChunkZ"), cells, seed(tag));
+    }
+    private static CompoundTag header(String type, String id, String kind, long seed) {
+        var value = new CompoundTag(); value.putInt("Schema", 21); value.putString("Type", type);
+        value.putString("Id", id); value.putString("Kind", kind); value.putLong("Seed", seed); return value;
+    }
+    private static void schema(CompoundTag tag, String expected, Set<String> keys) {
+        if (!tag.keySet().equals(keys) || integer(tag, "Schema") != 21 || !string(tag, "Type").equals(expected))
+            throw new IllegalArgumentException("Unsupported or incomplete saved heritage schema");
+    }
+    private static CompoundTag compound(CompoundTag tag, String key, Set<String> keys) {
+        type(tag, key, Tag.TAG_COMPOUND); return element(tag.get(key), keys);
+    }
+    private static CompoundTag element(Tag tag, Set<String> keys) {
+        if (!(tag instanceof CompoundTag value) || !value.keySet().equals(keys))
+            throw new IllegalArgumentException("Unsupported or incomplete saved heritage element");
+        return value;
+    }
+    private static ListTag list(CompoundTag tag, String key, int maximum) {
+        type(tag, key, Tag.TAG_LIST); var value = tag.getList(key).orElseThrow();
+        if (value.size() > maximum) throw new IllegalArgumentException("Oversized saved heritage list"); return value;
+    }
+    private static long seed(CompoundTag tag) { type(tag, "Seed", Tag.TAG_LONG); return tag.getLong("Seed").orElseThrow(); }
+    private static String id(CompoundTag tag, String key) {
+        var value = string(tag, key);
+        if (value.isBlank() || value.length() > 128) throw new IllegalArgumentException("Invalid saved heritage identifier"); return value;
+    }
+    private static String string(CompoundTag tag, String key) { type(tag, key, Tag.TAG_STRING); return tag.getString(key).orElseThrow(); }
+    private static int coordinate(CompoundTag tag, String key) {
+        int value = integer(tag, key);
+        if (value < -30_000_000 || value > 30_000_000) throw new IllegalArgumentException("Heritage coordinate outside world bounds"); return value;
+    }
+    private static int integer(CompoundTag tag, String key) { type(tag, key, Tag.TAG_INT); return tag.getInt(key).orElseThrow(); }
+    private static void type(CompoundTag tag, String key, byte id) {
+        if (tag.get(key) == null || tag.get(key).getId() != id) throw new IllegalArgumentException("Invalid saved heritage field: " + key);
+    }
+    @Override public void postProcess(WorldGenLevel level, StructureManager manager, ChunkGenerator generator,
+            RandomSource random, BoundingBox clip, ChunkPos chunk, BlockPos pivot) {
+        final int x0 = isSite() ? site.minX() : segment.minX();
+        final int y0 = isSite() ? site.floorY() : segment.minY();
+        final int z0 = isSite() ? site.minZ() : segment.minZ();
+        var writer = new LostCityRenderer.BlockWriter() {
+            private BlockPos world(int x, int y, int z) { return new BlockPos(Math.addExact(x0, x), Math.addExact(y0, y), Math.addExact(z0, z)); }
+            @Override public void set(int x, int y, int z, BlockState block) {
+                var position = world(x, y, z);
+                if (getBoundingBox().isInside(position) && clip.isInside(position))
+                    placeBlock(level, block, position.getX(), position.getY(), position.getZ(), clip);
+            }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> loot, long seed) {
+                var position = world(x, y, z);
+                if (getBoundingBox().isInside(position) && clip.isInside(position))
+                    createChest(level, clip, RandomSource.create(seed), position, loot, null);
+            }
+        };
+        HeritageStructures19.placing(() -> {
+            if (isSite()) HeritageRenderer21.render(site, writer);
+            else HeritageRenderer21.renderSegment(segment, writer);
+        });
+    }
+    public static BoundingBox bounds(HeritagePlan19.Site site) {
+        return new BoundingBox(site.minX(), site.boundsMinY(), site.minZ(), site.maxX(), site.boundsMaxY(), site.maxZ());
+    }
+    public static BoundingBox bounds(HeritagePlan19.Segment segment) {
+        return new BoundingBox(segment.minX(), segment.boundsMinY(), segment.minZ(), segment.maxX(), segment.boundsMaxY(), segment.maxZ());
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritagePlanner21.java

@@ -0,0 +1,616 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.worldgen.heritage.HeritagePlan19.*;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+
+/** Generation21 only. A finite catalogue is admitted before complete, repairable routes are published.
+ * Everything samples native columns; no chunk, player object or future continent is requested. */
+public final class HeritagePlanner21 {
+    public static final int MAX_COLUMNS = HeritagePlan19.MAX_COLUMNS, MAX_SAMPLES = HeritagePlan19.MAX_SAMPLES;
+    // Local17x17 sites may cut8 blocks, with the same at-most8-block slab and certified short piers.
+    // Three-wide paths may cut4/fill5; grade stays one block, and water/old construction is never waived.
+    public static final int MAX_SITE_CUT = 8, MAX_ROUTE_CUT = 4, MAX_ROUTE_FILL = 5;
+    private static final int SITE_COLUMNS = 11_000, SITE_SAMPLES = 540_000;
+    private static final int INVALID = Integer.MIN_VALUE;
+    private static final int[] DX = {0, 1, 0, -1}, DZ = {-1, 0, 1, 0};
+    private HeritagePlanner21() {}
+    public interface Terrain extends HeritagePlanner19.Terrain {
+        boolean owns(int x, int z);
+        int surfaceY(int x, int z);
+        boolean solid(int x, int y, int z);
+        boolean protectedAt(int x, int y, int z);
+        default List<Landmark> landmarks() { return List.of(); }
+    }
+
+    public static HeritagePlan19 plan(long seed, int cx, int cz, int diameter, Terrain terrain) {
+        if (!List.of(512, 724, 1024).contains(diameter)) throw new IllegalArgumentException("Heritage21 requires a starter size");
+        var probe = new Probe(terrain, cx, cz, diameter);
+        List<Landmark> landmarks = List.copyOf(terrain.landmarks()).stream().limit(16).toList();
+        var sites = new ArrayList<Site>(); var cells = new LinkedHashMap<Long, OwnedCell>(); var diagnostics = new EnumMap<Kind, String>(Kind.class);
+        for (var kind : Kind.values()) {
+            int remaining = Kind.values().length - kind.ordinal() - 1;
+            probe.columnLimit = SITE_COLUMNS - remaining * (SITE_COLUMNS / 14);
+            probe.sampleLimit = SITE_SAMPLES - remaining * (SITE_SAMPLES / 14);
+            SiteDraft admitted = null; int attempts = 0;
+            var reasons = new java.util.TreeMap<String, Integer>(); probe.reasons = reasons;
+            try {
+                for (var candidate : candidates(seed, kind, cx, cz, diameter, sites, landmarks, probe)) {
+                    attempts++;
+                    admitted = site(seed, kind, candidate, sites, landmarks, cells, probe);
+                    if (admitted != null) break;
+                }
+            } catch (BudgetExceeded exhausted) { reasons.merge(exhausted.columns ? "column-budget" : "probe-budget", 1, Integer::sum); }
+            if (admitted != null) {
+                sites.add(admitted.site());
+                Request landing = new Request(admitted.site().id() + "_landing", admitted.site().id(), admitted.site().id(), RouteKind.PATH);
+                for (var cell : admitted.landings()) cells.put(key(cell.x(), cell.z()), new OwnedCell(landing, cell));
+            }
+            diagnostics.put(kind, (admitted == null ? "not admitted" : "admitted") + "; candidates=" + attempts + "; " + reasons);
+        }
+        probe.columnLimit = MAX_COLUMNS; probe.sampleLimit = MAX_SAMPLES;
+        var links = new ArrayList<Link>();
+        var routeResults = new LinkedHashMap<String, String>();
+        var routeReasons = new java.util.TreeMap<String, Integer>(); probe.reasons = routeReasons;
+        Map<String, Endpoint> endpoints = new LinkedHashMap<>();
+        for (var site : sites) endpoints.put(site.id(), new Endpoint(site.id(), site.entry(), false));
+        for (var landmark : landmarks) if (!endpoints.containsKey(landmark.id()))
+            endpoints.put(landmark.id(), new Endpoint(landmark.id(), landmark.entry(), true));
+        var requests = new ArrayList<>(requests(sites, landmarks).stream()
+            .filter(r -> endpoints.containsKey(r.from()) && endpoints.containsKey(r.to())).toList());
+        var components = new Components(endpoints.keySet());
+        // Multiple exterior entries into the certified connected city represent one already walkable destination.
+        String firstCity = null;
+        for (var landmark : landmarks) if (landmark.kind() == LandmarkKind.CITY) {
+            if (firstCity == null) firstCity = landmark.id(); else components.join(firstCity, landmark.id());
+        }
+        Request longFreight = requests.stream().filter(r -> r.kind() == RouteKind.FREIGHT
+                && span(endpoints.get(r.from()).entry(), endpoints.get(r.to()).entry()) >= diameter / 4)
+            .max(Comparator.comparingInt(r -> span(endpoints.get(r.from()).entry(), endpoints.get(r.to()).entry()))).orElse(null);
+        var siteIds = new HashSet<String>(); sites.forEach(site -> siteIds.add(site.id()));
+        var addressed = new HashSet<String>();
+        var destinationAttempts = new HashMap<String, Integer>();
+        int attempted = 0;
+        while (!requests.isEmpty() && attempted < 36 && links.size() < 24) {
+            // Give each isolated site a first useful route before spending its columns on a cycle.
+            // Repeated city gates already belong to one walkable component; no redundant freight bypass is needed.
+            requests.removeIf(r -> components.same(r.from(), r.to()));
+            if (requests.isEmpty()) break;
+            requests.sort(Comparator.comparingInt((Request r) -> isolatedSites(r, siteIds, addressed) > 0
+                    && isolatedAttempts(r, siteIds, addressed, destinationAttempts) == 0 ? 0 : 1)
+                .thenComparingInt(r -> span(endpoints.get(r.from()).entry(), endpoints.get(r.to()).entry()))
+                .thenComparingInt(r -> r.kind() == RouteKind.FREIGHT ? 0 : 1).thenComparing(Request::id));
+            var request = attempted == 0 && longFreight != null ? longFreight : requests.getFirst(); requests.remove(request);
+            attempted++;
+            int distance = Math.abs(endpoints.get(request.from()).entry().x() - endpoints.get(request.to()).entry().x())
+                + Math.abs(endpoints.get(request.from()).entry().z() - endpoints.get(request.to()).entry().z());
+            boolean longAxis = span(endpoints.get(request.from()).entry(), endpoints.get(request.to()).entry()) >= diameter / 4;
+            int isolated = isolatedSites(request, siteIds, addressed);
+            var waiting = new HashSet<String>();
+            for (var next : requests) for (var id : List.of(next.from(), next.to()))
+                if (siteIds.contains(id) && !addressed.contains(id) && !id.equals(request.from()) && !id.equals(request.to())) waiting.add(id);
+            int reserve = Math.min(Math.min(waiting.size(), 8), 36 - attempted) * 100;
+            int allowance = longAxis && attempted == 1 ? 3_800 : isolated > 0 ? Math.clamp(distance * 5 + 350, 900, 2_400) : 900;
+            probe.columnLimit = Math.min(MAX_COLUMNS - reserve, probe.columns.size() + allowance);
+            probe.sampleLimit = Math.min(MAX_SAMPLES - reserve * 20, probe.samples + (longAxis ? 150_000 : 80_000));
+            for (var id : List.of(request.from(), request.to())) if (siteIds.contains(id) && !addressed.contains(id))
+                destinationAttempts.merge(id, 1, Integer::sum);
+            Endpoint from = endpoints.get(request.from()), to = endpoints.get(request.to());
+            int beforeRouteColumns = probe.columns.size();
+            var beforeReasons = new HashMap<>(routeReasons);
+            try {
+                RouteDraft route = route(seed, request, from, to, sites, landmarks, cells, probe);
+                if (route == null) { probe.reject("no-complete-route"); routeResults.put(request.id(), "refused; columns=" + (probe.columns.size() - beforeRouteColumns) + rejectionDelta(beforeReasons, routeReasons, probe.routeBlock)); continue; }
+                var groups = new HashSet<SegmentKey>();
+                cells.values().forEach(c -> groups.add(new SegmentKey(c.request(), c.cell().x() >> 4, c.cell().z() >> 4)));
+                route.cells().values().stream().filter(c -> !cells.containsKey(key(c.x(), c.z())))
+                    .forEach(c -> groups.add(new SegmentKey(request, c.x() >> 4, c.z() >> 4)));
+                if (groups.size() > 512) { routeResults.put(request.id(), "refused; native-piece-budget"); continue; }
+                links.add(new Link(request.id(), request.from(), request.to(), request.kind(), route.path()));
+                components.join(request.from(), request.to());
+                addressed.add(request.from()); addressed.add(request.to());
+                routeResults.put(request.id(), "admitted; span=" + span(from.entry(), to.entry()) + "; length=" + route.path().size() + "; columns=" + (probe.columns.size() - beforeRouteColumns));
+                for (var cell : route.cells().values()) {
+                    long key = key(cell.x(), cell.z());
+                    OwnedCell old = cells.get(key);
+                    if (old == null) cells.put(key, new OwnedCell(request, cell));
+                    else if (cell.rail() != Rail.NONE && old.cell().rail() == Rail.NONE)
+                        cells.put(key, new OwnedCell(old.request(), cell));
+                    else if (cell.rail() != Rail.NONE && old.cell().rail() != Rail.NONE && cell.rail() != old.cell().rail()) {
+                        // A missing switch is intentional; never emit a rail with contradictory connections.
+                        var c = old.cell(); cells.put(key, new OwnedCell(old.request(),
+                            new Cell(c.x(), c.floorY(), c.z(), c.foundationDepth(), c.rail(), false)));
+                    }
+                }
+            } catch (BudgetExceeded exhausted) { probe.reject(exhausted.columns ? "route-column-budget" : "route-probe-budget"); routeResults.put(request.id(), "budget; columns=" + (probe.columns.size() - beforeRouteColumns) + rejectionDelta(beforeReasons, routeReasons, probe.routeBlock)); }
+        }
+        for (var site : sites) {
+            var incident = links.stream().filter(l -> l.fromId().equals(site.id()) || l.toId().equals(site.id())).map(Link::id).toList();
+            var attempts = new LinkedHashMap<String, String>();
+            routeResults.forEach((id, value) -> { if (id.contains(site.id())) attempts.put(id, value); });
+            diagnostics.put(site.kind(), diagnostics.get(site.kind()) + "; connected=" + !incident.isEmpty()
+                + "; accepted-links=" + incident + "; route-attempts=" + attempts);
+        }
+        var segments = segments(seed, cells);
+        if (Boolean.getBoolean("sanctuary.test.heritage21") || Boolean.getBoolean("sanctuary.heritage.plannerDiagnostics"))
+            System.getLogger(HeritagePlanner21.class.getName()).log(System.Logger.Level.INFO,
+                "Heritage21 seed=" + seed + " diameter=" + diameter + " sites=" + sites.stream().map(Site::kind).toList()
+                + " links=" + links.size() + " segments=" + segments.size() + " columns=" + probe.columns.size()
+                + " samples=" + probe.samples + " catalogue=" + diagnostics + " routes=" + routeReasons + " routeResults=" + routeResults);
+        return new HeritagePlan19(sites, landmarks, links, segments, probe.samples, probe.columns.size(), diagnostics);
+    }
+
+    private static List<Candidate> candidates(long seed, Kind kind, int cx, int cz, int diameter,
+            List<Site> sites, List<Landmark> landmarks, Probe probe) {
+        double angle = unit(mix(seed ^ 0x19ACEL)) * Math.PI * 2 + kind.ordinal() * 2.399963229728653;
+        double radius = diameter * (kind == Kind.VOID_DOCK ? .40 : kind == Kind.OBSERVATORY || kind == Kind.RADIO_RELAY ? .31 : .22);
+        int x = cx + (int) Math.round(Math.cos(angle) * radius), z = cz + (int) Math.round(Math.sin(angle) * radius);
+        Kind parent = switch (kind) {
+            case POST_OFFICE, COMMUNAL_DEPOT, RAIL_WORKSHOP -> Kind.FREIGHT_STATION;
+            case EXPEDITION_OFFICE, PHOTO_CLUB -> Kind.POST_OFFICE;
+            case SUBSTATION, CONSTRUCTION_REFUGE -> Kind.RAIL_WORKSHOP;
+            case GREENHOUSE, IMPOSSIBLE_SERVICE -> Kind.PUMP_STATION;
+            default -> null;
+        };
+        Site neighbor = parent == null ? null : find(sites, parent);
+        if (neighbor != null) {
+            double local = unit(mix(seed ^ kind.ordinal() * 179L)) * Math.PI * 2;
+            int distance = kind == Kind.RAIL_WORKSHOP ? 65 : 40;
+            x = neighbor.centerX() + (int) Math.round(Math.cos(local) * distance);
+            z = neighbor.centerZ() + (int) Math.round(Math.sin(local) * distance);
+        }
+        var candidates = new ArrayList<Candidate>();
+        for (int i = 0; i < 16; i++) {
+            double turn = angle + i * Math.PI / 3;
+            int offset = i == 0 ? 0 : i < 5 ? 24 : i < 8 ? 48 : i < 12 ? 72 : 96;
+            int px = x + (int) Math.round(Math.cos(turn) * offset), pz = z + (int) Math.round(Math.sin(turn) * offset);
+            if (Math.hypot((double) px - cx, (double) pz - cz) > diameter / 2.0 - 18) continue;
+            if (overlapsSites(px - 15, pz - 15, px + 15, pz + 15, sites)) continue;
+            int low = 384, high = -1; boolean dry = true;
+            for (int dz : new int[] {-8, 0, 8}) for (int dx : new int[] {-8, 0, 8}) {
+                int top = probe.surface(px + dx, pz + dz);
+                if (top < 48 || top > 330 || !probe.solid(px + dx, top, pz + dz)
+                        || probe.protectedAt(px + dx, top, pz + dz)) { dry = false; break; }
+                low = Math.min(low, top); high = Math.max(high, top);
+            }
+            if (!dry || high - low > MAX_SITE_CUT + 7) { probe.reject("coarse-terrain"); continue; }
+            int facing = direction(px, pz, neighbor == null ? cx : neighbor.centerX(), neighbor == null ? cz : neighbor.centerZ());
+            if (kind == Kind.VOID_DOCK) facing = (direction(px, pz, cx, cz) + 2) & 3;
+            int score = (i >= 8 ? 1_000 : 0) + high - low + (kind == Kind.OBSERVATORY || kind == Kind.RADIO_RELAY ? (300 - high) / 4 : 0);
+            candidates.add(new Candidate(px - 8, pz - 8, facing, score, mix(seed ^ kind.ordinal() * 463L ^ i)));
+        }
+        candidates.sort(Comparator.comparingInt(Candidate::score).thenComparingLong(Candidate::seed));
+        return candidates;
+    }
+
+    private static SiteDraft site(long seed, Kind kind, Candidate candidate, List<Site> previous,
+            List<Landmark> landmarks, Map<Long, OwnedCell> existing, Probe probe) {
+        int x = candidate.x(), z = candidate.z(), low = 384, high = -1;
+        for (var landmark : landmarks) if (landmark.entry().x() >= x - 2 && landmark.entry().x() <= x + 18
+                && landmark.entry().z() >= z - 2 && landmark.entry().z() <= z + 18) { probe.reject("existing-entry"); return null; }
+        var heights = new ArrayList<Integer>();
+        for (int dz = 0; dz < 17; dz++) for (int dx = 0; dx < 17; dx++) {
+            int top = probe.surface(x + dx, z + dz);
+            if (top < 48 || top > 330 || !probe.solid(x + dx, top, z + dz)) { probe.reject("dry-footprint"); return null; }
+            heights.add(top); low = Math.min(low, top); high = Math.max(high, top);
+        }
+        int minimum = Math.max(48, high - MAX_SITE_CUT), maximum = Math.min(330, low + 7);
+        if (minimum > maximum) { probe.reject("site-slope"); return null; }
+        heights.sort(Integer::compareTo);
+        int floor = Math.clamp(heights.get(heights.size() / 2), minimum, maximum);
+        int foundation = Math.max(3, floor - low + 1), height = height(kind);
+        int base = floor - foundation;
+        for (int dz = 0; dz < 17; dz++) for (int dx = 0; dx < 17; dx++)
+            for (int y = base; y <= floor + height; y++) if (probe.protectedAt(x + dx, y, z + dz)) {
+                probe.reject("site-protected-volume"); return null;
+            }
+        var supports = new ArrayList<Support>();
+        for (int dz : new int[] {1, 8, 15}) for (int dx : new int[] {1, 8, 15}) {
+            int bottom = base - 1, rock = bottom;
+            while (rock >= Math.max(2, base - 13) && (!probe.solid(x + dx, rock, z + dz)
+                    || !probe.solid(x + dx, rock - 1, z + dz))) rock--;
+            if (rock < Math.max(2, base - 13)) { probe.reject("site-no-bearing"); return null; }
+            for (int y = rock - 1; y <= bottom; y++) if (probe.protectedAt(x + dx, y, z + dz)) { probe.reject("support-protected"); return null; }
+            if (rock < bottom) supports.add(new Support(x + dx, rock + 1, z + dz, bottom));
+        }
+        // The square envelope and bearing grid have already been certified. A difficult front slope
+        // should try another real facade before rejecting the entire building; no terrain is weakened.
+        for (int turn : new int[]{0, 1, 3, 2}) {
+            int facing = (candidate.facing() + turn) & 3;
+            int ex = facing == 1 ? x + 17 : facing == 3 ? x - 1 : x + 8;
+            int ez = facing == 2 ? z + 17 : facing == 0 ? z - 1 : z + 8;
+            Entry entry = new Entry(ex, floor + 1, ez, facing);
+            Site result = new Site(id(kind), kind, x, floor, z, 17, 17, height, facing,
+                mix(seed ^ candidate.seed()), foundation, supports, entry);
+            var landings = landing(result.entry(), previous, probe);
+            if (landings == null) { probe.reject("entry-landing"); continue; }
+            boolean collision = false;
+            for (var cell : landings) {
+                OwnedCell old = existing.get(key(cell.x(), cell.z()));
+                if (old != null && old.cell().floorY() != cell.floorY()) { collision = true; break; }
+            }
+            if (collision) { probe.reject("landing-collision"); continue; }
+            if (turn != 0) probe.reject("admitted-other-facade");
+            return new SiteDraft(result, landings);
+        }
+        return null;
+    }
+
+    private static int height(Kind kind) {
+        return switch (kind) {
+            case FREIGHT_STATION, POST_OFFICE, RAIL_WORKSHOP, SUBSTATION, GREENHOUSE, PHOTO_CLUB -> 10;
+            case EXPEDITION_OFFICE, IMPOSSIBLE_SERVICE -> 12;
+            case COMMUNAL_DEPOT, VOID_DOCK, CONSTRUCTION_REFUGE -> 14;
+            case PUMP_STATION -> 18; case OBSERVATORY -> 20; case RADIO_RELAY -> 22;
+        };
+    }
+    private static List<Request> requests(List<Site> sites, List<Landmark> landmarks) {
+        var result = new LinkedHashMap<String, Request>();
+        var endpoints = new ArrayList<Endpoint>();
+        sites.forEach(s -> endpoints.add(new Endpoint(s.id(), s.entry(), false)));
+        landmarks.forEach(l -> endpoints.add(new Endpoint(l.id(), l.entry(), true)));
+        var freight = new HashSet<String>();
+        for (var kind : new Kind[] {Kind.FREIGHT_STATION, Kind.COMMUNAL_DEPOT, Kind.RAIL_WORKSHOP, Kind.PUMP_STATION}) {
+            var site = find(sites, kind); if (site != null) freight.add(site.id());
+        }
+        landmarks.stream().filter(l -> l.kind() == LandmarkKind.MINE).forEach(l -> freight.add(l.id()));
+        for (var a : endpoints) {
+            // Four alternatives per entrance tolerate one protected cut without a quadratic terrain search.
+            var nearest = endpoints.stream().filter(b -> !a.id().equals(b.id()))
+                .sorted(Comparator.comparingInt((Endpoint b) -> span(a.entry(), b.entry())).thenComparing(Endpoint::id)).limit(4).toList();
+            for (var b : nearest) addRequest(result, a, b, freight.contains(a.id()) && freight.contains(b.id()) ? RouteKind.FREIGHT : RouteKind.PATH);
+        }
+        for (var pair : List.of(new Kind[]{Kind.FREIGHT_STATION, Kind.COMMUNAL_DEPOT},
+                new Kind[]{Kind.FREIGHT_STATION, Kind.RAIL_WORKSHOP}, new Kind[]{Kind.COMMUNAL_DEPOT, Kind.PUMP_STATION})) {
+            var a = find(sites, pair[0]); var b = find(sites, pair[1]);
+            if (a != null && b != null) addRequest(result, new Endpoint(a.id(), a.entry(), false), new Endpoint(b.id(), b.entry(), false), RouteKind.FREIGHT);
+        }
+        return List.copyOf(result.values());
+    }
+    private static void addRequest(Map<String, Request> result, Endpoint a, Endpoint b, RouteKind kind) {
+        if (a.id().compareTo(b.id()) > 0) { var swap = a; a = b; b = swap; }
+        String key = a.id() + "__" + b.id(); var old = result.get(key);
+        if (old == null || kind == RouteKind.FREIGHT) result.put(key, new Request("graph_" + key, a.id(), b.id(), kind));
+    }
+    private static String rejectionDelta(Map<String, Integer> before, Map<String, Integer> after, XZ obstacle) {
+        var changes = new java.util.TreeMap<String, Integer>();
+        after.forEach((key, count) -> { int difference = count - before.getOrDefault(key, 0); if (difference > 0) changes.put(key, difference); });
+        return "; reasons=" + changes + (obstacle == null ? "" : "; last-column=" + obstacle.x() + "," + obstacle.z());
+    }
+    private static int isolatedSites(Request request, Set<String> siteIds, Set<String> addressed) {
+        return (siteIds.contains(request.from()) && !addressed.contains(request.from()) ? 1 : 0)
+            + (siteIds.contains(request.to()) && !addressed.contains(request.to()) ? 1 : 0);
+    }
+    private static int isolatedAttempts(Request request, Set<String> siteIds, Set<String> addressed, Map<String, Integer> attempts) {
+        int result = Integer.MAX_VALUE;
+        for (var id : List.of(request.from(), request.to())) if (siteIds.contains(id) && !addressed.contains(id))
+            result = Math.min(result, attempts.getOrDefault(id, 0));
+        return result == Integer.MAX_VALUE ? 0 : result;
+    }
+    private static final class Components {
+        final Map<String, String> parents = new HashMap<>();
+        Components(Set<String> ids) { for (var id : ids) parents.put(id, id); }
+        String root(String id) { String parent = parents.get(id); while (!parent.equals(id)) { id = parent; parent = parents.get(id); } return parent; }
+        boolean same(String a, String b) { return root(a).equals(root(b)); }
+        void join(String a, String b) { parents.put(root(b), root(a)); }
+    }
+
+    /** Always persisted, including for an isolated destination: five steps return to natural terrain. */
+    private static List<Cell> landing(Entry entry, List<Site> sites, Probe probe) {
+        int facing = entry.facing(), floor = entry.y() - 1;
+        int endX = entry.x() + DX[facing] * 4, endZ = entry.z() + DZ[facing] * 4;
+        int target = probe.surface(endX, endZ);
+        if (target < 14 || target > 350 || Math.abs(target - floor) > 3) return null;
+        var result = new ArrayList<Cell>();
+        for (int step = 0; step < 5; step++) {
+            // Keep the first two rows flat for the facade and the first rail turn.
+            int y = floor + (int) Math.round((target - floor) * Math.max(0, step - 1) / 3.0);
+            for (int cross = -1; cross <= 1; cross++) {
+                int x = entry.x() + DX[facing] * step + DZ[facing] * cross;
+                int z = entry.z() + DZ[facing] * step - DX[facing] * cross;
+                if (overlapsSites(x, z, x, z, sites)) return null;
+                Cell cell = routeCell(x, y, z, Rail.NONE, false, probe);
+                if (cell == null) return null;
+                result.add(cell);
+                if (step == 4) {
+                    int beyond = probe.surface(x + DX[facing], z + DZ[facing]);
+                    if (Math.abs(beyond - y) > 1 || !probe.solid(x + DX[facing], beyond, z + DZ[facing])) return null;
+                }
+            }
+        }
+        return List.copyOf(result);
+    }
+
+    private static RouteDraft route(long seed, Request request, Endpoint from, Endpoint to, List<Site> sites,
+            List<Landmark> landmarks, Map<Long, OwnedCell> existing, Probe probe) {
+        Entry a = from.entry(), b = to.entry();
+        XZ start = new XZ(a.x(), a.z()), end = new XZ(b.x(), b.z());
+        XZ outA = start.move(a.facing(), 6), outB = end.move(b.facing(), 6);
+        int middleX = (outA.x() + outB.x()) / 2, middleZ = (outA.z() + outB.z()) / 2;
+        var alternatives = List.of(
+            List.of(outA, new XZ(outB.x(), outA.z()), outB),
+            List.of(outA, new XZ(outA.x(), outB.z()), outB),
+            List.of(outA, new XZ(middleX, outA.z()), new XZ(middleX, outB.z()), outB),
+            List.of(outA, new XZ(outA.x(), middleZ), new XZ(outB.x(), middleZ), outB),
+            List.of(outA, new XZ(outA.x(), middleZ - 16), new XZ(outB.x(), middleZ - 16), outB),
+            List.of(outA, new XZ(middleX + 16, outA.z()), new XZ(middleX + 16, outB.z()), outB));
+        for (var waypoints : alternatives) {
+            var points = new ArrayList<XZ>(); points.add(start);
+            boolean okay = true;
+            for (var waypoint : waypoints) if (!line(points, waypoint)) { okay = false; break; }
+            if (!okay || !line(points, end) || points.size() > 1024 || new HashSet<>(points).size() != points.size()) continue;
+            RouteDraft result = profile(seed, request, from, to, points, sites, landmarks, existing, probe);
+            if (result != null) return result;
+        }
+        return adaptive(seed, request, from, to, start, end, outA, outB, sites, landmarks, existing, probe);
+    }
+
+    /** Adaptive fallback. The coarse graph only proposes an alignment; it grants no writing permission. */
+    private static RouteDraft adaptive(long seed, Request request, Endpoint from, Endpoint to, XZ start, XZ end,
+            XZ outA, XZ outB, List<Site> sites, List<Landmark> landmarks, Map<Long, OwnedCell> existing, Probe probe) {
+        int stepSize = span(from.entry(), to.entry()) >= 160 ? 8 : 4;
+        int certificateReserve = Math.min(2_200, distance(outA, outB) * 3 + 80);
+        var excluded = new HashSet<XZ>();
+        for (int attempt = 0; attempt < 3; attempt++) {
+            var open = new java.util.PriorityQueue<SearchNode>(Comparator.comparingDouble(SearchNode::priority)
+                .thenComparingDouble(SearchNode::cost).thenComparingInt(n -> n.position().x()).thenComparingInt(n -> n.position().z()));
+            var best = new HashMap<XZ, Double>(); var parents = new HashMap<XZ, XZ>(); var closed = new HashSet<XZ>();
+            var terrainHeights = new HashMap<XZ, Integer>();
+            int begin = coarseRoute(outA, sites, terrainHeights, probe);
+            if (begin == INVALID) return null;
+            open.add(new SearchNode(outA, 0, distance(outA, outB))); best.put(outA, 0.0);
+            List<XZ> found = null;
+            int searchColumns = Math.max(probe.columns.size() + 150, probe.columnLimit - certificateReserve);
+            while (!open.isEmpty() && closed.size() < 500 && probe.columns.size() < searchColumns) {
+                var current = open.remove(); XZ p = current.position();
+                if (!closed.add(p) || current.cost() > best.getOrDefault(p, Double.POSITIVE_INFINITY)) continue;
+                if (distance(p, outB) <= stepSize * 2) {
+                    var reversed = new ArrayList<XZ>(); XZ ancestor = p;
+                    while (ancestor != null) { reversed.add(ancestor); ancestor = parents.get(ancestor); }
+                    java.util.Collections.reverse(reversed);
+                    for (int order = 0; order < 2 && found == null; order++) {
+                        var candidate = new ArrayList<XZ>(); candidate.add(start); boolean valid = true;
+                        for (XZ step : reversed) if (!line(candidate, step)) { valid = false; break; }
+                        XZ turn = order == 0 ? new XZ(outB.x(), p.z()) : new XZ(p.x(), outB.z());
+                        if (valid && line(candidate, turn) && line(candidate, outB) && line(candidate, end)
+                                && new HashSet<>(candidate).size() == candidate.size()) found = candidate;
+                    }
+                    if (found != null) break;
+                }
+                int top = terrainHeights.get(p); XZ parent = parents.get(p);
+                for (int d = 0; d < 4; d++) {
+                    if (parent == null && d == ((from.entry().facing() + 2) & 3)) continue;
+                    XZ next = p.move(d, stepSize);
+                    if (closed.contains(next) || excluded.contains(next)
+                            || Math.min(distance(next, outA), distance(next, outB)) > distance(outA, outB) + 64) continue;
+                    int height = coarseRoute(next, sites, terrainHeights, probe);
+                    if (height == INVALID || Math.abs(height - top) > stepSize + 3) continue;
+                    double turnCost = parent == null || parent.x() == next.x() || parent.z() == next.z() ? 0 : 1.5;
+                    double cost = current.cost() + stepSize + Math.abs(height - top) * 1.1 + turnCost;
+                    if (cost >= best.getOrDefault(next, Double.POSITIVE_INFINITY)) continue;
+                    best.put(next, cost); parents.put(next, p);
+                    open.add(new SearchNode(next, cost, cost + distance(next, outB) * 1.6));
+                }
+            }
+            if (found == null) { probe.reject("adaptive-no-alignment"); return null; }
+            RouteDraft certified = profile(seed, request, from, to, found, sites, landmarks, existing, probe);
+            if (certified != null) { probe.reject("adaptive-admitted"); return certified; }
+            if (probe.routeBlock == null) return null;
+            // A failed exact corridor removes only nearby coarse nodes on the next proposal.
+            XZ bad = probe.routeBlock;
+            int gx = outA.x() + (int) Math.round((bad.x() - outA.x()) / (double) stepSize) * stepSize;
+            int gz = outA.z() + (int) Math.round((bad.z() - outA.z()) / (double) stepSize) * stepSize;
+            excluded.add(new XZ(gx, gz));
+            for (int d = 0; d < 4; d++) excluded.add(new XZ(gx, gz).move(d, stepSize));
+        }
+        return null;
+    }
+    private record SearchNode(XZ position, double cost, double priority) {}
+    private static int distance(XZ a, XZ b) { return Math.abs(a.x() - b.x()) + Math.abs(a.z() - b.z()); }
+    private static int coarseRoute(XZ p, List<Site> sites, Map<XZ, Integer> cache, Probe probe) {
+        Integer old = cache.get(p); if (old != null) return old;
+        if (overlapsSites(p.x() - 2, p.z() - 2, p.x() + 2, p.z() + 2, sites)) { cache.put(p, INVALID); return INVALID; }
+        int top = probe.surface(p.x(), p.z());
+        if (top < 14 || top > 350 || !probe.solid(p.x(), top, p.z()) || probe.protectedAt(p.x(), top, p.z())) {
+            cache.put(p, INVALID); return INVALID;
+        }
+        for (int d = 0; d < 4; d++) {
+            XZ side = p.move(d, 1); int sideTop = probe.surface(side.x(), side.z());
+            if (sideTop < 14 || sideTop > 350 || Math.abs(sideTop - top) > MAX_ROUTE_CUT + 1 || probe.protectedAt(side.x(), sideTop, side.z())) {
+                cache.put(p, INVALID); return INVALID;
+            }
+        }
+        cache.put(p, top); return top;
+    }
+
+    /** Finite orthogonal alignments, each certified at full block resolution before publication. */
+    private static boolean line(List<XZ> points, XZ destination) {
+        XZ p = points.getLast();
+        if (p.x() != destination.x() && p.z() != destination.z()) return false;
+        int dx = Integer.signum(destination.x() - p.x()), dz = Integer.signum(destination.z() - p.z());
+        while (!p.equals(destination)) {
+            p = new XZ(p.x() + dx, p.z() + dz); points.add(p);
+            if (points.size() > 1024) return false;
+        }
+        return true;
+    }
+
+    private static RouteDraft profile(long seed, Request request, Endpoint from, Endpoint to, List<XZ> points,
+            List<Site> sites, List<Landmark> landmarks, Map<Long, OwnedCell> existing, Probe probe) {
+        int size = points.size(); probe.routeBlock = null;
+        int[] lo = new int[size], hi = new int[size], desired = new int[size], group = new int[size];
+        boolean[] flat = new boolean[size - 1];
+        for (int i = 1; i < size - 1; i++) if (turn(points, i)) { flat[i - 1] = true; flat[i] = true; }
+        for (int i = 0; i < size; i++) {
+            XZ point = points.get(i); probe.routeBlock = point; lo[i] = 14; hi[i] = 350;
+            desired[i] = probe.surface(point.x(), point.z());
+            boolean readOnly = i == 0 && from.readOnly() || i == size - 1 && to.readOnly();
+            for (XZ column : strip(points, i)) {
+                if (overlapsSites(column.x(), column.z(), column.x(), column.z(), sites)) { probe.reject("route-building"); return null; }
+                int top = probe.surface(column.x(), column.z());
+                if (top < 14 || top > 350 || !probe.solid(column.x(), top, column.z())) { probe.reject("route-dry-ground"); return null; }
+                lo[i] = Math.max(lo[i], top - MAX_ROUTE_CUT); hi[i] = Math.min(hi[i], top + MAX_ROUTE_FILL);
+                OwnedCell old = existing.get(key(column.x(), column.z()));
+                if (old != null) { lo[i] = Math.max(lo[i], old.cell().floorY()); hi[i] = Math.min(hi[i], old.cell().floorY()); }
+                if (readOnly && top != (i == 0 ? from.entry().y() : to.entry().y()) - 1) return null;
+            }
+            if (i == 0 || i == size - 1) {
+                int exact = (i == 0 ? from.entry().y() : to.entry().y()) - 1;
+                lo[i] = Math.max(lo[i], exact); hi[i] = Math.min(hi[i], exact);
+            }
+            if (lo[i] > hi[i]) { probe.reject("route-grade-interval"); return null; }
+        }
+        // Curves and both adjacent rails share one elevation; a Minecraft curved rail cannot slope.
+        int groups = 1;
+        for (int i = 1; i < size; i++) { if (!flat[i - 1]) groups++; group[i] = groups - 1; }
+        int[] gl = new int[groups], gh = new int[groups], gd = new int[groups], y = new int[groups];
+        java.util.Arrays.fill(gl, 14); java.util.Arrays.fill(gh, 350);
+        for (int i = 0; i < size; i++) { int g = group[i]; gl[g] = Math.max(gl[g], lo[i]); gh[g] = Math.min(gh[g], hi[i]); gd[g] = desired[i]; }
+        for (int g = 1; g < groups; g++) { gl[g] = Math.max(gl[g], gl[g - 1] - 1); gh[g] = Math.min(gh[g], gh[g - 1] + 1); }
+        for (int g = groups - 2; g >= 0; g--) { gl[g] = Math.max(gl[g], gl[g + 1] - 1); gh[g] = Math.min(gh[g], gh[g + 1] + 1); }
+        for (int g = 0; g < groups; g++) {
+            if (gl[g] > gh[g]) { probe.reject("route-grade"); return null; }
+            int lower = g == 0 ? gl[g] : Math.max(gl[g], y[g - 1] - 1), upper = g == 0 ? gh[g] : Math.min(gh[g], y[g - 1] + 1);
+            y[g] = Math.clamp(gd[g], lower, upper);
+        }
+        var path = new ArrayList<Point>(); var floors = new LinkedHashMap<Long, Integer>();
+        for (int i = 0; i < size; i++) {
+            XZ point = points.get(i); int floor = y[group[i]]; path.add(new Point(point.x(), floor, point.z()));
+            if (i == 0 && from.readOnly() || i == size - 1 && to.readOnly()) continue;
+            for (XZ column : strip(points, i)) {
+                long key = key(column.x(), column.z()); Integer old = floors.putIfAbsent(key, floor);
+                if (old != null && old != floor) { probe.reject("route-self-grade"); return null; }
+                // Historical endpoints and their lateral landing are read-only, even at another nearby turn.
+                for (var landmark : landmarks) if (landingColumn(landmark.entry(), column)) {
+                    boolean actualEnd = from.readOnly() && landmark.id().equals(from.id())
+                        || to.readOnly() && landmark.id().equals(to.id());
+                    if (!actualEnd || floor != landmark.entry().y() - 1) { probe.reject("route-historical-entry"); return null; }
+                    floors.remove(key); break;
+                }
+            }
+        }
+        var cells = new LinkedHashMap<Long, Cell>();
+        for (var entry : floors.entrySet()) {
+            int x = (int) (entry.getKey() >> 32), z = (int) (long) entry.getKey();
+            probe.routeBlock = new XZ(x, z);
+            Cell cell = routeCell(x, entry.getValue(), z, Rail.NONE, false, probe);
+            if (cell == null) { probe.reject("route-column-certificate"); return null; }
+            cells.put(entry.getKey(), cell);
+        }
+        if (request.kind() == RouteKind.FREIGHT) for (int i = 0; i < path.size(); i++) {
+            Point point = path.get(i); long key = key(point.x(), point.z()); Cell cell = cells.get(key);
+            if (cell == null) continue;
+            Rail rail = rail(path, i);
+            // A one-block valley cannot carry two ascending slopes on the same rail. Keep a repairable rail gap.
+            boolean intact = rail != Rail.NONE && Math.floorMod(mix(seed ^ key ^ request.id().hashCode()), 19) != 0;
+            if (rail == Rail.NONE) rail = points.get(Math.max(0, i - 1)).x() == points.get(Math.min(size - 1, i + 1)).x() ? Rail.NORTH_SOUTH : Rail.EAST_WEST;
+            cells.put(key, new Cell(cell.x(), cell.floorY(), cell.z(), cell.foundationDepth(), rail, intact));
+        }
+        return new RouteDraft(List.copyOf(path), cells);
+    }
+
+    private static boolean landingColumn(Entry entry, XZ column) {
+        int dx = column.x() - entry.x(), dz = column.z() - entry.z();
+        return DX[entry.facing()] * dx + DZ[entry.facing()] * dz == 0 && Math.abs(dx) + Math.abs(dz) <= 1;
+    }
+    private static List<XZ> strip(List<XZ> points, int i) {
+        XZ p = points.get(i); var result = new ArrayList<XZ>();
+        if (turn(points, i)) {
+            for (int dx = -1; dx <= 1; dx++) for (int dz = -1; dz <= 1; dz++) result.add(new XZ(p.x() + dx, p.z() + dz));
+        } else {
+            XZ other = points.get(i == points.size() - 1 ? i - 1 : i + 1);
+            int dx = Integer.signum(other.x() - p.x()), dz = Integer.signum(other.z() - p.z());
+            for (int cross = -1; cross <= 1; cross++) result.add(new XZ(p.x() + dz * cross, p.z() - dx * cross));
+        }
+        return result;
+    }
+    private static boolean turn(List<XZ> points, int i) {
+        if (i == 0 || i == points.size() - 1) return false;
+        XZ a = points.get(i - 1), b = points.get(i + 1);
+        return a.x() != b.x() && a.z() != b.z();
+    }
+    private static Rail rail(List<Point> path, int i) {
+        Point p = path.get(i), a = path.get(Math.max(0, i - 1)), b = path.get(Math.min(path.size() - 1, i + 1));
+        if (a.floorY() > p.floorY() && b.floorY() > p.floorY()) return Rail.NONE;
+        Point high = a.floorY() > p.floorY() ? a : b.floorY() > p.floorY() ? b : null;
+        if (high != null) return switch (direction(p.x(), p.z(), high.x(), high.z())) {
+            case 0 -> Rail.ASCENDING_NORTH; case 1 -> Rail.ASCENDING_EAST; case 2 -> Rail.ASCENDING_SOUTH; default -> Rail.ASCENDING_WEST;
+        };
+        if (a.x() == b.x()) return Rail.NORTH_SOUTH;
+        if (a.z() == b.z()) return Rail.EAST_WEST;
+        boolean n = a.z() < p.z() || b.z() < p.z(), s = a.z() > p.z() || b.z() > p.z();
+        boolean e = a.x() > p.x() || b.x() > p.x();
+        return n ? e ? Rail.NORTH_EAST : Rail.NORTH_WEST : s && e ? Rail.SOUTH_EAST : Rail.SOUTH_WEST;
+    }
+    private static Cell routeCell(int x, int floor, int z, Rail rail, boolean present, Probe probe) {
+        int top = probe.surface(x, z);
+        if (floor < 14 || floor > 350 || top < floor - MAX_ROUTE_FILL || top > floor + MAX_ROUTE_CUT) return null;
+        int foundation = Math.max(1, floor - top + 1), base = floor - foundation;
+        if (!probe.solid(x, base - 1, z) || !probe.solid(x, base, z)) return null;
+        for (int y = base - 1; y <= floor + 3; y++) if (probe.protectedAt(x, y, z)) return null;
+        return new Cell(x, floor, z, foundation, rail, present);
+    }
+    private record XZ(int x, int z) { XZ move(int facing, int distance) { return new XZ(x + DX[facing] * distance, z + DZ[facing] * distance); } }
+    private record SegmentKey(Request request, int cx, int cz) {}
+    private static List<Segment> segments(long seed, Map<Long, OwnedCell> cells) {
+        var groups = new LinkedHashMap<SegmentKey, List<Cell>>();
+        for (var owned : cells.values()) {
+            Cell c = owned.cell(); var key = new SegmentKey(owned.request(), c.x() >> 4, c.z() >> 4);
+            groups.computeIfAbsent(key, ignored -> new ArrayList<>()).add(c);
+        }
+        var result = new ArrayList<Segment>();
+        for (var entry : groups.entrySet()) {
+            var k = entry.getKey(); var r = k.request();
+            // IDs are stable, bounded and independent of native generation order.
+            String id = "piece_" + r.id() + "_" + k.cx() + "_" + k.cz();
+            result.add(new Segment(id, r.from(), r.to(), r.kind(), k.cx(), k.cz(), entry.getValue(), mix(seed ^ key(k.cx(), k.cz()) ^ r.id().hashCode())));
+        }
+        return List.copyOf(result);
+    }
+
+
+    private static int span(Entry a, Entry b) { return Math.max(Math.abs(a.x() - b.x()), Math.abs(a.z() - b.z())); }
+    private static Site find(List<Site> sites, Kind kind) { return sites.stream().filter(site -> site.kind() == kind).findFirst().orElse(null); }
+    private static String id(Kind kind) { return kind.name().toLowerCase(Locale.ROOT); }
+    private static int direction(int x, int z, int tx, int tz) { return Math.abs(tx - x) >= Math.abs(tz - z) ? tx > x ? 1 : 3 : tz > z ? 2 : 0; }
+    private static boolean overlapsSites(int x0, int z0, int x1, int z1, List<Site> sites) {
+        for (var site : sites) if (x0 <= site.maxX() && x1 >= site.minX() && z0 <= site.maxZ() && z1 >= site.minZ()) return true;
+        return false;
+    }
+    private record SiteDraft(Site site, List<Cell> landings) {}
+    private record Candidate(int x, int z, int facing, int score, long seed) {}
+    private record Endpoint(String id, Entry entry, boolean readOnly) {}
+    private record Request(String id, String from, String to, RouteKind kind) {}
+    private record OwnedCell(Request request, Cell cell) {}
+    private record RouteDraft(List<Point> path, Map<Long, Cell> cells) {}
+    private static final class BudgetExceeded extends RuntimeException {
+        final boolean columns; BudgetExceeded(boolean columns) { this.columns = columns; }
+    }
+    private static final class Probe {
+        final Terrain terrain; final int cx, cz; final double radius;
+        final Map<Long, Integer> columns = new HashMap<>();
+        XZ routeBlock; Map<String, Integer> reasons = new HashMap<>(); int samples, columnLimit, sampleLimit;
+        Probe(Terrain terrain, int cx, int cz, int diameter) { this.terrain = java.util.Objects.requireNonNull(terrain); this.cx = cx; this.cz = cz; radius = diameter / 2.0 - 2; }
+        int surface(int x, int z) {
+            if (Math.hypot((double) x - cx, (double) z - cz) > radius || !terrain.owns(x, z)) return INVALID;
+            long key = key(x, z); var cached = columns.get(key); if (cached != null) return cached;
+            if (columns.size() >= columnLimit) throw new BudgetExceeded(true);
+            count(); int top = terrain.surfaceY(x, z); columns.put(key, top); return top;
+        }
+        boolean solid(int x, int y, int z) { if (y < 1 || y > 383 || surface(x, z) == INVALID) return false; count(); return terrain.solid(x, y, z); }
+        boolean protectedAt(int x, int y, int z) { if (y < 1 || y > 383 || surface(x, z) == INVALID) return true; count(); return terrain.protectedAt(x, y, z); }
+        void count() { if (samples >= sampleLimit) throw new BudgetExceeded(false); samples++; }
+        void reject(String reason) { reasons.merge(reason, 1, Integer::sum); }
+    }
+    private static long key(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+    private static double unit(long value) { return (value >>> 11) * 0x1.0p-53; }
+    private static long mix(long value) { value = (value ^ value >>> 30) * 0xbf58476d1ce4e5b9L; value = (value ^ value >>> 27) * 0x94d049bb133111ebL; return value ^ value >>> 31; }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritageRenderer21.java

@@ -0,0 +1,770 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.worldgen.city.LostCityPalette;
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import fr.koka.sanctuary.worldgen.detail.ConnectedBlocks20;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import net.minecraft.core.Direction;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.Rotation;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.AttachFace;
+import net.minecraft.world.level.block.state.properties.BedPart;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.block.state.properties.DoorHingeSide;
+import net.minecraft.world.level.block.state.properties.DoubleBlockHalf;
+import net.minecraft.world.level.block.state.properties.Half;
+import net.minecraft.world.level.block.state.properties.RailShape;
+
+/** Generation21 restrained architectural rendition of the immutable generation19 site geometry. The saved site controls all geometry and loot.
+ * Site writes are local to minX/floorY/minZ; route writes are local to the segment's minimum bounds. */
+public final class HeritageRenderer21 {
+    private HeritageRenderer21() {}
+    public record Target(String name, int x, int y, int z) {}
+
+    /** These are already rotated local standing positions, not world coordinates. */
+    public static List<Target> targets(HeritagePlan19.Site site) {
+        var b = new Builder(site, null); b.layout(); return List.copyOf(b.targets);
+    }
+    public static void render(HeritagePlan19.Site site, LostCityRenderer.BlockWriter writer) {
+        var buffer = ConnectedBlocks20.buffer(writer);
+        var b = new Builder(site, buffer); b.ground(); b.layout();
+        // Footings have absolute saved coordinates and must not undergo a second facade rotation.
+        for (var support : site.supports()) for (int y = support.minY(); y <= support.maxY(); y++)
+            buffer.set(support.x() - site.minX(), y - site.floorY(), support.z() - site.minZ(),
+                y == support.minY() ? Blocks.CHISELED_TUFF_BRICKS.defaultBlockState() : Blocks.STONE_BRICKS.defaultBlockState());
+        buffer.flush();
+    }
+    public static void renderSegment(HeritagePlan19.Segment segment, LostCityRenderer.BlockWriter writer) {
+        var buffer = ConnectedBlocks20.buffer(writer);
+        var occupied = new java.util.HashSet<Long>();
+        for (var cell : segment.cells()) occupied.add(columnKey(cell.x(), cell.z()));
+        int x0 = segment.minX(), y0 = segment.minY(), z0 = segment.minZ();
+        for (var cell : segment.cells()) {
+            int x = cell.x() - x0, z = cell.z() - z0, floor = cell.floorY() - y0;
+            for (int y = cell.minY() - y0; y <= floor; y++) {
+                Block material = Blocks.STONE_BRICKS;
+                if (y == floor) {
+                    boolean edge = false;
+                    for (Direction d : new Direction[] {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST}) {
+                        int nx = cell.x() + d.getStepX(), nz = cell.z() + d.getStepZ();
+                        // Unknown neighboring chunks are continuations, not artificial crosswise curbs.
+                        if ((nx >> 4) == segment.startChunkX() && (nz >> 4) == segment.startChunkZ()
+                                && !occupied.contains(columnKey(nx, nz))) edge = true;
+                    }
+                    if (cell.rail() != HeritagePlan19.Rail.NONE) material = Math.floorMod(cell.x() + cell.z(), 3) == 0 ? Blocks.OAK_PLANKS : Blocks.GRAVEL;
+                    else if (edge) material = Math.floorMod(cell.x() + cell.z(), 8) == 0 ? Blocks.CHISELED_TUFF_BRICKS : Blocks.TUFF_BRICKS;
+                    else material = LostCityPalette.roll(segment.seed(), cell.x(), 0, cell.z(), 5) == 0 ? Blocks.TUFF : Blocks.POLISHED_TUFF;
+                }
+                buffer.set(x, y, z, material.defaultBlockState());
+            }
+            for (int y = floor + 1; y <= floor + 3; y++) buffer.set(x, y, z, Blocks.AIR.defaultBlockState());
+            if (cell.railPresent()) buffer.set(x, floor + 1, z, Blocks.RAIL.defaultBlockState()
+                .setValue(BlockStateProperties.RAIL_SHAPE, RailShape.valueOf(cell.rail().name())));
+        }
+        buffer.flush();
+    }
+    private static long columnKey(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+
+    private static final class Builder {
+        final HeritagePlan19.Site s;
+        final LostCityRenderer.BlockWriter out;
+        final List<Target> targets = new ArrayList<>();
+        final Rotation rotation;
+        Builder(HeritagePlan19.Site s, LostCityRenderer.BlockWriter out) {
+            this.s = s; this.out = out;
+            rotation = switch (s.facing()) { case 1 -> Rotation.CLOCKWISE_90; case 2 -> Rotation.CLOCKWISE_180;
+                case 3 -> Rotation.COUNTERCLOCKWISE_90; default -> Rotation.NONE; };
+        }
+        int rx(int x, int z) { return switch (s.facing()) { case 1 -> 16 - z; case 2 -> 16 - x; case 3 -> z; default -> x; }; }
+        int rz(int x, int z) { return switch (s.facing()) { case 1 -> x; case 2 -> 16 - z; case 3 -> 16 - x; default -> z; }; }
+        void set(int x, int y, int z, BlockState state) {
+            if (x < 0 || x > 16 || z < 0 || z > 16 || y < -s.foundationDepth() || y > s.height())
+                throw new IllegalArgumentException("Heritage " + s.kind() + " renderer escaped saved site: " + x + "/" + y + "/" + z);
+            if (out != null) out.set(rx(x, z), y, rz(x, z), palette(state, x, y, z).rotate(rotation));
+        }
+        void set(int x, int y, int z, Block b) { set(x, y, z, b.defaultBlockState()); }
+        void box(int x0, int y0, int z0, int x1, int y1, int z1, Block b) {
+            for (int y = y0; y <= y1; y++) for (int z = z0; z <= z1; z++) for (int x = x0; x <= x1; x++) set(x, y, z, b);
+        }
+        void target(String name, int x, int y, int z) { targets.add(new Target(name, rx(x, z), y, rz(x, z))); }
+        void ground() {
+            for (int y = -s.foundationDepth(); y <= s.height(); y++) for (int z = 0; z <= 16; z++) for (int x = 0; x <= 16; x++)
+                set(x, y, z, y < 0 ? Blocks.STONE_BRICKS.defaultBlockState() : y == 0
+                    ? (x == 0 || z == 0 || x == 16 || z == 16 ? Blocks.TUFF_BRICKS
+                        : x >= 7 && x <= 9 ? Blocks.POLISHED_TUFF
+                        : LostCityPalette.roll(s.seed(), x, 0, z, 7) == 0 ? Blocks.TUFF : Blocks.ANDESITE).defaultBlockState()
+                    : Blocks.AIR.defaultBlockState());
+        }
+        void layout() {
+            target("main_entry", 8, 1, 0);
+            switch (s.kind()) {
+                case FREIGHT_STATION -> station();
+                case POST_OFFICE -> post();
+                case COMMUNAL_DEPOT -> depot();
+                case EXPEDITION_OFFICE -> expedition();
+                case OBSERVATORY -> observatory();
+                case RAIL_WORKSHOP -> railway();
+                case PUMP_STATION -> pumping();
+                case SUBSTATION -> substation();
+                case GREENHOUSE -> greenhouse();
+                case VOID_DOCK -> dock();
+                case RADIO_RELAY -> radio();
+                case PHOTO_CLUB -> photo();
+                case IMPOSSIBLE_SERVICE -> impossible();
+                case CONSTRUCTION_REFUGE -> refuge();
+            }
+            architecture();
+            roofs21();
+        }
+        void shell(int x0, int floor, int z0, int x1, int ceiling, int z1) {
+            for (int y = floor; y <= ceiling; y++) for (int z = z0; z <= z1; z++) for (int x = x0; x <= x1; x++) {
+                boolean wall = x == x0 || x == x1 || z == z0 || z == z1;
+                set(x, y, z, y == floor ? floorMaterial().defaultBlockState() : y == ceiling ? Blocks.SMOOTH_STONE.defaultBlockState()
+                    : wall ? wallMaterial(y - floor, ceiling - floor).defaultBlockState() : Blocks.AIR.defaultBlockState());
+            }
+        }
+        Block floorMaterial() {
+            return switch (s.kind()) {
+                case POST_OFFICE, EXPEDITION_OFFICE, RADIO_RELAY, CONSTRUCTION_REFUGE -> Blocks.OAK_PLANKS;
+                case PHOTO_CLUB, GREENHOUSE -> Blocks.BIRCH_PLANKS;
+                case IMPOSSIBLE_SERVICE -> Blocks.POLISHED_DIORITE;
+                default -> Blocks.POLISHED_ANDESITE;
+            };
+        }
+        Block wallMaterial(int y, int height) {
+            if (y == 1) return Blocks.STONE_BRICKS;
+            if (y == height - 1) return Blocks.ANDESITE;
+            return s.kind() == HeritagePlan19.Kind.GREENHOUSE ? Blocks.BIRCH_PLANKS : Blocks.SMOOTH_STONE;
+        }
+        BlockState palette(BlockState state, int x, int y, int z) {
+            Block original = state.getBlock(), replacement = original;
+            boolean birch = s.kind() == HeritagePlan19.Kind.GREENHOUSE;
+            if (original == Blocks.DARK_OAK_PLANKS || original == Blocks.OAK_PLANKS || original == Blocks.BIRCH_PLANKS)
+                replacement = birch ? Blocks.BIRCH_PLANKS : Blocks.OAK_PLANKS;
+            else if (original == Blocks.OAK_WOOD || original == Blocks.BIRCH_WOOD || original == Blocks.STRIPPED_OAK_WOOD)
+                replacement = birch ? Blocks.BIRCH_WOOD : Blocks.OAK_WOOD;
+            else if (original == Blocks.OAK_LOG || original == Blocks.BIRCH_LOG || original == Blocks.STRIPPED_OAK_LOG)
+                replacement = birch ? Blocks.STRIPPED_BIRCH_LOG : Blocks.STRIPPED_OAK_LOG;
+            else if (original == Blocks.DARK_OAK_SLAB || original == Blocks.OAK_SLAB || original == Blocks.BIRCH_SLAB)
+                replacement = birch ? Blocks.BIRCH_SLAB : Blocks.OAK_SLAB;
+            else if (original == Blocks.DARK_OAK_STAIRS || original == Blocks.OAK_STAIRS || original == Blocks.BIRCH_STAIRS)
+                replacement = birch ? Blocks.BIRCH_STAIRS : Blocks.OAK_STAIRS;
+            else if (original == Blocks.DARK_OAK_FENCE || original == Blocks.OAK_FENCE || original == Blocks.BIRCH_FENCE)
+                replacement = birch ? Blocks.BIRCH_FENCE : Blocks.OAK_FENCE;
+            else if (original == Blocks.DARK_OAK_DOOR || original == Blocks.OAK_DOOR || original == Blocks.BIRCH_DOOR)
+                replacement = birch ? Blocks.BIRCH_DOOR : Blocks.OAK_DOOR;
+            else if (original == Blocks.DARK_OAK_TRAPDOOR || original == Blocks.OAK_TRAPDOOR || original == Blocks.BIRCH_TRAPDOOR)
+                replacement = birch ? Blocks.BIRCH_TRAPDOOR : Blocks.OAK_TRAPDOOR;
+            else if (original == Blocks.GRANITE || original == Blocks.POLISHED_GRANITE || original == Blocks.DIORITE
+                    || original == Blocks.POLISHED_DIORITE || original == Blocks.POLISHED_ANDESITE)
+                replacement = original == Blocks.POLISHED_ANDESITE ? Blocks.ANDESITE : Blocks.SMOOTH_STONE;
+            else if (original == Blocks.POLISHED_GRANITE_SLAB || original == Blocks.POLISHED_DIORITE_SLAB
+                    || original == Blocks.POLISHED_ANDESITE_SLAB) replacement = Blocks.SMOOTH_STONE_SLAB;
+            if (y > 0) {
+                if (original == Blocks.TUFF || original == Blocks.POLISHED_TUFF) replacement = Blocks.SMOOTH_STONE;
+                else if (original == Blocks.TUFF_BRICKS) replacement = Blocks.STONE_BRICKS;
+                else if (original == Blocks.CHISELED_TUFF || original == Blocks.CHISELED_TUFF_BRICKS) replacement = Blocks.CHISELED_STONE_BRICKS;
+                else if (original == Blocks.TUFF_BRICK_SLAB) replacement = Blocks.SMOOTH_STONE_SLAB;
+                else if (original == Blocks.TUFF_BRICK_STAIRS) replacement = Blocks.STONE_BRICK_STAIRS;
+                else if (original == Blocks.TUFF_BRICK_WALL) replacement = Blocks.STONE_BRICK_WALL;
+            }
+            if ((original == Blocks.STONE_BRICKS || original == Blocks.CRACKED_STONE_BRICKS
+                    || original == Blocks.MOSSY_STONE_BRICKS) && y > 1 && y % 5 != 0)
+                replacement = Blocks.SMOOTH_STONE;
+            if (replacement == Blocks.ANDESITE && y > 0 && Math.floorMod(x + z, 4) == 0)
+                replacement = Blocks.STONE;
+            // Quiet, reproducible weathering follows construction joints, never random holes in access floors.
+            if (replacement == Blocks.STONE_BRICKS && y > 0) {
+                int weather = LostCityPalette.roll(s.seed(), x, y, z, 23);
+                if (weather == 0) replacement = Blocks.CRACKED_STONE_BRICKS;
+                else if (weather == 1 && y <= 3) replacement = Blocks.MOSSY_STONE_BRICKS;
+            }
+            if (replacement == original) return state;
+            var mapped = replacement.defaultBlockState();
+            for (var property : state.getProperties()) mapped = copyProperty(mapped, state, property);
+            return mapped;
+        }
+        private static <T extends Comparable<T>> BlockState copyProperty(BlockState destination, BlockState source,
+                net.minecraft.world.level.block.state.properties.Property<T> property) {
+            return destination.hasProperty(property) ? destination.setValue(property, source.getValue(property)) : destination;
+        }
+        // These additions compose each use separately; all thresholds and maintenance passages stay in the saved footprint.
+        void architecture() {
+            switch (s.kind()) {
+                case FREIGHT_STATION -> stationArchitecture();
+                case POST_OFFICE -> postArchitecture();
+                case COMMUNAL_DEPOT -> depotArchitecture();
+                case EXPEDITION_OFFICE -> expeditionArchitecture();
+                case OBSERVATORY -> observatoryArchitecture();
+                case RAIL_WORKSHOP -> railwayArchitecture();
+                case PUMP_STATION -> pumpingArchitecture();
+                case SUBSTATION -> substationArchitecture();
+                case GREENHOUSE -> greenhouseArchitecture();
+                case VOID_DOCK -> dockArchitecture();
+                case RADIO_RELAY -> radioArchitecture();
+                case PHOTO_CLUB -> photoArchitecture();
+                case IMPOSSIBLE_SERVICE -> impossibleArchitecture();
+                case CONSTRUCTION_REFUGE -> refugeArchitecture();
+            }
+        }
+        void slab(int x, int y, int z, Block block) { set(x, y, z, block.defaultBlockState().setValue(BlockStateProperties.SLAB_TYPE, net.minecraft.world.level.block.state.properties.SlabType.BOTTOM)); }
+        void stair(int x, int y, int z, Block block, Direction direction, Half half) {
+            set(x, y, z, block.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, direction).setValue(BlockStateProperties.HALF, half));
+        }
+        /** Cut only the four exterior corner cells; the two adjacent wall faces keep the interior sealed. */
+        void bevel(int x0, int z0, int x1, int z1, int low, int high) {
+            for (int x : new int[] {x0, x1}) for (int z : new int[] {z0, z1}) {
+                box(x, low, z, x, high, z, Blocks.AIR);
+                set(x, low - 1, z, Blocks.CHISELED_STONE_BRICKS);
+            }
+        }
+        void rim(int x0, int z0, int x1, int z1, int y, Block material) {
+            for (int x = x0; x <= x1; x++) { slab(x, y, z0, material); slab(x, y, z1, material); }
+            for (int z = z0 + 1; z < z1; z++) { slab(x0, y, z, material); slab(x1, y, z, material); }
+        }
+        void screen(int x0, int z, int x1, int y) {
+            for (int x = x0; x <= x1; x++) set(x, y, z, Blocks.BIRCH_TRAPDOOR.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH).setValue(BlockStateProperties.OPEN, true));
+        }
+        void stationArchitecture() {
+            bevel(4, 3, 12, 11, 1, 6);
+            box(4, 7, 3, 12, 10, 11, Blocks.AIR);
+            rim(3, 2, 13, 12, 6, Blocks.TUFF_BRICK_SLAB);
+            for (int z = 5; z <= 9; z++) for (int x = 5; x <= 11; x++) {
+                if (x == 5 || x == 11 || z == 5 || z == 9) box(x, 7, z, x, 8, z, Blocks.GLASS_PANE);
+                slab(x, 9, z, Blocks.POLISHED_DIORITE_SLAB);
+            }
+            // Open the former ceiling beneath the sealed roof glazing. The middle beam
+            // still supports the existing hanging lantern and joins the two hall walls.
+            for (int z = 6; z <= 8; z++) for (int x = 6; x <= 10; x++) {
+                if (z != 7) set(x, 6, z, Blocks.AIR);
+                set(x, 9, z, Blocks.GLASS);
+            }
+            // The long cantilever reads as a train platform, distinct from the glazed passenger hall.
+            box(0, 5, 4, 3, 5, 12, Blocks.OAK_PLANKS);
+            for (int z : new int[] {4, 8, 12}) stair(0, 4, z, Blocks.TUFF_BRICK_STAIRS, Direction.EAST, Half.TOP);
+            for (int z : new int[] {5, 11}) box(1, 1, z, 1, 4, z, Blocks.OAK_WOOD);
+            for (int x : new int[] {4, 12}) box(x, 2, 4, x, 4, 4, Blocks.CHISELED_TUFF_BRICKS);
+            screen(5, 4, 6, 3); box(5, 0, 4, 11, 0, 10, Blocks.POLISHED_DIORITE);
+            box(7, 0, 3, 9, 0, 10, Blocks.BIRCH_PLANKS);
+            rim(9, 11, 15, 15, 4, Blocks.TUFF_BRICK_SLAB);
+        }
+        void postArchitecture() {
+            bevel(2, 2, 14, 14, 1, 6); rim(1, 1, 15, 15, 6, Blocks.POLISHED_GRANITE_SLAB);
+            box(4, 7, 4, 12, 7, 12, Blocks.TUFF_BRICKS);
+            rim(4, 4, 12, 12, 8, Blocks.TUFF_BRICK_SLAB);
+            for (int x : new int[] {2, 7, 9, 14}) {
+                box(x, 3, 1, x, 4, 1, Blocks.POLISHED_DIORITE);
+                stair(x, 5, 1, Blocks.TUFF_BRICK_STAIRS, Direction.SOUTH, Half.TOP);
+            }
+            box(5, 4, 1, 11, 4, 1, Blocks.CHISELED_TUFF_BRICKS);
+            box(4, 1, 6, 6, 1, 6, Blocks.BIRCH_PLANKS); screen(4, 6, 6, 3);
+            for (int z = 9; z <= 12; z++) { set(3, 3, z, Blocks.OAK_TRAPDOOR.defaultBlockState().setValue(BlockStateProperties.HALF, Half.TOP)); }
+            for (int x = 4; x <= 12; x++) set(x, 0, 5, x % 2 == 0 ? Blocks.POLISHED_GRANITE : Blocks.OAK_PLANKS);
+            box(10, 0, 8, 13, 0, 9, Blocks.DIORITE);
+        }
+        void depotArchitecture() {
+            bevel(1, 2, 15, 14, 1, 9); box(1, 10, 2, 15, 14, 14, Blocks.AIR);
+            // Three industrial north-light roof bays, not another pitched house roof.
+            for (int z : new int[] {3, 7, 11}) {
+                box(2, 10, z, 14, 11, z, Blocks.GLASS_PANE);
+                for (int x = 2; x <= 14; x++) {
+                    slab(x, 12, z, Blocks.TUFF_BRICK_SLAB);
+                    stair(x, 11, z + 1, Blocks.TUFF_BRICK_STAIRS, Direction.NORTH, Half.BOTTOM);
+                    stair(x, 10, z + 2, Blocks.TUFF_BRICK_STAIRS, Direction.NORTH, Half.BOTTOM);
+                    if (x > 2 && x < 14) {
+                        // Both transparent faces close the north-light well, while the
+                        // retained roof outside these bands keeps the warehouse sealed.
+                        set(x, 9, z, Blocks.GLASS);
+                        set(x, 12, z, Blocks.GLASS);
+                    }
+                }
+            }
+            for (int z : new int[] {3, 7, 11}) for (int x : new int[] {1, 15}) box(x, 1, z, x, 9, z, Blocks.POLISHED_ANDESITE);
+            for (int x : new int[] {6, 10}) { box(x, 1, 1, x, 3, 1, Blocks.CHISELED_TUFF); stair(x, 4, 1, Blocks.TUFF_BRICK_STAIRS, Direction.SOUTH, Half.TOP); }
+            box(6, 4, 1, 10, 4, 1, Blocks.TUFF_BRICKS);
+            for (int z : new int[] {5, 8}) {
+                // Thin wooden covers sit directly on the barrel stack and the lower packing bench.
+                set(4, 3, z, Blocks.OAK_TRAPDOOR.defaultBlockState().setValue(BlockStateProperties.HALF, Half.BOTTOM));
+                set(12, 2, z, Blocks.OAK_TRAPDOOR.defaultBlockState().setValue(BlockStateProperties.HALF, Half.BOTTOM));
+            }
+            for (int z = 3; z <= 9; z++) { set(6, 0, z, Blocks.TUFF_BRICKS); set(10, 0, z, Blocks.TUFF_BRICKS); }
+            box(2, 5, 11, 9, 5, 13, Blocks.BIRCH_PLANKS);
+        }
+        void expeditionArchitecture() {
+            bevel(2, 2, 12, 12, 1, 6); rim(1, 1, 13, 13, 6, Blocks.TUFF_BRICK_SLAB);
+            box(3, 7, 3, 6, 9, 7, Blocks.BIRCH_WOOD); rim(3, 3, 6, 7, 10, Blocks.TUFF_BRICK_SLAB);
+            box(4, 8, 3, 5, 8, 3, Blocks.GLASS_PANE);
+            // Sheltered map table, archive wing and broad shaded rear balcony.
+            box(7, 4, 1, 9, 4, 1, Blocks.CHISELED_TUFF_BRICKS);
+            for (int x : new int[] {2, 12}) box(x, 2, 3, x, 5, 3, Blocks.OAK_WOOD);
+            screen(3, 4, 5, 3); box(3, 3, 9, 5, 3, 9, Blocks.OAK_PLANKS);
+            for (int x = 3; x <= 14; x++) for (int z = 13; z <= 15; z++) set(x, 0, z, x % 3 == 0 ? Blocks.OAK_WOOD : Blocks.OAK_PLANKS);
+            for (int x = 3; x <= 14; x++) slab(x, 5, 14, Blocks.BIRCH_SLAB);
+            box(3, 1, 14, 3, 4, 14, Blocks.BIRCH_FENCE); box(14, 1, 14, 14, 4, 14, Blocks.BIRCH_FENCE);
+        }
+        void observatoryArchitecture() {
+            // Eight faceted buttresses below a broken observatory dome with an open central viewing slot.
+            for (int[] p : new int[][] {{3, 8}, {5, 4}, {11, 4}, {13, 8}, {11, 12}, {5, 12}}) {
+                box(p[0], 1, p[1], p[0], 11, p[1], Blocks.DIORITE);
+                set(p[0], 5, p[1], Blocks.CHISELED_TUFF_BRICKS);
+                stair(p[0], 12, p[1], Blocks.TUFF_BRICK_STAIRS, p[0] < 8 ? Direction.EAST : Direction.WEST, Half.BOTTOM);
+            }
+            for (int z = 4; z <= 12; z++) for (int x = 4; x <= 12; x++) {
+                int distance = Math.max(Math.abs(x - 8), Math.abs(z - 8));
+                if (distance == 4) set(x, 15, z, Blocks.GLASS_PANE);
+                if (distance == 3 && x != 8) slab(x, 17, z, Blocks.TUFF_BRICK_SLAB);
+            }
+            for (int x : new int[] {4, 12}) for (int z : new int[] {5, 11}) box(x, 13, z, x, 14, z, Blocks.CHISELED_TUFF_BRICKS);
+            // Four short ribs visibly carry the inset crown; the central viewing slot stays open.
+            for (int x : new int[] {4, 12}) for (int z : new int[] {5, 11}) {
+                box(x, 15, z, x, 16, z, Blocks.CHISELED_TUFF_BRICKS);
+                stair(x < 8 ? x + 1 : x - 1, 16, z, Blocks.TUFF_BRICK_STAIRS,
+                    x < 8 ? Direction.EAST : Direction.WEST, Half.BOTTOM);
+            }
+            box(7, 0, 5, 9, 0, 11, Blocks.BIRCH_PLANKS);
+            box(7, 6, 5, 9, 6, 10, Blocks.POLISHED_DIORITE);
+        }
+        void railwayArchitecture() {
+            bevel(1, 2, 15, 14, 1, 6); box(1, 7, 2, 15, 10, 14, Blocks.AIR);
+            // Broad barrel-vault ribs sit above the two inspection tracks.
+            for (int z = 2; z <= 14; z++) for (int x = 1; x <= 15; x++) {
+                int rise = Math.min(3, Math.min(x - 1, 15 - x));
+                if (z % 4 == 2) set(x, 6 + rise, z, Blocks.TUFF_BRICKS);
+                else if (x >= 6 && x <= 10) set(x, 6 + rise, z, Blocks.GLASS);
+                else slab(x, 6 + rise, z, Blocks.TUFF_BRICK_SLAB);
+            }
+            for (int z : new int[] {3, 7, 11}) for (int x : new int[] {1, 15}) box(x, 2, z, x, 5, z, Blocks.GRANITE);
+            box(7, -2, 5, 9, -2, 11, Blocks.POLISHED_ANDESITE);
+            for (int z = 6; z <= 11; z++) { set(7, -1, z, Blocks.CHISELED_TUFF_BRICKS); set(9, -1, z, Blocks.CHISELED_TUFF_BRICKS); }
+            // Side ledges leave the one-block maintenance aisle and its stairs clear.
+            screen(2, 3, 3, 3); box(2, 3, 11, 4, 3, 11, Blocks.OAK_PLANKS);
+        }
+        void pumpingArchitecture() {
+            bevel(2, 3, 9, 12, 1, 6); rim(1, 2, 9, 13, 6, Blocks.TUFF_BRICK_SLAB);
+            for (int x : new int[] {10, 15}) for (int z : new int[] {5, 11}) {
+                box(x, 1, z, x, 7, z, Blocks.CHISELED_TUFF_BRICKS);
+                set(x, 8, z, Blocks.POLISHED_ANDESITE);
+            }
+            rim(9, 4, 16, 12, 13, Blocks.TUFF_BRICK_SLAB);
+            for (int x = 10; x <= 15; x++) for (int z = 5; z <= 11; z++) slab(x, 14, z, Blocks.POLISHED_ANDESITE_SLAB);
+            box(3, 7, 5, 3, 12, 5, Blocks.TUFF_BRICK_WALL);
+            box(3, 3, 6, 3, 5, 8, Blocks.IRON_BARS);
+            box(3, 0, 4, 8, 0, 9, Blocks.ANDESITE); box(5, 0, 4, 7, 0, 10, Blocks.POLISHED_DIORITE);
+            screen(3, 11, 4, 3);
+        }
+        void substationArchitecture() {
+            bevel(10, 4, 15, 10, 1, 5); rim(9, 3, 16, 15, 5, Blocks.TUFF_BRICK_SLAB);
+            for (int z : new int[] {2, 6, 10, 14}) for (int x : new int[] {1, 15}) {
+                set(x, 0, z, Blocks.STONE_BRICKS); set(x, 1, z, Blocks.CHISELED_TUFF_BRICKS);
+            }
+            box(2, 4, 5, 5, 4, 5, Blocks.IRON_BARS); box(2, 4, 8, 5, 4, 8, Blocks.IRON_BARS);
+            for (int x : new int[] {2, 5}) for (int z : new int[] {5, 8}) box(x, 1, z, x, 3, z, Blocks.TUFF_BRICK_WALL);
+            box(11, 6, 5, 14, 6, 9, Blocks.POLISHED_TUFF);
+            for (int z = 5; z <= 9; z += 2) screen(11, z, 14, 7);
+            for (int z = 3; z <= 8; z++) set(7, 0, z, Blocks.GRANITE);
+            box(6, -2, 10, 7, -2, 13, Blocks.CHISELED_TUFF_BRICKS);
+        }
+        void greenhouseArchitecture() {
+            // Tall birch ribs and a steep glass ridge give the glasshouse an agricultural silhouette.
+            for (int z = 2; z <= 14; z++) for (int x = 1; x <= 11; x++) {
+                int rise = Math.min(3, Math.min(x - 1, 11 - x));
+                if (z == 2 || z == 8 || z == 14 || x == 6) set(x, 6 + rise, z, Blocks.BIRCH_WOOD);
+                else set(x, 6 + rise, z, Blocks.GLASS);
+            }
+            for (int z : new int[] {3, 7, 11}) { box(1, 1, z, 1, 5, z, Blocks.BIRCH_WOOD); box(11, 1, z, 11, 5, z, Blocks.BIRCH_WOOD); }
+            rim(11, 9, 15, 15, 5, Blocks.TUFF_BRICK_SLAB);
+            box(12, 3, 10, 14, 3, 10, Blocks.OAK_PLANKS); screen(12, 10, 14, 4);
+            for (int z = 3; z <= 13; z++) set(6, 0, z, z % 3 == 0 ? Blocks.CHISELED_TUFF_BRICKS : Blocks.POLISHED_TUFF);
+        }
+        void dockArchitecture() {
+            for (int x = 1; x <= 15; x++) for (int z = 0; z <= 15; z++) set(x, 0, z, x % 4 == 0 ? Blocks.OAK_WOOD : Blocks.OAK_PLANKS);
+            bevel(2, 3, 7, 10, 1, 5); rim(1, 2, 8, 15, 5, Blocks.BIRCH_SLAB);
+            for (int z : new int[] {2, 8, 14}) {
+                box(0, 1, z, 0, 2, z, Blocks.CHISELED_TUFF_BRICKS);
+                box(16, 1, z, 16, 2, z, Blocks.CHISELED_TUFF_BRICKS);
+                slab(0, 3, z, Blocks.TUFF_BRICK_SLAB); slab(16, 3, z, Blocks.TUFF_BRICK_SLAB);
+            }
+            // Brackets and a separated customs roof leave the departure platform open to the void.
+            for (int x = 2; x <= 7; x++) for (int z = 3; z <= 15; z++) if (z % 4 == 0) slab(x, 6, z, Blocks.BIRCH_SLAB);
+            stair(11, 9, 5, Blocks.OAK_STAIRS, Direction.EAST, Half.TOP);
+            stair(13, 9, 5, Blocks.OAK_STAIRS, Direction.WEST, Half.TOP);
+            screen(3, 4, 6, 3);
+        }
+        void radioArchitecture() {
+            bevel(2, 3, 10, 12, 1, 6); rim(1, 2, 10, 13, 6, Blocks.TUFF_BRICK_SLAB);
+            for (int x = 2; x <= 10; x++) for (int z = 3; z <= 12; z++) {
+                int roofY = 7 + Math.min(2, Math.min(x - 2, 10 - x));
+                slab(x, roofY, z, x <= 5 ? Blocks.BIRCH_SLAB : Blocks.TUFF_BRICK_SLAB);
+            }
+            box(9, 7, 4, 9, 11, 4, Blocks.CHISELED_TUFF_BRICKS);
+            for (int y : new int[] {10, 14, 18}) { box(12, y, 8, 14, y, 8, Blocks.IRON_BARS); box(13, y, 7, 13, y, 9, Blocks.IRON_BARS); }
+            box(3, 0, 8, 5, 0, 11, Blocks.BIRCH_PLANKS); screen(7, 4, 9, 3);
+        }
+        void photoArchitecture() {
+            bevel(2, 2, 14, 14, 1, 6); rim(1, 1, 15, 15, 6, Blocks.POLISHED_DIORITE_SLAB);
+            box(3, 7, 9, 13, 7, 13, Blocks.TUFF_BRICKS); rim(3, 9, 13, 13, 8, Blocks.TUFF_BRICK_SLAB);
+            for (int x : new int[] {3, 6, 10, 13}) stair(x, 4, 1, Blocks.TUFF_BRICK_STAIRS, Direction.SOUTH, Half.TOP);
+            box(3, 5, 1, 13, 5, 1, Blocks.CHISELED_TUFF_BRICKS);
+            for (int x = 4; x <= 12; x++) set(x, 0, 4, x % 2 == 0 ? Blocks.POLISHED_GRANITE : Blocks.BIRCH_PLANKS);
+            box(3, 0, 9, 7, 0, 13, Blocks.POLISHED_ANDESITE);
+            screen(10, 5, 12, 2); box(3, 3, 10, 3, 3, 12, Blocks.OAK_PLANKS);
+        }
+        void impossibleArchitecture() {
+            bevel(1, 7, 15, 15, 1, 10); rim(0, 6, 16, 16, 10, Blocks.TUFF_BRICK_SLAB);
+            box(4, 11, 9, 12, 11, 13, Blocks.TUFF_BRICKS);
+            for (int x : new int[] {4, 12}) for (int z : new int[] {9, 13}) set(x, 12, z, Blocks.CHISELED_TUFF);
+            // A cramped civil facade gives way to an over-scaled, deliberately ceremonial service hall.
+            for (int x : new int[] {3, 11}) box(x, 1, 1, x, 4, 1, Blocks.CHISELED_TUFF_BRICKS);
+            box(3, 5, 1, 11, 5, 1, Blocks.TUFF_BRICKS);
+            for (int x : new int[] {3, 6, 10, 13}) { set(x, 1, 11, Blocks.CHISELED_TUFF_BRICKS); set(x, 8, 11, Blocks.CHISELED_TUFF_BRICKS); }
+            screen(4, 3, 4, 3); box(12, 3, 14, 14, 3, 14, Blocks.BIRCH_PLANKS);
+        }
+        void refugeArchitecture() {
+            bevel(5, 6, 13, 14, 5, 10);
+            box(5, 11, 6, 13, 14, 14, Blocks.AIR);
+            for (int z = 6; z <= 14; z++) for (int x = 5; x <= 13; x++) {
+                int rise = Math.min(3, (x - 5) / 2);
+                slab(x, 11 + rise, z, (z & 1) == 0 ? Blocks.BIRCH_SLAB : Blocks.TUFF_BRICK_SLAB);
+            }
+            for (int x : new int[] {3, 14}) for (int z : new int[] {5, 15}) { box(x, 1, z, x, 3, z, Blocks.CHISELED_TUFF_BRICKS); set(x, 4, z, Blocks.OAK_WOOD); }
+            for (int z = 6; z <= 14; z += 4) box(4, 1, z, 4, 7, z, Blocks.IRON_BARS);
+            box(2, 1, 3, 3, 10, 4, Blocks.TUFF_BRICKS); box(2, 11, 3, 14, 11, 4, Blocks.OAK_WOOD);
+            // Upper lockers and a birch sleeping corner avoid the saved hatch and its complete ladder shaft.
+            screen(11, 7, 12, 7); box(7, 4, 7, 11, 4, 9, Blocks.BIRCH_PLANKS);
+        }
+
+        /** Replacement roofs: one weather skin, connected rafters and retained lamp-bearing beams.
+         * Clearing starts at the old roof, never at a floor, furnishing or standing threshold. */
+        void roofs21() {
+            switch (s.kind()) {
+                case RAIL_WORKSHOP -> {
+                    vaultRoof(1, 2, 15, 14, 6, false, true);
+                    box(1, 6, 8, 15, 6, 8, Blocks.OAK_WOOD); // existing workshop lamp
+                    // Two missing panes expose an intact neighbouring rafter, not a floating roof fragment.
+                    box(7, 9, 4, 8, 9, 4, Blocks.AIR);
+                }
+                case GREENHOUSE -> {
+                    vaultRoof(1, 2, 11, 14, 6, true, true);
+                    box(1, 6, 5, 11, 6, 5, Blocks.BIRCH_WOOD); // existing aisle lamp
+                }
+                case COMMUNAL_DEPOT -> sawtoothRoof();
+                case RADIO_RELAY -> {
+                    vaultRoof(2, 3, 10, 12, 6, true, false);
+                    box(2, 6, 6, 10, 6, 6, Blocks.OAK_WOOD);
+                    box(2, 6, 10, 10, 6, 10, Blocks.OAK_WOOD);
+                    box(9, 7, 4, 9, 11, 4, Blocks.STONE_BRICKS);
+                }
+                case CONSTRUCTION_REFUGE -> {
+                    shedRoof(5, 6, 13, 14, 10);
+                    box(5, 10, 8, 13, 10, 8, Blocks.OAK_WOOD); // lamp above the shared sleeping room
+                }
+                case POST_OFFICE -> box(5, 7, 5, 11, 7, 11, Blocks.AIR); // a parapet, not a second slab ceiling
+                case PHOTO_CLUB -> box(4, 7, 10, 12, 7, 12, Blocks.AIR);
+                default -> { } // Other roofs already have a single supported slab or a sealed working tank.
+            }
+        }
+        void vaultRoof(int x0, int z0, int x1, int z1, int eave, boolean timber, boolean glazed) {
+            box(x0, eave, z0, x1, s.height(), z1, Blocks.AIR);
+            int mid = (z0 + z1) / 2;
+            for (int z = z0; z <= z1; z++) for (int x = x0; x <= x1; x++) {
+                int top = vaultY(x, x0, x1, eave);
+                int adjoining = Math.min(vaultY(Math.max(x0, x - 1), x0, x1, eave),
+                    vaultY(Math.min(x1, x + 1), x0, x1, eave));
+                boolean rib = z == z0 || z == mid || z == z1;
+                Block skin = rib ? Blocks.OAK_WOOD : glazed && x > x0 + 2 && x < x1 - 2
+                    ? Blocks.GLASS : timber ? Blocks.OAK_PLANKS : Blocks.SMOOTH_STONE;
+                // This short riser joins neighbouring height steps by a face, not just a diagonal corner.
+                box(x, Math.min(top, adjoining), z, x, top, z, skin);
+                if (z == z0 || z == z1) box(x, eave, z, x, top, z,
+                    glazed && x > x0 + 1 && x < x1 - 1 ? Blocks.GLASS : Blocks.OAK_WOOD);
+            }
+            // Truss feet sit on the existing two long walls; no columns are introduced in an aisle.
+            box(x0, eave, mid, x1, eave, mid, Blocks.OAK_WOOD);
+            for (int x : new int[] {x0, x1}) box(x, eave, z0, x, eave, z1, Blocks.OAK_WOOD);
+        }
+        int vaultY(int x, int x0, int x1, int eave) {
+            return eave + Math.min(3, Math.min(x - x0, x1 - x));
+        }
+        void shedRoof(int x0, int z0, int x1, int z1, int eave) {
+            box(x0, eave, z0, x1, s.height(), z1, Blocks.AIR);
+            for (int z = z0; z <= z1; z++) for (int x = x0; x <= x1; x++) {
+                int top = eave + (x - x0) / 3;
+                int previous = eave + Math.max(0, x - 1 - x0) / 3;
+                box(x, previous, z, x, top, z,
+                    z == z0 || z == z1 || z == (z0 + z1) / 2 ? Blocks.OAK_WOOD : Blocks.OAK_PLANKS);
+                if (z == z0 || z == z1 || x == x1) box(x, eave, z, x, top, z, Blocks.OAK_WOOD);
+            }
+        }
+        void sawtoothRoof() {
+            box(1, 9, 2, 15, s.height(), 14, Blocks.AIR);
+            for (int z = 2; z <= 14; z++) for (int x = 1; x <= 15; x++) {
+                int phase = Math.floorMod(z - 2, 4), top = z == 14 ? 9 : 12 - phase;
+                boolean frame = x == 1 || x == 15;
+                if (phase == 0 && z != 14) box(x, 9, z, x, top, z, frame ? Blocks.OAK_WOOD : Blocks.GLASS);
+                else box(x, Math.max(9, top - 1), z, x, top, z,
+                    frame ? Blocks.OAK_WOOD : phase == 1 ? Blocks.GLASS : Blocks.SMOOTH_STONE);
+                if (frame) box(x, 9, z, x, top, z, Blocks.OAK_WOOD);
+            }
+            box(1, 9, 6, 15, 9, 6, Blocks.OAK_WOOD); // carries the original hall lamp
+            // Local, readable storm damage. The perimeter frame and remaining panes still share their bearings.
+            box(12, 10, 11, 13, 11, 11, Blocks.AIR);
+        }
+
+        void gable(int x0, int z0, int x1, int z1, int y) {
+            int rise = Math.min(3, (x1 - x0) / 2);
+            for (int step = 0; step <= rise; step++)
+                box(x0 + step, y + step, z0, x1 - step, y + step, z1, step == rise ? Blocks.STONE_BRICK_SLAB : Blocks.STONE_BRICKS);
+        }
+        void door(int x, int y, int z, Direction facing) { door(x, y, z, facing, false); }
+        void door(int x, int y, int z, Direction facing, boolean right) {
+            BlockState state = Blocks.DARK_OAK_DOOR.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, facing)
+                .setValue(BlockStateProperties.DOOR_HINGE, right ? DoorHingeSide.RIGHT : DoorHingeSide.LEFT)
+                .setValue(BlockStateProperties.OPEN, false).setValue(BlockStateProperties.POWERED, false);
+            set(x, y, z, state.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF, DoubleBlockHalf.LOWER));
+            set(x, y + 1, z, state.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF, DoubleBlockHalf.UPPER));
+        }
+        void doubleDoor(int x, int y, int z) { door(x, y, z, Direction.SOUTH, true); door(x + 1, y, z, Direction.SOUTH, false); }
+        void northWindows(int x0, int x1, int z, int y) { box(x0, y, z, x1, y + 1, z, Blocks.GLASS_PANE); }
+        void hang(int x, int ceiling, int z) { set(x, ceiling - 1, z, Blocks.LANTERN.defaultBlockState().setValue(BlockStateProperties.HANGING, true)); }
+        void seat(int x, int y, int z, Direction view) {
+            set(x, y, z, Blocks.DARK_OAK_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, view.getOpposite()));
+        }
+        void lever(int x, int y, int z, Direction facing) {
+            set(x, y, z, Blocks.LEVER.defaultBlockState().setValue(BlockStateProperties.ATTACH_FACE, AttachFace.FLOOR)
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, facing));
+        }
+        void rail(int x, int z, RailShape shape) { set(x, 1, z, Blocks.RAIL.defaultBlockState().setValue(BlockStateProperties.RAIL_SHAPE, shape)); }
+        void loot(int x, int y, int z, int approachX, int approachZ) {
+            target("loot_approach", approachX, y, approachZ);
+            if (out != null) out.chest(rx(x, z), y, rz(x, z), ResourceKey.create(Registries.LOOT_TABLE,
+                SanctuaryMod.id("chests/heritage19/" + s.kind().name().toLowerCase(Locale.ROOT))), s.seed() ^ 0x19CA7A10L);
+        }
+        void stairs(int x, int z, int base, int rise) {
+            for (int step = 1; step <= rise; step++) for (int xx = x; xx <= x + 1; xx++) {
+                box(xx, base + step + 1, z + step - 1, xx, base + step + 3, z + step - 1, Blocks.AIR);
+                set(xx, base + step - 1, z + step - 1, Blocks.STONE_BRICKS);
+                set(xx, base + step, z + step - 1, Blocks.STONE_BRICK_STAIRS.defaultBlockState()
+                    .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+            }
+        }
+        void bed(int x, int y, int z, Direction facing) {
+            BlockState state = Blocks.BED.white().defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, facing);
+            set(x, y, z, state.setValue(BlockStateProperties.BED_PART, BedPart.FOOT));
+            set(x + facing.getStepX(), y, z + facing.getStepZ(), state.setValue(BlockStateProperties.BED_PART, BedPart.HEAD));
+            int wx = x + facing.getStepX() * 2, wz = z + facing.getStepZ() * 2;
+            Direction along = facing.getClockWise();
+            for (int side = -1; side <= 1; side++) for (int up = 0; up <= 2; up++)
+                set(wx + along.getStepX() * side, y + up, wz + along.getStepZ() * side, Blocks.SMOOTH_STONE);
+        }
+
+        void station() {
+            shell(4, 0, 3, 12, 6, 11); gable(4, 3, 12, 11, 6);
+            door(8, 1, 3, Direction.SOUTH); northWindows(5, 6, 3, 2); northWindows(10, 11, 3, 2);
+            box(5, 1, 5, 6, 1, 5, Blocks.SMOOTH_STONE); set(5, 1, 8, Blocks.BARREL); seat(10, 1, 5, Direction.WEST);
+            for (int z = 2; z <= 14; z++) rail(2, z, RailShape.NORTH_SOUTH);
+            set(2, 1, 15, Blocks.DARK_OAK_FENCE);
+            rail(8, 0, RailShape.NORTH_SOUTH); rail(8, 1, RailShape.NORTH_WEST);
+            for (int x = 3; x <= 7; x++) rail(x, 1, RailShape.EAST_WEST);
+            rail(2, 1, RailShape.SOUTH_EAST);
+            box(0, 5, 5, 3, 5, 11, Blocks.DARK_OAK_PLANKS);
+            for (int z : new int[] {5, 11}) box(1, 1, z, 1, 4, z, Blocks.STRIPPED_OAK_LOG);
+            shell(9, 0, 11, 15, 4, 15); door(10, 1, 11, Direction.SOUTH); door(12, 1, 15, Direction.NORTH);
+            set(10, 1, 13, Blocks.SMOOTH_STONE); lever(10, 2, 13, Direction.EAST);
+            northWindows(13, 14, 15, 2); hang(8, 6, 7); hang(12, 4, 12);
+            target("ticket_counter", 8, 1, 5); target("freight_platform", 3, 1, 9); target("signal_office", 12, 1, 12);
+            target("secondary_entry", 12, 1, 16); loot(14, 1, 14, 13, 14);
+        }
+        void post() {
+            shell(2, 0, 2, 14, 6, 14); door(8, 1, 2, Direction.SOUTH);
+            northWindows(3, 6, 2, 2); northWindows(10, 13, 2, 2);
+            box(3, 1, 7, 13, 5, 7, Blocks.SMOOTH_STONE); door(8, 1, 7, Direction.SOUTH);
+            box(4, 1, 6, 6, 1, 6, Blocks.DARK_OAK_PLANKS);
+            for (int z = 9; z <= 11; z++) { set(3, 1, z, Blocks.BARREL); set(3, 2, z, Blocks.BARREL); }
+            set(6, 1, 10, Blocks.CRAFTING_TABLE); set(8, 1, 12, Blocks.BARREL);
+            shell(10, 0, 10, 14, 6, 14); door(10, 1, 12, Direction.EAST); door(14, 1, 12, Direction.WEST);
+            set(11, 1, 11, Blocks.CARTOGRAPHY_TABLE); hang(8, 6, 4); hang(7, 6, 10); hang(12, 6, 12);
+            target("public_hall", 8, 1, 4); target("sorting_aisle", 7, 1, 10); target("factor_office", 12, 1, 12);
+            target("secondary_entry", 15, 1, 12); loot(13, 1, 13, 12, 13);
+        }
+        void depot() {
+            shell(1, 0, 2, 15, 9, 14); gable(1, 2, 15, 14, 9);
+            box(7, 1, 2, 9, 3, 2, Blocks.AIR); door(4, 1, 2, Direction.SOUTH);
+            for (int z : new int[] {5, 8}) {
+                box(4, 1, z, 5, 1, z + 1, Blocks.DARK_OAK_PLANKS); set(4, 2, z, Blocks.BARREL);
+                box(11, 1, z, 13, 1, z + 1, Blocks.DARK_OAK_PLANKS); set(13, 2, z + 1, Blocks.BARREL);
+            }
+            box(2, 5, 10, 14, 5, 13, Blocks.SMOOTH_STONE);
+            for (int x = 5; x <= 14; x++) set(x, 6, 10, Blocks.IRON_BARS);
+            shell(10, 5, 10, 14, 9, 14); door(10, 6, 12, Direction.EAST);
+            set(11, 6, 11, Blocks.LECTERN.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+            stairs(2, 5, 0, 5); door(15, 1, 12, Direction.WEST); hang(8, 9, 6); hang(12, 9, 12);
+            for (int z = 0; z <= 8; z++) rail(8, z, RailShape.NORTH_SOUTH);
+            set(8, 1, 9, Blocks.DARK_OAK_FENCE);
+            target("unloading_bay", 8, 1, 5); target("inventory_mezzanine", 5, 6, 12);
+            target("secondary_entry", 16, 1, 12); loot(13, 6, 13, 12, 13);
+        }
+        void expedition() {
+            shell(2, 0, 2, 12, 6, 12); door(8, 1, 2, Direction.SOUTH);
+            northWindows(3, 5, 2, 2); northWindows(10, 11, 2, 2);
+            set(4, 1, 4, Blocks.CARTOGRAPHY_TABLE); set(5, 1, 4, Blocks.LECTERN.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH)); set(3, 1, 6, Blocks.BARREL);
+            shell(2, 0, 8, 6, 6, 12); door(6, 1, 10, Direction.WEST); set(3, 1, 9, Blocks.BOOKSHELF);
+            box(3, 0, 13, 14, 0, 15, Blocks.DARK_OAK_PLANKS);
+            box(3, 1, 15, 14, 1, 15, Blocks.DARK_OAK_FENCE); door(10, 1, 12, Direction.NORTH);
+            seat(6, 1, 13, Direction.SOUTH); hang(8, 6, 5); hang(4, 6, 10);
+            target("expedition_table", 5, 1, 5); target("balcony", 10, 1, 14);
+            target("secondary_entry", 10, 1, 13); loot(3, 1, 11, 4, 11);
+        }
+        boolean tower(int x, int z) { return x >= 3 && x <= 13 && z >= 3 && z <= 13 && Math.abs(x - 8) + Math.abs(z - 8) <= 8; }
+        void observatory() {
+            for (int y = 0; y <= 12; y++) for (int z = 3; z <= 13; z++) for (int x = 3; x <= 13; x++) if (tower(x, z)) {
+                boolean wall = !tower(x - 1, z) || !tower(x + 1, z) || !tower(x, z - 1) || !tower(x, z + 1);
+                set(x, y, z, y == 0 || y == 6 || y == 12 ? Blocks.SMOOTH_STONE.defaultBlockState()
+                    : wall ? LostCityPalette.masonry(s.seed(), x, y, z) : Blocks.AIR.defaultBlockState());
+                if (y == 12 && wall) set(x, 13, z, Blocks.IRON_BARS);
+            }
+            door(8, 1, 3, Direction.SOUTH); door(8, 1, 13, Direction.NORTH);
+            northWindows(7, 9, 3, 8); box(13, 8, 7, 13, 9, 9, Blocks.GLASS_PANE);
+            shell(9, 0, 9, 12, 4, 12); door(9, 1, 10, Direction.EAST); set(10, 1, 11, Blocks.BARREL);
+            set(10, 7, 5, Blocks.CARTOGRAPHY_TABLE); set(11, 7, 8, Blocks.SMOOTH_STONE); lever(11, 8, 8, Direction.WEST);
+            stairs(4, 5, 0, 6); stairs(4, 5, 6, 6);
+            box(4, 12, 11, 6, 12, 11, Blocks.SMOOTH_STONE); box(4, 13, 11, 6, 15, 11, Blocks.AIR);
+            box(10, 13, 9, 10, 18, 9, Blocks.DARK_OAK_FENCE); box(9, 18, 9, 11, 18, 9, Blocks.IRON_BARS);
+            hang(8, 6, 6); hang(10, 4, 11);
+            target("instruments", 9, 7, 8); target("sky_platform", 8, 13, 8);
+            target("secondary_entry", 8, 1, 14); loot(11, 1, 11, 11, 10);
+        }
+        void railway() {
+            shell(1, 0, 2, 15, 6, 14); gable(1, 2, 15, 14, 6); doubleDoor(7, 1, 2);
+            for (int z = 3; z <= 13; z++) for (int x : new int[] {5, 11}) set(x, 1, z, Blocks.RAIL);
+            box(4, 1, 2, 6, 3, 2, Blocks.AIR); rail(8, 0, RailShape.NORTH_SOUTH); rail(8, 1, RailShape.NORTH_WEST);
+            rail(7, 1, RailShape.EAST_WEST); rail(6, 1, RailShape.EAST_WEST); rail(5, 1, RailShape.SOUTH_EAST); rail(5, 2, RailShape.NORTH_SOUTH);
+            box(7, -2, 5, 9, -2, 11, Blocks.SMOOTH_STONE); box(7, -1, 5, 9, 0, 11, Blocks.AIR);
+            for (int step = 0; step <= 2; step++) set(8, -step, 4 + step, Blocks.STONE_BRICK_STAIRS.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.NORTH));
+            for (int z = 6; z <= 11; z++) { set(6, 1, z, Blocks.IRON_BARS); set(10, 1, z, Blocks.IRON_BARS); }
+            set(2, 1, 4, Blocks.CRAFTING_TABLE); set(3, 1, 4, Blocks.FURNACE.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.SOUTH));
+            set(2, 1, 6, Blocks.GRINDSTONE.defaultBlockState().setValue(BlockStateProperties.ATTACH_FACE, AttachFace.FLOOR));
+            shell(1, 0, 10, 5, 5, 14); door(5, 1, 12, Direction.WEST); door(8, 1, 14, Direction.NORTH);
+            set(5, 1, 9, Blocks.DARK_OAK_FENCE);
+            set(2, 1, 11, Blocks.ANVIL); hang(8, 6, 8); hang(3, 5, 12);
+            target("maintenance_pit", 8, -1, 9); target("workbench", 3, 1, 5);
+            target("secondary_entry", 8, 1, 15); loot(2, 1, 13, 3, 13);
+        }
+        void pumping() {
+            shell(2, 0, 3, 9, 6, 12); door(8, 1, 3, Direction.SOUTH);
+            set(3, 1, 5, Blocks.DISPENSER.defaultBlockState().setValue(BlockStateProperties.FACING, Direction.EAST));
+            set(4, 1, 5, Blocks.WATER_CAULDRON.defaultBlockState().setValue(BlockStateProperties.LEVEL_CAULDRON, 3));
+            set(3, 2, 5, Blocks.POLISHED_ANDESITE); box(3, 3, 5, 3, 5, 8, Blocks.IRON_BARS);
+            for (int x : new int[] {10, 15}) for (int z : new int[] {5, 11}) box(x, 1, z, x, 7, z, Blocks.POLISHED_ANDESITE);
+            shell(10, 8, 5, 15, 13, 11); box(11, 9, 6, 14, 11, 10, Blocks.WATER);
+            box(10, 3, 6, 14, 3, 13, Blocks.SMOOTH_STONE); stairs(10, 3, 0, 3);
+            shell(2, 0, 10, 6, 5, 15); door(5, 1, 10, Direction.SOUTH); door(5, 1, 15, Direction.NORTH);
+            set(3, 1, 11, Blocks.BARREL); hang(7, 6, 7); hang(4, 5, 12);
+            target("pump_room", 6, 1, 6); target("reservoir_walkway", 13, 4, 12);
+            target("secondary_entry", 5, 1, 16); loot(3, 1, 14, 4, 14);
+        }
+        void substation() {
+            for (int z = 2; z <= 14; z++) { set(1, 1, z, Blocks.IRON_BARS); set(15, 1, z, Blocks.IRON_BARS); }
+            for (int x = 1; x <= 15; x++) if (x < 7 || x > 9) set(x, 1, 2, Blocks.IRON_BARS);
+            for (int z : new int[] {5, 8}) {
+                box(3, 1, z, 4, 2, z + 1, Blocks.POLISHED_ANDESITE); box(3, 3, z, 4, 3, z, Blocks.IRON_BARS);
+            }
+            shell(10, 0, 4, 15, 5, 10); door(10, 1, 6, Direction.EAST); northWindows(12, 14, 4, 2);
+            set(12, 1, 5, Blocks.SMOOTH_STONE); lever(12, 2, 5, Direction.SOUTH); set(14, 1, 5, Blocks.CRAFTING_TABLE);
+            shell(10, 0, 10, 15, 5, 15); door(12, 1, 10, Direction.SOUTH); door(15, 1, 13, Direction.WEST);
+            box(6, -2, 10, 7, -2, 13, Blocks.SMOOTH_STONE); box(6, -1, 10, 7, 0, 13, Blocks.AIR);
+            for (int step = 0; step <= 2; step++) set(6, -step, 9 + step, Blocks.STONE_BRICK_STAIRS.defaultBlockState()
+                .setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.NORTH));
+            hang(13, 5, 7); hang(12, 5, 13); target("distribution_yard", 8, 1, 6); target("cable_trench", 6, -1, 12);
+            target("secondary_entry", 16, 1, 13); loot(14, 1, 14, 13, 14);
+        }
+        void greenhouse() {
+            shell(1, 0, 2, 11, 6, 14);
+            for (int y = 2; y <= 5; y++) for (int z = 3; z <= 13; z++) { set(1, y, z, Blocks.GLASS); set(11, y, z, Blocks.GLASS); }
+            northWindows(2, 5, 2, 2); northWindows(7, 10, 2, 2); door(6, 1, 2, Direction.SOUTH);
+            for (int x = 2; x <= 10; x++) for (int z = 3; z <= 13; z++) set(x, 6, z, x == 6 ? Blocks.SMOOTH_STONE : Blocks.GLASS);
+            for (int x : new int[] {2, 3, 4, 8, 9, 10}) for (int z = 4; z <= 10; z++) {
+                set(x, 0, z, Blocks.FARMLAND.defaultBlockState().setValue(BlockStateProperties.MOISTURE, 7));
+                set(x, 1, z, Blocks.WHEAT.defaultBlockState().setValue(BlockStateProperties.AGE_7,
+                    2 + LostCityPalette.roll(s.seed(), x, 1, z, 6)));
+            }
+            set(3, 0, 6, Blocks.WATER); set(9, 0, 6, Blocks.WATER);
+            set(3, 1, 6, Blocks.AIR); set(9, 1, 6, Blocks.AIR);
+            shell(11, 0, 9, 15, 5, 15); door(11, 1, 12, Direction.EAST); door(13, 1, 15, Direction.NORTH);
+            set(12, 1, 10, Blocks.CRAFTING_TABLE); set(13, 1, 10, Blocks.FLOWER_POT); set(9, 1, 12, Blocks.COMPOSTER);
+            hang(6, 6, 5); hang(13, 5, 12); target("glasshouse_aisle", 6, 1, 7); target("potting_shed", 13, 1, 12);
+            target("secondary_entry", 13, 1, 16); loot(14, 1, 14, 13, 14);
+        }
+        void dock() {
+            box(0, 0, 0, 16, 0, 16, Blocks.DARK_OAK_PLANKS); box(0, 1, 16, 16, 1, 16, Blocks.DARK_OAK_FENCE);
+            box(0, 1, 1, 0, 1, 15, Blocks.DARK_OAK_FENCE); box(16, 1, 1, 16, 1, 15, Blocks.DARK_OAK_FENCE);
+            shell(2, 0, 3, 7, 5, 10); door(7, 1, 6, Direction.WEST); seat(3, 1, 5, Direction.EAST);
+            shell(2, 0, 10, 7, 5, 15); door(5, 1, 10, Direction.SOUTH); door(7, 1, 13, Direction.WEST);
+            box(12, 1, 5, 12, 11, 5, Blocks.STRIPPED_OAK_LOG); box(8, 11, 5, 14, 11, 5, Blocks.STRIPPED_OAK_LOG);
+            box(14, 7, 5, 14, 10, 5, Blocks.IRON_CHAIN); hang(10, 11, 5); hang(5, 5, 6); hang(5, 5, 12);
+            target("departure_deck", 8, 1, 14); target("waiting_room", 5, 1, 6); target("secondary_entry", 8, 1, 13);
+            loot(3, 1, 14, 4, 14);
+        }
+        void radio() {
+            shell(2, 0, 3, 10, 6, 12); door(8, 1, 3, Direction.SOUTH); northWindows(3, 5, 3, 2);
+            bed(4, 1, 5, Direction.NORTH); set(8, 1, 5, Blocks.CARTOGRAPHY_TABLE);
+            shell(2, 0, 8, 6, 6, 12); door(6, 1, 10, Direction.WEST); door(2, 1, 10, Direction.EAST);
+            box(11, 5, 6, 15, 5, 10, Blocks.SMOOTH_STONE);
+            for (int x : new int[] {11, 15}) for (int z : new int[] {6, 10}) box(x, 1, z, x, 4, z, Blocks.POLISHED_ANDESITE);
+            box(13, 1, 8, 13, 18, 8, Blocks.POLISHED_ANDESITE); box(11, 17, 8, 15, 17, 8, Blocks.IRON_BARS);
+            box(13, 19, 8, 13, 21, 8, Blocks.IRON_BARS); stairs(11, 1, 0, 5);
+            hang(7, 6, 6); hang(4, 6, 10);
+            target("caretaker_room", 7, 1, 6); target("antenna_platform", 12, 6, 9); target("secondary_entry", 1, 1, 10);
+            loot(3, 1, 11, 4, 11);
+        }
+        void photo() {
+            shell(2, 0, 2, 14, 6, 14); door(8, 1, 2, Direction.SOUTH); northWindows(3, 6, 2, 2); northWindows(10, 13, 2, 2);
+            box(3, 1, 8, 13, 5, 8, Blocks.SMOOTH_STONE); door(4, 1, 8, Direction.SOUTH);
+            box(8, 1, 9, 8, 5, 13, Blocks.SMOOTH_STONE); door(8, 1, 11, Direction.EAST);
+            box(10, 1, 5, 12, 1, 5, Blocks.DARK_OAK_PLANKS); set(3, 1, 4, Blocks.BOOKSHELF);
+            for (int z : new int[] {10, 12}) set(3, 1, z, Blocks.WATER_CAULDRON.defaultBlockState().setValue(BlockStateProperties.LEVEL_CAULDRON, 3));
+            box(11, 4, 10, 11, 5, 12, Blocks.IRON_CHAIN); set(12, 1, 10, Blocks.CRAFTING_TABLE);
+            door(12, 1, 14, Direction.NORTH); hang(8, 6, 4); hang(5, 6, 11); hang(12, 6, 12);
+            target("club_room", 8, 1, 4); target("darkroom", 5, 1, 11); target("drying_room", 10, 1, 11);
+            target("secondary_entry", 12, 1, 15); loot(13, 1, 13, 12, 13);
+        }
+        void impossible() {
+            shell(3, 0, 2, 11, 4, 7); door(8, 1, 2, Direction.SOUTH);
+            for (int z = 3; z <= 5; z++) { set(4, 1, z, Blocks.BARREL); set(4, 2, z, Blocks.BARREL); }
+            seat(10, 1, 4, Direction.WEST);
+            shell(1, 0, 7, 15, 10, 15); door(8, 1, 7, Direction.SOUTH);
+            for (int x = 2; x <= 14; x++) for (int z = 8; z <= 14; z++) set(x, 0, z,
+                ((x + z) & 1) == 0 ? Blocks.CALCITE : Blocks.POLISHED_ANDESITE);
+            for (int x : new int[] {3, 6, 10, 13}) box(x, 1, 11, x, 9, 11, Blocks.CALCITE);
+            shell(1, 0, 12, 5, 5, 15); door(5, 1, 13, Direction.WEST); door(3, 1, 15, Direction.NORTH);
+            set(2, 2, 12, Blocks.GLASS); set(2, 1, 13, Blocks.WATER_CAULDRON.defaultBlockState().setValue(BlockStateProperties.LEVEL_CAULDRON, 2));
+            hang(8, 4, 4); hang(8, 10, 11); hang(3, 5, 13);
+            target("lockers", 8, 1, 4); target("oversized_tiled_hall", 8, 1, 11);
+            target("secondary_entry", 3, 1, 16); loot(2, 1, 14, 3, 14);
+        }
+        void refuge() {
+            box(3, 4, 5, 14, 4, 15, Blocks.DARK_OAK_PLANKS);
+            for (int x : new int[] {3, 14}) for (int z : new int[] {5, 15}) box(x, 1, z, x, 3, z, Blocks.STONE_BRICKS);
+            shell(5, 4, 6, 13, 10, 14); gable(5, 6, 13, 14, 10); door(8, 5, 6, Direction.SOUTH);
+            bed(6, 5, 8, Direction.NORTH); set(12, 5, 8, Blocks.CRAFTING_TABLE);
+            shell(6, 0, 9, 11, 4, 14); door(6, 1, 11, Direction.EAST);
+            // Carry the ladder through the floor so opening the hatch leaves a climbable lip.
+            for (int y = 1; y <= 4; y++) set(10, y, 11, Blocks.LADDER.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.WEST));
+            set(10, 5, 11, Blocks.DARK_OAK_TRAPDOOR.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.WEST)
+                .setValue(BlockStateProperties.HALF, Half.BOTTOM));
+            stairs(7, 1, 0, 4); box(2, 1, 3, 3, 11, 4, Blocks.STONE_BRICKS); box(2, 11, 3, 14, 11, 4, Blocks.STRIPPED_OAK_LOG);
+            hang(10, 10, 8); hang(8, 4, 12);
+            target("suspended_hut", 9, 5, 8); target("hidden_floor_hatch", 10, 5, 11); target("secondary_entry", 5, 1, 11);
+            loot(7, 1, 13, 8, 13);
+        }
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritageStructure19.java

@@ -14,7 +14,7 @@ public final class HeritageStructure19 extends Structure {
 
     @Override protected Optional<GenerationStub> findGenerationPoint(GenerationContext context) {
         if (!(context.chunkGenerator() instanceof SanctuaryChunkGenerator generator)
-                || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20) || !generator.experimentalStructures()) return Optional.empty();
+                || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21) || !generator.experimentalStructures()) return Optional.empty();
         var island = generator.islandForChunk(context.chunkPos().x(), context.chunkPos().z());
         if (island == null || !island.origin() || (island.generation() != generator.rootGeneration())) return Optional.empty();
         var plan = generator.heritagePlan19();
@@ -23,9 +23,9 @@ public final class HeritageStructure19 extends Structure {
         // Local route segments render before buildings. No piece needs a distant link endpoint loaded.
         for (var segment : plan.segments())
             if (segment.startChunkX() == x && segment.startChunkZ() == z)
-                pieces.add(generator.rootGeneration() == 20 ? new HeritagePiece20(segment) : new HeritagePiece19(segment));
+                pieces.add(generator.rootGeneration() == 21 ? new HeritagePiece21(segment) : generator.rootGeneration() == 20 ? new HeritagePiece20(segment) : new HeritagePiece19(segment));
         for (var site : plan.sites()) if (site.startChunkX() == x && site.startChunkZ() == z)
-            pieces.add(generator.rootGeneration() == 20 ? new HeritagePiece20(site) : new HeritagePiece19(site));
+            pieces.add(generator.rootGeneration() == 21 ? new HeritagePiece21(site) : generator.rootGeneration() == 20 ? new HeritagePiece20(site) : new HeritagePiece19(site));
         if (pieces.isEmpty()) return Optional.empty();
         for (var piece : pieces) {
             var box = piece.getBoundingBox();
@@ -35,7 +35,7 @@ public final class HeritageStructure19 extends Structure {
                     || Math.abs((long) Math.floorDiv(box.maxZ(), 16) - z) > 7)
                 throw new IllegalStateException("Heritage piece exceeds its local native reference contract");
         }
-        var locator = pieces.stream().filter(piece -> piece instanceof HeritagePiece19 old && old.isSite() || piece instanceof HeritagePiece20 detail && detail.isSite()).findFirst().orElse(pieces.getFirst()).getLocatorPosition();
+        var locator = pieces.stream().filter(piece -> piece instanceof HeritagePiece19 old && old.isSite() || piece instanceof HeritagePiece20 detail && detail.isSite() || piece instanceof HeritagePiece21 current && current.isSite()).findFirst().orElse(pieces.getFirst()).getLocatorPosition();
         return Optional.of(new GenerationStub(locator, builder -> pieces.forEach(builder::addPiece)));
     }
     @Override public StructureType<?> type() { return HeritageStructures19.TYPE; }

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritageStructures19.java

@@ -35,6 +35,8 @@ public final class HeritageStructures19 {
         SanctuaryMod.id("heritage_networks_v19"), () -> HeritageStructure19.CODEC);
     public static final StructurePieceType PIECE = Registry.register(BuiltInRegistries.STRUCTURE_PIECE,
         SanctuaryMod.id("heritage_piece_v19"), HeritagePiece19::new);
+    public static final StructurePieceType PIECE21 = Registry.register(BuiltInRegistries.STRUCTURE_PIECE,
+        SanctuaryMod.id("heritage_piece_v21"), HeritagePiece21::new);
     public static final StructurePieceType PIECE20 = Registry.register(BuiltInRegistries.STRUCTURE_PIECE,
         SanctuaryMod.id("heritage_piece_v20"), HeritagePiece20::new);
     private static final ThreadLocal<Integer> PLACEMENT_DEPTH = ThreadLocal.withInitial(() -> 0);
@@ -55,7 +57,7 @@ public final class HeritageStructures19 {
             ChunkGeneratorStructureState state, StructureManager manager, ChunkAccess chunk,
             StructureTemplateManager templates, ResourceKey<Level> level) {
         if (!Level.OVERWORLD.equals(level) || !manager.shouldGenerateStructures()
-                || !(generator instanceof SanctuaryChunkGenerator sanctuary) || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20)
+                || !(generator instanceof SanctuaryChunkGenerator sanctuary) || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21)
                 || !sanctuary.experimentalStructures()) return;
         var island = generator.islandForChunk(chunk.getPos().x(), chunk.getPos().z());
         if (island == null || !island.origin() || island.generation() != generator.rootGeneration()) return;
@@ -77,7 +79,7 @@ public final class HeritageStructures19 {
             BlockPos origin, int radius, boolean skipReferenced) {
         if (!Level.OVERWORLD.equals(level.dimension())
                 || !(level.getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator generator)
-                || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20) || !generator.experimentalStructures()
+                || (generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21) || !generator.experimentalStructures()
                 || !level.structureManager().shouldGenerateStructures()) return null;
         Holder<Structure> holder = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(KEY);
         if (!structures.contains(holder)) return null;
@@ -99,7 +101,7 @@ public final class HeritageStructures19 {
             if (start == null || !start.isValid() || skipReferenced && !start.canBeReferenced()) continue;
             if (skipReferenced) level.structureManager().addReference(start);
             var entrance = start.getPieces().stream().filter(p -> (p instanceof HeritagePiece19 site && site.isSite())
-                || (p instanceof HeritagePiece20 detail && detail.isSite())).findFirst().orElseThrow();
+                || (p instanceof HeritagePiece20 detail && detail.isSite()) || (p instanceof HeritagePiece21 current && current.isSite())).findFirst().orElseThrow();
             return Pair.of(entrance.getLocatorPosition(), holder);
         }
         return null;

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/heritage/HeritageTerrain21.java

@@ -0,0 +1,113 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.expansion.ExpansionIsland;
+import fr.koka.sanctuary.worldgen.city.LostCityPlan;
+import fr.koka.sanctuary.worldgen.ruins.RuinsPlan17;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Predicate;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.levelgen.NoiseBasedChunkGenerator;
+import net.minecraft.world.level.levelgen.RandomState;
+
+/** Read-only pre-decoration terrain. No loaded chunks or player-edited blocks enter a plan. */
+public final class HeritageTerrain21 implements HeritagePlanner21.Terrain {
+    private static final int[] DX = {0, 1, 0, -1}, DZ = {-1, 0, 1, 0};
+    private final ExpansionIsland island;
+    private final NoiseBasedChunkGenerator generator;
+    private final RandomState random;
+    private final LevelHeightAccessor height;
+    private final Predicate<BlockPos> protection;
+    private final Map<Long, NoiseColumn> columns = new HashMap<>();
+    private List<HeritagePlan19.Landmark> landmarks = List.of();
+
+    public HeritageTerrain21(ExpansionIsland island, NoiseBasedChunkGenerator generator, RandomState random,
+            LevelHeightAccessor height, Predicate<BlockPos> protection) {
+        this.island = island; this.generator = generator; this.random = random;
+        this.height = height; this.protection = protection;
+    }
+    private NoiseColumn column(int x, int z) {
+        if (!owns(x, z)) return null;
+        long key = ((long) x << 32) ^ (z & 0xffffffffL);
+        var previous = columns.get(key);
+        if (previous != null) return previous;
+        if (columns.size() >= HeritagePlan19.MAX_COLUMNS) return null;
+        var result = generator.getBaseColumn(x, z, height, random);
+        columns.put(key, result);
+        return result;
+    }
+    @Override public boolean owns(int x, int z) { return island.contains(x, z); }
+    @Override public boolean solid(int x, int y, int z) {
+        if (y < 0 || y >= 384) return false;
+        var column = column(x, z);
+        return column != null && column.getBlock(y).isSolid() && column.getBlock(y).getFluidState().isEmpty();
+    }
+    @Override public boolean protectedAt(int x, int y, int z) {
+        if (y < 0 || y >= 384) return true;
+        var column = column(x, z);
+        return column == null || !column.getBlock(y).getFluidState().isEmpty()
+            || protection.test(new BlockPos(x, y, z));
+    }
+    @Override public int surfaceY(int x, int z) {
+        var column = column(x, z);
+        if (column == null) return -1;
+        for (int y = 380; y >= 1; y--) {
+            var state = column.getBlock(y);
+            if (!state.isAir()) return state.isSolid() && state.getFluidState().isEmpty() ? y : -1;
+        }
+        return -1;
+    }
+    @Override public List<HeritagePlan19.Landmark> landmarks() { return landmarks; }
+    public int columnsUsed() { return columns.size(); }
+
+    /** Select actual dry ground abutting existing walkable platforms. Their protected blocks stay intact. */
+    public void discoverLandmarks(LostCityPlan city, RuinsPlan17 ruins) {
+        var result = new ArrayList<HeritagePlan19.Landmark>();
+        for (var network : ruins.networks()) {
+            var access = network.rooms().stream().filter(r -> r.kind() == RuinsPlan17.Kind.ACCESS).findFirst().orElse(null);
+            if (access == null) continue;
+            int deck = access.maxY() - 2;
+            for (int direction = 0; direction < 4; direction++) {
+                var entry = dryEntry(access.centerX() + DX[direction] * 3, access.centerZ() + DZ[direction] * 3, deck, direction);
+                if (entry == null) continue;
+                var kind = network.family() == RuinsPlan17.Family.MINE ? HeritagePlan19.LandmarkKind.MINE : HeritagePlan19.LandmarkKind.UTILITY;
+                result.add(new HeritagePlan19.Landmark("old_" + network.id(), kind, entry));
+                break;
+            }
+        }
+        int cityEntries = 0;
+        for (var district : city.districts()) {
+        int districtEntries = 0;
+        districtLoop: for (var parcel : district.parcels()) {
+            if (parcel.kind() != LostCityPlan.Kind.STREET || parcel.width() < 3 || parcel.depth() < 3) continue;
+            for (int direction = 0; direction < 4; direction++) {
+                int x = direction == 1 ? parcel.width() - 1 : direction == 3 ? 0 : parcel.width() / 2;
+                int z = direction == 2 ? parcel.depth() - 1 : direction == 0 ? 0 : parcel.depth() / 2;
+                var entry = dryEntry(parcel.minX() + x + DX[direction], parcel.minZ() + z + DZ[direction], parcel.surfaceY(x, z), direction);
+                if (entry == null) continue;
+                result.add(new HeritagePlan19.Landmark("old_city_" + cityEntries++, HeritagePlan19.LandmarkKind.CITY, entry));
+                if (++districtEntries == 2 || result.size() >= 16) break districtLoop;
+            }
+        }
+        if (result.size() >= 16) break;
+        }
+        landmarks = List.copyOf(result);
+    }
+    private HeritagePlan19.Entry dryEntry(int x, int z, int deck, int direction) {
+        int y = surfaceY(x, z);
+        if (y < 32 || y > 348 || Math.abs(y - deck) > 1) return null;
+        // A three-wide arrival can abut a platform without cutting its wall or footings.
+        for (int side = -1; side <= 1; side++) {
+            int px = x + DZ[direction] * side, pz = z + DX[direction] * side;
+            var column = column(px, pz);
+            if (column == null || surfaceY(px, pz) != y || !solid(px, y, pz)) return null;
+            for (int by = y - 1; by <= y + 3; by++) if (protectedAt(px, by, pz)) return null;
+            for (int by = y + 1; by <= y + 3; by++) if (!column.getBlock(by).isAir()) return null;
+        }
+        return new HeritagePlan19.Entry(x, y + 1, z, direction);
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/ruins/RuinsStructure17.java

@@ -13,7 +13,7 @@ public final class RuinsStructure17 extends Structure {
 
     @Override protected Optional<GenerationStub> findGenerationPoint(GenerationContext context) {
         if (!(context.chunkGenerator() instanceof SanctuaryChunkGenerator generator)
-                || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20) || !generator.experimentalStructures()) return Optional.empty();
+                || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21) || !generator.experimentalStructures()) return Optional.empty();
         var island = generator.islandForChunk(context.chunkPos().x(), context.chunkPos().z());
         if (island == null || !island.origin() || island.generation() != generator.rootGeneration()) return Optional.empty();
         var networks = generator.ruinsPlan17().networks().stream()
@@ -30,9 +30,9 @@ public final class RuinsStructure17 extends Structure {
         return Optional.of(new GenerationStub(RuinsStructures17.locator(networks.getFirst()), pieces -> {
             // Shafts come last so their surface hatches cannot be filled by a connected room.
             networks.forEach(n -> n.rooms().stream().filter(r -> r.kind() != RuinsPlan17.Kind.ACCESS)
-                .forEach(r -> pieces.addPiece(generator.rootGeneration() == 20 ? new RuinsPiece20(r) : new RuinsPiece17(r))));
+                .forEach(r -> pieces.addPiece((generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? new RuinsPiece20(r) : new RuinsPiece17(r))));
             networks.forEach(n -> n.rooms().stream().filter(r -> r.kind() == RuinsPlan17.Kind.ACCESS)
-                .forEach(r -> pieces.addPiece(generator.rootGeneration() == 20 ? new RuinsPiece20(r) : new RuinsPiece17(r))));
+                .forEach(r -> pieces.addPiece((generator.rootGeneration() == 20 || generator.rootGeneration() == 21) ? new RuinsPiece20(r) : new RuinsPiece17(r))));
         }));
     }
     @Override public StructureType<?> type() { return RuinsStructures17.TYPE; }

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/ruins/RuinsStructures17.java

@@ -55,7 +55,7 @@ public final class RuinsStructures17 {
             ChunkGeneratorStructureState state, StructureManager manager, ChunkAccess chunk,
             StructureTemplateManager templates, ResourceKey<Level> level) {
         if (!Level.OVERWORLD.equals(level) || !manager.shouldGenerateStructures()
-                || !(generator instanceof SanctuaryChunkGenerator sanctuary) || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20)
+                || !(generator instanceof SanctuaryChunkGenerator sanctuary) || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21)
                 || !sanctuary.experimentalStructures()) return;
         var island = generator.islandForChunk(chunk.getPos().x(), chunk.getPos().z());
         if (island == null || !island.origin() || island.generation() != generator.rootGeneration()) return;
@@ -78,7 +78,7 @@ public final class RuinsStructures17 {
             BlockPos origin, int radius, boolean skipReferenced) {
         if (!Level.OVERWORLD.equals(level.dimension())
                 || !(level.getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator generator)
-                || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20) || !generator.experimentalStructures()
+                || (generator.rootGeneration() != 17 && generator.rootGeneration() != 19 && generator.rootGeneration() != 20 && generator.rootGeneration() != 21) || !generator.experimentalStructures()
                 || !level.structureManager().shouldGenerateStructures()) return null;
         Holder<Structure> holder = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(KEY);
         if (!structures.contains(holder)) return null;

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitPiece21.java

@@ -0,0 +1,114 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import java.util.ArrayList;
+import java.util.Set;
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import net.minecraft.core.BlockPos;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.ListTag;
+import net.minecraft.nbt.Tag;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.StructureManager;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.levelgen.structure.BoundingBox;
+import net.minecraft.world.level.levelgen.structure.StructurePiece;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceSerializationContext;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** Saved generation21 room geometry is rendered without replanning or reading neighboring chunks. */
+public final class TransitPiece21 extends StructurePiece {
+    private static final Set<String> MODULE_KEYS = Set.of("Schema", "Kind", "MinX", "MinY", "MinZ", "Width",
+        "Height", "Depth", "Facing", "Openings", "ModuleSeed", "Supports");
+    private static final Set<String> SUPPORT_KEYS = Set.of("X", "MinY", "Z", "MaxY");
+    private final TransitPlan21.Module room;
+
+    public TransitPiece21(TransitPlan21.Module room) {
+        super(TransitStructures21.PIECE, 0, bounds(room));
+        this.room = room;
+        setOrientation(null);
+    }
+    public TransitPiece21(StructurePieceSerializationContext context, CompoundTag tag) {
+        super(TransitStructures21.PIECE, tag);
+        room = decodeModule(tag.getCompound("SanctuaryModule")
+            .orElseThrow(() -> new IllegalArgumentException("Missing saved transit room")));
+        if (!getBoundingBox().equals(bounds(room)))
+            throw new IllegalArgumentException("Transit room disagrees with its saved native bounding box");
+        setOrientation(null);
+    }
+    public TransitPlan21.Module module() { return room; }
+    @Override public BlockPos getLocatorPosition() { return locator(room); }
+    public static BlockPos locator(TransitPlan21.Module room) {
+        return new BlockPos(room.minX() + room.width() / 2,
+            room.kind() == TransitPlan21.Kind.ACCESS ? room.surfaceY() + 1 : room.floorY() + 1,
+            room.kind() == TransitPlan21.Kind.ACCESS ? room.minZ() : room.minZ() + room.depth() / 2);
+    }
+    @Override protected void addAdditionalSaveData(StructurePieceSerializationContext context, CompoundTag tag) {
+        tag.put("SanctuaryModule", encodeModule(room));
+    }
+    public static CompoundTag encodeModule(TransitPlan21.Module room) {
+        var tag = new CompoundTag(); tag.putInt("Schema", 1); tag.putString("Kind", room.kind().name());
+        tag.putInt("MinX", room.minX()); tag.putInt("MinY", room.minY()); tag.putInt("MinZ", room.minZ());
+        tag.putInt("Width", room.width()); tag.putInt("Height", room.height()); tag.putInt("Depth", room.depth());
+        tag.putInt("Facing", room.facing()); tag.putInt("Openings", room.openings()); tag.putLong("ModuleSeed", room.seed());
+        var supports = new ListTag();
+        for (var support : room.supports()) {
+            var value = new CompoundTag(); value.putInt("X", support.x()); value.putInt("MinY", support.minY());
+            value.putInt("Z", support.z()); value.putInt("MaxY", support.maxY()); supports.add(value);
+        }
+        tag.put("Supports", supports);
+        return tag;
+    }
+    public static TransitPlan21.Module decodeModule(CompoundTag tag) {
+        if (!tag.keySet().equals(MODULE_KEYS)) throw new IllegalArgumentException("Incomplete or unknown transit room fields");
+        if (integer(tag, "Schema") != 1) throw new IllegalArgumentException("Unsupported transit room schema");
+        var kind = TransitPlan21.Kind.valueOf(tag.getString("Kind").orElseThrow(() -> new IllegalArgumentException("Missing room kind")));
+        type(tag, "ModuleSeed", Tag.TAG_LONG); type(tag, "Supports", Tag.TAG_LIST);
+        var saved = tag.getList("Supports").orElseThrow();
+        if (saved.size() > 64) throw new IllegalArgumentException("Too many saved transit room supports");
+        var supports = new ArrayList<TransitPlan21.Support>();
+        for (var entry : saved) {
+            if (!(entry instanceof CompoundTag value) || !value.keySet().equals(SUPPORT_KEYS))
+                throw new IllegalArgumentException("Invalid transit room support fields");
+            supports.add(new TransitPlan21.Support(integer(value, "X"), integer(value, "MinY"), integer(value, "Z"), integer(value, "MaxY")));
+        }
+        return new TransitPlan21.Module(kind, integer(tag, "MinX"), integer(tag, "MinY"), integer(tag, "MinZ"),
+            integer(tag, "Width"), integer(tag, "Height"), integer(tag, "Depth"), integer(tag, "Facing"), integer(tag, "Openings"),
+            tag.getLong("ModuleSeed").orElseThrow(), supports);
+    }
+    private static int integer(CompoundTag tag, String key) {
+        type(tag, key, Tag.TAG_INT);
+        return tag.getInt(key).orElseThrow();
+    }
+    private static void type(CompoundTag tag, String key, byte id) {
+        if (tag.get(key) == null || tag.get(key).getId() != id)
+            throw new IllegalArgumentException("Invalid saved transit room field: " + key);
+    }
+    @Override public void postProcess(WorldGenLevel level, StructureManager manager, ChunkGenerator generator,
+            RandomSource random, BoundingBox clip, ChunkPos chunk, BlockPos pivot) {
+        TransitStructures21.placing(() -> TransitRenderer21.render(room, new LostCityRenderer.BlockWriter() {
+            private BlockPos world(int x, int y, int z) { return new BlockPos(room.minX() + x, room.minY() + y, room.minZ() + z); }
+            @Override public void set(int x, int y, int z, BlockState block) {
+                var position = world(x, y, z);
+                if (getBoundingBox().isInside(position) && clip.isInside(position))
+                    placeBlock(level, block, position.getX(), position.getY(), position.getZ(), clip);
+            }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> loot, long seed) {
+                var position = world(x, y, z);
+                if (getBoundingBox().isInside(position) && clip.isInside(position))
+                    createChest(level, clip, RandomSource.create(seed), position, loot, null);
+            }
+        }));
+    }
+    public static BoundingBox bounds(TransitPlan21.Module room) {
+        int minY = room.minY(), maxY = Math.addExact(room.minY(), room.height() - 1);
+        for (var support : room.supports()) {
+            minY = Math.min(minY, support.minY()); maxY = Math.max(maxY, support.maxY());
+        }
+        return new BoundingBox(room.minX(), minY, room.minZ(), Math.addExact(room.minX(), room.width() - 1),
+            maxY, Math.addExact(room.minZ(), room.depth() - 1));
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitPlan21.java

@@ -0,0 +1,86 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import java.util.HashSet;
+import java.util.List;
+
+/** Immutable final geometry. Each module owns a small native start, never an island-wide start. */
+public record TransitPlan21(List<Module> modules, int samples, String diagnostic) {
+    public static final int MAX_SAMPLES = 3_000_000;
+    public static final TransitPlan21 EMPTY = new TransitPlan21(List.of(), 0, "disabled");
+    public enum Kind { GALLERY, JUNCTION, HALL, ACCESS }
+    public record Support(int x, int minY, int z, int maxY) {
+        public Support {
+            if (minY < 8 || maxY > 375 || minY > maxY || maxY - minY >= 16)
+                throw new IllegalArgumentException("Invalid transit footing");
+        }
+    }
+    /** World-aligned bounds. Openings N1/E2/S4/W8 are seven wide, local y2..8.
+     * Access top deck is maxY-4. Its north gate, at centerX/minZ, has a certified natural approach. */
+    public record Module(Kind kind, int minX, int minY, int minZ, int width, int height, int depth,
+                         int facing, int openings, long seed, List<Support> supports) {
+        public Module {
+            supports = List.copyOf(supports);
+            if (kind == null || width < 9 || width > 25 || depth < 9 || depth > 25
+                    || (width & 1) == 0 || (depth & 1) == 0 || height < 10 || height > 160
+                    || minY < 16 || minY + height > 383 || facing < 0 || facing > 3
+                    || openings < 1 || openings > 15 || supports.size() > 64)
+                throw new IllegalArgumentException("Invalid transit module");
+            if (kind == Kind.ACCESS && (width != 17 || depth != 17 || height < 20))
+                throw new IllegalArgumentException("Transit stair access needs its complete 17x17 shaft");
+            if (kind != Kind.ACCESS && height != 10) throw new IllegalArgumentException("Unexpected gallery height");
+            var seen = new HashSet<Long>();
+            for (var s : supports) if (s.x() < minX || s.x() >= minX + width || s.z() < minZ
+                    || s.z() >= minZ + depth || s.maxY() != minY - 1 || !seen.add(key(s.x(), s.z())))
+                throw new IllegalArgumentException("Transit footing does not belong to its floor");
+        }
+        public int maxX() { return minX + width - 1; }
+        public int maxY() { return minY + height - 1; }
+        public int maxZ() { return minZ + depth - 1; }
+        public int centerX() { return minX + width / 2; }
+        public int centerZ() { return minZ + depth / 2; }
+        public int floorY() { return minY + 1; }
+        public int surfaceY() { return maxY() - 4; }
+        public int startChunkX() { return centerX() >> 4; }
+        public int startChunkZ() { return centerZ() >> 4; }
+        public int boundsMinY() { return supports.stream().mapToInt(Support::minY).min().orElse(minY); }
+        public boolean contains(int x, int y, int z) {
+            if (x < minX || x > maxX() || z < minZ || z > maxZ()) return false;
+            if (y >= minY && y <= maxY()) return true;
+            return supports.stream().anyMatch(s -> x == s.x() && z == s.z() && y >= s.minY() && y <= s.maxY());
+        }
+        public boolean protects(int x, int y, int z) {
+            if (contains(x, y, z)) return true;
+            if (kind == Kind.ACCESS && x >= centerX() - 2 && x <= centerX() + 2
+                    && z >= minZ - 3 && z < minZ && y >= surfaceY() - 2 && y <= surfaceY() + 3) return true;
+            // Two untouched layers carry the slab and the certified short piers.
+            if (x >= minX && x <= maxX() && z >= minZ && z <= maxZ() && y >= minY - 2 && y < minY) return true;
+            return supports.stream().anyMatch(s -> x == s.x() && z == s.z() && y >= s.minY() - 2 && y < s.minY());
+        }
+    }
+    public TransitPlan21 {
+        modules = List.copyOf(modules);
+        if (modules.size() > 64 || samples < 0 || samples > MAX_SAMPLES || diagnostic == null || diagnostic.length() > 1024)
+            throw new IllegalArgumentException("Invalid transit planning result");
+        if (!modules.isEmpty() && modules.stream().filter(m -> m.kind() == Kind.ACCESS).count() != 2)
+            throw new IllegalArgumentException("A through-gallery needs two surface accesses");
+        for (int i = 0; i < modules.size(); i++) for (int j = i + 1; j < modules.size(); j++) {
+            var a = modules.get(i); var b = modules.get(j);
+            if (a.minX() <= b.maxX() && a.maxX() >= b.minX() && a.minZ() <= b.maxZ() && a.maxZ() >= b.minZ())
+                throw new IllegalArgumentException("Transit modules overlap");
+        }
+    }
+    public boolean isEmpty() { return modules.isEmpty(); }
+    public List<Module> modulesForChunk(int x, int z) {
+        return modules.stream().filter(m -> m.startChunkX() == x && m.startChunkZ() == z).toList();
+    }
+    public boolean contains(int x, int y, int z) { return modules.stream().anyMatch(m -> m.contains(x, y, z)); }
+    public boolean protects(int x, int y, int z) { return modules.stream().anyMatch(m -> m.protects(x, y, z)); }
+    public boolean intersectsProtection(int x0, int y0, int z0, int x1, int y1, int z1) {
+        for (var m : modules) if (m.kind() == Kind.ACCESS && x0 <= m.centerX() + 2 && x1 >= m.centerX() - 2
+                && z0 < m.minZ() && z1 >= m.minZ() - 3 && y0 <= m.surfaceY() + 3 && y1 >= m.surfaceY() - 2) return true;
+        for (var m : modules) if (x0 <= m.maxX() && x1 >= m.minX() && z0 <= m.maxZ() && z1 >= m.minZ()
+                && y0 <= m.maxY() && y1 >= m.boundsMinY() - 2) return true;
+        return false;
+    }
+    private static long key(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitPlanner21.java

@@ -0,0 +1,220 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Kind;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Module;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Support;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/** A bounded read-only through-route. Failed candidates never publish partial corridors or shafts. */
+public final class TransitPlanner21 {
+    public static final int MAX_COLUMNS = 12_000;
+    private TransitPlanner21() {}
+    public interface Terrain {
+        boolean owns(int x, int z);
+        boolean solid(int x, int y, int z);
+        boolean protectedAt(int x, int y, int z);
+        int surfaceY(int x, int z);
+        default String obstruction(int x, int y, int z) { return "protected terrain"; }
+    }
+    public static TransitPlan21 plan(long seed, int centerX, int centerZ, int diameter, Terrain terrain) {
+        if (diameter < 512 || diameter > 1024) throw new IllegalArgumentException("Unsupported transit island diameter");
+        var probe = new Probe(terrain);
+        int count = (int) Math.ceil(diameter * .42 / 17);
+        if ((count & 1) == 0) count++;
+        String last = "no dry supported through-route";
+        var choices = new ArrayList<Choice>();
+        // Reserve most of the native-column budget for the exact scan of selected routes.
+        probe.sampleLimit = 1_800_000; probe.columnLimit = 7_500;
+        try {
+            search: for (int advance : new int[]{0, -34, 34}) for (boolean alongX : new boolean[]{true, false}) for (int shift : new int[]{-diameter / 8, diameter / 8, -diameter / 16, diameter / 16, 0, -3 * diameter / 16, 3 * diameter / 16}) {
+                int cx = centerX + (alongX ? advance : shift), cz = centerZ + (alongX ? shift : advance);
+                for (int floor : new int[]{216, 200, 224, 208, 184, 232, 160}) {
+                    var route = candidate(seed, cx, cz, count, floor, alongX, probe, false);
+                    String label = "axis=" + (alongX ? "east-west" : "north-south") + " offset=" + shift + " advance=" + advance + " floor=" + floor;
+                    if (route == null) {
+                        last = probe.reason;
+                        diagnostic("preselection reject " + label + " " + last + " columns=" + probe.columns.size());
+                        continue;
+                    }
+                    int cost = route.stream().mapToInt(m -> m.supports().stream().mapToInt(pier -> pier.maxY() - pier.minY() + 1).sum()
+                        + (m.kind() == Kind.ACCESS ? m.surfaceY() - m.floorY() : 0)).sum();
+                    // Try the intermediate levels first; within each level prefer the better supported axis.
+                    int heightOrder = switch (floor) { case 216 -> 0; case 200 -> 1; case 224 -> 2; case 208 -> 3; case 184 -> 4; case 232 -> 5; default -> 6; };
+                    choices.add(new Choice(route, floor, alongX, heightOrder * 100_000 + cost, label));
+                    diagnostic("preselection admitted " + label + " bearing_cost=" + cost);
+                    if (choices.size() >= 8) break search;
+                }
+            }
+        } catch (BudgetExceeded exhausted) { diagnostic("prescreen budget reached; retain " + choices.size() + " candidates"); }
+        probe.sampleLimit = TransitPlan21.MAX_SAMPLES; probe.columnLimit = MAX_COLUMNS;
+        choices.sort(java.util.Comparator.comparingInt(Choice::cost));
+        try {
+            for (var choice : choices) {
+                var finalRoute = new ArrayList<Module>();
+                for (var rough : choice.route()) {
+                    var complete = certify(rough, probe, true);
+                    if (complete == null) { last = probe.reason; break; }
+                    finalRoute.add(complete);
+                }
+                if (finalRoute.size() != choice.route().size()) {
+                    diagnostic("exact reject " + choice.label() + " " + last); continue;
+                }
+                addBranch(finalRoute, choice.floor(), choice.alongX(), seed, probe);
+                return new TransitPlan21(finalRoute, probe.samples, "accepted " + choice.label()
+                    + " span=" + ((count + 1) * 17) + " columns=" + probe.columns.size()
+                    + " candidates=" + choices.size() + " hall=" + finalRoute.stream().anyMatch(m -> m.kind() == Kind.HALL));
+            }
+        } catch (BudgetExceeded exhausted) { last = "bounded exact search exhausted: " + probe.reason; }
+        return new TransitPlan21(List.of(), probe.samples, last + "; candidates=" + choices.size() + "; columns=" + probe.columns.size());
+    }
+    private record Choice(List<Module> route, int floor, boolean alongX, int cost, String label) {}
+    private static List<Module> candidate(long seed, int cx, int cz, int count, int floor,
+            boolean alongX, Probe probe, boolean full) {
+        int first = -(count + 1) * 17 / 2;
+        int ax = cx + (alongX ? first : 0), az = cz + (alongX ? 0 : first);
+        int bx = cx - (alongX ? first : 0), bz = cz - (alongX ? 0 : first);
+        // Cheap route witnesses reject deep obstacles before two tall shafts are scanned in full.
+        for (int d = first + 17; d <= -first - 17; d += 8) for (int side : new int[]{-4, 0, 4})
+            for (int y : new int[]{floor - 2, floor, floor + 4, floor + 8}) {
+                int x = cx + (alongX ? d : side), z = cz + (alongX ? side : d);
+                if (probe.protectedAt(x, y, z)) {
+                    probe.reason = "coarse route [" + x + "," + y + "," + z + "] " + probe.terrain.obstruction(x, y, z); return null;
+                }
+            }
+        // Certify the two indispensable exits before spending the route's column budget.
+        Module left = access(ax, az, floor, alongX ? 2 : 4, seed ^ 0x2101L, probe, full);
+        if (left == null) return null;
+        Module right = access(bx, bz, floor, alongX ? 8 : 1, seed ^ 0x2102L, probe, full);
+        if (right == null) return null;
+        var result = new ArrayList<Module>(); result.add(left);
+        int unanchoredRun = 0;
+        for (int n = 0; n < count; n++) {
+            int d = first + 17 * (n + 1);
+            int x = cx + (alongX ? d - 8 : -4), z = cz + (alongX ? -4 : d - 8);
+            var module = new Module(Kind.GALLERY, x, floor - 1, z, alongX ? 17 : 9, 10, alongX ? 9 : 17,
+                alongX ? 1 : 0, alongX ? 10 : 5, seed ^ (n * 0x9E3779B97F4A7C15L), List.of());
+            module = certify(module, probe, full);
+            if (module == null) return null;
+            unanchoredRun = probe.bearings.get(module) == 15 ? 0 : unanchoredRun + 1;
+            if (unanchoredRun > 2) { probe.reason = "unsupported span exceeds 34 blocks"; return null; }
+            result.add(module);
+        }
+        result.add(right);
+        return result;
+    }
+    private static Module access(int cx, int cz, int floor, int opening, long seed, Probe probe, boolean full) {
+        int top = -1, low = 384;
+        for (int x = cx - 2; x <= cx + 2; x++) for (int z = cz - 11; z <= cz - 9; z++) {
+            int surface = probe.surface(x, z); top = Math.max(top, surface); low = Math.min(low, surface);
+        }
+        if (low < 0 || top - low > 1) { probe.reason = "access approach relief [" + cx + "," + cz + "] " + low + ".." + top; return null; }
+        if (top < floor + 18 || top > floor + 145) { probe.reason = "surface access height"; return null; }
+        // Its visible north portico meets real ground; its three-wide approach is never an unsupported threshold.
+        for (int x = cx - 2; x <= cx + 2; x++) for (int z = cz - 11; z <= cz - 9; z++) {
+            int y = probe.surface(x, z);
+            if (y < top - 1 || y > top || probe.protectedAt(x, y, z)
+                    || probe.protectedAt(x, top + 1, z) || probe.protectedAt(x, top + 2, z)) {
+                probe.reason = "access approach [" + x + "," + top + "," + z + "] terrain=" + y; return null;
+            }
+        }
+        for (int x : new int[]{cx - 8, cx, cx + 8}) for (int z : new int[]{cz - 8, cz, cz + 8}) {
+            int y = probe.surface(x, z);
+            // The portico alone needs level terrain. A buried shaft can follow a hillside;
+            // its local walls and checked footings carry the deck without flattening the hill.
+            if (y < Math.max(floor + 8, top - 24) || y > top + 16) { probe.reason = "access hillside [" + x + "," + top + "," + z + "] terrain=" + y; return null; }
+        }
+        return certify(new Module(Kind.ACCESS, cx - 8, floor - 1, cz - 8, 17,
+            top - (floor - 1) + 5, 17, 0, opening, seed, List.of()), probe, full);
+    }
+    private static void addBranch(List<Module> route, int floor, boolean alongX, long seed, Probe probe) {
+        int index = 1 + (route.size() - 2) / 2;
+        var junction = route.get(index);
+        if (probe.bearings.getOrDefault(junction, 0) != 15) return;
+        for (int side : new int[]{-1, 1}) {
+            try {
+                int x = alongX ? junction.centerX() - 4 : side < 0 ? junction.minX() - 17 : junction.maxX() + 1;
+                int z = alongX ? side < 0 ? junction.minZ() - 17 : junction.maxZ() + 1 : junction.centerZ() - 4;
+                int width = alongX ? 9 : 17, depth = alongX ? 17 : 9;
+                var passage = certify(new Module(Kind.GALLERY, x, floor - 1, z, width, 10, depth,
+                    alongX ? 0 : 1, alongX ? 5 : 10, seed ^ 0x21B1L ^ side, List.of()), probe, true);
+                if (passage == null) continue;
+                int hx = alongX ? junction.centerX() - 8 : side < 0 ? passage.minX() - 21 : passage.maxX() + 1;
+                int hz = alongX ? side < 0 ? passage.minZ() - 21 : passage.maxZ() + 1 : junction.centerZ() - 8;
+                int opening = alongX ? side < 0 ? 4 : 1 : side < 0 ? 2 : 8;
+                var hall = certify(new Module(Kind.HALL, hx, floor - 1, hz, alongX ? 17 : 21, 10,
+                    alongX ? 21 : 17, alongX ? 0 : 1, opening, seed ^ 0x21A1L ^ side, List.of()), probe, true);
+                if (hall == null) continue;
+                int branch = alongX ? side < 0 ? 1 : 4 : side < 0 ? 8 : 2;
+                route.set(index, new Module(Kind.JUNCTION, junction.minX(), junction.minY(), junction.minZ(),
+                    junction.width(), 10, junction.depth(), junction.facing(), junction.openings() | branch,
+                    junction.seed(), junction.supports()));
+                route.add(passage); route.add(hall); return;
+            } catch (BudgetExceeded exhausted) { return; } // The already certified traversal remains complete.
+        }
+    }
+    private static Module certify(Module module, Probe probe, boolean full) {
+        var supports = new ArrayList<Support>();
+        int bearingQuadrants = 0;
+        for (int z = module.minZ();; z = Math.min(z + 4, module.maxZ())) {
+            for (int x = module.minX();; x = Math.min(x + 4, module.maxX())) {
+                if (!probe.owns(x, z)) { probe.reason = "outside island"; return null; }
+                if (!full) for (int y = module.minY(); y <= module.maxY(); y += 4)
+                    if (probe.protectedAt(x, y, z)) {
+                        probe.reason = "coarse " + module.kind() + " [" + x + "," + y + "," + z + "] " + probe.terrain.obstruction(x, y, z); return null;
+                    }
+                int anchor = module.minY() - 1;
+                while (anchor >= module.minY() - 17 && !(probe.solid(x, anchor, z) && probe.solid(x, anchor - 1, z))) anchor--;
+                if (anchor >= module.minY() - 17) {
+                    for (int y = anchor - 1; y < module.minY(); y++) if (probe.protectedAt(x, y, z)) {
+                        probe.reason = "protected footing"; return null;
+                    }
+                    if (anchor < module.minY() - 1) supports.add(new Support(x, anchor + 1, z, module.minY() - 1));
+                    bearingQuadrants |= 1 << ((x < module.centerX() ? 0 : 1) + (z < module.centerZ() ? 0 : 2));
+                }
+                if (x == module.maxX()) break;
+            }
+            if (z == module.maxZ()) break;
+        }
+        // The continuous two-block deck can span gaps between its bearings. Require
+        // untouched rock in each quarter, not a pier at every point above a cavity.
+        if (bearingQuadrants != 15 && module.kind() != Kind.GALLERY) { probe.reason = "unsupported quarters " + module.kind()
+            + " [" + module.minX() + "," + module.minY() + "," + module.minZ() + "] mask=" + bearingQuadrants; return null; }
+        if (full) {
+            // Hydrology and all previous structures are checked at every edited voxel after the cheap footing test.
+            for (int z = module.minZ(); z <= module.maxZ(); z++) for (int x = module.minX(); x <= module.maxX(); x++) {
+                if (!probe.owns(x, z)) { probe.reason = "outside island"; return null; }
+                for (int y = module.minY() - 2; y <= module.maxY(); y++) if (probe.protectedAt(x, y, z)) {
+                    probe.reason = "volume " + module.kind() + " [" + x + "," + y + "," + z + "] " + probe.terrain.obstruction(x, y, z); return null;
+                }
+            }
+        }
+        var certified = new Module(module.kind(), module.minX(), module.minY(), module.minZ(), module.width(), module.height(),
+            module.depth(), module.facing(), module.openings(), module.seed(), supports);
+        probe.bearings.put(certified, bearingQuadrants);
+        return certified;
+    }
+    private static void diagnostic(String message) {
+        if (Boolean.getBoolean("sanctuary.test.transit21") || Boolean.getBoolean("sanctuary.transit.plannerDiagnostics"))
+            System.getLogger(TransitPlanner21.class.getName()).log(System.Logger.Level.INFO, "Transit21 " + message);
+    }
+    private static final class Probe {
+        final Terrain terrain; final Set<Long> columns = new HashSet<>(); int samples; int sampleLimit = TransitPlan21.MAX_SAMPLES, columnLimit = MAX_COLUMNS; String reason = "budget";
+        final java.util.Map<Module, Integer> bearings = new java.util.HashMap<>();
+        Probe(Terrain terrain) { this.terrain = terrain; }
+        void visit(int x, int z) {
+            if (samples >= sampleLimit) throw new BudgetExceeded();
+            samples++;
+            long key = (long) x << 32 ^ z & 0xffffffffL;
+            if (!columns.contains(key) && columns.size() >= columnLimit) throw new BudgetExceeded();
+            columns.add(key);
+        }
+        boolean owns(int x, int z) { visit(x, z); return terrain.owns(x, z); }
+        boolean solid(int x, int y, int z) { visit(x, z); return terrain.solid(x, y, z); }
+        boolean protectedAt(int x, int y, int z) { visit(x, z); return terrain.protectedAt(x, y, z); }
+        int surface(int x, int z) { visit(x, z); return terrain.surfaceY(x, z); }
+    }
+    private static final class BudgetExceeded extends RuntimeException { private static final long serialVersionUID = 1L; }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitRenderer21.java

@@ -0,0 +1,208 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import fr.koka.sanctuary.worldgen.detail.ConnectedBlocks20;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Kind;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Module;
+import java.util.ArrayList;
+import java.util.List;
+import net.minecraft.core.Direction;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.storage.loot.BuiltInLootTables;
+
+/** A seven-wide abandoned industrial route: five roadway cells and one pavement on each side. */
+public final class TransitRenderer21 {
+    private TransitRenderer21() {}
+    public record Target(String name, int x, int y, int z) {}
+    public static List<Target> targets(Module m) {
+        var result = new ArrayList<Target>();
+        result.add(new Target("roadway", m.width() / 2, 2, m.depth() / 2));
+        if ((m.openings() & 1) != 0) result.add(new Target("north_connection", m.width() / 2, 2, 0));
+        if ((m.openings() & 2) != 0) result.add(new Target("east_connection", m.width() - 1, 2, m.depth() / 2));
+        if ((m.openings() & 4) != 0) result.add(new Target("south_connection", m.width() / 2, 2, m.depth() - 1));
+        if ((m.openings() & 8) != 0) result.add(new Target("west_connection", 0, 2, m.depth() / 2));
+        if (m.kind() == Kind.ACCESS) {
+            result.add(new Target("surface_portico", 8, m.surfaceY() - m.minY() + 1, 0));
+            result.add(new Target("surface_landing", 8, m.surfaceY() - m.minY() + 1, 12));
+        }
+        if (m.kind() == Kind.HALL) {
+            result.add(new Target("maintenance_bench", 3, 2, 4));
+            result.add(new Target("shared_tool_chest", m.width() - 4, 2, m.depth() - 4));
+            result.add(new Target("unfinished_rock_face", m.facing() == 1 ? m.width() / 2 : 3,
+                2, m.facing() == 1 ? 3 : m.depth() / 2));
+        }
+        return List.copyOf(result);
+    }
+    public static void render(Module module, LostCityRenderer.BlockWriter output) {
+        var connected = ConnectedBlocks20.buffer(output);
+        new Painter(module, connected).render();
+        connected.flush();
+    }
+    private static final class Painter {
+        final Module m; final LostCityRenderer.BlockWriter out;
+        Painter(Module module, LostCityRenderer.BlockWriter out) { m = module; this.out = out; }
+        void set(int x, int y, int z, Block block) { set(x, y, z, block.defaultBlockState()); }
+        void set(int x, int y, int z, BlockState state) { out.set(x, y, z, state); }
+        void box(int x0, int y0, int z0, int x1, int y1, int z1, Block block) {
+            for (int x = x0; x <= x1; x++) for (int z = z0; z <= z1; z++) for (int y = y0; y <= y1; y++) set(x, y, z, block);
+        }
+        BlockState stair(Direction direction) {
+            return Blocks.STONE_BRICK_STAIRS.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, direction);
+        }
+        void render() {
+            int w = m.width(), d = m.depth();
+            for (var support : m.supports()) box(support.x() - m.minX(), support.minY() - m.minY(), support.z() - m.minZ(),
+                support.x() - m.minX(), -1, support.z() - m.minZ(), Blocks.STONE_BRICKS);
+            box(0, 0, 0, w - 1, 0, d - 1, Blocks.STONE_BRICKS);
+            box(0, 1, 0, w - 1, 1, d - 1, Blocks.SMOOTH_STONE);
+            box(0, 2, 0, w - 1, m.height() - 1, d - 1, Blocks.AIR);
+            if (m.kind() == Kind.ACCESS) { access(); return; }
+            for (int x = 0; x < w; x++) for (int z = 0; z < d; z++) {
+                boolean edge = x == 0 || x == w - 1 || z == 0 || z == d - 1;
+                if (edge) for (int y = 2; y <= 8; y++) set(x, y, z,
+                    y == 2 || y == 7 ? Blocks.TUFF_BRICKS : ((x + z) % 5 == 0 ? Blocks.STONE_BRICKS : Blocks.SMOOTH_STONE));
+                set(x, 9, z, Blocks.STONE_BRICKS);
+                boolean alongX = m.facing() == 1;
+                int across = alongX ? z - d / 2 : x - w / 2;
+                if (Math.abs(across) <= 2) set(x, 1, z, Blocks.POLISHED_ANDESITE);
+                else if (Math.abs(across) == 3) set(x, 2, z, Blocks.SMOOTH_STONE_SLAB);
+            }
+            openings();
+            if (m.kind() == Kind.JUNCTION) {
+                // The side branch's mouth and central crossing retain all five roadway cells.
+                for (int x = w / 2 - 2; x <= w / 2 + 2; x++) for (int z = 0; z < d; z++) set(x, 2, z, Blocks.AIR);
+                for (int z = d / 2 - 2; z <= d / 2 + 2; z++) for (int x = 0; x < w; x++) set(x, 2, z, Blocks.AIR);
+            }
+            // Ceiling ribs and luminaires are physically joined to the continuous roof slab.
+            for (int n = 3; n < (m.facing() == 1 ? w : d) - 2; n += 6) {
+                int x = m.facing() == 1 ? n : w / 2, z = m.facing() == 1 ? d / 2 : n;
+                set(x, 8, z, Blocks.LANTERN.defaultBlockState().setValue(BlockStateProperties.HANGING, true));
+                if (m.facing() == 1) box(x, 8, 1, x, 8, 2, Blocks.POLISHED_TUFF);
+                else box(1, 8, z, 2, 8, z, Blocks.POLISHED_TUFF);
+            }
+            if (m.kind() == Kind.HALL) hall();
+            exposedRock();
+        }
+        void openings() {
+            for (int y = 2; y <= 8; y++) {
+                if ((m.openings() & 1) != 0) box(m.width() / 2 - 3, y, 0, m.width() / 2 + 3, y, 0, Blocks.AIR);
+                if ((m.openings() & 4) != 0) box(m.width() / 2 - 3, y, m.depth() - 1, m.width() / 2 + 3, y, m.depth() - 1, Blocks.AIR);
+                if ((m.openings() & 2) != 0) box(m.width() - 1, y, m.depth() / 2 - 3, m.width() - 1, y, m.depth() / 2 + 3, Blocks.AIR);
+                if ((m.openings() & 8) != 0) box(0, y, m.depth() / 2 - 3, 0, y, m.depth() / 2 + 3, Blocks.AIR);
+            }
+        }
+        void hall() {
+            // Flush crossings join the work bays to the road through the raised pavements.
+            // They also provide an accessible route without requiring a jump over the curb.
+            if (m.facing() == 0) {
+                for (int x : new int[]{m.width() / 2 - 3, m.width() / 2 + 3})
+                    for (int z0 : new int[]{4, m.depth() - 4}) box(x, 2, z0 - 1, x, 2, z0 + 1, Blocks.AIR);
+            } else {
+                for (int z : new int[]{m.depth() / 2 - 3, m.depth() / 2 + 3})
+                    for (int x0 : new int[]{3, m.width() - 4}) box(x0 - 1, 2, z, x0 + 1, 2, z, Blocks.AIR);
+            }
+            // Maintenance workshop occupies side bays; the centered arrival and return remain unobstructed.
+            for (int z : new int[]{3, m.depth() - 4}) {
+                box(1, 2, z, 1, 7, z, Blocks.CHISELED_TUFF_BRICKS);
+                box(m.width() - 2, 2, z, m.width() - 2, 7, z, Blocks.CHISELED_TUFF_BRICKS);
+                box(1, 8, z, m.width() - 2, 8, z, Blocks.TUFF_BRICKS);
+            }
+            set(2, 2, 3, Blocks.CRAFTING_TABLE); set(2, 2, 4, Blocks.GRINDSTONE);
+            set(2, 2, 5, Blocks.FURNACE.defaultBlockState().setValue(BlockStateProperties.HORIZONTAL_FACING, Direction.EAST));
+            for (int z = m.depth() - 6; z <= m.depth() - 3; z++) set(2, 2, z, Blocks.BARREL);
+            set(m.width() - 3, 2, 3, Blocks.CAULDRON);
+            out.chest(m.width() - 3, 2, m.depth() - 4, BuiltInLootTables.VILLAGE_TOOLSMITH, m.seed() ^ 0x21A1100L);
+        }
+        void exposedRock() {
+            // Abandoned cuts expose finite, ordinary mineable ore in the saved wall geometry.
+            // No ticking reward or regeneration: once mined, these blocks remain gone.
+            if (m.kind() != Kind.HALL && (m.kind() != Kind.GALLERY || Math.floorMod(m.seed(), 4) != 0)) return;
+            boolean alongX = m.facing() == 1;
+            int middle = alongX ? m.width() / 2 : m.depth() / 2;
+            Block[] ore = {Blocks.COAL_ORE, Blocks.COPPER_ORE, Blocks.IRON_ORE,
+                Blocks.GOLD_ORE, Blocks.REDSTONE_ORE, Blocks.LAPIS_ORE};
+            Block deposit = ore[Math.floorMod(m.seed() ^ 0x21CAFE, ore.length)];
+            for (int across = -2; across <= 2; across++) for (int y = 2; y <= 6; y++) {
+                int x = alongX ? middle + across : 0, z = alongX ? 0 : middle + across;
+                Block rock = y == 2 ? Blocks.TUFF : y >= 5 ? Blocks.STONE : Blocks.DEEPSLATE;
+                if (Math.abs(across) + Math.abs(y - 4) <= 1) rock = deposit;
+                if (m.kind() == Kind.HALL && y == 3 && across == -1) rock = Blocks.DEEPSLATE_DIAMOND_ORE;
+                if (m.kind() == Kind.HALL && y == 4 && across == 1) rock = Blocks.EMERALD_ORE;
+                set(x, y, z, rock);
+            }
+            if (m.kind() == Kind.HALL) {
+                // An unfinished excavation bay interrupts the masonry: irregular rock
+                // shoulders and a low stone arch leave its mineral face accessible.
+                for (int across = -3; across <= 3; across++) for (int reach = 0; reach <= 2; reach++) {
+                    int x = alongX ? middle + across : reach, z = alongX ? reach : middle + across;
+                    set(x, 1, z, Math.abs(across) == 3 ? Blocks.MOSSY_COBBLESTONE : Blocks.TUFF);
+                    int ceiling = 7 + ((across + reach) & 1);
+                    box(x, ceiling, z, x, 8, z, reach == 0 ? Blocks.DEEPSLATE : Blocks.STONE);
+                    if (Math.abs(across) == 3) box(x, 2, z, x, 6 - reach, z,
+                        reach == 2 ? Blocks.COBBLESTONE : Blocks.TUFF);
+                }
+            }
+        }
+        void access() {
+            int top = m.surfaceY() - m.minY();
+            // Enclosed local shaft, not a filled foundation under the whole route.
+            for (int n = 0; n <= 16; n++) {
+                box(n, 2, 0, n, top, 0, Blocks.SMOOTH_STONE);
+                box(n, 2, 16, n, top, 16, Blocks.SMOOTH_STONE);
+                box(0, 2, n, 0, top, n, Blocks.STONE_BRICKS);
+                box(16, 2, n, 16, top, n, Blocks.STONE_BRICKS);
+            }
+            box(1, top, 1, 15, top, 15, Blocks.SMOOTH_STONE);
+            // Narrow bearing walls sit beside the flights, with the bottom route crossing at z8..9.
+            box(2, 2, 3, 2, top - 1, 7, Blocks.STONE_BRICKS);
+            box(14, 2, 3, 14, top - 1, 7, Blocks.STONE_BRICKS);
+            openings();
+            int rise = top - 1;
+            for (int step = 1; step <= rise; step++) {
+                int flight = (step - 1) / 5, within = (step - 1) % 5 + 1;
+                boolean south = (flight & 1) == 0;
+                int z = south ? 2 + within : 8 - within, x0 = south ? 3 : 11, y = 1 + step;
+                box(x0, y, z, x0 + 2, Math.min(top + 3, y + 3), z, Blocks.AIR);
+                for (int x = x0; x <= x0 + 2; x++) set(x, y, z, stair(south ? Direction.SOUTH : Direction.NORTH));
+                if (within == 5) {
+                    int z0 = south ? 8 : 1;
+                    box(3, y, z0, 13, y, z0 + 1, Blocks.SMOOTH_STONE);
+                    box(3, y + 1, z0, 13, Math.min(top + 3, y + 3), z0 + 1, Blocks.AIR);
+                    if (y + 3 <= top) {
+                        set(6, y + 3, z0, Blocks.SMOOTH_STONE);
+                        set(6, y + 2, z0, Blocks.LANTERN.defaultBlockState().setValue(BlockStateProperties.HANGING, true));
+                        // The bracket reaches an actual shaft wall; the last open-air landing needs no hanging lamp.
+                        box(6, y + 3, south ? z0 : 0, 6, y + 3, south ? 16 : z0, Blocks.STONE_BRICKS);
+                    }
+                }
+            }
+            // A north landing just below the surface needs a descending threshold instead
+            // of a slab sealing its headroom. The last flight still reaches the real top deck.
+            int belowNorthLanding = rise % 10;
+            if (belowNorthLanding >= 1 && belowNorthLanding <= 3) {
+                for (int z = 0; z <= belowNorthLanding; z++) for (int x = 7; x <= 9; x++) {
+                    box(x, top - z, z, x, top + 3, z, Blocks.AIR);
+                    set(x, top - z - 1, z, Blocks.STONE_BRICKS);
+                    set(x, top - z, z, stair(Direction.NORTH));
+                }
+                if (belowNorthLanding == 3) {
+                    for (int x : new int[]{6, 10}) {
+                        set(x, top - 3, 3, Blocks.SMOOTH_STONE);
+                        box(x, top - 2, 3, x, top - 1, 3, Blocks.AIR);
+                    }
+                }
+            }
+            // A short, grounded portico identifies each naturally approachable surface gate.
+            for (int n = 0; n <= 16; n++) {
+                if (n < 6 || n > 10) set(n, top + 1, 0, Blocks.IRON_BARS);
+                set(n, top + 1, 16, Blocks.IRON_BARS);
+                set(0, top + 1, n, Blocks.IRON_BARS); set(16, top + 1, n, Blocks.IRON_BARS);
+            }
+            for (int x : new int[]{6, 10}) box(x, top + 1, 0, x, top + 3, 0, Blocks.STONE_BRICKS);
+            box(6, top + 4, 0, 10, top + 4, 1, Blocks.STONE_BRICK_SLAB);
+        }
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitStructure21.java

@@ -0,0 +1,31 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import com.mojang.serialization.MapCodec;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import java.util.Optional;
+import net.minecraft.world.level.levelgen.structure.Structure;
+import net.minecraft.world.level.levelgen.structure.StructureType;
+
+/** A local group of neighboring modules; long routes deliberately have multiple native starts. */
+public final class TransitStructure21 extends Structure {
+    public static final MapCodec<TransitStructure21> CODEC = simpleCodec(TransitStructure21::new);
+    public TransitStructure21(StructureSettings settings) { super(settings); }
+    @Override protected Optional<GenerationStub> findGenerationPoint(GenerationContext context) {
+        if (!(context.chunkGenerator() instanceof SanctuaryChunkGenerator generator)
+                || generator.rootGeneration() != 21 || !generator.experimentalStructures()) return Optional.empty();
+        var island = generator.islandForChunk(context.chunkPos().x(), context.chunkPos().z());
+        if (island == null || !island.origin() || island.generation() != 21) return Optional.empty();
+        var modules = generator.transitPlan21().modulesForChunk(context.chunkPos().x(), context.chunkPos().z());
+        if (modules.isEmpty()) return Optional.empty();
+        for (var module : modules) {
+            if (Math.abs((module.minX() >> 4) - module.startChunkX()) > 7
+                    || Math.abs((module.maxX() >> 4) - module.startChunkX()) > 7
+                    || Math.abs((module.minZ() >> 4) - module.startChunkZ()) > 7
+                    || Math.abs((module.maxZ() >> 4) - module.startChunkZ()) > 7)
+                throw new IllegalStateException("Transit module exceeds local native reference range");
+        }
+        return Optional.of(new GenerationStub(TransitPiece21.locator(modules.getFirst()), pieces ->
+            modules.forEach(module -> pieces.addPiece(new TransitPiece21(module)))));
+    }
+    @Override public StructureType<?> type() { return TransitStructures21.TYPE; }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitStructures21.java

@@ -0,0 +1,85 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import com.mojang.datafixers.util.Pair;
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.expansion.ExpansionChunkGenerator;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import java.util.Comparator;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Holder;
+import net.minecraft.core.HolderSet;
+import net.minecraft.core.Registry;
+import net.minecraft.core.RegistryAccess;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.StructureManager;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkGeneratorStructureState;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.levelgen.densityfunction.SamplerContext;
+import net.minecraft.world.level.levelgen.structure.Structure;
+import net.minecraft.world.level.levelgen.structure.StructureStart;
+import net.minecraft.world.level.levelgen.structure.StructureType;
+import net.minecraft.world.level.levelgen.structure.pieces.StructurePieceType;
+import net.minecraft.world.level.levelgen.structure.templatesystem.StructureTemplateManager;
+
+public final class TransitStructures21 {
+    public static final ResourceKey<Structure> KEY = ResourceKey.create(Registries.STRUCTURE, SanctuaryMod.id("industrial_transit"));
+    public static final StructureType<TransitStructure21> TYPE = Registry.register(BuiltInRegistries.STRUCTURE_TYPE,
+        SanctuaryMod.id("industrial_transit_v21"), () -> TransitStructure21.CODEC);
+    public static final StructurePieceType PIECE = Registry.register(BuiltInRegistries.STRUCTURE_PIECE,
+        SanctuaryMod.id("industrial_transit_module_v21"), TransitPiece21::new);
+    private static final ThreadLocal<Integer> PLACEMENT_DEPTH = ThreadLocal.withInitial(() -> 0);
+    private TransitStructures21() {}
+    public static void register() {}
+    public static boolean isPlacing() { return PLACEMENT_DEPTH.get() > 0; }
+    static void placing(Runnable action) {
+        int previous = PLACEMENT_DEPTH.get(); PLACEMENT_DEPTH.set(previous + 1);
+        try { action.run(); } finally { if (previous == 0) PLACEMENT_DEPTH.remove(); else PLACEMENT_DEPTH.set(previous); }
+    }
+    public static void generate(ExpansionChunkGenerator generator, RegistryAccess registries,
+            ChunkGeneratorStructureState state, StructureManager manager, ChunkAccess chunk,
+            StructureTemplateManager templates, ResourceKey<Level> level) {
+        if (!Level.OVERWORLD.equals(level) || !manager.shouldGenerateStructures()
+                || !(generator instanceof SanctuaryChunkGenerator sanctuary) || generator.rootGeneration() != 21
+                || !sanctuary.experimentalStructures()) return;
+        var island = generator.islandForChunk(chunk.getPos().x(), chunk.getPos().z());
+        if (island == null || !island.origin() || island.generation() != 21) return;
+        if (sanctuary.transitPlan21().modulesForChunk(chunk.getPos().x(), chunk.getPos().z()).isEmpty()) return;
+        Holder<Structure> holder = registries.lookupOrThrow(Registries.STRUCTURE).getOrThrow(KEY);
+        StructureStart previous = manager.getStartForStructure(holder.value(), chunk);
+        if (previous != null && previous.isValid()) return;
+        var random = generator.randomState(island);
+        var sampler = random.createClimateSampler(SamplerContext.builder().enableCaches().build());
+        var start = holder.value().generate(holder, level, registries, generator, generator.getBiomeSource(), sampler,
+            random, templates, island.seed(), chunk.getPos(), previous == null ? 0 : previous.getReferences(),
+            chunk, holder.value().biomes()::contains);
+        if (start.isValid()) manager.setStartForStructure(holder.value(), start, chunk);
+    }
+    /** Locate selects a saved surface portico rather than teleporting the player into a deep road. */
+    public static Pair<BlockPos, Holder<Structure>> findNearest(ServerLevel level, HolderSet<Structure> structures,
+            BlockPos origin, int radius, boolean skipReferenced) {
+        if (!Level.OVERWORLD.equals(level.dimension())
+                || !(level.getChunkSource().getGenerator() instanceof SanctuaryChunkGenerator generator)
+                || generator.rootGeneration() != 21 || !generator.experimentalStructures()
+                || !level.structureManager().shouldGenerateStructures()) return null;
+        Holder<Structure> holder = level.registryAccess().lookupOrThrow(Registries.STRUCTURE).getOrThrow(KEY);
+        if (!structures.contains(holder)) return null;
+        var candidates = generator.transitPlan21().modules().stream()
+            .filter(m -> m.kind() == TransitPlan21.Kind.ACCESS)
+            .filter(m -> Math.abs((long) m.startChunkX() - (origin.getX() >> 4)) <= radius
+                && Math.abs((long) m.startChunkZ() - (origin.getZ() >> 4)) <= radius)
+            .sorted(Comparator.comparingDouble(m -> origin.distSqr(TransitPiece21.locator(m)))).toList();
+        for (var module : candidates) {
+            var chunk = level.getChunk(module.startChunkX(), module.startChunkZ(), ChunkStatus.STRUCTURE_STARTS, true);
+            var start = level.structureManager().getStartForStructure(holder.value(), chunk);
+            if (start == null || !start.isValid() || skipReferenced && !start.canBeReferenced()) continue;
+            if (skipReferenced) level.structureManager().addReference(start);
+            return Pair.of(TransitPiece21.locator(module), holder);
+        }
+        return null;
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/transit/TransitTerrain21.java

@@ -0,0 +1,67 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import fr.koka.sanctuary.expansion.ExpansionIsland;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Predicate;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.levelgen.NoiseBasedChunkGenerator;
+import net.minecraft.world.level.levelgen.RandomState;
+
+/** Read-only, bounded native-noise cache. Unknown columns always reject construction. */
+public final class TransitTerrain21 implements TransitPlanner21.Terrain {
+    public static final int MAX_COLUMNS = 12_000;
+    private final ExpansionIsland island;
+    private final NoiseBasedChunkGenerator generator;
+    private final RandomState random;
+    private final LevelHeightAccessor height;
+    private final Predicate<BlockPos> protection;
+    private final Map<Long, NoiseColumn> columns = new HashMap<>();
+
+    public TransitTerrain21(ExpansionIsland island, NoiseBasedChunkGenerator generator, RandomState random,
+            LevelHeightAccessor height, Predicate<BlockPos> protection) {
+        this.island = island; this.generator = generator; this.random = random;
+        this.height = height; this.protection = protection;
+    }
+    private NoiseColumn column(int x, int z) {
+        if (!owns(x, z)) return null;
+        long key = ((long) x << 32) ^ (z & 0xffffffffL);
+        var found = columns.get(key);
+        if (found != null) return found;
+        if (columns.size() >= MAX_COLUMNS) return null;
+        var result = generator.getBaseColumn(x, z, height, random);
+        columns.put(key, result);
+        return result;
+    }
+    @Override public boolean owns(int x, int z) { return island.contains(x, z); }
+    @Override public boolean solid(int x, int y, int z) {
+        if (y < 0 || y >= 384) return false;
+        var column = column(x, z);
+        return column != null && column.getBlock(y).isSolid() && column.getBlock(y).getFluidState().isEmpty();
+    }
+    @Override public boolean protectedAt(int x, int y, int z) {
+        if (y < 0 || y >= 384) return true;
+        var column = column(x, z);
+        return column == null || !column.getBlock(y).getFluidState().isEmpty()
+            || protection.test(new BlockPos(x, y, z));
+    }
+    @Override public int surfaceY(int x, int z) {
+        var column = column(x, z);
+        if (column == null) return -1;
+        for (int y = 380; y >= 1; y--) {
+            var state = column.getBlock(y);
+            if (!state.isAir()) return state.isSolid() && state.getFluidState().isEmpty() ? y : -1;
+        }
+        return -1;
+    }
+    @Override public String obstruction(int x, int y, int z) {
+        var sample = column(x, z);
+        if (sample == null) return "unknown/unowned column";
+        var state = sample.getBlock(y);
+        if (!state.getFluidState().isEmpty()) return "native fluid " + state;
+        return protection.test(new BlockPos(x, y, z)) ? "earlier structure/hydrology mask" : "none";
+    }
+    public int columnsUsed() { return columns.size(); }
+}

mods/sanctuary/src/main/resources/assets/sanctuary/lang/en_us.json

@@ -144,7 +144,8 @@
   "sanctuary.heritage.kind.photo_club": "Photography club",
   "sanctuary.heritage.kind.impossible_service": "Changing rooms and strange service rooms",
   "sanctuary.heritage.kind.construction_refuge": "Construction refuge",
-  "sanctuary.heritage.unavailable": "This survey requires a Sanctuary alpha.19 or alpha.20 world with experimental structures enabled.",
+  "sanctuary.heritage.unavailable": "This survey requires a recent Sanctuary world with experimental structures enabled.",
   "sanctuary.heritage.header": "Abandoned infrastructure: %s planned sites and %s links. Entrance coordinates:",
-  "sanctuary.heritage.entry": "%s : %s / %s / %s"
+  "sanctuary.heritage.entry": "%s : %s / %s / %s",
+  "sanctuary.transit.entry": "Industrial galleries — entrance: %s %s %s"
 }

mods/sanctuary/src/main/resources/assets/sanctuary/lang/fr_fr.json

@@ -144,7 +144,8 @@
   "sanctuary.heritage.kind.photo_club": "Club photo",
   "sanctuary.heritage.kind.impossible_service": "Vestiaires et salles étranges",
   "sanctuary.heritage.kind.construction_refuge": "Refuge de chantier",
-  "sanctuary.heritage.unavailable": "Ce relevé nécessite un monde Sanctuary alpha.19 ou alpha.20 avec les structures expérimentales activées.",
+  "sanctuary.heritage.unavailable": "Ce relevé nécessite un monde Sanctuary récent avec les structures expérimentales activées.",
   "sanctuary.heritage.header": "Anciennes infrastructures : %s lieux et %s liaisons prévus. Coordonnées des entrées :",
-  "sanctuary.heritage.entry": "%s : %s / %s / %s"
+  "sanctuary.heritage.entry": "%s : %s / %s / %s",
+  "sanctuary.transit.entry": "Galeries industrielles — entrée : %s %s %s"
 }

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/structure/industrial_transit.json

@@ -0,0 +1,7 @@
+{
+  "type": "sanctuary:industrial_transit_v21",
+  "biomes": "#sanctuary:has_structure/forgotten_networks",
+  "step": "underground_structures",
+  "terrain_adaptation": "none",
+  "spawn_overrides": {}
+}

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/world_preset/sanctuary.json

@@ -3,7 +3,7 @@
     "minecraft:overworld": {
       "type": "sanctuary:sanctuary_384",
       "generator": {
-        "type": "sanctuary:island_v20",
+        "type": "sanctuary:island_v21",
         "biome_source": {
           "biomes": [
             "minecraft:the_void",

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/world_preset/sanctuary_v20.json

@@ -0,0 +1,81 @@
+{
+  "dimensions": {
+    "minecraft:overworld": {
+      "type": "sanctuary:sanctuary_384",
+      "generator": {
+        "type": "sanctuary:island_v20",
+        "biome_source": {
+          "biomes": [
+            "minecraft:the_void",
+            "minecraft:forest",
+            "minecraft:birch_forest",
+            "minecraft:flower_forest",
+            "minecraft:plains",
+            "minecraft:meadow",
+            "minecraft:taiga",
+            "minecraft:snowy_taiga",
+            "minecraft:snowy_plains",
+            "minecraft:grove",
+            "minecraft:ice_spikes",
+            "minecraft:frozen_peaks",
+            "minecraft:old_growth_spruce_taiga",
+            "minecraft:dark_forest",
+            "minecraft:swamp",
+            "minecraft:pale_garden",
+            "minecraft:jungle",
+            "minecraft:sparse_jungle",
+            "minecraft:bamboo_jungle",
+            "minecraft:mangrove_swamp",
+            "minecraft:savanna",
+            "minecraft:savanna_plateau",
+            "minecraft:desert",
+            "minecraft:badlands",
+            "minecraft:eroded_badlands",
+            "minecraft:wooded_badlands",
+            "minecraft:windswept_hills",
+            "minecraft:windswept_gravelly_hills",
+            "minecraft:stony_peaks",
+            "minecraft:dappled_forest",
+            "minecraft:cherry_grove",
+            "minecraft:lush_caves",
+            "minecraft:dripstone_caves",
+            "minecraft:sulfur_caves",
+            "sanctuary:population_oak_forest",
+            "sanctuary:population_birch_forest",
+            "sanctuary:population_clearing",
+            "sanctuary:population_dry_woodland",
+            "sanctuary:population_rocky_heath",
+            "sanctuary:population_dark_grove",
+            "sanctuary:population_bamboo_grove",
+            "sanctuary:population_sulfur_depths",
+            "sanctuary:population_lush_caves",
+            "sanctuary:population_dripstone_caves",
+            "sanctuary:lost_city"
+          ]
+        },
+        "initial_diameter": 724
+      }
+    },
+    "minecraft:the_end": {
+      "type": "minecraft:the_end",
+      "generator": {
+        "type": "minecraft:noise",
+        "biome_source": {
+          "type": "minecraft:the_end"
+        },
+        "settings": "minecraft:end"
+      }
+    },
+    "minecraft:the_nether": {
+      "type": "minecraft:the_nether",
+      "generator": {
+        "type": "minecraft:noise",
+        "biome_source": {
+          "type": "minecraft:multi_noise",
+          "preset": "minecraft:nether"
+        },
+        "settings": "minecraft:nether"
+      }
+    }
+  }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/expansion/ExpansionJournalSmoke.java

@@ -72,6 +72,18 @@ public final class ExpansionJournalSmoke {
             require(Arrays.equals(unifiedMediumBytes, Files.readAllBytes(unifiedMediumDirectory.resolve(ExpansionJournal.FILE_NAME))),
                     "Rejected cross-generation read changed its journal");
 
+            for (int generation : List.of(20, 21)) {
+                var saved = scratch.resolve("architecture-cross-version-" + generation);
+                var root21 = ExpansionIsland.origin(724, SEED, generation);
+                var journal21 = new ExpansionJournal(saved, SEED, 724, generation);
+                var child = ExpansionPlacement.candidates(SEED, List.of(root21), "city21", "sanctuary", "east", "lost_city", 256, "natural", 0).getFirst();
+                journal21.commit(List.of(root21, child));
+                byte[] bytes = Files.readAllBytes(saved.resolve(ExpansionJournal.FILE_NAME));
+                require(new ExpansionJournal(saved, SEED, 724, generation).islands().equals(List.of(root21, child)), "Architecture journal round trip");
+                reject(() -> new ExpansionJournal(saved, SEED, 724, generation == 20 ? 21 : 20), "Cross-generation architecture journal");
+                require(Arrays.equals(bytes, Files.readAllBytes(saved.resolve(ExpansionJournal.FILE_NAME))), "Rejected upgrade altered saved journal");
+            }
+
             Path cityDirectory = scratch.resolve("city-generation");
             var cityRoot = ExpansionIsland.origin(724, SEED, 14);
             var city = new ExpansionJournal(cityDirectory, SEED, 724, 14,

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/city/LostCityInteriors21Smoke.java

@@ -0,0 +1,555 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Kind;
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Parcel;
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.EmptyBlockGetter;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.DoorBlock;
+import net.minecraft.world.level.block.Rotation;
+import net.minecraft.world.level.block.StairBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BedPart;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.block.state.properties.DoubleBlockHalf;
+import net.minecraft.world.level.storage.loot.LootTable;
+import net.minecraft.world.phys.AABB;
+
+/** Exercises final block geometry rather than reconstructing the painter's room allocation. */
+public final class LostCityInteriors21Smoke {
+    private static final Kind[] KINDS = {Kind.APARTMENT, Kind.HOTEL, Kind.LIBRARY,
+        Kind.RESTAURANT, Kind.BARRACKS, Kind.HALL};
+    private static final Direction[] HORIZONTAL = {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST};
+
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+        run();
+        System.out.println("LostCityInteriors21Smoke: six building uses, alternating physical floor plans, four rotations, connected rooms, fully enclosed bathrooms, wall-backed beds with lateral access, native door/seat geometry, supported lanterns, touching roof supports, oak/smooth-stone palette and deferred loot passed.");
+    }
+
+    /** Also usable after the engine has already bootstrapped its registries. */
+    public static void run() {
+        var failures = new java.util.ArrayList<String>();
+        Set<Map<BlockPos, BlockState>> distinct = new HashSet<>();
+        Set<Set<BlockPos>> distinctVolumes = new HashSet<>();
+        var previews = new java.util.ArrayList<Object>();
+        for (Kind kind : KINDS) for (int floors : new int[]{2, 3, 5}) for (long seed : new long[]{0, 43}) {
+            try {
+                Capture canonical = render(parcel(kind, floors, seed, 0));
+                if (floors == 2 && seed == 0) {
+                    distinct.add(canonical.blocks);
+                    Set<BlockPos> volume = new HashSet<>();
+                    canonical.blocks.forEach((at, state) -> { if (!state.isAir() && at.getY() > 0
+                        && (at.getY() > 10 || at.getX() == 0 || at.getX() == 16 || at.getZ() == 0 || at.getZ() == 16)) volume.add(at); });
+                    require(distinctVolumes.add(volume), kind + " only recolors an existing facade/roof volume");
+                }
+                if (floors == 3 && seed == 43 && System.getProperty("sanctuary.city21.preview") != null) {
+                    var blocks = new java.util.ArrayList<Object>();
+                    canonical.blocks.forEach((at, state) -> { if (!state.isAir()) blocks.add(java.util.List.of(at.getX(), at.getY(), at.getZ(), state.toString())); });
+                    previews.add(Map.of("kind", kind.name(), "seed", seed, "floors", floors, "facing", 0, "blocks", blocks));
+                }
+                for (int facing = 0; facing < 4; facing++) {
+                    Parcel parcel = parcel(kind, floors, seed, facing);
+                    Capture result = facing == 0 ? canonical : render(parcel);
+                    Capture repeated = render(parcel);
+                    require(result.blocks.equals(repeated.blocks) && result.loot.equals(repeated.loot), "Saved parcel is not deterministic");
+                    rotationMatches(canonical, result, facing);
+                    require(result.blocks.values().stream().anyMatch(state -> state.is(Blocks.STONE_BRICKS)), "Missing stone-brick foundations");
+                    require(result.blocks.values().stream().anyMatch(state -> state.is(Blocks.SMOOTH_STONE)), "Missing smooth stone");
+                    require(result.blocks.values().stream().noneMatch(state -> state.is(Blocks.SPAWNER)
+                        || !state.getFluidState().isEmpty()), "Building introduced a spawner or free flowing fluid");
+                    require(result.loot.size() == 1, "Building must keep one deferred loot chest");
+                    var entrance = LostCityInteriors21.rooms(parcel).getFirst();
+                    Set<BlockPos> reached = walk(result, position(entrance));
+                    for (var room : LostCityInteriors21.rooms(parcel)) require(reached.contains(position(room)),
+                        label(parcel) + " cannot walk from its entrance to " + room.name() + " at " + position(room));
+                    verifyDoors(result, reached);
+                    verifyBeds(result, reached);
+                    verifyBathrooms(result, reached);
+                    verifyFurnitureDirections(result);
+                    verifyLanternSupports(result);
+                    for (BlockPos chest : result.loot.keySet()) require(adjacentReached(chest, reached),
+                        label(parcel) + " loot cannot be approached");
+                    semantics(result);
+                    if (facing == 0) verifyStoreyVariation(result);
+                    verifyArchitecture(result);
+                }
+            } catch (AssertionError | RuntimeException failure) {
+                failures.add(kind + " floors=" + floors + " seed=" + seed + ": " + failure.getMessage());
+            }
+        }
+        require(failures.isEmpty(), "City21 interior fixture failures (" + failures.size() + "):\n" + String.join("\n", failures));
+        require(distinct.size() == KINDS.length, "Building uses only labels to vary an identical interior");
+        boolean rejected = false;
+        try { LostCityInteriors21.rooms(new Parcel(Kind.PARK, 0, 0, 17, 17, 160, 2, 0, 0, 4, new int[0])); }
+        catch (IllegalArgumentException expected) { rejected = true; }
+        require(rejected, "Interior dispatch must reject non-building parcels");
+        String preview = System.getProperty("sanctuary.city21.preview");
+        if (preview != null) try {
+            var file = java.nio.file.Path.of(preview); if (file.getParent() != null) java.nio.file.Files.createDirectories(file.getParent());
+            java.nio.file.Files.writeString(file, new com.google.gson.Gson().toJson(previews));
+        } catch (java.io.IOException e) { throw new AssertionError("Cannot write requested architecture preview", e); }
+    }
+
+    private static Parcel parcel(Kind kind, int floors, long seed, int facing) {
+        return new Parcel(kind, -81, 119, 17, 17, 160, floors, facing, seed, 4, new int[0]);
+    }
+    private static Capture render(Parcel parcel) {
+        var result = new Capture(parcel);
+        LostCityInteriors21.render(parcel, result);
+        return result;
+    }
+    private static String label(Parcel p) { return p.kind() + " floors=" + p.floors() + " facing=" + p.facing() + " seed=" + p.seed(); }
+    private static BlockPos position(LostCityInteriors21.Room room) { return new BlockPos(room.x(), room.y(), room.z()); }
+
+    private static void rotationMatches(Capture canonical, Capture rotated, int facing) {
+        require(canonical.blocks.size() == rotated.blocks.size(), "Rotation changed the number of emitted positions");
+        Rotation rotation = switch (facing) {
+            case 0 -> Rotation.NONE; case 1 -> Rotation.CLOCKWISE_90;
+            case 2 -> Rotation.CLOCKWISE_180; default -> Rotation.COUNTERCLOCKWISE_90;
+        };
+        for (var entry : canonical.blocks.entrySet()) {
+            BlockPos target = rotate(entry.getKey(), facing);
+            // Native chest placement owns its final facing, so its loot position is checked separately.
+            if (canonical.loot.containsKey(entry.getKey())) continue;
+            require(rotated.block(target).equals(entry.getValue().rotate(rotation)), "Geometry or block-state rotation drifted at " + target);
+        }
+        for (var entry : canonical.loot.entrySet()) require(entry.getValue().equals(rotated.loot.get(rotate(entry.getKey(), facing))),
+            "Rotation changed deferred loot identity or position");
+    }
+
+    private static void verifyDoors(Capture result, Set<BlockPos> reached) {
+        long lowerDoors = 0, pairedLeaves = 0;
+        for (var entry : result.blocks.entrySet()) {
+            BlockState state = entry.getValue();
+            if (!(state.getBlock() instanceof DoorBlock)) continue;
+            require(state.is(Blocks.OAK_DOOR) && !state.getValue(BlockStateProperties.POWERED), "A room door cannot be opened by an ordinary player");
+            boolean lower = state.getValue(BlockStateProperties.DOUBLE_BLOCK_HALF) == DoubleBlockHalf.LOWER;
+            BlockPos partner = lower ? entry.getKey().above() : entry.getKey().below();
+            BlockState expected = state.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF,
+                lower ? DoubleBlockHalf.UPPER : DoubleBlockHalf.LOWER);
+            require(result.block(partner).equals(expected), label(result.parcel) + " has an incomplete/mismatched door at " + entry.getKey());
+            if (!lower) continue;
+            lowerDoors++;
+            require(result.block(entry.getKey().below()).isSolid(), "Door has no solid threshold");
+            Direction normal = state.getValue(BlockStateProperties.HORIZONTAL_FACING);
+            require(reached.contains(entry.getKey().relative(normal)) && reached.contains(entry.getKey().relative(normal.getOpposite())),
+                label(result.parcel) + " door does not connect two walkable sides at " + entry.getKey());
+            for (Direction side : new Direction[]{normal.getClockWise(), normal.getCounterClockWise()}) {
+                BlockState neighbor = result.block(entry.getKey().relative(side));
+                if (!neighbor.is(Blocks.OAK_DOOR)
+                        || neighbor.getValue(BlockStateProperties.DOUBLE_BLOCK_HALF) != DoubleBlockHalf.LOWER
+                        || neighbor.getValue(BlockStateProperties.HORIZONTAL_FACING) != normal) continue;
+                AABB opened = state.setValue(BlockStateProperties.OPEN, true)
+                    .getCollisionShape(EmptyBlockGetter.INSTANCE, entry.getKey()).bounds();
+                require(againstOppositeEdge(opened, side), label(result.parcel) + " double door opens into its partner at " + entry.getKey());
+                pairedLeaves++;
+            }
+        }
+        require(lowerDoors >= result.parcel.floors() * 3L + 2, "Missing actual doors between distinct rooms");
+        require(pairedLeaves >= 2, "Entrance must retain a double door with its hinges against the outside jambs");
+        for (var room : LostCityInteriors21.rooms(result.parcel)) if (room.name().endsWith("/stair_landing")) {
+            BlockPos landing = position(room);
+            boolean opensIntoStairwell = false;
+            for (Direction side : HORIZONTAL) {
+                BlockPos at = landing.relative(side);
+                BlockState state = result.block(at);
+                if (state.is(Blocks.OAK_DOOR)) opensIntoStairwell |=
+                    at.relative(state.getValue(BlockStateProperties.HORIZONTAL_FACING)).equals(landing);
+            }
+            require(opensIntoStairwell, "Stairwell door must open into its landing, away from the central corridor");
+        }
+    }
+
+    private static boolean againstOppositeEdge(AABB box, Direction towardPartner) {
+        return switch (towardPartner) {
+            case EAST -> box.maxX <= .25; case WEST -> box.minX >= .75;
+            case SOUTH -> box.maxZ <= .25; case NORTH -> box.minZ >= .75;
+            default -> throw new AssertionError("Door partner must be horizontal");
+        };
+    }
+
+    private static void verifyFurnitureDirections(Capture result) {
+        int tableSeats = 0;
+        for (var entry : result.blocks.entrySet()) {
+            if (!entry.getValue().is(Blocks.OAK_FENCE)
+                    || !result.block(entry.getKey().above()).is(Blocks.OAK_PRESSURE_PLATE)) continue;
+            int aroundThisTable = 0;
+            for (Direction side : HORIZONTAL) {
+                BlockPos chair = entry.getKey().relative(side);
+                if (!result.block(chair).is(Blocks.OAK_STAIRS)) continue;
+                seatLooksToward(result, chair, side.getOpposite());
+                aroundThisTable++; tableSeats++;
+            }
+            require(aroundThisTable > 0, "A desk/table lost every chair facing its surface");
+        }
+        if (result.parcel.kind() != Kind.BARRACKS)
+            require(tableSeats >= result.parcel.floors(), "Every furnished storey needs a usable table or desk seat");
+        if (result.parcel.kind() == Kind.HALL) for (int x : new int[]{3, 4, 5, 11, 12, 13})
+            seatLooksToward(result, rotate(new BlockPos(x, 1, 11), result.parcel.facing()), rotated(Direction.SOUTH, result.parcel.facing()));
+        if (result.parcel.kind() == Kind.HOTEL) for (int x = 2; x <= 4; x++)
+            seatLooksToward(result, rotate(new BlockPos(x, 1, 14), result.parcel.facing()), rotated(Direction.NORTH, result.parcel.facing()));
+        if (result.parcel.kind() == Kind.BARRACKS) for (int floor = 0; floor < result.parcel.floors(); floor++)
+            if (LostCityInteriors21.layout(result.parcel, floor) == 0)
+                seatLooksToward(result, rotate(new BlockPos(13, floor * 5 + 1, 6), result.parcel.facing()), rotated(Direction.NORTH, result.parcel.facing()));
+        for (var entry : result.blocks.entrySet()) if (entry.getValue().is(Blocks.POLISHED_ANDESITE_STAIRS)) {
+            Direction look = entry.getValue().getValue(BlockStateProperties.HORIZONTAL_FACING).getOpposite();
+            require(clear(result.block(entry.getKey().relative(look))), "Sanitary seat faces a wall instead of its cubicle");
+        }
+    }
+
+    private static void seatLooksToward(Capture result, BlockPos chair, Direction towardUse) {
+        BlockState state = result.block(chair);
+        require(state.is(Blocks.OAK_STAIRS), "Missing chair at " + chair);
+        var boxes = state.getCollisionShape(EmptyBlockGetter.INSTANCE, chair).toAabbs();
+        double frontX = .5 + towardUse.getStepX() * .25, frontZ = .5 + towardUse.getStepZ() * .25;
+        double backX = .5 - towardUse.getStepX() * .25, backZ = .5 - towardUse.getStepZ() * .25;
+        require(boxes.stream().noneMatch(box -> box.contains(frontX, .75, frontZ))
+            && boxes.stream().anyMatch(box -> box.contains(backX, .75, backZ)),
+            label(result.parcel) + " chair's native back faces its table/stage at " + chair);
+        require(result.block(chair.below()).isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, chair.below()),
+            "Chair does not rest on a complete floor");
+    }
+
+    private static Direction rotated(Direction direction, int facing) {
+        for (int turn = 0; turn < facing; turn++) direction = direction.getClockWise();
+        return direction;
+    }
+
+    private static void verifyLanternSupports(Capture result) {
+        int lanterns = 0;
+        for (var entry : result.blocks.entrySet()) if (entry.getValue().is(Blocks.LANTERN)) {
+            BlockPos support = entry.getValue().getValue(BlockStateProperties.HANGING) ? entry.getKey().above() : entry.getKey().below();
+            require(result.block(support).isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, support),
+                label(result.parcel) + " lantern floats against a slab or lacks a full support block at " + entry.getKey());
+            lanterns++;
+        }
+        require(lanterns == result.parcel.floors(), "A junction lost its supported lamp");
+    }
+
+    private static void verifyBeds(Capture result, Set<BlockPos> reached) {
+        for (var entry : result.blocks.entrySet()) {
+            BlockState state = entry.getValue();
+            if (!state.is(Blocks.BED.white())) continue;
+            Direction direction = state.getValue(BlockStateProperties.HORIZONTAL_FACING);
+            BedPart part = state.getValue(BlockStateProperties.BED_PART);
+            BlockPos partner = entry.getKey().relative(part == BedPart.FOOT ? direction : direction.getOpposite());
+            require(result.block(partner).equals(state.setValue(BlockStateProperties.BED_PART,
+                part == BedPart.FOOT ? BedPart.HEAD : BedPart.FOOT)), label(result.parcel) + " has a severed bed at " + entry.getKey());
+            require(result.block(entry.getKey().below()).isSolid(), "Bed does not sit on a floor");
+            require(adjacentReached(entry.getKey(), reached) || adjacentReached(partner, reached),
+                label(result.parcel) + " bed cannot be approached from its room");
+            if (part == BedPart.HEAD) {
+                var backing = entry.getKey().relative(direction);
+                for (int up = 0; up < 3; up++) require(result.block(backing.above(up))
+                    .isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, backing.above(up)),
+                    label(result.parcel) + " bed head is not against a complete wall at " + entry.getKey());
+            } else {
+                boolean lateral = false;
+                for (Direction side : new Direction[]{direction.getClockWise(), direction.getCounterClockWise()})
+                    lateral |= reached.contains(entry.getKey().relative(side)) && reached.contains(partner.relative(side));
+                require(lateral, label(result.parcel) + " bed lacks a reachable side along its full length at " + entry.getKey());
+            }
+        }
+    }
+
+    private static void verifyBathrooms(Capture result, Set<BlockPos> reached) {
+        for (var bath : LostCityInteriors21.bathrooms(result.parcel)) {
+            BlockPos door = new BlockPos(bath.doorX(), bath.doorY(), bath.doorZ());
+            require(result.block(door).is(Blocks.OAK_DOOR), "Enclosed bathroom lost its actual door: " + bath.name());
+            Direction intoRoom = result.block(door).getValue(BlockStateProperties.HORIZONTAL_FACING);
+            require(reached.contains(door.relative(intoRoom)), "Bathroom cannot be entered through its door: " + bath.name());
+            require(bath.minX() == 1 || bath.minZ() == 1 || bath.maxX() == 15 || bath.maxZ() == 15,
+                "Bathroom enclosure is detached from the exterior room wall");
+            for (int x = bath.minX(); x <= bath.maxX(); x++) for (int z = bath.minZ(); z <= bath.maxZ(); z++)
+                for (int y = bath.minY(); y <= bath.maxY(); y++) {
+                    boolean shell = x == bath.minX() || x == bath.maxX() || z == bath.minZ() || z == bath.maxZ()
+                        || y == bath.minY() || y == bath.maxY();
+                    if (!shell) continue;
+                    BlockPos at = new BlockPos(x, y, z);
+                    if (at.equals(door) || at.equals(door.above())) continue;
+                    require(result.block(at).isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, at),
+                        label(result.parcel) + " bathroom has an incomplete floor, ceiling or connected wall at " + at + " in " + bath.name());
+                }
+        }
+    }
+
+    private static void verifyStoreyVariation(Capture result) {
+        for (int floor = 1; floor < result.parcel.floors(); floor++) {
+            require(LostCityInteriors21.layout(result.parcel, floor - 1) != LostCityInteriors21.layout(result.parcel, floor),
+                "Adjacent storeys selected the same plan");
+            Set<BlockPos> before = rearPartitions(result, floor - 1), after = rearPartitions(result, floor);
+            require(!before.equals(after), label(result.parcel) + " only changed furniture or labels between storeys " + (floor - 1) + " and " + floor);
+            Map<BlockPos, BlockState> beforeFixtures = furnishings(result, floor - 1), afterFixtures = furnishings(result, floor);
+            require(!beforeFixtures.equals(afterFixtures), label(result.parcel)
+                + " copied the same furniture between storeys " + (floor - 1) + " and " + floor);
+        }
+    }
+
+    private static Set<BlockPos> rearPartitions(Capture result, int floor) {
+        Set<BlockPos> walls = new HashSet<>();
+        for (int x = 2; x <= 14; x++) for (int z = 9; z <= 14; z++) {
+            boolean continuous = true;
+            for (int y = 1; y <= 3; y++) continuous &= result.block(new BlockPos(x, floor * 5 + y, z)).is(Blocks.SMOOTH_STONE);
+            if (continuous) walls.add(new BlockPos(x, 0, z));
+        }
+        return walls;
+    }
+
+    private static Map<BlockPos, BlockState> furnishings(Capture result, int floor) {
+        Map<BlockPos, BlockState> objects = new HashMap<>();
+        for (int x = 2; x <= 14; x++) for (int z = 2; z <= 14; z++) for (int up = 1; up <= 3; up++) {
+            BlockState state = result.block(new BlockPos(x, floor * 5 + up, z));
+            if (state.is(Blocks.BED.white()) || state.is(Blocks.BARREL) || state.is(Blocks.FURNACE)
+                    || state.is(Blocks.BOOKSHELF) || state.is(Blocks.WATER_CAULDRON) || state.is(Blocks.OAK_FENCE)
+                    || state.is(Blocks.LECTERN) || state.is(Blocks.CRAFTING_TABLE) || state.is(Blocks.OAK_STAIRS)
+                    || state.is(Blocks.OAK_PLANKS) || state.is(Blocks.OAK_PLANKS) || state.is(Blocks.OAK_PLANKS)) objects.put(new BlockPos(x, up, z), state);
+        }
+        return objects;
+    }
+
+    private static void semantics(Capture result) {
+        Map<BlockState, Long> counts = new HashMap<>();
+        result.blocks.values().forEach(state -> counts.merge(state, 1L, Long::sum));
+        java.util.function.Predicate<net.minecraft.world.level.block.Block> has = block ->
+            counts.keySet().stream().anyMatch(state -> state.is(block));
+        switch (result.parcel.kind()) {
+            case APARTMENT -> require(has.test(Blocks.FURNACE) && has.test(Blocks.BED.white())
+                && has.test(Blocks.WATER_CAULDRON), "Apartment lacks cooking, sleeping or washing fixtures");
+            case HOTEL -> require(has.test(Blocks.LOOM) && has.test(Blocks.BED.white())
+                && has.test(Blocks.WATER_CAULDRON), "Hotel lacks guest rooms or laundry fixtures");
+            case LIBRARY -> require(result.blocks.values().stream().filter(state -> state.is(Blocks.BOOKSHELF)).count() >= result.parcel.floors() * 12L
+                && has.test(Blocks.LECTERN), "Library is missing usable stacks and reading fixtures");
+            case RESTAURANT -> require(has.test(Blocks.SMOKER) && has.test(Blocks.FURNACE)
+                && has.test(Blocks.CRAFTING_TABLE) && has.test(Blocks.WATER_CAULDRON), "Restaurant lacks kitchen and washroom services");
+            case BARRACKS -> require(has.test(Blocks.BED.white()) && has.test(Blocks.FLETCHING_TABLE)
+                && has.test(Blocks.GRINDSTONE), "Barracks lacks dormitory and equipment fixtures");
+            case HALL -> {
+                require(has.test(Blocks.LECTERN) && has.test(Blocks.IRON_BARS), "Hall lacks stage or gallery guards");
+                require(result.block(rotate(new BlockPos(8, 5, 12), result.parcel.facing())).isAir(), "Auditorium lost its double-height volume");
+            }
+            default -> throw new AssertionError("Unexpected building");
+        }
+    }
+
+    /** Player-sized path: two clear cells above support, one-block steps and manually openable doors. */
+    private static Set<BlockPos> walk(Capture result, BlockPos start) {
+        require(standable(result, start), label(result.parcel) + " has a blocked entrance");
+        Set<BlockPos> seen = new HashSet<>();
+        ArrayDeque<BlockPos> queue = new ArrayDeque<>();
+        seen.add(start); queue.add(start);
+        while (!queue.isEmpty()) {
+            BlockPos current = queue.removeFirst();
+            for (Direction direction : HORIZONTAL) for (int dy = -1; dy <= 1; dy++) {
+                BlockPos next = current.relative(direction).offset(0, dy, 0);
+                if (dy > 0 && !clearBody(result, current.above())) continue;
+                if (standable(result, next) && seen.add(next)) queue.addLast(next);
+            }
+        }
+        return seen;
+    }
+    private static boolean standable(Capture result, BlockPos pos) {
+        if (pos.getX() < 0 || pos.getX() > 16 || pos.getZ() < 0 || pos.getZ() > 16
+            || pos.getY() < 1 || pos.getY() > result.parcel.floors() * 5 + 4) return false;
+        if (!clearBody(result, pos)) return false;
+        var below = pos.below();
+        return opened(result.block(below)).getCollisionShape(EmptyBlockGetter.INSTANCE, below).toAabbs().stream()
+            .anyMatch(b -> b.maxY >= .5 && b.minX <= .5 && b.maxX >= .5 && b.minZ <= .5 && b.maxZ >= .5);
+    }
+    private static BlockState opened(BlockState state) {
+        return state.getBlock() instanceof net.minecraft.world.level.block.DoorBlock
+            || state.getBlock() instanceof net.minecraft.world.level.block.TrapDoorBlock
+            ? state.setValue(BlockStateProperties.OPEN, true) : state;
+    }
+    private static boolean clearBody(Capture result, BlockPos pos) {
+        var body = new AABB(pos.getX() + .2, pos.getY(), pos.getZ() + .2, pos.getX() + .8, pos.getY() + 1.8, pos.getZ() + .8);
+        for (var at : new BlockPos[]{pos, pos.above()}) {
+            var state = opened(result.block(at));
+            if (!state.getFluidState().isEmpty()) return false;
+            for (var shape : state.getCollisionShape(EmptyBlockGetter.INSTANCE, at).toAabbs())
+                if (shape.move(at.getX(), at.getY(), at.getZ()).intersects(body)) return false;
+        }
+        return true;
+    }
+    private static boolean clear(BlockState state) { return state.isAir() || state.is(Blocks.OAK_DOOR); }
+    private static void verifyArchitecture(Capture c) {
+        for (int x = 0; x <= 16; x++) for (int z = 0; z <= 16; z++)
+            require(c.block(new BlockPos(x, -1, z)).is(Blocks.STONE_BRICKS), "Foundation is not dressed stone brick");
+        long outsideVolume = c.blocks.entrySet().stream().filter(e -> e.getKey().getY() > 0
+            && (e.getKey().getX() == 0 || e.getKey().getX() == 16 || e.getKey().getZ() == 0 || e.getKey().getZ() == 16)
+            && !e.getValue().isAir()).count();
+        require(outsideVolume >= 40, label(c.parcel) + " has no cornice, bay, fins or entrance projection");
+        verifyPalette(c.blocks, true, label(c.parcel));
+        verifyGroundedGeometry(c.blocks, 0, label(c.parcel));
+        if (c.parcel.kind() == Kind.BARRACKS) for (int floor = 0; floor < c.parcel.floors(); floor++) {
+            var grinder = rotate(new BlockPos(12, floor * 5 + 1, 11), c.parcel.facing());
+            require(c.block(grinder).is(Blocks.GRINDSTONE)
+                    && c.block(grinder).getValue(BlockStateProperties.ATTACH_FACE)
+                        == net.minecraft.world.level.block.state.properties.AttachFace.FLOOR,
+                label(c.parcel) + " workshop grinder lacks its floor-mounted frame");
+        }
+        if (c.parcel.kind() == Kind.HOTEL) for (int x : new int[]{12, 14}) {
+            var counter = rotate(new BlockPos(x, 1, 14), c.parcel.facing());
+            require(c.block(counter).is(Blocks.BARREL)
+                    && c.block(counter.above()).is(Blocks.OAK_PLANKS)
+                    && c.block(counter.above(2)).is(Blocks.OAK_SLAB),
+                label(c.parcel) + " laundry shelf lacks its counter-mounted timber frame");
+        }
+        long smooth = 0, facingMaterial = 0;
+        for (int x = 1; x <= 15; x++) for (int z = 1; z <= 15; z++) {
+            if (x != 1 && x != 15 && z != 1 && z != 15) continue;
+            for (int y = 1; y < c.parcel.floors() * 5; y++) {
+                var at = rotate(new BlockPos(x, y, z), c.parcel.facing());
+                var state = c.block(at);
+                if (state.isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, at)) {
+                    facingMaterial++;
+                    if (state.is(Blocks.SMOOTH_STONE)) smooth++;
+                }
+            }
+        }
+        require(smooth * 2 >= facingMaterial, label(c.parcel) + " no longer has predominantly smooth-stone facades: " + smooth + "/" + facingMaterial);
+        if (c.parcel.kind() == Kind.APARTMENT || c.parcel.kind() == Kind.LIBRARY)
+            require(c.block(rotate(new BlockPos(1, 2, 1), c.parcel.facing())).isAir(), "Front corner was not physically cut back");
+        if (c.parcel.kind() == Kind.LIBRARY) {
+            int roof = c.parcel.floors() * 5;
+            for (int x = 11; x <= 12; x++) for (int z = 4; z <= 6; z++) {
+                for (int y = roof - 1; y <= roof; y++)
+                    require(c.block(rotate(new BlockPos(x, y, z), c.parcel.facing())).isAir(),
+                        label(c.parcel) + " skylight is blocked by the roof plate or last-storey ceiling");
+                require(c.block(rotate(new BlockPos(x, roof + 1, z), c.parcel.facing())).isAir(),
+                    label(c.parcel) + " skylight contains a redundant glazed floor under its cap");
+                require(c.block(rotate(new BlockPos(x, roof + 2, z), c.parcel.facing())).is(Blocks.GLASS),
+                        label(c.parcel) + " skylight lost its continuous transparent cap");
+                for (int y = roof + 3; y <= roof + 4; y++)
+                    require(c.block(rotate(new BlockPos(x, y, z), c.parcel.facing())).isAir(),
+                        label(c.parcel) + " another roof feature shades the light well");
+            }
+            for (int x = 10; x <= 13; x++) for (int z = 3; z <= 7; z++) {
+                if (x > 10 && x < 13 && z > 3 && z < 7) continue;
+                var base = rotate(new BlockPos(x, roof, z), c.parcel.facing());
+                require(c.block(base).isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, base)
+                        && c.block(base.above()).is(Blocks.STRIPPED_OAK_LOG),
+                    label(c.parcel) + " skylight cut through its supporting perimeter or timber frame");
+            }
+        }
+        if (c.parcel.kind() == Kind.HOTEL || c.parcel.kind() == Kind.BARRACKS) {
+            int roof = c.parcel.floors() * 5;
+            int x = c.parcel.kind() == Kind.HOTEL ? 9 : 1;
+            int z = c.parcel.kind() == Kind.HOTEL ? 3 : 2;
+            var top = rotate(new BlockPos(x, roof + 4, z), c.parcel.facing());
+            require(c.block(top).is(Blocks.STONE_BRICK_SLAB)
+                    && c.block(top).getValue(BlockStateProperties.SLAB_TYPE)
+                        == net.minecraft.world.level.block.state.properties.SlabType.BOTTOM,
+                label(c.parcel) + " pavilion roof floats half a block above its walls");
+            require(c.block(top.below()).isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, top.below()),
+                label(c.parcel) + " pavilion lost the wall carrying its roof");
+        }
+        // Resolve every glazing edge from final neighbors, not precomputed straight strips.
+        for (var e : c.blocks.entrySet()) if (e.getValue().is(Blocks.GLASS_PANE)) {
+            for (Direction d : HORIZONTAL) {
+                var neighbor = c.block(e.getKey().relative(d));
+                if (!neighbor.isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, e.getKey().relative(d))) continue;
+                var property = switch(d) { case NORTH -> BlockStateProperties.NORTH; case EAST -> BlockStateProperties.EAST;
+                    case SOUTH -> BlockStateProperties.SOUTH; case WEST -> BlockStateProperties.WEST; default -> throw new AssertionError(); };
+                require(e.getValue().getValue(property), "Window does not meet its actual stone or timber jamb");
+            }
+        }
+    }
+    /** The construction palette is explicit; functional fixtures and planting retain vanilla materials. */
+    public static void verifyPalette(Map<BlockPos, BlockState> blocks, boolean building, String label) {
+        for (var e : blocks.entrySet()) {
+            String name = e.getValue().toString();
+            require(!name.matches(".*(?:birch|dark_oak|spruce|jungle|acacia|mangrove|cherry|pale_oak|bamboo)_.*"),
+                label + " introduced a second timber palette at " + e.getKey() + ": " + name);
+            require(!name.contains("granite") && !name.contains("diorite"),
+                label + " introduced contrasting granite/diorite at " + e.getKey());
+            require(!name.contains("tuff") || !building && e.getKey().getY() <= 0,
+                label + " used tuff above the ground/subsoil at " + e.getKey());
+        }
+    }
+
+    /** Contact uses native collision volumes: merely neighboring slabs can still leave a real gap.
+     * Every solid fixture, roof and facade must join the foundation through touching material. */
+    public static void verifyGroundedGeometry(Map<BlockPos, BlockState> blocks, int groundY, String label) {
+        Map<BlockState, java.util.List<AABB>> shapes = new HashMap<>();
+        Map<BlockPos, java.util.List<AABB>> geometry = new HashMap<>();
+        for (var entry : blocks.entrySet()) {
+            // A lantern's collision omits its thin hanging chain. Its explicit native support
+            // is checked below instead of pretending that invisible collision gap is floating masonry.
+            if (entry.getValue().is(Blocks.LANTERN)) continue;
+            var shape = shapes.computeIfAbsent(entry.getValue(), state ->
+                state.getCollisionShape(EmptyBlockGetter.INSTANCE, BlockPos.ZERO).toAabbs());
+            if (!shape.isEmpty()) geometry.put(entry.getKey(), shape);
+        }
+        Set<BlockPos> supported = new HashSet<>();
+        ArrayDeque<BlockPos> queue = new ArrayDeque<>();
+        for (BlockPos at : geometry.keySet()) if (at.getY() <= groundY) {
+            supported.add(at); queue.add(at);
+        }
+        while (!queue.isEmpty()) {
+            var at = queue.removeFirst();
+            for (Direction direction : Direction.values()) {
+                var next = at.relative(direction);
+                if (supported.contains(next) || !geometry.containsKey(next)) continue;
+                boolean touches = false;
+                for (AABB a : geometry.get(at)) for (AABB b : geometry.get(next)) {
+                    double dx = Math.min(a.maxX, b.maxX + direction.getStepX()) - Math.max(a.minX, b.minX + direction.getStepX());
+                    double dy = Math.min(a.maxY, b.maxY + direction.getStepY()) - Math.max(a.minY, b.minY + direction.getStepY());
+                    double dz = Math.min(a.maxZ, b.maxZ + direction.getStepZ()) - Math.max(a.minZ, b.minZ + direction.getStepZ());
+                    if (dx >= -1e-7 && dy >= -1e-7 && dz >= -1e-7
+                            && (dx > 1e-7 && dy > 1e-7 || dx > 1e-7 && dz > 1e-7 || dy > 1e-7 && dz > 1e-7)) touches = true;
+                }
+                if (touches) { supported.add(next); queue.addLast(next); }
+            }
+        }
+        for (var at : geometry.keySet()) require(supported.contains(at),
+            label + " has a floating structural/fixture island at " + at + ": " + blocks.get(at));
+        for (var entry : blocks.entrySet()) if (entry.getValue().is(Blocks.LANTERN)) {
+            var anchor = entry.getValue().getValue(BlockStateProperties.HANGING) ? entry.getKey().above() : entry.getKey().below();
+            var state = blocks.getOrDefault(anchor, Blocks.AIR.defaultBlockState());
+            require(state.isCollisionShapeFullBlock(EmptyBlockGetter.INSTANCE, anchor) && supported.contains(anchor),
+                label + " lamp lacks a full, grounded native support at " + entry.getKey());
+        }
+    }
+
+    private static boolean adjacentReached(BlockPos pos, Set<BlockPos> reached) {
+        for (Direction direction : HORIZONTAL) if (reached.contains(pos.relative(direction))) return true;
+        return false;
+    }
+    private static BlockPos rotate(BlockPos pos, int facing) {
+        return switch (facing) {
+            case 0 -> pos; case 1 -> new BlockPos(16 - pos.getZ(), pos.getY(), pos.getX());
+            case 2 -> new BlockPos(16 - pos.getX(), pos.getY(), 16 - pos.getZ());
+            default -> new BlockPos(pos.getZ(), pos.getY(), 16 - pos.getX());
+        };
+    }
+
+    private record Loot(ResourceKey<LootTable> table, long seed) {}
+    private static final class Capture implements LostCityRenderer.BlockWriter {
+        final Parcel parcel;
+        final Map<BlockPos, BlockState> blocks = new HashMap<>();
+        final Map<BlockPos, Loot> loot = new HashMap<>();
+        Capture(Parcel parcel) { this.parcel = parcel; }
+        @Override public void set(int x, int y, int z, BlockState state) {
+            require(x >= 0 && x < 17 && z >= 0 && z < 17 && y >= parcel.minY() - parcel.floorY()
+                && y <= parcel.maxY() - parcel.floorY(), label(parcel) + " writes outside its saved bounds at " + x + "," + y + "," + z);
+            blocks.put(new BlockPos(x, y, z), state);
+        }
+        @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+            set(x, y, z, Blocks.CHEST.defaultBlockState());
+            loot.put(new BlockPos(x, y, z), new Loot(table, seed));
+        }
+        BlockState block(BlockPos pos) { return blocks.getOrDefault(pos, Blocks.AIR.defaultBlockState()); }
+    }
+    private static void require(boolean condition, String message) { if (!condition) throw new AssertionError(message); }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/city/LostCityPlanner21Smoke.java

@@ -0,0 +1,92 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.function.IntBinaryOperator;
+
+/** Natural extensions publish only with a supported player route; the old core/fallback is retained verbatim. */
+public final class LostCityPlanner21Smoke {
+    public static void main(String[] args) {
+        int extras = 0;
+        for (int size : new int[]{512, 724, 1024}) for (long seed : new long[]{0, 42}) {
+            var terrain = new Terrain((x, z) -> 220);
+            var result = LostCityPlanner21.plan(seed, 0, 0, size, true, terrain); verify(result, terrain);
+            require(!result.core().surface().isEmpty(), "New solver lost the old starter core");
+            require(result.surface().districts().size() == 1 + result.connections().size(), "An isolated district was published");
+            extras += result.connections().size();
+            var repeat = LostCityPlanner21.plan(seed, 0, 0, size, true, new Terrain((x, z) -> 220));
+            require(signature(result).equals(signature(repeat)), "Extension depends on invocation order");
+        }
+        require(extras >= 6, "Flat fixtures do not demonstrate modest connected neighborhoods: " + extras);
+        var baseline = LostCityPlanner21.plan(0, 0, 0, 724, true, new Terrain((x, z) -> 220));
+        var core = baseline.core().surface().districts().getFirst();
+        Terrain cutoff = new Terrain((x, z) -> 220);
+        cutoff.blocked = (x, y, z) -> x < core.minX() - 2 || x > core.maxX() + 2 || z < core.minZ() - 2 || z > core.maxZ() + 2;
+        var stopped = LostCityPlanner21.plan(0, 0, 0, 724, true, cutoff); verify(stopped, cutoff);
+        require(stopped.connections().isEmpty(), "Protected outskirts acquired fictional connecting roads");
+        int northSouthGrades = 0;
+        for (int sign : new int[]{-1, 1}) for (long seed : new long[]{0, 42}) {
+            Terrain slope = new Terrain((x, z) -> 220 + sign * Math.floorDiv(z, 15));
+            northSouthGrades += verify(LostCityPlanner21.plan(seed, 0, 0, 724, true, slope), slope);
+        }
+        require(northSouthGrades > 0, "Slope witnesses never exercise a real north/south stair inside a connecting road");
+        Terrain empty = new Terrain((x, z) -> 0);
+        var fallback = LostCityPlanner21.plan(0, 0, 0, 512, true, empty);
+        require(fallback.connections().isEmpty() && fallback.reservation() != null && fallback.reservation().width() == 49,
+            "Void expanded the architectural fallback into a larger platform");
+        var continent = LostCityPlanner21.plan(0, 0, 0, 256, false, new Terrain((x, z) -> 220));
+        require(continent.connections().isEmpty() && continent.surface() != null, "Root extension policy leaked onto a continent");
+        System.out.println("LostCityPlanner21Smoke: preserved core, modest connected neighborhoods, bounded routes, terrain gaps, native bounds and no enlarged fallback passed.");
+    }
+    private static int verify(LostCityPlanner21.Result result, Terrain terrain) {
+        int northSouthGrades = 0;
+        require(result.columns() <= LostCityPlanner21.MAX_COLUMNS && result.volumeChecks() <= LostCityPlanner21.MAX_VOLUME_CHECKS, "Budget exceeded");
+        require(result.surface().districts().size() <= 3, "Town sprawls into more than three blocks");
+        if (!result.core().surface().isEmpty()) require(result.surface().districts().getFirst() == result.core().surface().districts().getFirst(), "Core was rewritten");
+        var columns = new HashMap<Long, Integer>(); var kinds = new HashMap<Long, LostCityPlan.Kind>();
+        var owners = new HashMap<Long, LostCityPlan.Parcel>();
+        for (var district : result.surface().districts()) for (var p : district.parcels()) {
+            require(p.width() <= 25 && p.depth() <= 25, "Road escaped parcel limits");
+            for (int z = p.minZ(); z <= p.maxZ(); z++) for (int x = p.minX(); x <= p.maxX(); x++) {
+                long key = key(x, z); Integer old = columns.putIfAbsent(key, p.surfaceY(x - p.minX(), z - p.minZ()));
+                require(old == null, "A road and cluster paint the same column twice"); kinds.put(key, p.kind()); owners.put(key, p);
+            }
+        }
+        for (var link : result.connections()) {
+            require(link.districtIndex() > 0 && link.districtIndex() < result.surface().districts().size(), "Connection points to an absent district");
+            require(link.path().size() >= 14 && link.path().size() <= 192, "Route lacks the intended natural gap or exceeds reach");
+            for (int i = 0; i < link.path().size(); i++) {
+                var p = link.path().get(i); var key = key(p.x(), p.z());
+                require(columns.get(key) != null && columns.get(key) == p.floorY() && kinds.get(key) == LostCityPlan.Kind.STREET, "Connection centerline has no rendered floor");
+                require(!terrain.blocked.test(p.x(), p.floorY(), p.z()), "Connection crosses protected terrain");
+                if (i > 0) {
+                    var a = link.path().get(i - 1);
+                    require(Math.abs(p.x() - a.x()) + Math.abs(p.z() - a.z()) == 1 && Math.abs(p.floorY() - a.floorY()) <= 1, "Player route is discontinuous");
+                    if (p.floorY() != a.floorY()) {
+                        require(owners.get(key) == owners.get(key(a.x(), a.z())),
+                            "A road grade crosses a parcel boundary, so the native renderer cannot build its connecting stair");
+                        if (p.z() != a.z()) northSouthGrades++;
+                    }
+                }
+            }
+        }
+        return northSouthGrades;
+    }
+    private static String signature(LostCityPlanner21.Result r) {
+        var result = new StringBuilder().append(r.connections()).append(r.columns()).append(r.volumeChecks()).append(r.diagnostics());
+        for (var d : r.surface().districts()) for (var p : d.parcels()) result.append(p.kind()).append(p.minX()).append(p.minZ()).append(p.floorY()).append(java.util.Arrays.toString(p.surfaceHeights()));
+        return result.toString();
+    }
+    private interface Protection { boolean test(int x, int y, int z); }
+    private static final class Terrain implements LostCityPlanner16.Terrain {
+        final IntBinaryOperator height; Protection blocked = (x, y, z) -> false;
+        Terrain(IntBinaryOperator height) { this.height = height; }
+        public boolean owns(int x, int z) { return Math.abs(x) < 600 && Math.abs(z) < 600; }
+        public LostCityPlanner.Ground ground(int x, int z) { int h = height.applyAsInt(x, z); return new LostCityPlanner.Ground(h, h > 0 ? 24 : 0, h > 0, blocked.test(x, h, z)); }
+        public boolean solid(int x, int y, int z) { return y > 0 && y <= height.applyAsInt(x, z); }
+        public boolean protectedAt(int x, int y, int z) { return blocked.test(x, y, z); }
+    }
+    private static long key(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+    private static void require(boolean value, String message) { if (!value) throw new AssertionError(message); }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/city/LostCitySurface21Smoke.java

@@ -0,0 +1,286 @@
+package fr.koka.sanctuary.worldgen.city;
+
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Kind;
+import fr.koka.sanctuary.worldgen.city.LostCityPlan.Parcel;
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.StairBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BedPart;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.storage.loot.LootTable;
+
+/** Real block-state geometry, without creating a world: clipping, rotations and walkable floors. */
+public final class LostCitySurface21Smoke {
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+        run();
+        System.out.println("LostCitySurface21Smoke: all exterior amenities, supported lamps, basements, contained pools, excavation access, carved park variants, grounded canopies, restrained oak palette and suspended tuff roads passed.");
+    }
+
+    /** Also callable from an already bootstrapped native GameTest. */
+    public static void run() {
+        var failures = new java.util.ArrayList<String>();
+        for (Kind kind : Kind.values()) {
+            if (kind.building()) continue;
+            for (int facing = 0; facing < 4; facing++) {
+                for (long seed : new long[] {0, 42, -61872}) {
+                    try {
+                        int floors = kind == Kind.HALL ? 2 : 3;
+                        int foundation = kind == Kind.POOL || kind == Kind.EXCAVATION ? 8 : 4;
+                        Parcel parcel = new Parcel(kind, 0, 0, 17, 17, 170, floors, facing, seed, foundation, new int[0]);
+                        Capture result = render(parcel);
+                        require(result.blocks.equals(render(parcel).blocks), "Renderer changed for identical saved parcel");
+                        require(result.blocks.values().stream().noneMatch(state -> state.is(Blocks.SPAWNER)), "City introduced a spawner");
+                        if (kind != Kind.STREET && kind != Kind.BRIDGE) {
+                            LostCityInteriors21Smoke.verifyPalette(result.blocks, false, kind + " facing=" + facing);
+                            LostCityInteriors21Smoke.verifyGroundedGeometry(result.blocks,
+                                kind == Kind.EXCAVATION && foundation >= 8 ? -5 : kind == Kind.POOL && foundation >= 8 ? -4 : 0,
+                                kind + " facing=" + facing + " seed=" + seed);
+                        }
+                        if (kind.building()) {
+                            require(result.blocks.values().stream().anyMatch(state -> state.is(Blocks.STONE_BRICKS)), "Missing explicit stone palette");
+                            require(result.blocks.values().stream().anyMatch(state -> state.is(Blocks.SMOOTH_STONE)), "Missing smooth stone palette");
+                            Set<BlockPos> reached = walk(result, rotate(8, 1, 0, facing));
+                            for (int floor = 1; floor <= floors; floor++) {
+                                int elevation = floor * 5 + 1;
+                                require(reached.stream().anyMatch(pos -> pos.getY() == elevation),
+                                    kind + " facing " + facing + " cannot reach floor/roof " + floor);
+                            }
+                            require(result.loot.size() == 1, kind + " must keep exactly one deferred, limited loot chest");
+                        }
+                        for (var entry : result.blocks.entrySet()) {
+                            if (entry.getValue().is(Blocks.LANTERN)) {
+                                var support = entry.getValue().getValue(BlockStateProperties.HANGING) ? entry.getKey().above() : entry.getKey().below();
+                                require(result.block(support).isCollisionShapeFullBlock(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, support), kind + " lantern lacks full support at " + entry.getKey());
+                            }
+                            BlockState state = entry.getValue();
+                            if (state.is(Blocks.BED.white()) && state.getValue(BlockStateProperties.BED_PART) == BedPart.FOOT) {
+                                Direction direction = state.getValue(BlockStateProperties.HORIZONTAL_FACING);
+                                BlockState head = result.block(entry.getKey().relative(direction));
+                                require(head.is(Blocks.BED.white()) && head.getValue(BlockStateProperties.BED_PART) == BedPart.HEAD,
+                                    "Rotated bedroom has an incomplete bed");
+                            }
+                        }
+                    } catch (AssertionError | RuntimeException failure) {
+                        failures.add(kind + " facing=" + facing + " seed=" + seed + ": " + failure.getMessage());
+                    }
+                }
+            }
+        }
+        for (int facing = 0; facing < 4; facing++) {
+            try {
+                Parcel garage = new Parcel(Kind.PARKING, 0, 0, 17, 17, 170, 1, facing, 9, 8, new int[0]);
+                Capture result = render(garage);
+                Set<BlockPos> reached = walk(result, rotate(8, 1, 0, facing));
+                require(reached.contains(rotate(8, -4, 10, facing)), "Underground garage is not reachable from its street ramp");
+                require(result.block(rotate(8, -6, 10, facing)).is(Blocks.STONE_BRICKS), "Garage excavation removed the certified rock below its floor");
+                for (int z = 0; z <= 4; z++) for (int x = 6; x <= 10; x++) for (int y = -5; y < -z; y++) {
+                    var below = rotate(x, y, z, facing);
+                    require(result.block(below).isCollisionShapeFullBlock(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, below),
+                        "Garage ramp is suspended above its floor instead of resting on its masonry wedge");
+                }
+                LostCityInteriors21Smoke.verifyGroundedGeometry(result.blocks, -5, "Underground garage facing=" + facing);
+                var threshold = rotate(8, 0, 0, facing);
+                require(result.block(threshold).isCollisionShapeFullBlock(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, threshold)
+                        && result.block(threshold.above()).isAir() && result.block(threshold.above(2)).isAir(),
+                    "Garage entry lost its level, clear ramp threshold");
+            } catch (AssertionError | RuntimeException failure) {
+                failures.add("Underground garage facing=" + facing + ": " + failure.getMessage());
+            }
+            try {
+                Parcel pit = new Parcel(Kind.EXCAVATION, 0, 0, 17, 17, 170, 0, facing, 9, 8, new int[0]);
+                Capture excavation = render(pit);
+                require(walk(excavation, rotate(8, 1, 0, facing)).contains(rotate(8, -4, 10, facing)),
+                    "Excavation has no walkable stairs from the street");
+                require(excavation.block(rotate(8, -6, 10, facing)).is(Blocks.STONE_BRICKS), "Excavation removed its certified bottom support");
+                LostCityInteriors21Smoke.verifyGroundedGeometry(excavation.blocks, -5, "Excavation frame facing=" + facing);
+                for (int x : new int[]{3, 13}) for (int z : new int[]{10, 13}) {
+                    for (int y = -4; y <= 3; y++) require(!excavation.block(rotate(x, y, z, facing)).isAir(),
+                        "Excavation roof lacks an unbroken post to its real floor at " + x + "," + y + "," + z);
+                    require(excavation.block(rotate(x, 4, z, facing)).is(Blocks.OAK_SLAB)
+                            || excavation.block(rotate(x, 4, z, facing)).is(Blocks.OAK_PLANKS),
+                        "Excavation's only canopy is detached from its post");
+                }
+            } catch (AssertionError | RuntimeException failure) {
+                failures.add("Excavation facing=" + facing + ": " + failure.getMessage());
+            }
+            try {
+                Parcel pool = new Parcel(Kind.POOL, 0, 0, 17, 17, 170, 0, facing, 9, 8, new int[0]);
+                Capture water = render(pool);
+                sealedPool(water, facing);
+                for (int step = 1; step <= 3; step++) for (int x = 7; x <= 9; x++) {
+                    var tread = rotate(x, -step, step + 4, facing);
+                    require(water.block(tread).getBlock() instanceof StairBlock
+                            && water.block(tread).getValue(BlockStateProperties.WATERLOGGED),
+                        "Pool lost its submerged stair tread");
+                    for (int y = -4; y < -step; y++) {
+                        var below = rotate(x, y, step + 4, facing);
+                        require(water.block(below).isCollisionShapeFullBlock(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, below),
+                            "Pool tread is not carried continuously by its sealed basin floor");
+                    }
+                }
+                require(walk(water, rotate(8, 1, 0, facing)).contains(rotate(8, -2, 7, facing)),
+                    "Pool submerged steps cannot be reached from the deck");
+            } catch (AssertionError | RuntimeException failure) {
+                failures.add("Pool facing=" + facing + ": " + failure.getMessage());
+            }
+        }
+        // Every public type keeps a usable north approach, and its furniture does not consume the street threshold.
+        for (Kind kind : Kind.values()) if (!kind.building() && kind != Kind.STREET && kind != Kind.BRIDGE)
+            for (int facing = 0; facing < 4; facing++) {
+                try {
+                    Capture c = render(new Parcel(kind, 0, 0, 17, 17, 170, 0, facing, 42, 8, new int[0]));
+                    var reached = walk(c, rotate(8, 1, 0, facing));
+                    require(reached.size() >= 100, kind + " lost its public circulation");
+                    for (var chest : c.loot.keySet()) require(java.util.Arrays.stream(new Direction[]{Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST})
+                        .anyMatch(d -> reached.contains(chest.relative(d))), kind + " loot is not approachable");
+                } catch (AssertionError | RuntimeException failure) {
+                    failures.add(kind + " public access facing=" + facing + ": " + failure.getMessage());
+                }
+            }
+        require(failures.isEmpty(), "City21 surface fixture failures (" + failures.size() + "):\n" + String.join("\n", failures));
+        exportPreviews();
+        Set<Map<BlockPos, BlockState>> parks = new HashSet<>();
+        for (Kind park : new Kind[] {Kind.PARK, Kind.PARK_GARDEN, Kind.PARK_PLAYGROUND, Kind.PARK_MEMORIAL}) {
+            parks.add(render(new Parcel(park, 0, 0, 17, 17, 170, 0, 0, 42, 4, new int[0])).blocks);
+        }
+        require(parks.size() == 4, "Park variants must have distinct geometry");
+        for (Kind kind : new Kind[] {Kind.POOL, Kind.EXCAVATION}) {
+            Capture fallback = render(new Parcel(kind, 0, 0, 17, 17, 170, 0, 0, 42, 4, new int[0]));
+            require(fallback.blocks.values().stream().noneMatch(state -> !state.getFluidState().isEmpty()),
+                "Uncertified ground produced a wet excavation");
+            require(fallback.block(new BlockPos(8, -1, 8)).is(Blocks.STONE_BRICKS), "Uncertified ground was excavated");
+        }
+        int[] heights = new int[17 * 5];
+        for (int z = 0; z < 17; z++) for (int x = 0; x < 5; x++) heights[z * 5 + x] = 170 + z / 4;
+        Parcel bridge = new Parcel(Kind.BRIDGE, 0, 0, 5, 17, 170, 0, 0, 33, 0, heights);
+        Capture result = render(bridge);
+        require(result.blocks.entrySet().stream().noneMatch(entry -> !entry.getValue().isAir()
+                && entry.getKey().getY() < bridge.surfaceY(entry.getKey().getX(), entry.getKey().getZ()) - bridge.floorY()),
+            "Bridge grew a column below its suspended deck");
+        for (var e : result.blocks.entrySet()) if (e.getValue().is(Blocks.TUFF_BRICK_STAIRS)) {
+            var face = e.getValue().getValue(BlockStateProperties.HORIZONTAL_FACING);
+            var high = e.getKey().relative(face);
+            require(bridge.surfaceY(high.getX(), high.getZ()) - bridge.floorY() == e.getKey().getY(),
+                "Bridge stair fails to meet the higher deck");
+        }
+        Set<BlockPos> reached = walk(result, new BlockPos(2, 1, 0));
+        require(reached.contains(new BlockPos(2, 5, 16)), "Stepped bridge cannot be crossed");
+    }
+
+    private static void exportPreviews() {
+        String path = System.getProperty("sanctuary.city21.exteriorPreview");
+        if (path == null) return;
+        var examples = new java.util.ArrayList<Object>();
+        for (Kind kind : Kind.values()) if (!kind.building() && kind != Kind.STREET && kind != Kind.BRIDGE) {
+            var p = new Parcel(kind, 0, 0, 17, 17, 170, 0, 0, 42, 8, new int[0]); var c = render(p);
+            var blocks = new java.util.ArrayList<Object>();
+            c.blocks.forEach((at, state) -> { if (!state.isAir()) blocks.add(java.util.List.of(at.getX(), at.getY(), at.getZ(), state.toString())); });
+            examples.add(Map.of("kind", kind.name(), "seed", p.seed(), "facing", 0, "blocks", blocks));
+        }
+        try { var output = java.nio.file.Path.of(path); if (output.getParent() != null) java.nio.file.Files.createDirectories(output.getParent());
+            java.nio.file.Files.writeString(output, new com.google.gson.Gson().toJson(examples)); }
+        catch (java.io.IOException e) { throw new AssertionError("Cannot write requested geometry preview", e); }
+    }
+
+    private static Capture render(Parcel parcel) {
+        Capture result = new Capture(parcel);
+        LostCitySurface21.render(parcel, result);
+        return result;
+    }
+
+    /** Flood the cells a source can reach horizontally/downward, without permitting water to rise. */
+    private static void sealedPool(Capture result, int facing) {
+        Set<BlockPos> flooded = new HashSet<>();
+        ArrayDeque<BlockPos> queue = new ArrayDeque<>();
+        result.blocks.forEach((pos, state) -> {
+            if (!state.getFluidState().isEmpty()) { flooded.add(pos); queue.add(pos); }
+        });
+        require(flooded.size() > 150, "Pool must contain a real basin of water");
+        while (!queue.isEmpty()) {
+            BlockPos pos = queue.removeFirst();
+            require(pos.getY() >= -3 && pos.getY() <= -1, "Pool leaks vertically through its floor or coping");
+            BlockPos canonical = rotate(pos.getX(), pos.getY(), pos.getZ(), (4 - facing) % 4);
+            require(canonical.getX() >= 4 && canonical.getX() <= 12 && canonical.getZ() >= 5 && canonical.getZ() <= 12,
+                "Pool leaks outside its continuous side walls");
+            for (Direction direction : new Direction[] {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST, Direction.DOWN}) {
+                BlockPos next = pos.relative(direction);
+                BlockState state = result.block(next);
+                if ((state.isAir() || !state.getFluidState().isEmpty()) && flooded.add(next)) queue.addLast(next);
+            }
+        }
+    }
+
+    /** Conservative full-block walking with one-block steps and two blocks of clear headroom. */
+    private static Set<BlockPos> walk(Capture result, BlockPos start) {
+        require(standable(result, start), "Entrance is blocked: " + start);
+        Set<BlockPos> seen = new HashSet<>();
+        ArrayDeque<BlockPos> queue = new ArrayDeque<>();
+        queue.add(start);
+        seen.add(start);
+        while (!queue.isEmpty()) {
+            BlockPos current = queue.removeFirst();
+            for (Direction direction : new Direction[] {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST}) {
+                for (int dy = -1; dy <= 1; dy++) {
+                    BlockPos next = current.relative(direction).offset(0, dy, 0);
+                    if (standable(result, next) && seen.add(next)) queue.addLast(next);
+                }
+            }
+        }
+        return seen;
+    }
+
+    private static boolean standable(Capture result, BlockPos pos) {
+        if (pos.getX() < 0 || pos.getZ() < 0 || pos.getX() >= result.parcel.width() || pos.getZ() >= result.parcel.depth()) return false;
+        BlockState support = result.block(pos.below());
+        return (support.isSolid() || support.getBlock() instanceof StairBlock)
+            && clear(result.block(pos)) && clear(result.block(pos.above()));
+    }
+
+    private static boolean clear(BlockState state) { return state.isAir() || state.is(Blocks.WATER); }
+
+    private static BlockPos rotate(int x, int y, int z, int facing) {
+        return switch (facing) {
+            case 0 -> new BlockPos(x, y, z);
+            case 1 -> new BlockPos(16 - z, y, x);
+            case 2 -> new BlockPos(16 - x, y, 16 - z);
+            default -> new BlockPos(z, y, 16 - x);
+        };
+    }
+
+    private static final class Capture implements LostCityRenderer.BlockWriter {
+        private final Parcel parcel;
+        private final Map<BlockPos, BlockState> blocks = new HashMap<>();
+        private final Map<BlockPos, ResourceKey<LootTable>> loot = new HashMap<>();
+        Capture(Parcel parcel) { this.parcel = parcel; }
+
+        @Override public void set(int x, int y, int z, BlockState state) {
+            require(x >= 0 && z >= 0 && x < parcel.width() && z < parcel.depth()
+                    && y >= parcel.minY() - parcel.floorY() && y <= parcel.maxY() - parcel.floorY(),
+                parcel.kind() + " emitted a block outside its saved bounds at " + x + "," + y + "," + z);
+            blocks.put(new BlockPos(x, y, z), state);
+        }
+
+        @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long lootSeed) {
+            set(x, y, z, Blocks.CHEST.defaultBlockState());
+            loot.put(new BlockPos(x, y, z), table);
+        }
+
+        BlockState block(BlockPos pos) { return blocks.getOrDefault(pos, Blocks.AIR.defaultBlockState()); }
+    }
+
+    private static void require(boolean condition, String message) {
+        if (!condition) throw new AssertionError(message);
+    }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/heritage/HeritagePiece21Smoke.java

@@ -0,0 +1,85 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.IntTag;
+import net.minecraft.nbt.ListTag;
+
+/** Exact, bounded independent schema21 persistence for catalogue sites and chunk-local abandoned routes. */
+public final class HeritagePiece21Smoke {
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion(); Bootstrap.bootStrap(); run();
+        System.out.println("HeritagePiece21Smoke: 14 kinds, 4 facades, every rail profile, missing rails, strict NBT and local native bounds passed.");
+    }
+    public static void run() {
+        for (var kind : HeritagePlan19.Kind.values()) for (int face = 0; face < 4; face++) {
+            int x = -32, z = 40, floor = 160;
+            var entry = new HeritagePlan19.Entry(face == 1 ? x + 17 : face == 3 ? x - 1 : x + 8,
+                floor + 1, face == 2 ? z + 17 : face == 0 ? z - 1 : z + 8, face);
+            var supportList = new ArrayList<HeritagePlan19.Support>();
+            supportList.add(new HeritagePlan19.Support(x + 1, 150, z + 1, 155));
+            var site = new HeritagePlan19.Site("site_" + kind.name(), kind, x, floor, z, 17, 17, 20, face,
+                Long.MIN_VALUE + kind.ordinal(), 4, supportList, entry);
+            supportList.clear();
+            var saved = HeritagePiece21.encodeSite(site);
+            require(HeritagePiece21.decodeSite(saved).equals(site) && HeritagePiece21.encodeSite(HeritagePiece21.decodeSite(saved)).equals(saved), "Site roundtrip changed geometry");
+            require(site.supports().size() == 1 && HeritagePiece21.bounds(site).minY() == 150, "Support input is mutable or excluded from native bounds");
+            require(HeritagePiece21.locator(site).getX() == entry.x() && HeritagePiece21.locator(site).getY() == entry.y()
+                && HeritagePiece21.locator(site).getZ() == entry.z(), "Locate lost the rotated facade entry");
+            badSite(saved, t -> t.remove("Facing")); badSite(saved, t -> t.putInt("Schema", 17));
+            badSite(saved, t -> t.putString("Type", "ROUTE")); badSite(saved, t -> t.putString("Kind", "FUTURE"));
+            badSite(saved, t -> t.putDouble("FloorY", 160)); badSite(saved, t -> t.putInt("Seed", 1));
+            badSite(saved, t -> t.putInt("Future", 1)); badSite(saved, t -> t.putInt("MinX", Integer.MAX_VALUE));
+            badSite(saved, t -> t.putInt("Width", 18)); badSite(saved, t -> t.putInt("Facing", 4));
+            badSite(saved, t -> t.putInt("FoundationDepth", 0)); badSite(saved, t -> t.putString("Id", "x".repeat(129)));
+            badSite(saved, t -> t.getCompound("Entry").orElseThrow().putInt("X", entry.x() + 1));
+            badSite(saved, t -> t.getCompound("Entry").orElseThrow().putLong("Y", entry.y()));
+            badSite(saved, t -> t.getList("Supports").orElseThrow().getCompound(0).orElseThrow().putInt("MinY", 130));
+            badSite(saved, t -> t.getList("Supports").orElseThrow().getCompound(0).orElseThrow().putInt("X", site.maxX() + 1));
+            badSite(saved, t -> {
+                var list = t.getList("Supports").orElseThrow(); list.add(list.getFirst().copy());
+            });
+        }
+        var cells = new ArrayList<HeritagePlan19.Cell>();
+        int index = 0;
+        for (var rail : HeritagePlan19.Rail.values()) {
+            cells.add(new HeritagePlan19.Cell(-32 + index, 150 + index % 3, 32, 2 + index % 4, rail, rail != HeritagePlan19.Rail.NONE && index % 2 == 0)); index++;
+        }
+        var segment = new HeritagePlan19.Segment("freight/part0", "station", "mine", HeritagePlan19.RouteKind.FREIGHT, -2, 2, cells, Long.MAX_VALUE);
+        cells.clear();
+        var landing = new HeritagePlan19.Segment("station/landing", "station", "station", HeritagePlan19.RouteKind.PATH,
+            -2, 2, List.of(new HeritagePlan19.Cell(-32, 150, 32, 2, HeritagePlan19.Rail.NONE, false)), 42);
+        require(HeritagePiece21.decodeSegment(HeritagePiece21.encodeSegment(landing)).equals(landing), "Standalone entry landing lost its site binding");
+        var saved = HeritagePiece21.encodeSegment(segment);
+        require(HeritagePiece21.decodeSegment(saved).equals(segment) && HeritagePiece21.encodeSegment(HeritagePiece21.decodeSegment(saved)).equals(saved), "Route roundtrip changed shapes, supports or deliberate rail gaps");
+        require(segment.cells().size() == HeritagePlan19.Rail.values().length, "External route list mutation changed its saved cells");
+        require(HeritagePiece21.bounds(segment).intersectingChunks().count() == 1, "Segment escaped its one-chunk native start");
+        badRoute(saved, t -> t.putInt("Schema", 20)); badRoute(saved, t -> t.putString("Type", "SITE"));
+        badRoute(saved, t -> t.remove("FromId")); badRoute(saved, t -> t.putString("ToId", "station"));
+        badRoute(saved, t -> t.putString("Id", " ")); badRoute(saved, t -> t.putInt("StartChunkX", -1));
+        badRoute(saved, t -> t.putDouble("Seed", 42)); badRoute(saved, t -> t.put("Cells", new ListTag()));
+        badRoute(saved, t -> cell(t).putInt("RailPresent", 1)); badRoute(saved, t -> cell(t).putByte("RailPresent", (byte) 2));
+        badRoute(saved, t -> cell(t).putString("Rail", "FUTURE")); badRoute(saved, t -> cell(t).putBoolean("RailPresent", true));
+        badRoute(saved, t -> cell(t).putInt("X", -16)); badRoute(saved, t -> cell(t).putInt("FoundationDepth", 13));
+        badRoute(saved, t -> cell(t).putInt("FloorY", 2)); badRoute(saved, t -> cell(t).putInt("Extra", 0));
+        badRoute(saved, t -> { var list = t.getList("Cells").orElseThrow(); list.add(list.getFirst().copy()); });
+        badRoute(saved, t -> { var list = new ListTag(); list.add(IntTag.valueOf(1)); t.put("Cells", list); });
+        badRoute(saved, t -> { var list = t.getList("Cells").orElseThrow(); while (list.size() <= 256) list.add(list.getFirst().copy()); });
+    }
+    private static CompoundTag cell(CompoundTag tag) { return tag.getList("Cells").orElseThrow().getCompound(0).orElseThrow(); }
+    private static void badSite(CompoundTag original, Consumer<CompoundTag> mutation) {
+        var value = original.copy(); mutation.accept(value);
+        try { HeritagePiece21.decodeSite(value); } catch (IllegalArgumentException expected) { return; }
+        throw new AssertionError("Malformed saved site accepted: " + value);
+    }
+    private static void badRoute(CompoundTag original, Consumer<CompoundTag> mutation) {
+        var value = original.copy(); mutation.accept(value);
+        try { HeritagePiece21.decodeSegment(value); } catch (IllegalArgumentException expected) { return; }
+        throw new AssertionError("Malformed saved route accepted: " + value);
+    }
+    private static void require(boolean value, String message) { if (!value) throw new AssertionError(message); }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/heritage/HeritagePlanner21Smoke.java

@@ -0,0 +1,217 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.worldgen.heritage.HeritagePlan19.*;
+import java.util.ArrayDeque;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.IntBinaryOperator;
+
+/** Pure geography contract: full catalogue, actual destinations, independent entrances and supported axes. */
+public final class HeritagePlanner21Smoke {
+    private static final int[] DX = {0, 1, 0, -1}, DZ = {-1, 0, 1, 0};
+    public static void main(String[] args) {
+        var catalogue = EnumSet.noneOf(Kind.class);
+        int freight = 0, paths = 0, missingRails = 0, islandAxes = 0;
+        for (int diameter : new int[] {512, 724, 1024}) for (long seed : new long[] {0, 1, 42, -1}) {
+            Fixture terrain = new Fixture((x, z) -> 220);
+            var plan = HeritagePlanner21.plan(seed, 0, 0, diameter, terrain);
+            verify(plan, terrain);
+            require(plan.sites().size() >= 8, "Flat starter loses most of its small physical catalogue: " + plan.diagnostics());
+            require(plan.links().size() >= 2, "Flat starter has no useful inter-destination axes");
+            plan.sites().forEach(site -> catalogue.add(site.kind()));
+            freight += (int) plan.links().stream().filter(l -> l.kind() == RouteKind.FREIGHT).count();
+            islandAxes += (int) plan.links().stream().filter(l -> {
+                Point first = l.path().getFirst(), last = l.path().getLast();
+                return Math.max(Math.abs(first.x() - last.x()), Math.abs(first.z() - last.z())) >= diameter / 4;
+            }).count();
+            paths += (int) plan.links().stream().filter(l -> l.kind() == RouteKind.PATH).count();
+            missingRails += (int) plan.segments().stream().flatMap(s -> s.cells().stream())
+                .filter(c -> c.rail() != Rail.NONE && !c.railPresent()).count();
+            var repeat = HeritagePlanner21.plan(seed, 0, 0, diameter, new Fixture((x, z) -> 220));
+            require(plan.sites().equals(repeat.sites()) && plan.links().equals(repeat.links())
+                && plan.segments().equals(repeat.segments()) && plan.samples() == repeat.samples()
+                && plan.diagnostics().equals(repeat.diagnostics()), "Planning depends on generation order or mutable state");
+        }
+        require(catalogue.equals(EnumSet.allOf(Kind.class)), "A requested heritage family never appears: " + catalogue);
+        require(islandAxes > 0, "All published networks remain local; no axis reaches island scale");
+        require(freight > 0 && paths > 0 && missingRails > 0, "Both networks and repairable missing rails must be represented");
+        var flat = HeritagePlanner21.plan(0, 0, 0, 724, new Fixture((x, z) -> 220));
+        var oldFlat = HeritagePlanner19.plan(0, 0, 0, 724, new Fixture((x, z) -> 220));
+        var reached21 = new HashSet<String>(); flat.links().forEach(l -> { reached21.add(l.fromId()); reached21.add(l.toId()); });
+        var reached19 = new HashSet<String>(); oldFlat.links().forEach(l -> { reached19.add(l.fromId()); reached19.add(l.toId()); });
+        require(reached21.size() >= reached19.size(), "Proximity graph connects fewer real destinations than19 on its flat witness");
+        // Expensive duplicate edges must not consume the search reserved for a still isolated destination.
+        var components = new HashMap<String, String>();
+        flat.sites().forEach(site -> components.put(site.id(), site.id()));
+        for (var link : flat.links()) {
+            String from = root(components, link.fromId()), to = root(components, link.toId());
+            require(!from.equals(to), "An already connected flat destination receives a redundant budget-consuming cycle");
+            components.put(to, from);
+        }
+        require(flat.links().size() <= 24 && flat.segments().size() <= 512, "Route graph exceeded saved model limits");
+        require(!flat.sites().equals(HeritagePlanner21.plan(1, 0, 0, 724, new Fixture((x, z) -> 220)).sites()), "Seed does not affect sites");
+
+        Fixture wet = new Fixture((x, z) -> 220); wet.protection = (x, y, z) -> true;
+        var blocked = HeritagePlanner21.plan(0, 0, 0, 724, wet); verify(blocked, wet);
+        require(blocked.isEmpty() && blocked.links().isEmpty(), "Protected water or earlier city is overwritten");
+        Fixture voidTerrain = new Fixture((x, z) -> -1);
+        var absent = HeritagePlanner21.plan(0, 0, 0, 724, voidTerrain); verify(absent, voidTerrain);
+        require(absent.isEmpty() && absent.segments().isEmpty(), "Void receives unsupported structures or fictional routes");
+        Fixture thin = new Fixture((x, z) -> 220); thin.rock = (x, y, z) -> y >= 219 && y <= 220;
+        var thinPlan = HeritagePlanner21.plan(0, 0, 0, 724, thin); verify(thinPlan, thin);
+        require(thinPlan.isEmpty(), "Thin shelves receive buildings without anchored footings");
+
+        // Every site keeps its local access even when a protected ring rejects every inter-site alignment.
+        Set<Long> allowed = new HashSet<>();
+        for (var site : flat.sites()) for (int x = site.minX(); x <= site.maxX(); x++) for (int z = site.minZ(); z <= site.maxZ(); z++) allowed.add(key(x, z));
+        for (var segment : flat.segments()) if (segment.fromId().equals(segment.toId())) for (var c : segment.cells()) allowed.add(key(c.x(), c.z()));
+        Fixture isolated = new Fixture((x, z) -> 220); isolated.protection = (x, y, z) -> !allowed.contains(key(x, z));
+        var islands = HeritagePlanner21.plan(0, 0, 0, 724, isolated); verify(islands, isolated);
+        require(!islands.sites().isEmpty(), "Independent access fixture has no retained site");
+        require(islands.sites().stream().anyMatch(site -> islands.links().stream().noneMatch(l -> l.fromId().equals(site.id()) || l.toId().equals(site.id()))),
+            "The isolated destination witness unexpectedly has every long route");
+
+        // Historical landmark feet are read-only and have no mask bypass, even when a route reaches them.
+        Site station = flat.sites().stream().filter(s -> s.kind() == Kind.FREIGHT_STATION).findFirst().orElseThrow();
+        Entry historical = new Entry(station.entry().x() + DX[station.facing()] * 30,
+            221, station.entry().z() + DZ[station.facing()] * 30, (station.facing() + 2) & 3);
+        Fixture landmark = new Fixture((x, z) -> 220);
+        landmark.landmarks = List.of(new Landmark("old_mine", LandmarkKind.MINE, historical));
+        landmark.protection = (x, y, z) -> x == historical.x() && z == historical.z();
+        var linked = HeritagePlanner21.plan(0, 0, 0, 724, landmark); verify(linked, landmark);
+        require(!linked.contains(historical.x(), historical.y(), historical.z()), "A historical endpoint receives route painting");
+
+        Landmark left = new Landmark("left", LandmarkKind.CITY, new Entry(0, 101, 0, 1));
+        Landmark right = new Landmark("right", LandmarkKind.MINE, new Entry(1, 101, 0, 3));
+        Landmark unused = new Landmark("unused", LandmarkKind.UTILITY, new Entry(30, 101, 0, 0));
+        var dependency = new HeritagePlan19(List.of(), List.of(left, right, unused),
+            List.of(new Link("existing_access", "left", "right", RouteKind.PATH, List.of(new Point(0, 100, 0), new Point(1, 100, 0)))),
+            List.of(), 0, 0, Map.of());
+        for (int z = -1; z <= 1; z++) for (int y = 99; y <= 103; y++) {
+            require(dependency.protects(0, y, z) && dependency.intersectsProtection(0, y, z, 0, y, z), "Used historical access lost its rock/headroom dependency");
+            require(!dependency.contains(0, y, z), "Read-only historical access received writing permission");
+        }
+        require(!dependency.protects(30, 101, 0), "Unused historical landmark reserves unrelated terrain");
+
+        // Smooth slopes exercise certified cut/fill and route grade without allowing an unsupported plateau.
+        Fixture sloped = new Fixture((x, z) -> 220 + Math.floorDiv(z, 12));
+        var slopes = HeritagePlanner21.plan(42, 0, 0, 724, sloped); verify(slopes, sloped);
+        require(slopes.sites().size() >= 5, "A modest slope makes the entire catalogue inadmissible");
+        Fixture shifted = new Fixture((x, z) -> 220);
+        var translated = HeritagePlanner21.plan(42, -1024, 512, 724, shifted); verify(translated, shifted);
+        require(!translated.isEmpty(), "Negative chunk coordinates prevent generation");
+        require(flat.diagnostics().size() == Kind.values().length && blocked.diagnostics().size() == Kind.values().length,
+            "Missing kinds have no explicit diagnostic");
+        expectInvalid(() -> new Link("self", "a", "a", RouteKind.PATH, List.of(new Point(0, 100, 0), new Point(1, 100, 0))));
+        expectInvalid(() -> new Segment("self", "a", "a", RouteKind.FREIGHT, 0, 0, List.of(new Cell(0, 100, 0, 1, Rail.NONE, false)), 0));
+        expectInvalid(() -> new Cell(0, 100, 0, 13, Rail.NONE, false));
+        System.out.println("HeritagePlanner21Smoke passed: fourteen families, deterministic placements, persisted isolated entrances, real route destinations, bounded slopes and supported rails, unique chunk-local cells, indexed protection and budgets");
+    }
+
+    private static String root(Map<String, String> components, String id) {
+        String parent = components.get(id);
+        while (!parent.equals(id)) { id = parent; parent = components.get(id); }
+        return parent;
+    }
+    private static void verify(HeritagePlan19 plan, Fixture terrain) {
+        require(plan.samples() == terrain.samples && plan.samples() <= HeritagePlan19.MAX_SAMPLES, "Probe accounting differs from native calls");
+        require(plan.columns() == terrain.columns.size() && plan.columns() <= HeritagePlan19.MAX_COLUMNS, "Column budget exceeded");
+        Map<Long, Cell> cells = new HashMap<>(); Map<String, Entry> destinations = new HashMap<>();
+        Set<Long> footprints = new HashSet<>();
+        for (var site : plan.sites()) {
+            destinations.put(site.id(), site.entry());
+            require(site.foundationDepth() <= 8 && site.maxY() <= 380, "Architecture exceeds its bounded envelope");
+            require(Math.abs((site.minX() >> 4) - site.startChunkX()) <= 7 && Math.abs((site.maxX() >> 4) - site.startChunkX()) <= 7
+                && Math.abs((site.minZ() >> 4) - site.startChunkZ()) <= 7 && Math.abs((site.maxZ() >> 4) - site.startChunkZ()) <= 7, "Site exceeds native reference radius");
+            for (int z = site.minZ(); z <= site.maxZ(); z++) for (int x = site.minX(); x <= site.maxX(); x++) {
+                require(footprints.add(key(x, z)), "Two buildings overlap");
+                require(terrain.height.applyAsInt(x, z) - site.floorY() <= HeritagePlanner21.MAX_SITE_CUT, "Site cuts an excessive mound");
+                for (int y = site.minY(); y <= site.maxY(); y++) require(!terrain.protection.test(x, y, z), "Architecture intersects protected water/old structure");
+                require(plan.contains(x, site.floorY(), z) && plan.protects(x, site.maxY(), z)
+                    && plan.intersectsProtection(x, site.maxY(), z, x, site.maxY(), z), "Site is absent from indexed protection");
+            }
+            for (int dx : new int[] {1, 8, 15}) for (int dz : new int[] {1, 8, 15}) {
+                int x = site.minX() + dx, z = site.minZ() + dz;
+                var support = site.supports().stream().filter(s -> s.x() == x && s.z() == z).findFirst();
+                int rock = support.isPresent() ? support.get().minY() - 1 : site.minY() - 1;
+                require(terrain.rock.test(x, rock, z) && terrain.rock.test(x, rock - 1, z), "Site has no two-block rock bearing");
+            }
+            for (var support : site.supports()) {
+                require(support.maxY() - support.minY() < 12 && support.maxY() == site.minY() - 1, "Unbounded/disconnected architectural pier");
+                require(plan.protects(support.x(), support.minY() - 2, support.z()), "Pier bearing exposed to decoration");
+                for (int y = support.minY(); y <= support.maxY(); y++) require(!terrain.protection.test(support.x(), y, support.z()), "Pier overwrites protected terrain");
+            }
+        }
+        plan.landmarks().forEach(l -> destinations.put(l.id(), l.entry()));
+        for (var segment : plan.segments()) {
+            require(destinations.containsKey(segment.fromId()) && destinations.containsKey(segment.toId()), "Segment has a fictional destination");
+            for (Cell cell : segment.cells()) {
+                require(cells.put(key(cell.x(), cell.z()), cell) == null, "Two segments write the same column");
+                require(!footprints.contains(key(cell.x(), cell.z())), "Route crosses a building envelope");
+                require((cell.x() >> 4) == segment.startChunkX() && (cell.z() >> 4) == segment.startChunkZ(), "Route piece is not chunk-local");
+                require(terrain.rock.test(cell.x(), cell.minY() - 1, cell.z()), "Route ballast floats without bearing");
+                require(terrain.height.applyAsInt(cell.x(), cell.z()) - cell.floorY() <= HeritagePlanner21.MAX_ROUTE_CUT, "Route makes excessive terrain cuts");
+                require(cell.floorY() - terrain.height.applyAsInt(cell.x(), cell.z()) <= HeritagePlanner21.MAX_ROUTE_FILL,
+                    "Route uses an unbounded fill to force a connection");
+                for (int y = cell.minY(); y <= cell.maxY(); y++) require(!terrain.protection.test(cell.x(), y, cell.z()), "Route overwrites protected water/old structure");
+                require(plan.contains(cell.x(), cell.floorY(), cell.z()) && plan.protects(cell.x(), cell.minY() - 1, cell.z())
+                    && plan.intersectsProtection(cell.x(), cell.minY() - 1, cell.z(), cell.x(), cell.minY() - 1, cell.z()), "Route/ballast missing from protection index");
+                require(!cell.railPresent() || cell.rail() != Rail.NONE, "Present rail has no saved geometry");
+            }
+        }
+        for (var site : plan.sites()) {
+            Entry e = site.entry();
+            for (int cross = -1; cross <= 1; cross++) {
+                Cell cell = cells.get(key(e.x() + DZ[e.facing()] * cross, e.z() - DX[e.facing()] * cross));
+                require(cell != null && cell.floorY() == e.y() - 1, "Unlinked entrance has no independently painted three-wide landing");
+            }
+            // A five-row access profile must meet natural terrain; never stop on an isolated retaining ledge.
+            var reached = new HashSet<Long>(); var queue = new ArrayDeque<Long>();
+            queue.add(key(e.x(), e.z())); reached.add(key(e.x(), e.z())); boolean meetsGround = false;
+            while (!queue.isEmpty()) {
+                long key = queue.remove(); Cell c = cells.get(key);
+                if (Math.abs(c.x() - e.x()) + Math.abs(c.z() - e.z()) >= 4
+                    && Math.abs(c.floorY() - terrain.height.applyAsInt(c.x(), c.z())) <= 1) meetsGround = true;
+                for (int d = 0; d < 4; d++) {
+                    long next = key(c.x() + DX[d], c.z() + DZ[d]); Cell n = cells.get(next);
+                    if (n != null && Math.abs(n.floorY() - c.floorY()) <= 1 && reached.add(next)) queue.add(next);
+                }
+            }
+            require(meetsGround, "An entrance platform has no traversable return to the sampled terrain");
+        }
+        for (var link : plan.links()) {
+            Entry from = destinations.get(link.fromId()), to = destinations.get(link.toId());
+            require(link.path().getFirst().equals(new Point(from.x(), from.y() - 1, from.z()))
+                && link.path().getLast().equals(new Point(to.x(), to.y() - 1, to.z())), "Route does not actually join its promised entrances");
+            for (int i = 0; i < link.path().size(); i++) {
+                Point p = link.path().get(i); Cell c = cells.get(key(p.x(), p.z()));
+                boolean historical = plan.landmarks().stream().anyMatch(l -> l.entry().x() == p.x() && l.entry().z() == p.z() && l.entry().y() == p.floorY() + 1);
+                require(c != null && c.floorY() == p.floorY() || historical, "A complete route contains an unpainted gap");
+                if (i > 0) {
+                    Point a = link.path().get(i - 1);
+                    require(Math.abs(a.x() - p.x()) + Math.abs(a.z() - p.z()) == 1 && Math.abs(a.floorY() - p.floorY()) <= 1, "Route has a jump or excessive grade");
+                }
+            }
+        }
+        require(!plan.protects(100_000, 200, 100_000) && !plan.intersectsProtection(100_000, 0, 100_000, 100_002, 383, 100_002), "Protection escaped accepted constructions");
+    }
+    @FunctionalInterface private interface Volume { boolean test(int x, int y, int z); }
+    private static final class Fixture implements HeritagePlanner21.Terrain {
+        final IntBinaryOperator height; final Set<Long> columns = new HashSet<>(); int samples;
+        Volume protection = (x, y, z) -> false;
+        Volume rock; List<Landmark> landmarks = List.of();
+        Fixture(IntBinaryOperator height) { this.height = height; rock = (x, y, z) -> y >= 8 && y <= height.applyAsInt(x, z); }
+        public boolean owns(int x, int z) { return true; }
+        public int surfaceY(int x, int z) { samples++; columns.add(key(x, z)); return height.applyAsInt(x, z); }
+        public boolean solid(int x, int y, int z) { samples++; return rock.test(x, y, z); }
+        public boolean protectedAt(int x, int y, int z) { samples++; return protection.test(x, y, z); }
+        public List<Landmark> landmarks() { return landmarks; }
+    }
+    private static void expectInvalid(Runnable action) { boolean rejected = false; try { action.run(); } catch (IllegalArgumentException expected) { rejected = true; } require(rejected, "Invalid saved geometry was accepted"); }
+    private static void require(boolean value, String message) { if (!value) throw new AssertionError(message); }
+    private static long key(int x, int z) { return (long) x << 32 ^ z & 0xffffffffL; }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/heritage/HeritageRenderer21Smoke.java

@@ -0,0 +1,506 @@
+package fr.koka.sanctuary.worldgen.heritage;
+
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.EmptyBlockGetter;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.DoorBlock;
+import net.minecraft.world.level.block.Rotation;
+import net.minecraft.world.level.block.TrapDoorBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.block.state.properties.BedPart;
+import net.minecraft.world.level.block.state.properties.BlockStateProperties;
+import net.minecraft.world.level.block.state.properties.DoubleBlockHalf;
+import net.minecraft.world.level.block.state.properties.Half;
+import net.minecraft.world.level.storage.loot.LootTable;
+import net.minecraft.world.phys.AABB;
+
+/** Native shapes and final geometry: distinguish real rooms, reachable secrets and supported routes. */
+public final class HeritageRenderer21Smoke {
+    private HeritageRenderer21Smoke() {}
+    private static final Direction[] DIRECTIONS = {Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST};
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion(); Bootstrap.bootStrap(); run();
+        System.out.println("HeritageRenderer21Smoke passed: fourteen restrained generation21 palettes, four rotations, supported single roofs and daylight wells, reachable original targets, retained loot and connected block details");
+    }
+    public static void run() {
+        Set<Set<BlockPos>> silhouettes = new HashSet<>();
+        for (var kind : HeritagePlan19.Kind.values()) for (long seed : new long[] {0, 43}) {
+            var canonical = render(site(kind, 0, seed));
+            if (seed == 0) {
+                export(canonical);
+                Set<BlockPos> shape = new HashSet<>(); canonical.blocks.forEach((p, b) -> { if (p.getY() > 0 && !b.isAir()) shape.add(p); });
+                require(silhouettes.add(shape), kind + " only repaints another catalogue building");
+            }
+            for (int facing = 0; facing < 4; facing++) {
+                var c = facing == 0 ? canonical : render(site(kind, facing, seed));
+                var repeat = render(c.site);
+                require(c.blocks.equals(repeat.blocks) && c.loot.equals(repeat.loot), label(c) + " is not deterministic");
+                rotate(canonical, c);
+                var targets = HeritageRenderer21.targets(c.site);
+                var reached = walk(c, at(targets.getFirst()));
+                for (var target : targets) require(reached.contains(at(target)), label(c) + " cannot reach " + target.name() + " at " + at(target));
+                require(targets.stream().anyMatch(t -> t.name().equals("secondary_entry")), "Missing secondary physical approach");
+                var secondary = targets.stream().filter(t -> t.name().equals("secondary_entry")).findFirst().orElseThrow();
+                Set<BlockPos> returnPath = walk(c, at(secondary));
+                require(returnPath.contains(at(targets.getFirst())), label(c) + " service exit cannot return through the certified courtyard");
+                require(c.loot.size() == 1, label(c) + " must have one shared, deferred discovery chest");
+                var chest = c.loot.entrySet().iterator().next();
+                require(chest.getValue().table().identifier().toString().equals("sanctuary:chests/heritage19/" + kind.name().toLowerCase(java.util.Locale.ROOT)), "Loot table is not generation19-specific");
+                require(approachable(chest.getKey(), reached), label(c) + " hidden chest cannot be opened from a reachable standing cell");
+                for (var t : targets) if (t.name().equals("loot_approach")) require(at(t).distManhattan(chest.getKey()) == 1, "Secret witness is not next to the actual chest");
+                furnishings(c, reached);
+                refugeShaft(c, reached);
+                railConnection(c);
+                fluids(c);
+                require(c.blocks.values().stream().noneMatch(b -> b.is(Blocks.SPAWNER) || b.is(Blocks.LAVA)), "Heritage added an unrequested spawner or lava");
+                identity(c);
+                architecture21(c);
+                daylightAndCrown21(c);
+                roofBearings21(c);
+            }
+        }
+        require(silhouettes.size() == 14, "Catalogue does not contain fourteen physical architectures");
+        routes(); chunkPartition(); materials21();
+    }
+    private static HeritagePlan19.Site site(HeritagePlan19.Kind kind, int facing, long seed) {
+        int height = switch (kind) {
+            case COMMUNAL_DEPOT, VOID_DOCK, CONSTRUCTION_REFUGE -> 14;
+            case EXPEDITION_OFFICE, IMPOSSIBLE_SERVICE -> 12;
+            case OBSERVATORY -> 20; case PUMP_STATION -> 18; case RADIO_RELAY -> 22;
+            default -> 10;
+        };
+        int x = -43, y = 180, z = 59;
+        var entry = new HeritagePlan19.Entry(facing == 1 ? x + 17 : facing == 3 ? x - 1 : x + 8, y + 1,
+            facing == 2 ? z + 17 : facing == 0 ? z - 1 : z + 8, facing);
+        return new HeritagePlan19.Site("test", kind, x, y, z, 17, 17, height, facing, seed, 3,
+            List.of(new HeritagePlan19.Support(x, y - 7, z, y - 4)), entry);
+    }
+    private static String label(Capture c) { return c.site.kind() + " facing=" + c.site.facing() + " seed=" + c.site.seed(); }
+    private static Capture render(HeritagePlan19.Site site) { var c = new Capture(site); HeritageRenderer21.render(site, c); return c; }
+    private static BlockPos at(HeritageRenderer21.Target t) { return new BlockPos(t.x(), t.y(), t.z()); }
+    private static BlockPos rotate(BlockPos p, int facing) {
+        return switch (facing) { case 1 -> new BlockPos(16 - p.getZ(), p.getY(), p.getX());
+            case 2 -> new BlockPos(16 - p.getX(), p.getY(), 16 - p.getZ());
+            case 3 -> new BlockPos(p.getZ(), p.getY(), 16 - p.getX()); default -> p; };
+    }
+    private static void rotate(Capture base, Capture other) {
+        int facing = other.site.facing();
+        Rotation rotation = switch (facing) { case 1 -> Rotation.CLOCKWISE_90; case 2 -> Rotation.CLOCKWISE_180;
+            case 3 -> Rotation.COUNTERCLOCKWISE_90; default -> Rotation.NONE; };
+        for (var e : base.blocks.entrySet()) {
+            // Saved footings are already in world coordinates; they do not rotate with the facade.
+            if (e.getKey().getY() < -base.site.foundationDepth() || base.loot.containsKey(e.getKey())) continue;
+            require(other.block(rotate(e.getKey(), facing)).equals(e.getValue().rotate(rotation)), label(other) + " rotates shape and block state differently at " + e.getKey());
+        }
+        for (var e : base.loot.entrySet()) require(e.getValue().equals(other.loot.get(rotate(e.getKey(), facing))), "Rotating a site changes its deferred treasure");
+    }
+    private static void furnishings(Capture c, Set<BlockPos> reached) {
+        for (var e : c.blocks.entrySet()) {
+            var p = e.getKey(); var b = e.getValue();
+            if (b.getBlock() instanceof DoorBlock) {
+                var half = b.getValue(BlockStateProperties.DOUBLE_BLOCK_HALF);
+                var partner = half == DoubleBlockHalf.LOWER ? p.above() : p.below();
+                require(c.block(partner).equals(b.setValue(BlockStateProperties.DOUBLE_BLOCK_HALF,
+                    half == DoubleBlockHalf.LOWER ? DoubleBlockHalf.UPPER : DoubleBlockHalf.LOWER)), label(c) + " has a truncated door at " + p);
+                if (half == DoubleBlockHalf.LOWER) {
+                    require(full(c.block(p.below()), p.below()), "Door has no full threshold");
+                    Direction normal = b.getValue(BlockStateProperties.HORIZONTAL_FACING);
+                    require(reached.contains(p.relative(normal)) && reached.contains(p.relative(normal.getOpposite())),
+                        label(c) + " door does not connect two usable sides at " + p);
+                }
+            }
+            if (b.is(Blocks.LADDER)) require(full(c.block(p.relative(b.getValue(BlockStateProperties.HORIZONTAL_FACING).getOpposite())), p),
+                label(c) + " floating ladder at " + p);
+            if (b.is(Blocks.LANTERN)) require(b.getValue(BlockStateProperties.HANGING) && full(c.block(p.above()), p.above()),
+                label(c) + " lantern does not hang from a complete ceiling at " + p);
+            if (b.is(Blocks.LEVER) || b.is(Blocks.GRINDSTONE)) require(full(c.block(p.below()), p.below()), "Usable fixture has no full support");
+            if ((b.is(Blocks.OAK_STAIRS) || b.is(Blocks.BIRCH_STAIRS)) && p.getY() == 1) {
+                var front = p.relative(b.getValue(BlockStateProperties.HORIZONTAL_FACING).getOpposite());
+                require(reached.contains(front), label(c) + " seat faces an obstruction at " + p);
+            }
+            if (b.hasProperty(BlockStateProperties.BED_PART)) {
+                Direction direction = b.getValue(BlockStateProperties.HORIZONTAL_FACING);
+                boolean head = b.getValue(BlockStateProperties.BED_PART) == BedPart.HEAD;
+                var partner = p.relative(head ? direction.getOpposite() : direction);
+                require(c.block(partner).equals(b.setValue(BlockStateProperties.BED_PART, head ? BedPart.FOOT : BedPart.HEAD)), "Bed halves disagree");
+                if (head) {
+                    for (int y = 0; y < 3; y++) require(full(c.block(p.relative(direction).above(y)), p), "Bed head is not against its real wall");
+                    boolean side = false;
+                    for (Direction d : new Direction[] {direction.getClockWise(), direction.getCounterClockWise()})
+                        side |= reached.contains(p.relative(d)) && reached.contains(partner.relative(d));
+                    require(side, "Bed has no reachable full lateral approach");
+                }
+            }
+            if (b.is(Blocks.CRAFTING_TABLE) || b.is(Blocks.CARTOGRAPHY_TABLE) || b.is(Blocks.FURNACE)
+                    || b.is(Blocks.GRINDSTONE) || b.is(Blocks.LECTERN))
+                require(approachable(p, reached), label(c) + " functional furnishing cannot be approached at " + p);
+        }
+    }
+    private static boolean full(BlockState b, BlockPos p) {
+        return b.getFluidState().isEmpty() && b.getCollisionShape(EmptyBlockGetter.INSTANCE, p).toAabbs().stream()
+            .anyMatch(a -> a.minX == 0 && a.minY == 0 && a.minZ == 0 && a.maxX == 1 && a.maxY == 1 && a.maxZ == 1);
+    }
+    private static boolean approachable(BlockPos p, Set<BlockPos> reached) {
+        for (var d : DIRECTIONS) if (reached.contains(p.relative(d))) return true;
+        return false;
+    }
+    private static boolean clear(Capture c, BlockPos p) {
+        var body = new AABB(p.getX() + .2, p.getY(), p.getZ() + .2, p.getX() + .8, p.getY() + 1.8, p.getZ() + .8);
+        for (var at : new BlockPos[] {p, p.above()}) {
+            var b = opened(c.block(at)); if (!b.getFluidState().isEmpty()) return false;
+            for (var shape : b.getCollisionShape(EmptyBlockGetter.INSTANCE, at).toAabbs())
+                if (shape.move(at.getX(), at.getY(), at.getZ()).intersects(body)) return false;
+        }
+        return true;
+    }
+    private static boolean stand(Capture c, BlockPos p) {
+        if (p.getX() < 0 || p.getX() > 16 || p.getZ() < 0 || p.getZ() > 16
+                || p.getY() < -c.site.foundationDepth() + 1 || p.getY() >= c.site.height() || !clear(c, p)) return false;
+        if (climb(c.block(p)) || climb(c.block(p.below()))) return true;
+        return opened(c.block(p.below())).getCollisionShape(EmptyBlockGetter.INSTANCE, p.below()).toAabbs().stream()
+            .anyMatch(a -> a.maxY >= .5 && a.minX <= .5 && a.maxX >= .5 && a.minZ <= .5 && a.maxZ >= .5);
+    }
+    private static BlockState opened(BlockState state) {
+        return state.getBlock() instanceof DoorBlock || state.getBlock() instanceof TrapDoorBlock
+            ? state.setValue(BlockStateProperties.OPEN, true) : state;
+    }
+    private static void refugeShaft(Capture c, Set<BlockPos> reached) {
+        if (c.site.kind() != HeritagePlan19.Kind.CONSTRUCTION_REFUGE) return;
+        var hatch = rotate(new BlockPos(10, 5, 11), c.site.facing());
+        require(c.block(hatch).is(Blocks.OAK_TRAPDOOR)
+            && c.block(hatch).getValue(BlockStateProperties.HALF) == Half.BOTTOM,
+            label(c) + " hatch is not at the climbable upper lip");
+        var direction = c.block(hatch).getValue(BlockStateProperties.HORIZONTAL_FACING);
+        require(stand(c, hatch) && reached.contains(hatch), label(c) + " open hatch has no reachable climbable support");
+        for (int y = 1; y <= 4; y++) {
+            var rung = new BlockPos(hatch.getX(), y, hatch.getZ());
+            require(c.block(rung).is(Blocks.LADDER)
+                && c.block(rung).getValue(BlockStateProperties.HORIZONTAL_FACING) == direction,
+                label(c) + " hatch descent loses a matching ladder at " + rung);
+            require(stand(c, rung) && reached.contains(rung) && clear(c, rung.above()),
+                label(c) + " hatch descent cannot traverse vertically at " + rung);
+        }
+    }
+    private static boolean climb(BlockState b) { return b.is(Blocks.LADDER); }
+    private static Set<BlockPos> walk(Capture c, BlockPos start) {
+        require(stand(c, start), label(c) + " starts without a standing surface at " + start);
+        Set<BlockPos> seen = new HashSet<>(); var queue = new ArrayDeque<BlockPos>(); seen.add(start); queue.add(start);
+        while (!queue.isEmpty()) {
+            var p = queue.removeFirst();
+            for (var d : DIRECTIONS) for (int dy : new int[] {0, 1, -1}) {
+                var q = p.relative(d).offset(0, dy, 0);
+                if (dy > 0 && !clear(c, p.above())) continue;
+                if (stand(c, q) && seen.add(q)) queue.add(q);
+            }
+            for (int dy : new int[] {-1, 1}) {
+                var q = p.offset(0, dy, 0);
+                if ((climb(c.block(p)) || climb(c.block(q)) || climb(c.block(p.below()))) && stand(c, q) && seen.add(q)) queue.add(q);
+            }
+        }
+        return seen;
+    }
+    private static void fluids(Capture c) {
+        Set<BlockPos> water = new HashSet<>(); c.blocks.forEach((p, b) -> { if (!b.getFluidState().isEmpty()) water.add(p); });
+        int expected = c.site.kind() == HeritagePlan19.Kind.PUMP_STATION ? 60 : c.site.kind() == HeritagePlan19.Kind.GREENHOUSE ? 2 : 0;
+        require(water.size() == expected, label(c) + " has unexpected water quantity: " + water.size());
+        for (var p : water) {
+            require(c.block(p).is(Blocks.WATER), "Only explicitly contained water is allowed");
+            for (var d : new Direction[] {Direction.DOWN, Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST}) {
+                var q = p.relative(d);
+                require(water.contains(q) || !c.block(q).isAir(), label(c) + " lets tank/irrigation water escape into air at " + q);
+            }
+        }
+    }
+    private static void identity(Capture c) {
+        switch (c.site.kind()) {
+            case FREIGHT_STATION -> { has(c, Blocks.RAIL); has(c, Blocks.LEVER); }
+            case POST_OFFICE -> { has(c, Blocks.BARREL); has(c, Blocks.CARTOGRAPHY_TABLE); }
+            case COMMUNAL_DEPOT -> { has(c, Blocks.BARREL); has(c, Blocks.LECTERN); }
+            case EXPEDITION_OFFICE -> { has(c, Blocks.CARTOGRAPHY_TABLE); has(c, Blocks.BOOKSHELF); }
+            case OBSERVATORY -> { has(c, Blocks.CARTOGRAPHY_TABLE); has(c, Blocks.IRON_BARS); }
+            case RAIL_WORKSHOP -> { has(c, Blocks.GRINDSTONE); has(c, Blocks.RAIL); has(c, Blocks.FURNACE); }
+            case PUMP_STATION -> { has(c, Blocks.DISPENSER); has(c, Blocks.WATER); }
+            case SUBSTATION -> { has(c, Blocks.LEVER); has(c, Blocks.IRON_BARS); }
+            case GREENHOUSE -> { has(c, Blocks.WHEAT); has(c, Blocks.FARMLAND); has(c, Blocks.COMPOSTER); }
+            case VOID_DOCK -> { has(c, Blocks.IRON_CHAIN); has(c, Blocks.STRIPPED_OAK_LOG); }
+            case RADIO_RELAY -> { has(c, Blocks.BED.white()); has(c, Blocks.IRON_BARS); }
+            case PHOTO_CLUB -> { has(c, Blocks.WATER_CAULDRON); has(c, Blocks.IRON_CHAIN); }
+            case IMPOSSIBLE_SERVICE -> { has(c, Blocks.CALCITE); has(c, Blocks.WATER_CAULDRON); }
+            case CONSTRUCTION_REFUGE -> { has(c, Blocks.BED.white()); has(c, Blocks.LADDER); has(c, Blocks.OAK_TRAPDOOR); }
+        }
+    }
+    private static void architecture21(Capture c) {
+        if (c.site.kind() != HeritagePlan19.Kind.GREENHOUSE) has(c, Blocks.SMOOTH_STONE);
+        has(c, Blocks.STONE_BRICKS);
+        for (var e : c.blocks.entrySet()) {
+            String name = net.minecraft.core.registries.BuiltInRegistries.BLOCK.getKey(e.getValue().getBlock()).getPath();
+            require(e.getKey().getY() <= 0 || !name.contains("tuff"), label(c) + " uses tuff above ground: " + e.getKey());
+            boolean greenhouse = c.site.kind() == HeritagePlan19.Kind.GREENHOUSE;
+            for (String wood : List.of("dark_oak", "oak", "birch", "spruce", "jungle", "acacia", "mangrove", "cherry", "pale_oak")) {
+                boolean woodBlock = name.startsWith(wood + "_") || name.startsWith("stripped_" + wood + "_");
+                require(!woodBlock || wood.equals(greenhouse ? "birch" : "oak"),
+                    label(c) + " mixes timber species with " + name + " at " + e.getKey());
+            }
+        }
+        // The working destinations keep exactly their historical entrances and service witnesses.
+        var previous = HeritageRenderer19.targets(c.site).stream().map(t -> t.name() + ":" + t.x() + ":" + t.y() + ":" + t.z()).toList();
+        var current = HeritageRenderer21.targets(c.site).stream().map(t -> t.name() + ":" + t.x() + ":" + t.y() + ":" + t.z()).toList();
+        require(previous.equals(current), label(c) + " changes the saved functional access contract");
+        for (var e : c.blocks.entrySet()) if (e.getKey().getY() < 0 && e.getKey().getY() >= -c.site.foundationDepth()) {
+            // Workshop/trench cuts are deliberate; the exterior foundation always remains brick masonry.
+            int x = e.getKey().getX(), z = e.getKey().getZ();
+            if (x == 0 || x == 16 || z == 0 || z == 16) require(e.getValue().is(Blocks.STONE_BRICKS), "Visible foundations lost the stone-brick construction");
+        }
+    }
+    private static void daylightAndCrown21(Capture c) {
+        if (c.site.kind() == HeritagePlan19.Kind.FREIGHT_STATION) {
+            for (int x : new int[] {7, 9}) for (int z : new int[] {6, 8}) {
+                require(c.block(rotate(new BlockPos(x, 9, z), c.site.facing())).is(Blocks.GLASS),
+                    label(c) + " passenger skylight is open to the sky instead of glazed");
+                clearLightWell(c, x, z, 6, c.site.height());
+            }
+        }
+        if (c.site.kind() == HeritagePlan19.Kind.COMMUNAL_DEPOT) {
+            for (int x : new int[] {5, 9}) for (int z : new int[] {3, 7, 11}) {
+                require(c.block(rotate(new BlockPos(x, 11, z), c.site.facing())).is(Blocks.GLASS),
+                    label(c) + " warehouse roof light is no longer glazed");
+                require(c.block(rotate(new BlockPos(x, 9, z), c.site.facing())).isAir(),
+                    label(c) + " warehouse kept its obsolete flat ceiling beneath the new roof");
+                clearLightWell(c, x, z, 9, c.site.height());
+            }
+        }
+        if (c.site.kind() == HeritagePlan19.Kind.RAIL_WORKSHOP || c.site.kind() == HeritagePlan19.Kind.GREENHOUSE) {
+            int x = c.site.kind() == HeritagePlan19.Kind.GREENHOUSE ? 5 : 8, z = 3;
+            require(c.block(rotate(new BlockPos(x, 6, z), c.site.facing())).isAir(),
+                label(c) + " old ceiling remains beneath the vaulted roof");
+            require(c.block(rotate(new BlockPos(x, 9, z), c.site.facing())).is(Blocks.GLASS),
+                label(c) + " single vaulted roof lost its glazing");
+            clearLightWell(c, x, z, 6, c.site.height());
+        }
+        if (c.site.kind() == HeritagePlan19.Kind.RADIO_RELAY || c.site.kind() == HeritagePlan19.Kind.CONSTRUCTION_REFUGE) {
+            int x = c.site.kind() == HeritagePlan19.Kind.RADIO_RELAY ? 7 : 11;
+            // Sample between the radio's trusses (z6,7,10), not through its real middle tie beam.
+            int z = 9;
+            int former = c.site.kind() == HeritagePlan19.Kind.RADIO_RELAY ? 6 : 10;
+            require(c.block(rotate(new BlockPos(x, former, z), c.site.facing())).isAir(),
+                label(c) + " shelter kept two separate opaque roofs");
+            int runs = 0; boolean previous = false;
+            for (int y = former; y <= c.site.height(); y++) {
+                boolean occupied = !c.block(rotate(new BlockPos(x, y, z), c.site.facing())).isAir();
+                if (occupied && !previous) runs++;
+                previous = occupied;
+            }
+            require(runs == 1, label(c) + " shelter has an interrupted or duplicated roof profile");
+        }
+        if (c.site.kind() == HeritagePlan19.Kind.OBSERVATORY) {
+            // The inset crown must be joined through face-adjacent masonry to the tower roof.
+            // This detects a detached decorative ring even when every individual voxel is in bounds.
+            Set<BlockPos> connected = new HashSet<>(); var pending = new java.util.ArrayDeque<BlockPos>();
+            c.blocks.forEach((p, block) -> {
+                if (p.getY() == 12 && !block.isAir()) { connected.add(p); pending.add(p); }
+            });
+            while (!pending.isEmpty()) {
+                var p = pending.removeFirst();
+                for (Direction direction : Direction.values()) {
+                    var next = p.relative(direction);
+                    if (next.getX() < 0 || next.getX() > 16 || next.getZ() < 0 || next.getZ() > 16
+                            || next.getY() < 12 || next.getY() > 17 || c.block(next).isAir()) continue;
+                    if (connected.add(next)) pending.addLast(next);
+                }
+            }
+            c.blocks.forEach((p, block) -> {
+                if (p.getY() == 17 && block.is(Blocks.SMOOTH_STONE_SLAB))
+                    require(connected.contains(p), label(c) + " observatory crown floats above its buttresses at " + p);
+            });
+            require(c.block(rotate(new BlockPos(8, 17, 8), c.site.facing())).isAir(),
+                label(c) + " crown connection closes the sky-viewing slot");
+        }
+    }
+    private static void clearLightWell(Capture c, int x, int z, int low, int high) {
+        for (int y = low; y <= high; y++) {
+            var p = rotate(new BlockPos(x, y, z), c.site.facing());
+            var block = c.block(p);
+            require(block.isAir() || block.is(Blocks.GLASS) || block.is(Blocks.GLASS_PANE),
+                label(c) + " skylight is blocked by an opaque roof or ceiling at " + p + ": " + block);
+        }
+    }
+    private static void roofBearings21(Capture c) {
+        int roofLine = switch (c.site.kind()) {
+            case COMMUNAL_DEPOT -> 9;
+            case OBSERVATORY -> 12;
+            case CONSTRUCTION_REFUGE, IMPOSSIBLE_SERVICE -> 10;
+            case VOID_DOCK, SUBSTATION -> 5;
+            default -> 6;
+        };
+        Set<BlockPos> supported = new HashSet<>(); var queue = new ArrayDeque<BlockPos>();
+        for (int x = 0; x < 17; x++) for (int z = 0; z < 17; z++) {
+            var at = new BlockPos(x, 0, z);
+            if (bearing(c.block(at))) { supported.add(at); queue.addLast(at); }
+        }
+        while (!queue.isEmpty()) {
+            var at = queue.removeFirst();
+            for (var direction : Direction.values()) {
+                var next = at.relative(direction);
+                if (next.getX() < 0 || next.getX() > 16 || next.getZ() < 0 || next.getZ() > 16
+                        || next.getY() < 0 || next.getY() > c.site.height() || !bearing(c.block(next))) continue;
+                if (supported.add(next)) queue.addLast(next);
+            }
+        }
+        // Shutters and cabinet screens may hang from a wall or each other, but not hover
+        // over a counter. The playable floor hatch has its separately verified ladder/lip contract.
+        queue.addAll(supported);
+        while (!queue.isEmpty()) {
+            var at = queue.removeFirst();
+            for (var direction : Direction.values()) {
+                var next = at.relative(direction);
+                if (c.block(next).getBlock() instanceof TrapDoorBlock && supported.add(next)) queue.addLast(next);
+            }
+        }
+        for (var e : c.blocks.entrySet()) if (e.getKey().getY() > 0 && e.getValue().getBlock() instanceof TrapDoorBlock) {
+            boolean floorHatch = c.site.kind() == HeritagePlan19.Kind.CONSTRUCTION_REFUGE
+                && e.getKey().equals(rotate(new BlockPos(10, 5, 11), c.site.facing()));
+            require(floorHatch || supported.contains(e.getKey()), label(c) + " decorative screen has no frame or counter at " + e.getKey());
+        }
+        long witnesses = 0;
+        for (var e : c.blocks.entrySet()) if (e.getKey().getY() > 0 && bearing(e.getValue())) {
+            if (e.getKey().getY() >= roofLine) witnesses++;
+            require(supported.contains(e.getKey()), label(c) + " construction or ornament is detached from all grounded walls/frames at " + e.getKey());
+        }
+        require(witnesses > 0, label(c) + " roof-bearing test has no physical roof witness");
+    }
+    private static boolean bearing(BlockState block) {
+        return !block.isAir() && block.getFluidState().isEmpty() && !block.is(Blocks.LANTERN)
+            && !block.is(Blocks.LEVER) && !block.is(Blocks.LADDER) && !block.is(Blocks.RAIL)
+            && !(block.getBlock() instanceof DoorBlock) && !(block.getBlock() instanceof TrapDoorBlock)
+            && !block.hasProperty(BlockStateProperties.BED_PART);
+    }
+    private static void export(Capture c) {
+        String directory = System.getProperty("sanctuary.test.heritage21.export");
+        if (directory == null || directory.isBlank()) return;
+        var blocks = c.blocks.entrySet().stream().filter(e -> !e.getValue().isAir())
+            .sorted(java.util.Comparator.<Map.Entry<BlockPos, BlockState>>comparingInt(e -> e.getKey().getY())
+                .thenComparingInt(e -> e.getKey().getZ()).thenComparingInt(e -> e.getKey().getX()))
+            .map(e -> List.of(e.getKey().getX(), e.getKey().getY(), e.getKey().getZ(), e.getValue().toString())).toList();
+        var targets = HeritageRenderer21.targets(c.site).stream().map(t -> List.of(t.name(), t.x(), t.y(), t.z())).toList();
+        var document = Map.of("kind", c.site.kind().name(), "facing", c.site.facing(), "seed", c.site.seed(),
+            "width", 17, "depth", 17, "height", c.site.height(), "floor_y", 0, "blocks", blocks, "targets", targets);
+        try {
+            var root = java.nio.file.Path.of(directory); java.nio.file.Files.createDirectories(root);
+            java.nio.file.Files.writeString(root.resolve(c.site.kind().name().toLowerCase(java.util.Locale.ROOT) + ".json"),
+                new com.google.gson.GsonBuilder().setPrettyPrinting().create().toJson(document));
+        } catch (java.io.IOException error) { throw new AssertionError("Cannot export the requested architecture capture", error); }
+    }
+    private static void materials21() {
+        Map<Block, Long> counts = new HashMap<>();
+        for (var kind : HeritagePlan19.Kind.values()) render(site(kind, 0, 0)).blocks.forEach((p, b) -> {
+            if (p.getY() > 0 && !b.isAir()) counts.merge(b.getBlock(), 1L, Long::sum);
+        });
+        for (Block block : new Block[] {Blocks.SMOOTH_STONE, Blocks.STONE, Blocks.STONE_BRICKS,
+                Blocks.CRACKED_STONE_BRICKS, Blocks.MOSSY_STONE_BRICKS, Blocks.ANDESITE,
+                Blocks.OAK_WOOD, Blocks.BIRCH_WOOD, Blocks.OAK_PLANKS, Blocks.BIRCH_PLANKS})
+            require(counts.getOrDefault(block, 0L) > 0, "The restrained generation21 palette omits " + block);
+        require(counts.get(Blocks.SMOOTH_STONE) > counts.getOrDefault(Blocks.STONE_BRICKS, 0L)
+                && counts.get(Blocks.SMOOTH_STONE) > counts.getOrDefault(Blocks.ANDESITE, 0L),
+            "Smooth stone is no longer the principal masonry of the catalogue");
+    }
+    private static void has(Capture c, Block b) { require(c.blocks.values().stream().anyMatch(v -> v.is(b)), label(c) + " loses its " + b); }
+    private static void railConnection(Capture c) {
+        BlockPos destination = switch (c.site.kind()) {
+            case FREIGHT_STATION -> new BlockPos(2, 1, 8);
+            case RAIL_WORKSHOP -> new BlockPos(5, 1, 7);
+            case COMMUNAL_DEPOT -> new BlockPos(8, 1, 7);
+            default -> null;
+        };
+        if (destination == null) return;
+        var start = rotate(new BlockPos(8, 1, 0), c.site.facing());
+        destination = rotate(destination, c.site.facing());
+        Set<BlockPos> seen = new HashSet<>(); var queue = new ArrayDeque<BlockPos>(); seen.add(start); queue.add(start);
+        while (!queue.isEmpty()) {
+            var p = queue.removeFirst(); var b = c.block(p);
+            require(b.is(Blocks.RAIL), label(c) + " freight entry has no supported rail");
+            for (var d : railEnds(b)) {
+                var next = p.relative(d); var state = c.block(next);
+                if (state.is(Blocks.RAIL) && railEnds(state).contains(d.getOpposite()) && seen.add(next)) queue.add(next);
+            }
+        }
+        require(seen.contains(destination), label(c) + " interior rail does not connect to its real external freight entry");
+    }
+    private static List<Direction> railEnds(BlockState b) {
+        return switch (b.getValue(BlockStateProperties.RAIL_SHAPE)) {
+            case NORTH_SOUTH, ASCENDING_NORTH, ASCENDING_SOUTH -> List.of(Direction.NORTH, Direction.SOUTH);
+            case EAST_WEST, ASCENDING_EAST, ASCENDING_WEST -> List.of(Direction.EAST, Direction.WEST);
+            case SOUTH_EAST -> List.of(Direction.SOUTH, Direction.EAST);
+            case SOUTH_WEST -> List.of(Direction.SOUTH, Direction.WEST);
+            case NORTH_WEST -> List.of(Direction.NORTH, Direction.WEST);
+            case NORTH_EAST -> List.of(Direction.NORTH, Direction.EAST);
+        };
+    }
+    private static void routes() {
+        var cells = new ArrayList<HeritagePlan19.Cell>();
+        int x = -15;
+        for (var rail : HeritagePlan19.Rail.values()) {
+            cells.add(new HeritagePlan19.Cell(x++, 160, 2, 2, rail, rail != HeritagePlan19.Rail.NONE));
+        }
+        cells.add(new HeritagePlan19.Cell(-1, 161, 2, 3, HeritagePlan19.Rail.ASCENDING_EAST, false));
+        var segment = new HeritagePlan19.Segment("route", "a", "b", HeritagePlan19.RouteKind.FREIGHT, -1, 0, cells, 7);
+        Map<BlockPos, BlockState> result = new HashMap<>();
+        HeritageRenderer21.renderSegment(segment, new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState b) {
+                var p = new BlockPos(segment.minX() + x, segment.minY() + y, segment.minZ() + z);
+                var cell = cells.stream().filter(c -> c.x() == p.getX() && c.z() == p.getZ()).findFirst().orElseThrow();
+                require(p.getY() >= cell.minY() && p.getY() <= cell.maxY(), "Route escaped its saved column mask"); result.put(p, b);
+            }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) { throw new AssertionError("A route generated treasure"); }
+        });
+        for (var c : cells) {
+            var p = new BlockPos(c.x(), c.floorY() + 1, c.z());
+            require(full(result.get(p.below()), p.below()), "Rail or missing-rail witness lost its ballast support");
+            if (c.railPresent()) require(result.get(p).is(Blocks.RAIL)
+                && result.get(p).getValue(BlockStateProperties.RAIL_SHAPE).name().equals(c.rail().name()), "Saved rail shape was replaced by a straight track");
+            else require(result.get(p).isAir(), "An intentional abandoned-track gap was repaired by rendering");
+        }
+    }
+    private static void chunkPartition() {
+        var s = site(HeritagePlan19.Kind.CONSTRUCTION_REFUGE, 3, 43); var expected = render(s); var parts = new Capture(s);
+        for (int cz = s.maxZ() >> 4; cz >= s.minZ() >> 4; cz--) for (int cx = s.maxX() >> 4; cx >= s.minX() >> 4; cx--) {
+            final int chunkX = cx, chunkZ = cz;
+            HeritageRenderer21.render(s, new LostCityRenderer.BlockWriter() {
+                boolean owns(int x, int z) { return ((s.minX() + x) >> 4) == chunkX && ((s.minZ() + z) >> 4) == chunkZ; }
+                @Override public void set(int x, int y, int z, BlockState state) { if (owns(x, z)) parts.set(x, y, z, state); }
+                @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) { if (owns(x, z)) parts.chest(x, y, z, table, seed); }
+            });
+        }
+        require(parts.blocks.equals(expected.blocks) && parts.loot.equals(expected.loot), "Native chunk order changes a site");
+    }
+    private record Loot(ResourceKey<LootTable> table, long seed) {}
+    private static final class Capture implements LostCityRenderer.BlockWriter {
+        final HeritagePlan19.Site site;
+        final Map<BlockPos, BlockState> blocks = new HashMap<>();
+        final Map<BlockPos, Loot> loot = new HashMap<>();
+        Capture(HeritagePlan19.Site site) { this.site = site; }
+        @Override public void set(int x, int y, int z, BlockState state) {
+            int wy = y + site.floorY();
+            boolean main = x >= 0 && x <= 16 && z >= 0 && z <= 16 && wy >= site.minY() && wy <= site.maxY();
+            boolean footing = site.supports().stream().anyMatch(s -> s.x() == x + site.minX() && s.z() == z + site.minZ() && wy >= s.minY() && wy <= s.maxY());
+            require(main || footing, label(this) + " writes outside its exact body and footing mask"); blocks.put(new BlockPos(x, y, z), state);
+        }
+        @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) {
+            require(loot.put(new BlockPos(x, y, z), new Loot(table, seed)) == null, "Duplicate shared treasure"); set(x, y, z, Blocks.CHEST.defaultBlockState());
+        }
+        BlockState block(BlockPos p) { return blocks.getOrDefault(p, Blocks.AIR.defaultBlockState()); }
+    }
+    private static void require(boolean value, String message) { if (!value) throw new AssertionError(message); }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/transit/Transit21Smoke.java

@@ -0,0 +1,175 @@
+package fr.koka.sanctuary.worldgen.transit;
+
+import fr.koka.sanctuary.worldgen.city.LostCityInteriors21Smoke;
+import fr.koka.sanctuary.worldgen.city.LostCityRenderer;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Kind;
+import fr.koka.sanctuary.worldgen.transit.TransitPlan21.Module;
+import java.util.ArrayDeque;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.EmptyBlockGetter;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.storage.loot.LootTable;
+import net.minecraft.world.phys.AABB;
+
+/** Native block-shape paths across the entire planned route, plus refusal and exact saved geometry. */
+public final class Transit21Smoke {
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion(); Bootstrap.bootStrap(); run();
+        System.out.println("Transit21Smoke: bounded planning, two surface stair exits, through-road and hall, supported roofs, strict saved modules and all interior targets passed.");
+    }
+    public static void run() {
+        var terrain = new Plateau();
+        for (int diameter : new int[]{512, 724, 1024}) {
+            var plan = TransitPlanner21.plan(0, 0, 0, diameter, terrain);
+            require(!plan.isEmpty(), "Continuous native rock rejected its through-route: " + plan.diagnostic());
+            var accesses = plan.modules().stream().filter(m -> m.kind() == Kind.ACCESS).toList();
+            require(accesses.size() == 2, "Route lacks two surface stair exits");
+            int span = Math.abs(accesses.get(0).centerX() - accesses.get(1).centerX())
+                + Math.abs(accesses.get(0).centerZ() - accesses.get(1).centerZ());
+            require(span >= diameter * .4, "Route became a short unconnected cellar");
+            require(plan.modules().stream().anyMatch(m -> m.kind() == Kind.HALL), "Available space produced no industrial hall");
+            require(plan.equals(TransitPlanner21.plan(0, 0, 0, diameter, terrain)), "Identical input changed final saved geometry");
+            require(plan.samples() <= TransitPlan21.MAX_SAMPLES, "Planning exceeded its work bound");
+            for (var access : accesses) {
+                require(plan.protects(access.centerX(), access.surfaceY() + 2, access.minZ() - 1), "Outside access approach can be decorated shut");
+                require(!plan.contains(access.centerX(), access.surfaceY(), access.minZ() - 1), "Read-only approach became a painted platform");
+            }
+            if (diameter == 724) verifyWorld(plan);
+            for (var m : plan.modules()) {
+                var saved = TransitPiece21.encodeModule(m);
+                require(TransitPiece21.decodeModule(saved).equals(m), "Module changed its persisted geometry");
+                var foreign = saved.copy(); foreign.putInt("Foreign", 1); reject(foreign);
+                var wrongType = saved.copy(); wrongType.putLong("Width", m.width()); reject(wrongType);
+                var missing = saved.copy(); missing.remove("Supports"); reject(missing);
+            }
+        }
+        var blocked = TransitPlanner21.plan(0, 0, 0, 724, new Plateau() {
+            @Override public boolean protectedAt(int x, int y, int z) { return true; }
+        });
+        require(blocked.isEmpty(), "Transit destroyed protected construction/hydrology");
+        var voidFloor = TransitPlanner21.plan(0, 0, 0, 724, new Plateau() {
+            @Override public boolean solid(int x, int y, int z) { return y >= 245 && y <= 252; }
+        });
+        require(voidFloor.isEmpty(), "Transit built an unsupported island-wide bridge");
+        var shortGap = TransitPlanner21.plan(0, 0, 0, 512, new Plateau() {
+            @Override public boolean solid(int x, int y, int z) { return super.solid(x, y, z) && !(y >= 199 && y <= 214); }
+        });
+        require(!shortGap.isEmpty() && shortGap.modules().stream().flatMap(m -> m.supports().stream())
+            .anyMatch(s -> s.maxY() - s.minY() + 1 == 16), "Certified sixteen-block piers should bridge a bounded natural cavity");
+        boolean longPierRejected = false;
+        try { new TransitPlan21.Support(0, 200, 0, 216); } catch (IllegalArgumentException expected) { longPierRejected = true; }
+        require(longPierRejected, "A seventeen-block pier escaped the foundation contract");
+        var oneStepApproach = TransitPlanner21.plan(0, 0, 0, 512, new Plateau() {
+            @Override public int surfaceY(int x, int z) { return (x & 1) == 0 ? 251 : 252; }
+        });
+        require(!oneStepApproach.isEmpty() && oneStepApproach.modules().stream().filter(m -> m.kind() == Kind.ACCESS)
+            .allMatch(m -> m.surfaceY() == 252), "A one-step native approach should use its highest cell without levelling it");
+        // Different surface heights terminate a partial flight, not just multiples of five steps.
+        for (int height : new int[]{249, 250, 251, 252, 253, 254, 255, 256, 257, 258}) {
+            var p = TransitPlanner21.plan(3, 0, 0, 512, new Plateau() {
+                @Override public int surfaceY(int x, int z) { return height; }
+            });
+            require(!p.isEmpty(), "Admissible irregular stair rise was rejected");
+            for (var access : p.modules()) if (access.kind() == Kind.ACCESS) verifySingle(access);
+        }
+    }
+    private static void reject(CompoundTag tag) {
+        boolean rejected = false;
+        try { TransitPiece21.decodeModule(tag); } catch (IllegalArgumentException expected) { rejected = true; }
+        require(rejected, "Saved module accepted missing/foreign/wrong-typed geometry");
+    }
+    private static void verifySingle(Module m) {
+        var capture = new Capture(); renderInto(m, capture);
+        var entrance = world(m, TransitRenderer21.targets(m).stream().filter(t -> t.name().equals("surface_portico")).findFirst().orElseThrow());
+        var reached = walk(capture, entrance);
+        for (var target : TransitRenderer21.targets(m)) require(reached.contains(world(m, target)),
+            "Stair access rise=" + (m.surfaceY() - m.floorY()) + " cannot reach " + target.name() + " " + world(m, target));
+    }
+    private static void verifyWorld(TransitPlan21 plan) {
+        var capture = new Capture();
+        for (var module : plan.modules()) renderInto(module, capture);
+        var first = plan.modules().stream().filter(m -> m.kind() == Kind.ACCESS).findFirst().orElseThrow();
+        var entrance = new BlockPos(first.centerX(), first.surfaceY() + 1, first.minZ());
+        var reached = walk(capture, entrance);
+        for (var module : plan.modules()) for (var target : TransitRenderer21.targets(module))
+            require(reached.contains(world(module, target)), "Through-route cannot reach " + module.kind() + "/" + target.name() + " at " + world(module, target));
+        for (var chest : capture.loot) require(java.util.Arrays.stream(new Direction[]{Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST})
+            .anyMatch(d -> reached.contains(chest.relative(d))), "Tools chest has no reachable approach");
+        require(capture.loot.size() == 1, "Route must keep one modest shared tool chest");
+    }
+    private static void renderInto(Module m, Capture into) {
+        var local = new Capture();
+        TransitRenderer21.render(m, new LostCityRenderer.BlockWriter() {
+            @Override public void set(int x, int y, int z, BlockState state) {
+                require(x >= 0 && x < m.width() && z >= 0 && z < m.depth() && y >= m.boundsMinY() - m.minY() && y < m.height(),
+                    "Transit renderer escaped its saved native bounds");
+                local.set(x, y, z, state);
+            }
+            @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) { local.chest(x, y, z, table, seed); }
+        });
+        LostCityInteriors21Smoke.verifyGroundedGeometry(local.blocks, 0, "Transit " + m.kind() + " floor=" + m.floorY());
+        local.blocks.forEach((at, state) -> {
+            var position = at.offset(m.minX(), m.minY(), m.minZ());
+            require(into.blocks.putIfAbsent(position, state) == null, "Neighboring native modules overwrite each other");
+            require(!state.is(Blocks.SPAWNER) && state.getFluidState().isEmpty(), "Transit introduced a spawner or uncontrolled fluid");
+        });
+        for (var chest : local.loot) into.loot.add(chest.offset(m.minX(), m.minY(), m.minZ()));
+    }
+    private static BlockPos world(Module m, TransitRenderer21.Target t) { return new BlockPos(m.minX() + t.x(), m.minY() + t.y(), m.minZ() + t.z()); }
+    private static Set<BlockPos> walk(Capture capture, BlockPos first) {
+        require(standable(capture, first), "Blocked transit entrance " + first);
+        var seen = new HashSet<BlockPos>(); var queue = new ArrayDeque<BlockPos>(); seen.add(first); queue.add(first);
+        while (!queue.isEmpty()) {
+            var at = queue.removeFirst();
+            for (Direction direction : new Direction[]{Direction.NORTH, Direction.EAST, Direction.SOUTH, Direction.WEST})
+                for (int dy = -1; dy <= 1; dy++) {
+                    var next = at.relative(direction).offset(0, dy, 0);
+                    if (dy > 0 && (!clear(capture, at.above()) || !ascending(capture, next.below(), direction))) continue;
+                    if (dy < 0 && (!clear(capture, next.above()) || !ascending(capture, at.below(), direction.getOpposite()))) continue;
+                    if (standable(capture, next) && seen.add(next)) queue.addLast(next);
+                }
+        }
+        return seen;
+    }
+    private static boolean ascending(Capture c, BlockPos at, Direction direction) {
+        var state = c.block(at);
+        return state.getBlock() instanceof net.minecraft.world.level.block.StairBlock
+            && state.getValue(net.minecraft.world.level.block.state.properties.BlockStateProperties.HORIZONTAL_FACING) == direction
+            && state.getValue(net.minecraft.world.level.block.state.properties.BlockStateProperties.HALF)
+                == net.minecraft.world.level.block.state.properties.Half.BOTTOM;
+    }
+    private static boolean standable(Capture c, BlockPos at) {
+        if (!c.blocks.containsKey(at) || !clear(c, at)) return false;
+        return c.block(at.below()).getCollisionShape(EmptyBlockGetter.INSTANCE, at.below()).toAabbs().stream()
+            .anyMatch(box -> box.maxY >= .99 && box.minX < .8 && box.maxX > .2 && box.minZ < .8 && box.maxZ > .2);
+    }
+    private static boolean clear(Capture c, BlockPos at) {
+        var body = new AABB(.2, 0, .2, .8, 1.8, .8);
+        for (int up = 0; up < 2; up++) for (var box : c.block(at.above(up)).getCollisionShape(EmptyBlockGetter.INSTANCE, at.above(up)).toAabbs())
+            if (body.intersects(box.move(0, up, 0))) return false;
+        return true;
+    }
+    private static class Plateau implements TransitPlanner21.Terrain {
+        @Override public boolean owns(int x, int z) { return Math.abs(x) < 600 && Math.abs(z) < 600; }
+        @Override public boolean solid(int x, int y, int z) { return y >= 80 && y <= 252; }
+        @Override public boolean protectedAt(int x, int y, int z) { return false; }
+        @Override public int surfaceY(int x, int z) { return 252; }
+    }
+    private static final class Capture implements LostCityRenderer.BlockWriter {
+        final Map<BlockPos, BlockState> blocks = new HashMap<>(); final Set<BlockPos> loot = new HashSet<>();
+        @Override public void set(int x, int y, int z, BlockState state) { blocks.put(new BlockPos(x, y, z), state); }
+        @Override public void chest(int x, int y, int z, ResourceKey<LootTable> table, long seed) { set(x, y, z, Blocks.CHEST.defaultBlockState()); loot.add(new BlockPos(x, y, z)); }
+        BlockState block(BlockPos at) { return blocks.getOrDefault(at, Blocks.AIR.defaultBlockState()); }
+    }
+    private static void require(boolean condition, String message) { if (!condition) throw new AssertionError(message); }
+}

packwiz/pack.toml

@@ -1,6 +1,6 @@
 name = "Sanctuary"
 author = "KOKA99CAB"
-version = "0.1.0-alpha.20"
+version = "0.1.0-alpha.21"
 pack-format = "packwiz:1.1.0"
 
 [index]