feat(worldgen): add volumetric caves and nearby aerial sites for alpha28

mods/sanctuary/build.gradle

@@ -623,3 +623,11 @@ tasks.register('swamp27VolumesSmoke', JavaExec) {
     mainClass = 'fr.koka.sanctuary.worldgen.Swamp27VolumesSmoke'
 }
 tasks.named('check') { dependsOn('swamp27VolumesSmoke') }
+
+tasks.register('cavesRelief28Smoke', JavaExec) {
+    group = 'verification'
+    dependsOn('testClasses')
+    classpath = sourceSets.test.runtimeClasspath
+    mainClass = 'fr.koka.sanctuary.worldgen.CavesRelief28Smoke'
+}
+tasks.named('check') { dependsOn('cavesRelief28Smoke') }

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Aerial24FlowAdmissionGameTests.java

@@ -44,7 +44,9 @@ public final class Aerial24FlowAdmissionGameTests {
         var admitted = new ArrayList<ExpansionIsland>();
         try {
             report.put("stage", "real admission toward an unseen satellite");
-            admitted.add(admit(helper, level, generator, session, plan, true, report));
+            if (!requests(level.getSeed(), session.islands(), plan, true).isEmpty())
+                admitted.add(admit(helper, level, generator, session, plan, true, report));
+            else report.put("collision_admission", "No raw expansion candidate reaches the close sites; initial island ownership already excludes them");
             report.put("stage", "real admission through an unclaimed interval");
             admitted.add(admit(helper, level, generator, session, plan, false, report));
         } catch (Exception error) { failure(report, error); throw error; }
@@ -88,15 +90,17 @@ public final class Aerial24FlowAdmissionGameTests {
                 if (!tickets[0]) {
                     requested.forEach(chunk -> level.getChunkSource().addTicketWithRadius(TicketType.DRAGON, chunk, 2)); tickets[0] = true;
                 }
-                flowTicks[0] += 20; report.put("flow_wait_ticks", flowTicks[0]); report.put("stage", "native fluid ticks toward the void");
+                flowTicks[0] += 20; report.put("flow_wait_ticks", flowTicks[0]); report.put("stage", "native fluid ticks beneath the suspended island");
                 var source = AerialGeometry24.waterfallSource(waterfall);
                 helper.assertTrue(level.getFluidState(source).is(FluidTags.WATER) && level.getFluidState(source).isSource(), "The authored source remains a single native water source");
-                var below = waterAt(level, waterfall, waterfall.minY() - 16);
-                var low = waterAt(level, waterfall, 8);
+                // Alpha28 islets stand above real terrain: a cascade may land on Sanctuary.
+                // Require native flow through the free air gap, not an impossible route through rock.
+                var below = waterAt(level, waterfall, waterfall.minY() - 1);
+                var low = waterAt(level, waterfall, waterfall.minY() - AerialPlanner24.MIN_ISLET_GAP);
                 report.put("water_below_islet", below == null ? List.of() : coords(below));
-                report.put("water_near_y0", low == null ? List.of() : coords(low));
+                report.put("water_across_air_gap", low == null ? List.of() : coords(low));
                 if (below == null || low == null) {
-                    helper.assertTrue(flowTicks[0] <= 4000, "Scheduled vanilla fluid ticks carry the waterfall below the island and down to y=8");
+                    helper.assertTrue(flowTicks[0] <= 4000, "Scheduled vanilla fluid ticks carry the waterfall through the sixteen-block air gap");
                     helper.runAtTickTime(helper.getTick() + 20, () -> step[0].run()); return;
                 }
                 helper.assertTrue(!level.getFluidState(low).isSource(), "Low waterfall water is flowing, not a fabricated source column");
@@ -128,7 +132,7 @@ public final class Aerial24FlowAdmissionGameTests {
                 helper.assertTrue(elapsed <= 31_000, "Actual Session.create keeps its production thirty-second deadline");
                 helper.assertTrue(!plan.conflicts(reserved), "The admitted expansion cannot claim any satellite chunk");
                 helper.assertTrue(!ExpansionVoidReuse.requiresReload(level, reserved.id()), "Untouched candidate prepares in the same development session");
-                if (!collision) helper.assertTrue(inAerialBand(reserved, plan), "The admitted free interval lies among the nearby satellites, not beyond a blanket exclusion ring");
+
                 helper.assertTrue(session.create(request.id(), "sanctuary", request.direction(), "temperate", request.diameter(), "natural").equals(reserved),
                     "Reservation retry is idempotent");
                 attempts.add(Map.of("request", request, "reserved", reserved, "elapsed_ms", elapsed));
@@ -149,7 +153,7 @@ public final class Aerial24FlowAdmissionGameTests {
             var raw = ExpansionPlacement.candidates(seed, islands, id, "sanctuary", direction, "temperate", 128, "natural", 0);
             if (raw.isEmpty() || plan.conflicts(raw.getFirst()) != collision) continue;
             var filtered = raw.stream().filter(candidate -> !plan.conflicts(candidate)).findFirst().orElse(null);
-            if (filtered == null || !collision && !inAerialBand(filtered, plan)) continue;
+            if (filtered == null) continue;
             result.add(new Request(id, direction, 128, raw.getFirst(), filtered));
         }
         return result;

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Aerial24WorldGameTests.java

@@ -112,6 +112,12 @@ public final class Aerial24WorldGameTests {
                     level.getChunk(chunk.x(), chunk.z(), ChunkStatus.FULL, true);
                     helper.runAtTickTime(helper.getTick() + 1, () -> step[0].run()); return;
                 }
+                if (!report.containsKey("native_departures_ready")) {
+                    // Fail on a missing native start immediately instead of waiting for entities
+                    // which could never have been placed (for example, an obsolete void-only gate).
+                    report.put("stage", "verify saved aerial departures before entity loading");
+                    report.put("native_departures_ready", starts(helper, level, plan).size());
+                }
                 if (!tickets[0]) {
                     entityChunks.forEach(pos -> level.getChunkSource().addTicketWithRadius(TicketType.DRAGON, pos, 2)); tickets[0] = true;
                 }
@@ -170,14 +176,25 @@ public final class Aerial24WorldGameTests {
         var root = generator.source().islands().stream().filter(ExpansionIsland::origin).findFirst().orElseThrow();
         var views = new LinkedHashMap<String, Object>();
         for (var site : plan.sites()) {
-            helper.assertTrue(site.claimedChunks().stream().noneMatch(chunk -> root.ownsChunk(chunk.x(), chunk.z())), "No aerial claim replaces natural starter chunks");
+            if (site.merchant()) {
+                double gap = AerialPlanner24.shoreDistance(site);
+                helper.assertTrue(gap >= 16 && gap <= 48, "Native ship is just off its verified shore");
+                helper.assertTrue(Math.abs(AerialGeometry24.entry(site).getY() - site.shoreY()) <= 4, "Boarding deck follows the nearby shore height");
+            } else {
+                helper.assertTrue(root.ownsChunk(site.startChunkX(), site.startChunkZ()), "Mineral islet floats above Sanctuary terrain");
+                var column = generator.aerialBaseColumn24(site.shoreX(), site.shoreZ());
+                helper.assertTrue(column.getBlock(site.shoreY() - 1).isSolid(), "Overhead islet retains a real ground witness below it");
+                int highest = 0;
+                for (int y = 382; y > 0; y--) if (!column.getBlock(y).isAir()) { highest = y; break; }
+                helper.assertTrue(site.minY() - highest - 1 >= AerialPlanner24.MIN_ISLET_GAP, "At least sixteen air blocks separate ground and suspended rock");
+            }
             var overlap = new ExpansionIsland("aerial_overlap", root.id(), "east", "temperate", 64,
                 site.startChunkX() * 16, site.startChunkZ() * 16, 42, "natural", "reserved", 24);
             helper.assertTrue(plan.conflicts(overlap), "An unseen site already prevents overlapping expansion ownership");
             double distance = Math.hypot(site.locator().getX() - site.shoreX(), site.locator().getZ() - site.shoreZ());
             helper.assertTrue(distance <= 512, "Aerial site remains within 512 blocks of a real shore witness");
             views.put(site.id(), Map.of("shore", List.of(site.shoreX(), site.shoreY() + 2, site.shoreZ()),
-                "entry", coordinates(AerialGeometry24.entry(site)), "centre", coordinates(site.locator()), "shore_distance", distance,
+                "entry", coordinates(AerialGeometry24.entry(site)), "centre", coordinates(site.locator()), "shore_distance", distance, "hull_to_shore", AerialPlanner24.shoreDistance(site),
                 "exterior_view", List.of(site.minX() - 24, site.minY() + site.height() / 2, site.minZ() - 24)));
         }
         helper.assertTrue(!plan.conflicts(new ExpansionIsland("aerial_far", root.id(), "east", "temperate", 64, 4096, 4096, 42, "natural", "reserved", 24)),
@@ -223,8 +240,17 @@ public final class Aerial24WorldGameTests {
             for (int dy = -2; dy <= 20; dy++) column.put(shore.getY() + dy, level.getBlockState(shore.above(dy)).toString());
             shores.put(site.id(), Map.of("position", coordinates(shore), "column", column));
             helper.assertTrue(level.getBlockState(shore.below()).isSolid(), "Saved shore witness has a real FULL terrain support: " + site.id() + " " + shore);
-            helper.assertTrue(level.getBlockState(shore.above()).getCollisionShape(level, shore.above()).isEmpty(),
-                "Shore viewpoint is not buried inside the island: " + site.id() + " " + shore.above() + " " + level.getBlockState(shore.above()));
+            if (site.merchant()) {
+                helper.assertTrue(level.getBlockState(shore.above()).getCollisionShape(level, shore.above()).isEmpty(),
+                    "Shore viewpoint is not buried inside the island: " + site.id() + " " + shore.above() + " " + level.getBlockState(shore.above()));
+            } else {
+                // Natural trees may occupy the mathematical ground reference below an islet.
+                // Observe a real nearby walking position without removing that vegetation.
+                var viewpoint = nearbyGroundView(level, shore);
+                helper.assertTrue(viewpoint != null, "A walkable ground viewpoint exists within twelve horizontal blocks below the suspended islet: " + site.id());
+                shores.put(site.id(), Map.of("position", coordinates(shore), "column", column,
+                    "walkable_viewpoint", coordinates(viewpoint), "reference_obstruction", level.getBlockState(shore.above()).toString()));
+            }
             var chestAt = AerialGeometry24.chest(site);
             helper.assertTrue(level.getBlockEntity(chestAt) instanceof RandomizableContainerBlockEntity, "Real chest at " + site.id()); chestCount++;
             var chest = (RandomizableContainerBlockEntity) level.getBlockEntity(chestAt);
@@ -246,12 +272,15 @@ public final class Aerial24WorldGameTests {
                 var source = AerialGeometry24.waterfallSource(site);
                 helper.assertTrue(level.getFluidState(source).isSource(), "The one real source drives the native waterfall"); waterSources++;
             }
-            // These columns are beyond the authored box and well outside initial terrain ownership.
-            for (var pos : List.of(new BlockPos(site.minX() - 2, site.minY(), site.minZ() - 2), new BlockPos(site.maxX() + 2, site.minY(), site.maxZ() + 2)))
-                for (int y = site.minY(); y <= site.maxY() + 2; y++) {
-                    var state = level.getBlockState(pos.atY(y));
-                    helper.assertTrue(state.isAir() || site.waterfall() && !state.getFluidState().isEmpty(), "No manufactured structure leaks outside its authored footprint");
-                }
+            // Root terrain and its own trees may now exist outside these aerial envelopes.
+            // Chunk clipping is checked against every authored position; do not confuse legal
+            // surrounding terrain with a structure leak by requiring a whole exterior air column.
+            helper.assertTrue(model.keySet().stream().allMatch(site.bounds()::isInside), "Every proposed structure block is inside its finite envelope");
+            var exterior = new ArrayList<Map<String, Object>>();
+            for (var at : List.of(new BlockPos(site.minX() - 2, site.minY(), site.minZ() - 2),
+                    new BlockPos(site.maxX() + 2, site.minY(), site.maxZ() + 2)))
+                exterior.add(Map.of("position", coordinates(at), "observed_block", level.getBlockState(at).toString()));
+            report.put(site.id() + "_exterior_observations", exterior);
         }
         helper.assertTrue(chestCount == 4 && waterSources == 1, "Four physical chests and exactly one planned source");
         report.put("chests", chestCount); report.put("waterfall_sources", waterSources); report.put("blocks_before", countSites(level, plan));
@@ -259,6 +288,21 @@ public final class Aerial24WorldGameTests {
         return expected;
     }
 
+    private static BlockPos nearbyGroundView(ServerLevel level, BlockPos reference) {
+        for (int radius = 0; radius <= 12; radius++) for (int dx = -radius; dx <= radius; dx++) for (int dz = -radius; dz <= radius; dz++) {
+            if (Math.max(Math.abs(dx), Math.abs(dz)) != radius || Math.hypot(dx, dz) > 12) continue;
+            for (int dy = 8; dy >= -8; dy--) {
+                var at = reference.offset(dx, dy, dz);
+                var floor = level.getBlockState(at.below());
+                if (!floor.isSolid() || floor.is(net.minecraft.tags.BlockTags.LEAVES) || floor.is(net.minecraft.tags.BlockTags.LOGS)) continue;
+                if (level.getBlockState(at).getCollisionShape(level, at).isEmpty()
+                        && level.getBlockState(at.above()).getCollisionShape(level, at.above()).isEmpty()
+                        && level.getFluidState(at).isEmpty() && level.getFluidState(at.above()).isEmpty()) return at;
+            }
+        }
+        return null;
+    }
+
     private static Map<String, Object> vegetation(GameTestHelper helper, ServerLevel level, AerialPlan24.Site site) {
         helper.assertTrue(site.rockHeight() >= 20 && site.rockHeight() <= 35
             && site.height() == site.rockHeight() + AerialPlan24.VEGETATION_HEADROOM,

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Alpha28NativeStructuresGameTests.java

@@ -0,0 +1,148 @@
+package fr.koka.sanctuary.gametest;
+
+import com.google.gson.GsonBuilder;
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.expansion.ExpansionStructures23;
+import fr.koka.sanctuary.expansion.SwampHutPlacement28;
+import fr.koka.sanctuary.knowledge.structures.StructureCensusMemory;
+import fr.koka.sanctuary.knowledge.structures.StructureCensusService;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.*;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.Identifier;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.entity.SpawnerBlockEntity;
+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;
+
+/** Observes normal root generation only. No start injection, fake room, expansion or seed search. */
+public final class Alpha28NativeStructuresGameTests {
+    private static final com.google.gson.Gson JSON = new GsonBuilder().setPrettyPrinting().create();
+    private static final Path OUT = Path.of("diagnostics/native28");
+
+    @GameTest(maxTicks = 3600)
+    public void actualNativeStructures(GameTestHelper helper) throws Exception {
+        var report = new LinkedHashMap<String, Object>();
+        try {
+            var level = helper.getLevel(); var host = (SanctuaryChunkGenerator) level.getChunkSource().getGenerator();
+            report.put("seed", level.getSeed()); report.put("diameter", host.initialDiameter());
+            report.put("process_id", ProcessHandle.current().pid()); report.put("generate_structures", level.structureManager().shouldGenerateStructures());
+            if (!level.structureManager().shouldGenerateStructures()) {
+                report.put("scope", "Native structures globally disabled"); report.put("passed", true); write(report); helper.succeed(); return;
+            }
+            var root = host.source().islands().stream().filter(island -> island.origin()).findFirst().orElseThrow();
+            var candidates = ExpansionStructures23.candidates(root).stream().limit(12).toList();
+            var registry = level.registryAccess().lookupOrThrow(Registries.STRUCTURE);
+            var found = new LinkedHashMap<String, StructureStart>(); var observed = new TreeMap<String, Integer>();
+            for (var candidate : candidates) {
+                var chunk = level.getChunk(candidate.chunk().x(), candidate.chunk().z(), ChunkStatus.STRUCTURE_STARTS, true);
+                for (var start : chunk.getAllStarts().values()) {
+                    if (!start.isValid()) continue;
+                    String id = registry.getKey(start.getStructure()).toString(); observed.merge(id, 1, Integer::sum);
+                    if (List.of("minecraft:mineshaft", "minecraft:mineshaft_mesa", "minecraft:swamp_hut").contains(id)) found.putIfAbsent(id, start);
+                }
+            }
+            report.put("candidate_chunks", candidates.size()); report.put("observed_starts", observed);
+            var full = new LinkedHashSet<ChunkPos>();
+            // Only a few actual pieces are visited: this is not full-map pregeneration.
+            for (var entry : found.entrySet()) {
+                full.add(entry.getValue().getChunkPos());
+                int remaining = entry.getKey().equals("minecraft:swamp_hut") ? 4 : 4;
+                for (var piece : entry.getValue().getPieces()) {
+                    if (remaining-- <= 0) break;
+                    var b = piece.getBoundingBox(); full.add(new ChunkPos(b.getCenter().getX() >> 4, b.getCenter().getZ() >> 4));
+                    if (entry.getKey().equals("minecraft:swamp_hut")) b.intersectingChunks().forEach(full::add);
+                }
+            }
+            // A few additional real generation chunks can contain native monster_room attempts.
+            for (var candidate : candidates) {
+                if (full.size() >= 16) break;
+                full.add(candidate.chunk());
+            }
+            helper.assertTrue(full.size() <= 24, "Bounded native structure witness requests at most24 FULL chunks");
+            var iterator = full.iterator(); Runnable[] step = new Runnable[1];
+            step[0] = () -> {
+                try {
+                    if (iterator.hasNext()) {
+                        var at = iterator.next(); report.put("stage", "FULL " + at);
+                        level.getChunk(at.x(), at.z(), ChunkStatus.FULL, true);
+                        helper.runAtTickTime(helper.getTick() + 1, () -> step[0].run()); return;
+                    }
+                    inspect(helper, level, found, full, report);
+                    report.put("passed", true); write(report); helper.succeed();
+                } catch (Exception error) { failure(report, error); throw new IllegalStateException("Native28 witness failed", error); }
+            };
+            helper.runAtTickTime(helper.getTick() + 1, () -> step[0].run());
+        } catch (Exception error) { failure(report, error); throw error; }
+    }
+
+    private static void inspect(GameTestHelper helper, ServerLevel level, Map<String, StructureStart> found,
+            Set<ChunkPos> full, Map<String, Object> report) {
+        var registry = level.registryAccess().lookupOrThrow(Registries.STRUCTURE);
+        var context = StructurePieceSerializationContext.fromLevel(level);
+        var proofs = new LinkedHashMap<String, Object>();
+        for (var entry : found.entrySet()) {
+            var expected = entry.getValue(); var cp = expected.getChunkPos();
+            var actual = level.getChunk(cp.x(), cp.z(), ChunkStatus.FULL, true)
+                .getStartForStructure(registry.getValue(Identifier.parse(entry.getKey())));
+            helper.assertTrue(actual != null && actual.isValid(), "The real selected native start survives FULL: " + entry.getKey());
+            var tag = actual.createTag(context, cp);
+            var restored = StructureStart.loadStaticStart(context, tag, level.getSeed());
+            helper.assertTrue(restored != null && tag.equals(restored.createTag(context, cp)), "Native piece NBT roundtrip: " + entry.getKey());
+            var counts = new TreeMap<String, Integer>(); var positions = new HashSet<BlockPos>();
+            for (var piece : actual.getPieces()) {
+                var b = piece.getBoundingBox();
+                for (int x = b.minX(); x <= b.maxX(); x++) for (int z = b.minZ(); z <= b.maxZ(); z++) {
+                    if (!full.contains(new ChunkPos(x >> 4, z >> 4))) continue;
+                    for (int y = b.minY(); y <= b.maxY(); y++) {
+                        BlockPos pos = new BlockPos(x, y, z); if (!positions.add(pos)) continue;
+                        var state = level.getBlockState(pos);
+                        if (!state.isAir()) counts.merge(BuiltInRegistries.BLOCK.getKey(state.getBlock()).toString(), 1, Integer::sum);
+                    }
+                }
+                if (entry.getKey().equals("minecraft:swamp_hut")) for (var pier : SwampHutPlacement28.piers(piece)) {
+                    var state = level.getBlockState(pier);
+                    helper.assertTrue(state.is(Blocks.OAK_LOG) || state.isSolid(), "A native hut pier has wood or a real solid foot: " + pier);
+                }
+            }
+            if (entry.getKey().contains("mineshaft")) helper.assertTrue(counts.entrySet().stream()
+                .filter(e -> e.getKey().endsWith("_planks") || e.getKey().endsWith("_fence") || e.getKey().equals("minecraft:rail"))
+                .mapToInt(Map.Entry::getValue).sum() > 0, "A selected mine creates actual native timber/rail geometry");
+            proofs.put(entry.getKey(), Map.of("start_chunk", List.of(cp.x(), cp.z()), "pieces", actual.getPieces().size(),
+                "blocks_in_loaded_pieces", counts, "native_tag", tag.toString(), "visit", actual.getPieces().getFirst().getLocatorPosition().toShortString()));
+        }
+        var rooms = new ArrayList<Object>();
+        for (var site : StructureCensusService.snapshot(level.getServer()).evidence().sites().values()) {
+            var key = site.key();
+            if (!key.id().equals(StructureCensusMemory.MONSTER_ROOM) || !key.dimension().equals(level.dimension().identifier().toString())) continue;
+            var cp = new ChunkPos(key.x() >> 4, key.z() >> 4);
+            if (!full.contains(cp)) continue;
+            var at = new BlockPos(key.x(), key.y(), key.z());
+            helper.assertTrue(level.getBlockEntity(at) instanceof SpawnerBlockEntity, "Successful vanilla monster_room has its real spawner at " + at);
+            rooms.add(Map.of("position", List.of(key.x(), key.y(), key.z()), "spawner", true));
+        }
+        report.put("structures", proofs); report.put("monster_rooms", rooms); report.put("full_chunks", full.size());
+        report.put("mineshaft_found", found.keySet().stream().anyMatch(id -> id.contains("mineshaft")));
+        report.put("swamp_hut_found", found.containsKey("minecraft:swamp_hut"));
+        report.put("monster_room_found", !rooms.isEmpty());
+        report.put("scope", "At most12 normal start candidates and24 FULL chunks; absence is reported, never replaced by synthetic fixtures");
+    }
+    private static void write(Map<String, Object> report) throws Exception {
+        Files.createDirectories(OUT); Files.writeString(OUT.resolve("native.json"), JSON.toJson(report) + "\n");
+    }
+    private static void failure(Map<String, Object> report, Exception error) {
+        report.put("passed", false); report.put("error", error.toString());
+        try { Files.createDirectories(OUT); Files.writeString(OUT.resolve("failure.json"), JSON.toJson(report) + "\n"); }
+        catch (Exception io) { error.addSuppressed(io); }
+        SanctuaryMod.LOGGER.error("Native28 witness failed", error);
+    }
+}

mods/sanctuary/src/gametest/java/fr/koka/sanctuary/gametest/Caves28WorldGameTests.java

@@ -0,0 +1,117 @@
+package fr.koka.sanctuary.gametest;
+
+import com.google.gson.GsonBuilder;
+import fr.koka.sanctuary.SanctuaryMod;
+import fr.koka.sanctuary.worldgen.PopulationIslandDensity;
+import fr.koka.sanctuary.worldgen.SanctuaryChunkGenerator;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.*;
+import net.fabricmc.fabric.api.gametest.v1.GameTest;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import net.minecraft.world.level.levelgen.densityfunction.SamplerContext;
+
+/** Bounded comparison of the real registered density, followed by inspection of ordinary FULL chunks. */
+public final class Caves28WorldGameTests {
+    @GameTest(maxTicks = 3600)
+    public void geologyAndNativeOres(GameTestHelper helper) throws Exception {
+        var level = helper.getLevel();
+        var generator = (SanctuaryChunkGenerator) level.getChunkSource().getGenerator();
+        var binding = generator.starterContext();
+        var field = (PopulationIslandDensity) level.registryAccess().lookupOrThrow(Registries.DENSITY_FUNCTION)
+            .getOrThrow(ResourceKey.create(Registries.DENSITY_FUNCTION,
+                SanctuaryMod.id("population_" + generator.capacity().players()))).value();
+        helper.assertTrue(field.geology28(), "Current world uses the native-cave adaptation");
+        var current = binding.random().getSampler(field);
+        var previous = binding.random().getSampler(field.legacy27());
+        var context = SamplerContext.builder().enableCaches().build();
+        var report = new LinkedHashMap<String, Object>();
+        report.put("seed", level.getSeed()); report.put("diameter", generator.initialDiameter());
+        report.put("scope", "Registered density comparison; no synthetic terrain, water, ore or room is placed by the test");
+        var heights = new ArrayList<List<Integer>>();
+        long oldSolid = 0, remainingSolid = 0, excavated = 0, restored = 0;
+        int min = -Math.min(320, generator.initialDiameter() / 2), max = -min, raised = 0, lowered = 0, largestUplift = 0, largestSubsidence = 0;
+        for (int z = min; z <= max; z += 32) for (int x = min; x <= max; x += 32) {
+            int oldTop = 0, newTop = 0;
+            for (int y = 2; y <= 382; y += 2) {
+                boolean old = previous.sampleValue(context, x, y, z) > 0;
+                boolean now = current.sampleValue(context, x, y, z) > 0;
+                if (old) oldTop = y; if (now) newTop = y;
+                if (y >= 48 && y <= 202) {
+                    if (old) { oldSolid++; if (now) remainingSolid++; else excavated++; }
+                    else if (now) restored++;
+                }
+                if (Math.hypot(x, z) < 40 && y >= 240)
+                    helper.assertTrue(old == now, "High arrival neighbourhood remains unchanged");
+            }
+            if (newTop > oldTop && oldTop > 208) { raised++; largestUplift = Math.max(largestUplift, newTop - oldTop); }
+            if (newTop < oldTop && oldTop > 240) { lowered++; largestSubsidence = Math.max(largestSubsidence, oldTop - newTop); }
+            heights.add(List.of(x, z, oldTop, newTop));
+        }
+        report.put("heights", heights); report.put("old_solid_samples", oldSolid);
+        report.put("remaining_solid_samples", remainingSolid); report.put("excavated_samples", excavated);
+        report.put("restored_rift_samples", restored); report.put("raised_columns", raised);
+        report.put("largest_uplift", largestUplift);
+        report.put("lowered_columns", lowered); report.put("largest_subsidence", largestSubsidence);
+        helper.assertTrue(excavated > 0 && remainingSolid > excavated, "New passages exist while most sampled former rock remains");
+        helper.assertTrue(raised > 0, "Native volumetric deformation raises some uplands");
+        var childField = (PopulationIslandDensity) level.registryAccess().lookupOrThrow(Registries.DENSITY_FUNCTION)
+            .getOrThrow(ResourceKey.create(Registries.DENSITY_FUNCTION, SanctuaryMod.id("population_5"))).value();
+        var child = new fr.koka.sanctuary.expansion.ExpansionIsland("geology_witness", "sanctuary", "east", "temperate",
+            512, 2048, 0, level.getSeed(), "natural", "ready", 24);
+        var childSettings = level.registryAccess().lookupOrThrow(Registries.NOISE_SETTINGS)
+            .getOrThrow(ResourceKey.create(Registries.NOISE_SETTINGS, SanctuaryMod.id("population_5"))).value();
+        var childState = net.minecraft.world.level.levelgen.RandomState.create(level.registryAccess().lookupOrThrow(Registries.NOISE), child.seed(), childSettings);
+        var childNew = childState.getSampler(new fr.koka.sanctuary.expansion.ExpansionDensity(childField, child));
+        var childOld = childState.getSampler(new fr.koka.sanctuary.expansion.ExpansionDensity(childField.legacy27(), child));
+        long childExcavated = 0, childRemaining = 0;
+        for (int z = -160; z <= 160; z += 32) for (int dx = -160; dx <= 160; dx += 32)
+            for (int y = 48; y <= 202; y += 4) {
+                if (childOld.sampleValue(context, 2048 + dx, y, z) > 0) {
+                    if (childNew.sampleValue(context, 2048 + dx, y, z) <= 0) childExcavated++;
+                    else childRemaining++;
+                }
+            }
+        report.put("expansion_density", Map.of("diameter", 512, "excavated", childExcavated,
+            "remaining", childRemaining, "reserved_or_opened", false));
+        helper.assertTrue(childExcavated > 0 && childRemaining > childExcavated, "The actual expansion wrapper uses the same finite cave field");
+        var sections = new LinkedHashMap<String, Object>();
+        for (int z : new int[]{0, 96}) {
+            var before = new ArrayList<String>(); var after = new ArrayList<String>();
+            for (int y = 382; y >= 0; y -= 2) {
+                var a = new StringBuilder(); var b = new StringBuilder();
+                for (int x = min; x <= max; x += 2) {
+                    a.append(previous.sampleValue(context, x, y, z) > 0 ? '#' : '.');
+                    b.append(current.sampleValue(context, x, y, z) > 0 ? '#' : '.');
+                }
+                before.add(a.toString()); after.add(b.toString());
+            }
+            sections.put("z" + z, Map.of("before", before, "after", after, "min_x", min, "step", 2));
+        }
+        report.put("sections", sections);
+        var ores = new TreeMap<String, Integer>(); var oreDepths = new TreeMap<String, List<Integer>>();
+        for (int cx : new int[]{-6, 0, 6}) for (int cz : new int[]{-6, 0, 6}) {
+            var chunk = level.getChunk(cx, cz, ChunkStatus.FULL, true);
+            for (int x = 0; x < 16; x++) for (int z = 0; z < 16; z++) for (int y = 1; y < 383; y++) {
+                var state = chunk.getBlockState(new BlockPos(cx * 16 + x, y, cz * 16 + z));
+                String id = BuiltInRegistries.BLOCK.getKey(state.getBlock()).toString();
+                if (id.endsWith("_ore")) {
+                    ores.merge(id, 1, Integer::sum);
+                    var band = oreDepths.computeIfAbsent(id, ignored -> new ArrayList<>(List.of(384, 0)));
+                    band.set(0, Math.min(band.get(0), y)); band.set(1, Math.max(band.get(1), y));
+                }
+            }
+        }
+        report.put("full_chunks_inspected", 9); report.put("ores", ores); report.put("ore_y_ranges", oreDepths);
+        helper.assertTrue(!ores.isEmpty(), "Actual generated rock contains native ore deposits");
+        report.put("passed", true);
+        Path path = Path.of("diagnostics/alpha28/geology.json"); Files.createDirectories(path.getParent());
+        Files.writeString(path, new GsonBuilder().setPrettyPrinting().create().toJson(report));
+        helper.succeed();
+    }
+}

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

@@ -23,7 +23,7 @@ import net.minecraft.world.level.levelgen.densityfunction.DensitySampler;
 import net.minecraft.world.level.levelgen.densityfunction.DensityVolume;
 import net.minecraft.world.level.levelgen.densityfunction.SamplerContext;
 
-/** Compares production against the frozen alpha.10 implementation; no chunks are created. */
+/** Compares the explicit legacy27 mode against frozen alpha10, not the intentional alpha28 terrain changes. */
 final class PopulationDensityEquivalenceDiagnostics {
     private record Pair(int players, long seed, DensitySampler reference, DensitySampler actual) {}
 
@@ -39,7 +39,7 @@ final class PopulationDensityEquivalenceDiagnostics {
             var key = SanctuaryMod.id("population_" + players);
             var registered = densities.getOrThrow(ResourceKey.create(Registries.DENSITY_FUNCTION, key)).value();
             helper.assertTrue(registered instanceof PopulationIslandDensity, "Compare the real registered Population density");
-            var density = (PopulationIslandDensity) registered;
+            var density = ((PopulationIslandDensity) registered).legacy27();
             helper.assertTrue(ExactInterpolationSampler.supportsTerrain(density.terrain()),
                 "The shipped coordinate-only terrain must actually use the exact cache, not the fallback");
             var reference = new Alpha10PopulationDensityReference(density.terrain(), density.distortion(), density.sculpt(),
@@ -113,7 +113,7 @@ final class PopulationDensityEquivalenceDiagnostics {
             "reference_commit", "a26b72f", "reference_source_sha256", "fcc5a8a39b7c4d181d74ce4f9183a1ca93646137955ac64bab9d22e6db0752a1",
             "comparison", "Float.floatToRawIntBits; no tolerance", "profiles", reports, "adversarial", adversarial,
             "concurrent_comparisons", concurrentComparisons, "concurrent_workers", 3, "passed", true,
-            "scope", "Real compiled scalar/bulk densities, 4 capacities x 3 seeds (5/20/100 compatibility and new10 using the same parameterized algorithm), signed coordinates, region/coast/height boundaries, context switches and concurrency; no block changes")) + "\n");
+            "scope", "Explicit legacy27 mode versus frozen alpha10: real compiled scalar/bulk densities, 4 capacities x 3 seeds, signed coordinates, region/coast/height boundaries, context switches and concurrency. Geology28 is intentionally disabled only for this historical equivalence proof; no alpha28 generation claim.")) + "\n");
     }
 
     private static List<DensityVolume> volumes(IslandCapacity capacity) {

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

@@ -87,6 +87,7 @@ public final class PopulationDiagnostics {
             ResourceKey.create(Registries.DENSITY_FUNCTION, SanctuaryMod.id("population_" + capacity.players()))).value();
         helper.assertTrue(density instanceof PopulationIslandDensity, "Inspect the actual compiled population density");
         var island = (PopulationIslandDensity) density;
+        var legacyEnvelope = island.legacy27();
         helper.assertTrue(island.capacity() == capacity, "Noise settings and density must agree on saved capacity");
         var random = binding.random();
         var replay = RandomState.create(level.registryAccess().lookupOrThrow(Registries.NOISE), random.seed(), generator.generatorSettings().value());
@@ -102,7 +103,10 @@ public final class PopulationDiagnostics {
                 float value = random.sampleBlockValueUncached(density, x, y, z);
                 float raw = random.sampleBlockValueUncached(island.terrain(), x, y - 64, z);
                 helper.assertTrue(Float.isFinite(value), "Density remains finite at every sampled position");
-                helper.assertTrue(value <= 0 || raw > 0, "Enlarging the envelope must never invent terrain inside natural holes");
+                float historical = island.geology28()
+                    ? random.sampleBlockValueUncached(legacyEnvelope, x, y, z) : value;
+                helper.assertTrue(historical <= 0 || raw > 0,
+                    "The explicit legacy27 envelope never fills its raw natural holes; alpha28 uplands change sample Y");
                 if (value > 0) { if (bottom < 0) bottom = y; top = y; }
                 if (x % (step * 8) == 0 && z % (step * 8) == 0)
                     helper.assertTrue(Float.floatToIntBits(value) == Float.floatToIntBits(replay.sampleBlockValueUncached(density, x, y, z)),

mods/sanctuary/src/gametest/resources/fabric.mod.json

@@ -6,7 +6,7 @@
   "environment": "*",
   "license": "GPL-3.0-or-later",
   "entrypoints": {
-    "fabric-gametest": ["${gametest_entrypoint}", "fr.koka.sanctuary.gametest.Swamp27WorldGameTests", "fr.koka.sanctuary.gametest.BlockKnowledgeGameTests", "fr.koka.sanctuary.gametest.CensusGameTestsTerrain", "fr.koka.sanctuary.gametest.CensusStockGameTests", "fr.koka.sanctuary.gametest.MaterialActivityGameTests"],
+    "fabric-gametest": ["${gametest_entrypoint}", "fr.koka.sanctuary.gametest.Swamp27WorldGameTests", "fr.koka.sanctuary.gametest.Caves28WorldGameTests", "fr.koka.sanctuary.gametest.Alpha28NativeStructuresGameTests", "fr.koka.sanctuary.gametest.BlockKnowledgeGameTests", "fr.koka.sanctuary.gametest.CensusGameTestsTerrain", "fr.koka.sanctuary.gametest.CensusStockGameTests", "fr.koka.sanctuary.gametest.MaterialActivityGameTests"],
     "fabric-client-gametest": ["fr.koka.sanctuary.gametest.SanctuaryClientRenderTests"]
   },
   "mixins": ["sanctuary-gametest.mixins.json"],

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

@@ -146,9 +146,17 @@ public class ExpansionChunkGenerator extends ChunkGenerator {
     }
     @Override public void applyBiomeDecoration(net.minecraft.world.level.WorldGenLevel level, ChunkAccess chunk, StructureManager structures) {
         var island = islandAt(chunk.getPos().getMiddleBlockX(), chunk.getPos().getMiddleBlockZ());
-        if (!ExpansionOcean23.active(island)) { super.applyBiomeDecoration(level, chunk, structures); return; }
+        fr.koka.sanctuary.worldgen.IslandOres28.place(level, this, chunk, island);
+        if (!ExpansionOcean23.active(island)) {
+            super.applyBiomeDecoration(level, chunk, structures);
+            fr.koka.sanctuary.worldgen.CavityMonsterRoom28.decorate(level, this, chunk);
+            return;
+        }
         Integer previous = ExpansionOcean23.enterDecoration(ExpansionOcean23.seaLevel(island));
-        try { super.applyBiomeDecoration(level, chunk, structures); }
+        try {
+            super.applyBiomeDecoration(level, chunk, structures);
+            fr.koka.sanctuary.worldgen.CavityMonsterRoom28.decorate(level, this, chunk);
+        }
         finally { ExpansionOcean23.restoreDecoration(previous); }
     }
     @Override public int getSpawnHeight(LevelHeightAccessor level) { return 220; }

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

@@ -49,7 +49,11 @@ public final class ExpansionRelief {
     public static float sculpt(ExpansionIsland island, Column column, double y, float source) {
         if (source <= 0) return source;
         double reference = referenceY(island, y);
-        double canyon = 2.1 * column.canyonWeight() * smoothstep((reference - 120.0) / 34.0);
+        double canyonHeight = island.generation() == 24
+            ? smoothstep((reference - 126 - column.uplift() * .35) / 16)
+                * smoothstep((226 + column.uplift() * .35 - reference) / 18)
+            : smoothstep((reference - 120.0) / 34.0);
+        double canyon = 2.1 * column.canyonWeight() * canyonHeight;
         double crater = 2.1 * column.craterWeight() * smoothstep((reference - CRATER_FLOOR) / 14.0);
         return (float) Math.clamp(source - Math.max(canyon, crater), -1.0, 1.0);
     }

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/ExpansionStructures23.java

@@ -169,6 +169,15 @@ public final class ExpansionStructures23 {
         if (centre.top < 32) return null;
         var sampler = random.createClimateSampler(SamplerContext.builder().enableCaches().build());
         var resolver = view.getBiomeSource().createResolver(sampler);
+        var hutHeights = new ArrayList<Integer>();
+        // The biome is genuinely three dimensional: a swamp bank can be below another island floor.
+        for (int y = Math.min(centre.top + 1, 280); y >= 48 && hutHeights.size() < 4; y--) {
+            var floor = centre.column.getBlock(y - 1);
+            if ((!floor.isSolid() && !floor.getFluidState().is(net.minecraft.tags.FluidTags.WATER))
+                    || !centre.column.getBlock(y).isAir() || !centre.column.getBlock(y + 1).isAir()) continue;
+            if (!host.structureBiome(resolver.getNoiseBiome(x >> 2, y >> 2, z >> 2)).is(net.minecraft.world.level.biome.Biomes.SWAMP)) continue;
+            if (hutHeights.isEmpty() || hutHeights.getLast() - y >= 8) hutHeights.add(y);
+        }
         int undergroundY = Math.clamp(centre.top - 60, 50, 210);
         Holder<Biome> surfaceBiome = host.structureBiome(resolver.getNoiseBiome(x >> 2, centre.top >> 2, z >> 2));
         Holder<Biome> undergroundBiome = host.structureBiome(resolver.getNoiseBiome(x >> 2, undergroundY >> 2, z >> 2));
@@ -182,7 +191,8 @@ public final class ExpansionStructures23 {
             if (holder == null) continue;
             Holder<Biome> biome = entry.habitat() == Habitat.UNDERGROUND ? undergroundBiome
                 : entry.habitat() == Habitat.OCEAN ? waterBiome : surfaceBiome;
-            if (!holder.value().biomes().contains(biome)) continue;
+            if (entry.family().equals("swamp_hut")) { if (hutHeights.isEmpty()) continue; }
+            else if (!holder.value().biomes().contains(biome)) continue;
             if (entry.habitat() == Habitat.OCEAN && !ExpansionOcean23.column(island, x, z).water()) continue;
             long salt = mix(candidate.roll() ^ entry.id().hashCode() * 0x9e3779b97f4a7c15L);
             double unit = ((salt >>> 11) + 1.0) * 0x1.0p-53;
@@ -196,10 +206,14 @@ public final class ExpansionStructures23 {
             checkDeadline(deadlineNanos);
             Structure original = choice.holder().value();
             Entry entry = choice.entry();
-            int variants = entry.habitat() == Habitat.UNDERGROUND || entry.family().equals("ruined_portal") ? 3 : 1;
+            boolean hut = entry.family().equals("swamp_hut");
+            int variants = hut ? hutHeights.size() : entry.habitat() == Habitat.UNDERGROUND || entry.family().equals("ruined_portal") ? 3 : 1;
             for (int vertical = 0; vertical < variants; vertical++) {
                 checkDeadline(deadlineNanos);
-                int targetY = undergroundY - vertical * 20;
+                int targetY = hut ? hutHeights.get(vertical) : undergroundY - vertical * 20;
+                ExpansionChunkGenerator nativeView = hut && view instanceof NativeView local
+                    ? local.atHeight(targetY + 1) : view;
+                GroundSampler nativeGround = hut ? new GroundSampler(nativeView, chunk, random, deadlineNanos, targetY + 1) : ground;
                 Structure generated = original;
                 if (entry.family().equals("trial_chambers")) generated = withStartHeight(original, registries, targetY);
                 Predicate<Holder<Biome>> valid = b -> original.biomes().contains(host.structureBiome(b));
@@ -207,18 +221,18 @@ public final class ExpansionStructures23 {
                 if (original instanceof StrongholdStructure) {
                     // Vanilla stronghold piece weights are static mutable state.
                     synchronized (StrongholdStructure.class) {
-                        start = generated.generate(choice.holder(), dimension, registries, view, view.getBiomeSource(), sampler,
+                        start = generated.generate(choice.holder(), dimension, registries, nativeView, view.getBiomeSource(), sampler,
                             random, templates, island.seed(), candidate.chunk(), 0, chunk, valid);
                     }
                 } else {
-                    start = generated.generate(choice.holder(), dimension, registries, view, view.getBiomeSource(), sampler,
+                    start = generated.generate(choice.holder(), dimension, registries, nativeView, view.getBiomeSource(), sampler,
                         random, templates, island.seed(), candidate.chunk(), 0, chunk, valid);
                 }
                 if (!start.isValid()) { diagnostic(island, candidate, "native-refused", entry.id()); continue; }
                 // Only buried portal variants need the alternative underground elevations.
                 if (vertical > 0 && entry.family().equals("ruined_portal") && !undergroundPortal(start)) break;
-                start = adjustNativeStart(original, start, entry, island, targetY, ground);
-                String rejection = supportRejection(host, island, entry, start, ground);
+                start = adjustNativeStart(original, start, entry, island, targetY, nativeGround);
+                String rejection = supportRejection(host, island, entry, start, nativeGround);
                 if (rejection != null) { diagnostic(island, candidate, rejection, entry.id()); continue; }
                 ((NativeStructureMetadata23) (Object) start).sanctuary$native23(new NativeStructureMetadata23.Data(island.seed(), seaLevel));
                 return new Accepted(choice.holder(), start);
@@ -333,17 +347,35 @@ public final class ExpansionStructures23 {
                     || city.intersectsCityConstruction15(total.minX() - 2, total.minY() - 12, total.minZ() - 2, total.maxX() + 2, total.maxY() + 4, total.maxZ() + 2)
                     || city.intersectsCityConstruction16(total.minX() - 2, total.minY() - 12, total.minZ() - 2, total.maxX() + 2, total.maxY() + 4, total.maxZ() + 2)
                     || city.intersectsExperimentalStructures(total.minX() - 2, total.minY() - 12, total.minZ() - 2, total.maxX() + 2, total.maxY() + 4, total.maxZ() + 2)) return "reserved-secret";
-            if (island.origin()) {
+            if (island.origin() && !entry.family().equals("swamp_hut")) {
                 var binding = city.starterContext();
                 if (fr.koka.sanctuary.worldgen.PopulationHydrologyRuntime.protects(binding.generator(), binding.random(),
                         total.getCenter().atY(total.minY()), Math.max(total.getXSpan(), total.getZSpan()) / 2 + 3, total.getYSpan() + 16, 26)) return "protected-hydrology";
             }
         }
+        if (entry.family().equals("swamp_hut")) {
+            if (host instanceof SanctuaryChunkGenerator sanctuary && island.origin()) {
+                var binding = sanctuary.starterContext();
+                var box = new BoundingBox(total.minX(), total.minY() - SwampHutPlacement28.MAX_PIER_DROP - 2,
+                    total.minZ(), total.maxX(), total.maxY(), total.maxZ());
+                for (var region : fr.koka.sanctuary.worldgen.PopulationHydrologyRuntime.plansIntersecting(
+                        binding.generator(), binding.random(), total.minX() - 16, total.minZ() - 16, total.maxX() + 16, total.maxZ() + 16)) {
+                    String refusal = SwampHutPlacement28.hydrologyRejection(region, box);
+                    if (refusal != null) return refusal;
+                }
+            }
+            return SwampHutPlacement28.rejection(start, (x, z) -> ground.at(x, z).column);
+        }
         boolean underground = entry.habitat() == Habitat.UNDERGROUND || undergroundPortal(start);
         boolean aquatic = entry.habitat() == Habitat.OCEAN;
         int siteMin = Integer.MAX_VALUE, siteMax = Integer.MIN_VALUE;
         for (StructurePiece piece : start.getPieces()) {
             BoundingBox box = piece.getBoundingBox();
+            if (entry.family().equals("mineshaft")
+                    && piece instanceof net.minecraft.world.level.levelgen.structure.structures.MineshaftPieces.MineShaftCorridor) {
+                if (!MineshaftSupport28.anchored(piece, (x, z) -> ground.at(x, z).column)) return "mineshaft-no-native-support";
+                continue;
+            }
             int low = Integer.MAX_VALUE, high = Integer.MIN_VALUE, supported = 0, sampled = 0;
             boolean buriedPiece = underground || !aquatic && box.maxY() < ground.at(box.getCenter().getX(), box.getCenter().getZ()).top - 6;
             int step = buriedPiece ? 8 : 4;
@@ -474,7 +506,7 @@ public final class ExpansionStructures23 {
     }
     private static int weight(String family) {
         return switch (family) { case "camp" -> 6; case "ruined_portal", "mineshaft", "ocean_ruin" -> 3;
-            case "village", "shipwreck", "trail_ruins", "buried_treasure" -> 2; default -> 1; };
+            case "village", "shipwreck", "trail_ruins", "buried_treasure", "swamp_hut" -> 2; default -> 1; };
     }
     private static int[] samples(int low, int high, int step) {
         var values = new java.util.TreeSet<Integer>(); values.add(low); values.add(high); values.add((low + high) / 2);
@@ -493,9 +525,11 @@ public final class ExpansionStructures23 {
     private record Choice(Entry entry, Holder<Structure> holder, double score) {}
     private static final class Ground {
         final NoiseColumn column; final int top; final int thickness;
-        Ground(NoiseColumn column, int min, int max) {
+        Ground(NoiseColumn column, int min, int max) { this(column, min, max, false); }
+        Ground(NoiseColumn column, int min, int max, boolean waterSurface) {
             this.column = column; int y = max;
-            while (y >= min && !column.getBlock(y).isSolid()) y--;
+            while (y >= min && !column.getBlock(y).isSolid()
+                    && !(waterSurface && column.getBlock(y).getFluidState().is(net.minecraft.tags.FluidTags.WATER))) y--;
             top = y;
             while (y >= min && top - y < 24 && solid(y)) y--;
             thickness = top - y;
@@ -505,17 +539,23 @@ public final class ExpansionStructures23 {
     }
     private static final class GroundSampler {
         final ExpansionChunkGenerator generator; final LevelHeightAccessor level; final RandomState random; final long deadline;
+        final Integer localCeiling;
         final Map<Long, Ground> columns = new HashMap<>();
         fr.koka.sanctuary.worldgen.city.LostCityProtection16 localCity;
         GroundSampler(ExpansionChunkGenerator generator, LevelHeightAccessor level, RandomState random, long deadline) {
+            this(generator, level, random, deadline, null);
+        }
+        GroundSampler(ExpansionChunkGenerator generator, LevelHeightAccessor level, RandomState random, long deadline, Integer localCeiling) {
             this.generator = generator; this.level = level; this.random = random; this.deadline = deadline;
+            this.localCeiling = localCeiling;
         }
         Ground at(int x, int z) {
             long key = ((long) x << 32) ^ (z & 0xffffffffL);
             Ground old = columns.get(key); if (old != null) return old;
             checkDeadline(deadline);
             if (columns.size() >= MAX_COLUMN_SAMPLES) throw new SampleBudgetExceeded();
-            Ground result = new Ground(generator.getBaseColumn(x, z, level, random), level.getMinY(), level.getMaxY());
+            Ground result = new Ground(generator.getBaseColumn(x, z, level, random), level.getMinY(),
+                localCeiling == null ? level.getMaxY() : localCeiling, localCeiling != null);
             columns.put(key, result); return result;
         }
     }
@@ -536,14 +576,23 @@ public final class ExpansionStructures23 {
     /** Isolated biome snapshot during preflight, per-island sea level during native generation. */
     private static final class NativeView extends ExpansionChunkGenerator {
         private final ExpansionChunkGenerator host; private final ExpansionIsland island;
+        private Integer localCeiling;
         NativeView(ExpansionChunkGenerator host, ExpansionIsland island, ExpansionBiomeSource source, RegistryAccess registries) {
             super(source, host.initialDiameter(), true); this.host = host; this.island = island; this.registries = registries;
         }
+        NativeView atHeight(int ceiling) {
+            var result = new NativeView(host, island, source(), registries); result.localCeiling = ceiling; return result;
+        }
         @Override public int rootGeneration() { return island.generation(); }
         @Override public Holder<Biome> structureBiome(Holder<Biome> biome) { return host.structureBiome(biome); }
         @Override public int getSeaLevel() { return ExpansionOcean23.active(island) ? ExpansionOcean23.seaLevel(island) : 192; }
         @Override public RandomState randomState(ExpansionIsland candidate) { return island.origin() ? host.randomState(candidate) : super.randomState(candidate); }
         @Override public int getBaseHeight(int x, int z, Heightmap.Types type, LevelHeightAccessor level, RandomState random) {
+            if (localCeiling != null) {
+                var column = getBaseColumn(x, z, level, random);
+                for (int y = localCeiling; y >= level.getMinY(); y--) if (type.isOpaque().test(column.getBlock(y))) return y + 1;
+                return level.getMinY();
+            }
             return island.origin() ? host.getBaseHeight(x, z, type, level, random) : super.getBaseHeight(x, z, type, level, random);
         }
         @Override public NoiseColumn getBaseColumn(int x, int z, LevelHeightAccessor level, RandomState random) {

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/MineshaftSupport28.java

@@ -0,0 +1,32 @@
+package fr.koka.sanctuary.expansion;
+
+import java.util.function.BiFunction;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.levelgen.structure.StructurePiece;
+
+/** Certifies the support positions actually used by vanilla MineShaftCorridor, not a percentage of nearby rock. */
+public final class MineshaftSupport28 {
+    private MineshaftSupport28() {}
+    public static boolean anchored(StructurePiece piece, BiFunction<Integer, Integer, NoiseColumn> columns) {
+        var box = piece.getBoundingBox();
+        int length = piece.getOrientation().getAxis() == net.minecraft.core.Direction.Axis.Z ? box.getZSpan() : box.getXSpan();
+        for (int z : length > 5 ? new int[]{2, length - 3} : new int[]{2}) for (int x : new int[]{0, 2}) {
+            var pier = SwampHutPlacement28.worldPosition(piece, x, -1, z);
+            var column = columns.apply(pier.getX(), pier.getZ()); boolean anchor = false;
+            // Native wooden support searches at most20 below its floor plank.
+            for (int y = pier.getY() - 1; y >= pier.getY() - 20; y--) {
+                var state = column.getBlock(y);
+                if (!state.getFluidState().isEmpty()) break;
+                if (state.isSolid()) { anchor = true; break; }
+            }
+            // Its alternative is a chain up to50 blocks, anchored above the excavated corridor.
+            if (!anchor) for (int y = box.maxY() + 1; y <= pier.getY() + 50; y++) {
+                var state = column.getBlock(y);
+                if (!state.getFluidState().isEmpty()) break;
+                if (state.isSolid()) { anchor = true; break; }
+            }
+            if (!anchor) return false;
+        }
+        return true;
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/NativeStructurePlacement23.java

@@ -7,10 +7,34 @@ import net.minecraft.world.level.levelgen.structure.structures.OceanMonumentPiec
 /** Scoped native placement parameters; never change the sea level of another dimension or start. */
 public final class NativeStructurePlacement23 {
     private static final ThreadLocal<Integer> SEA_LEVEL = new ThreadLocal<>();
+    public record HutScope(java.util.List<net.minecraft.core.BlockPos> piers,
+            java.util.List<net.minecraft.world.level.levelgen.structure.BoundingBox> bodies) {}
+    private static final ThreadLocal<HutScope> HUT = new ThreadLocal<>();
     private NativeStructurePlacement23() {}
     public static Integer seaLevel() { return SEA_LEVEL.get(); }
     public static Integer enter(int seaLevel) { Integer previous = SEA_LEVEL.get(); SEA_LEVEL.set(seaLevel); return previous; }
     public static void restore(Integer previous) { if (previous == null) SEA_LEVEL.remove(); else SEA_LEVEL.set(previous); }
+    public static HutScope enterHut(net.minecraft.world.level.levelgen.structure.StructureStart start) {
+        var previous = HUT.get();
+        var pieces = start.getPieces().stream().filter(net.minecraft.world.level.levelgen.structure.structures.SwampHutPiece.class::isInstance).toList();
+        HUT.set(new HutScope(pieces.stream().flatMap(piece -> SwampHutPlacement28.piers(piece).stream()).toList(),
+            pieces.stream().map(StructurePiece::getBoundingBox).toList()));
+        return previous;
+    }
+    public static void restoreHut(HutScope previous) {
+        if (previous == null) HUT.remove(); else HUT.set(previous);
+    }
+    public static boolean allowsHutWrite(net.minecraft.core.BlockPos pos, net.minecraft.world.level.block.state.BlockState state,
+            net.minecraft.world.level.block.state.BlockState replaced) {
+        var scope = HUT.get(); if (scope == null) return false;
+        // Native construction in already empty air above a certified bank does not cut its retaining bed.
+        if (replaced.isAir() && scope.bodies().stream().anyMatch(box -> box.isInside(pos))) return true;
+        if (!state.is(net.minecraft.world.level.block.Blocks.OAK_LOG)
+                || !(replaced.isAir() || replaced.getFluidState().isSource()
+                    && replaced.getFluidState().is(net.minecraft.tags.FluidTags.WATER))) return false;
+        return scope.piers().stream().anyMatch(pier -> pier.getX() == pos.getX() && pier.getZ() == pos.getZ()
+            && pos.getY() <= pier.getY() && pos.getY() > pier.getY() - SwampHutPlacement28.MAX_PIER_DROP);
+    }
     public static void move(StructurePiece piece, int dy) {
         if (piece instanceof OceanMonumentPieces.MonumentBuilding monument) {
             for (StructurePiece child : ((MonumentChildren23Accessor) monument).sanctuary$children()) child.move(0, dy, 0);

mods/sanctuary/src/main/java/fr/koka/sanctuary/expansion/SwampHutPlacement28.java

@@ -0,0 +1,87 @@
+package fr.koka.sanctuary.expansion;
+
+import fr.koka.sanctuary.worldgen.PopulationHydrology;
+import fr.koka.sanctuary.worldgen.PopulationHydrologyRuntime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.BiFunction;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.levelgen.structure.BoundingBox;
+import net.minecraft.world.level.levelgen.structure.StructurePiece;
+import net.minecraft.world.level.levelgen.structure.StructureStart;
+import net.minecraft.world.level.levelgen.structure.structures.SwampHutPiece;
+import net.minecraft.world.level.material.Fluids;
+
+/** Native hut geometry on a real shallow bank, including banks below another island floor. */
+public final class SwampHutPlacement28 {
+    public static final int MAX_PIER_DROP = 8;
+    private SwampHutPlacement28() {}
+
+    public static String rejection(StructureStart start, BiFunction<Integer, Integer, NoiseColumn> columns) {
+        for (var piece : start.getPieces()) {
+            if (!(piece instanceof SwampHutPiece)) return "hut-unexpected-piece";
+            var box = piece.getBoundingBox();
+            for (int x = box.minX(); x <= box.maxX(); x++) for (int z = box.minZ(); z <= box.maxZ(); z++) {
+                var column = columns.apply(x, z);
+                int waterTop = Integer.MIN_VALUE, waterBottom = Integer.MAX_VALUE;
+                for (int y = box.minY() - MAX_PIER_DROP; y <= box.maxY(); y++) {
+                    var state = column.getBlock(y); var fluid = state.getFluidState();
+                    if (y >= box.minY() + 2 && !state.isAir()) return "hut-natural-headroom";
+                    if (fluid.isEmpty()) continue;
+                    if (fluid.getType() != Fluids.WATER || !fluid.isSource()) return "hut-flowing-or-nonwater";
+                    waterTop = Math.max(waterTop, y); waterBottom = Math.min(waterBottom, y);
+                }
+                if (waterTop != Integer.MIN_VALUE) {
+                    if (waterTop > box.minY() || waterTop - waterBottom + 1 > 4) return "hut-deep-water";
+                    if (!solid(column.getBlock(waterBottom - 1)) || !solid(column.getBlock(waterBottom - 2))) return "hut-unsealed-bed";
+                }
+            }
+            for (var pier : piers(piece)) {
+                var column = columns.apply(pier.getX(), pier.getZ()); int y = pier.getY(), depth = 0;
+                while (replaceable(column.getBlock(y)) && depth <= MAX_PIER_DROP) { y--; depth++; }
+                if (depth > MAX_PIER_DROP || !solid(column.getBlock(y)) || !solid(column.getBlock(y - 1))) return "hut-unsupported-pier";
+            }
+        }
+        return null;
+    }
+
+    /** Still water is compatible; springs, spills, channels and lava keep their protection. */
+    public static String hydrologyRejection(PopulationHydrologyRuntime.RegionPlan region, BoundingBox box) {
+        for (var spring : region.water().springs()) if (intersects(box, spring.flowBounds(), 3)) return "hut-protected-spring";
+        for (var spill : region.water().spills()) if (intersects(box, spill.flowBounds(), 3)) return "hut-protected-spill";
+        for (var flow : region.lava().flowBounds()) if (intersects(box, flow, 4)) return "hut-protected-lava";
+        var rivers = region.water().features().stream().filter(f -> f.kind() == PopulationHydrology.Kind.RIVER)
+            .map(PopulationHydrology.Feature::id).collect(java.util.stream.Collectors.toSet());
+        for (int x = box.minX(); x <= box.maxX(); x++) for (int z = box.minZ(); z <= box.maxZ(); z++)
+            for (var cell : region.water().cellsAt(x, z)) if (rivers.contains(cell.featureId())
+                    && box.minY() <= cell.carveTop() && box.maxY() >= cell.bedY() - cell.sedimentDepth() - 1) return "hut-protected-river";
+        return null;
+    }
+
+    /** Exact four support origins used by SwampHutPiece.postProcess. */
+    public static List<BlockPos> piers(StructurePiece piece) {
+        var result = new ArrayList<BlockPos>(4);
+        for (int z : new int[]{2, 7}) for (int x : new int[]{1, 5}) result.add(worldPosition(piece, x, -1, z));
+        return List.copyOf(result);
+    }
+    public static BlockPos worldPosition(StructurePiece piece, int x, int y, int z) {
+        var b = piece.getBoundingBox(); Direction facing = piece.getOrientation();
+        if (facing == null || facing.getAxis().isVertical()) throw new IllegalArgumentException("A hut requires horizontal orientation");
+        int wx = switch (facing) { case WEST -> b.maxX() - z; case EAST -> b.minX() + z; default -> b.minX() + x; };
+        int wz = switch (facing) { case NORTH -> b.maxZ() - z; case SOUTH -> b.minZ() + z; default -> b.minZ() + x; };
+        return new BlockPos(wx, b.minY() + y, wz);
+    }
+    private static boolean solid(BlockState state) { return state.isSolid() && state.getFluidState().isEmpty(); }
+    private static boolean replaceable(BlockState state) {
+        return state.isAir() || state.liquid() || state.is(Blocks.GLOW_LICHEN) || state.is(Blocks.SEAGRASS) || state.is(Blocks.TALL_SEAGRASS);
+    }
+    private static boolean intersects(BoundingBox b, PopulationHydrology.FlowBounds flow, int margin) {
+        return b.minX() <= flow.maxX() + margin && b.maxX() >= flow.minX() - margin
+            && b.minY() <= flow.maxY() + margin && b.maxY() >= flow.minY() - margin
+            && b.minZ() <= flow.maxZ() + margin && b.maxZ() >= flow.minZ() - margin;
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/mixin/NativeStructureStart23Mixin.java

@@ -67,8 +67,9 @@ public abstract class NativeStructureStart23Mixin implements NativeStructureMeta
             RandomSource random, BoundingBox bounds, ChunkPos pos, Operation<Void> original) {
         if (sanctuary$native23 == null) { original.call(level, structures, generator, random, bounds, pos); return; }
         Integer previous = NativeStructurePlacement23.enter(sanctuary$native23.seaLevel());
+        var previousHut = NativeStructurePlacement23.enterHut((StructureStart) (Object) this);
         try { original.call(level, structures, generator, random, bounds, pos); }
-        finally { NativeStructurePlacement23.restore(previous); }
+        finally { NativeStructurePlacement23.restoreHut(previousHut); NativeStructurePlacement23.restore(previous); }
     }
 
     @Unique private static Data sanctuary$read(CompoundTag tag) {

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

@@ -62,6 +62,10 @@ public abstract class UnifiedDecorationProtectionMixin {
         }
         // The dedicated shoreline feature still grows cane on its naturally valid dry banks.
         if (state.is(Blocks.SUGAR_CANE)) return;
+        // Admitted native huts use existing air and four bounded wooden piers in still water.
+        // The intact basin bed, all other water cells, island ownership and secrets remain protected.
+        if (!generator.protectsCityDecoration(pos)
+                && fr.koka.sanctuary.expansion.NativeStructurePlacement23.allowsHutWrite(pos, state, region.getBlockState(pos))) 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 || generator.rootGeneration() == 21 || generator.rootGeneration() == 22 || (generator.rootGeneration() == 23 || generator.rootGeneration() == 24))

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/CavesRelief28.java

@@ -0,0 +1,37 @@
+package fr.koka.sanctuary.worldgen;
+
+/** Bounded domain deformation around native rock noise, followed by native cave cuts. */
+public final class CavesRelief28 {
+    public static final int CAVE_OFFSET = 96;
+    public static final int DEFORMATION_START = 180;
+    public static final double MAX_HORIZONTAL_SHIFT = 16;
+    public static final double MAX_VERTICAL_SHIFT = 40;
+    private CavesRelief28() {}
+
+    public record Warp(double x, double y, double z) {}
+
+    public static double deformationWeight(int x, int y, int z, double radius) {
+        double distance = Math.hypot((double) x, z);
+        double arrival = smooth((distance - 48) / 48);
+        double coast = 1 - smooth((distance / radius - .66) / .26);
+        return smooth((y - DEFORMATION_START) / 48.0) * arrival * coast;
+    }
+
+    /** Signed smooth displacements: no folded ridge, plateau saturation or height-map uplift. */
+    public static Warp warp(double weight, float across, float vertical, float along) {
+        return new Warp(MAX_HORIZONTAL_SHIFT * Math.tanh(across * 1.6) * weight,
+            MAX_VERTICAL_SHIFT * Math.tanh(vertical * 1.6) * weight,
+            MAX_HORIZONTAL_SHIFT * Math.tanh(along * 1.6) * weight);
+    }
+
+    public static float carve(float rock, float nativeCaves, int y) {
+        if (rock <= 0) return rock;
+        double weight = smooth((y - 40) / 28.0) * (1 - smooth((y - 202) / 30.0));
+        if (weight <= 0) return rock;
+        return Math.min(rock, (float) Math.clamp(nativeCaves + (1 - weight) * 2, -1, 1));
+    }
+    private static double smooth(double value) {
+        double t = Math.clamp(value, 0, 1);
+        return t * t * (3 - 2 * t);
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/CavityMonsterRoom28.java

@@ -0,0 +1,65 @@
+package fr.koka.sanctuary.worldgen;
+
+import fr.koka.sanctuary.expansion.ExpansionChunkGenerator;
+import java.util.ArrayList;
+import java.util.Comparator;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.world.level.levelgen.feature.MonsterRoomFeature;
+
+/** A few attempts at real cave walls; the vanilla feature owns its shell, loot and spawner. */
+public final class CavityMonsterRoom28 {
+    private static final MonsterRoomFeature NATIVE = new MonsterRoomFeature();
+    private static final int MAX_ATTEMPTS = 8;
+    private CavityMonsterRoom28() {}
+
+    public static void decorate(WorldGenLevel level, ChunkGenerator generator, ChunkAccess chunk) {
+        if (!(generator instanceof ExpansionChunkGenerator host) || host.rootGeneration() != 24
+                || !level.getLevel().structureManager().shouldGenerateStructures()) return;
+        var pos = chunk.getPos(); var island = host.islandForChunk(pos.x(), pos.z());
+        if (island == null || island.generation() != 24) return;
+        long seed = WoodlandGroveGeometry.seed(island.seed(), pos.x(), 28, pos.z(), 0xD086E028L);
+        if (Math.floorMod(seed, 3) != 0) return;
+        var candidates = new ArrayList<BlockPos>();
+        int bottom = Math.max(level.getMinY() + 2, 32), top = Math.min(level.getMaxY() - 6, 280);
+        for (int dx : new int[]{4, 11}) for (int dz : new int[]{4, 11}) {
+            int x = pos.getMinBlockX() + dx, z = pos.getMinBlockZ() + dz;
+            for (int y = bottom; y <= top; y++) {
+                BlockPos at = new BlockPos(x, y, z);
+                if (!level.getBlockState(at.below()).isSolid() || !level.getBlockState(at.above(4)).isSolid()) continue;
+                boolean caveEdge = false;
+                for (Direction side : Direction.Plane.HORIZONTAL) {
+                    BlockPos opening = at.relative(side, 4);
+                    if (level.getBlockState(opening).isAir() && level.getBlockState(opening.above()).isAir()) { caveEdge = true; break; }
+                }
+                if (caveEdge) candidates.add(at);
+            }
+        }
+        candidates.sort(Comparator.<BlockPos>comparingLong(at -> WoodlandGroveGeometry.seed(seed, at.getX(), at.getY(), at.getZ(), 28)));
+        int attempts = 0;
+        for (BlockPos at : candidates) {
+            if (attempts++ >= MAX_ATTEMPTS) break;
+            if (!safe(level, host, at, island.id())) continue;
+            // No virtual solid floor/roof and no prebuilt room. Native rejection remains authoritative.
+            if (NATIVE.place(level, generator, RandomSource.create(WoodlandGroveGeometry.seed(seed, at.getX(), at.getY(), at.getZ(), 0xC0128)), at)) return;
+        }
+    }
+
+    private static boolean safe(WorldGenLevel level, ExpansionChunkGenerator host, BlockPos at, String owner) {
+        for (int dx = -4; dx <= 4; dx++) for (int dz = -4; dz <= 4; dz++) for (int dy = -1; dy <= 4; dy++) {
+            BlockPos block = at.offset(dx, dy, dz);
+            var destination = host.islandForChunk(block.getX() >> 4, block.getZ() >> 4);
+            if (destination == null || !destination.id().equals(owner)) return false;
+            var state = level.getBlockState(block);
+            if (!state.getFluidState().isEmpty() || state.hasBlockEntity() || state.is(Blocks.BEDROCK)) return false;
+            if (host instanceof SanctuaryChunkGenerator sanctuary
+                    && (sanctuary.protectsDecoration(block) || sanctuary.protectsCityDecoration(block))) return false;
+        }
+        return true;
+    }
+}

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/IslandOres28.java

@@ -0,0 +1,53 @@
+package fr.koka.sanctuary.worldgen;
+
+import fr.koka.sanctuary.expansion.ExpansionChunkGenerator;
+import fr.koka.sanctuary.expansion.ExpansionIsland;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.tags.BlockTags;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.chunk.ChunkAccess;
+
+/** Native finite ore veins, positioned within the whole floating rock column rather than vanilla sea-level bands. */
+public final class IslandOres28 {
+    private IslandOres28() {}
+    private record Deposit(String feature, int attempts, double minDepth, double maxDepth) {}
+    // Small supplementary populations shared by all climates. Existing biome ores remain in place.
+    private static final Deposit[] DEPOSITS = {
+        new Deposit("ore_coal", 8, .05, .65), new Deposit("ore_iron", 7, .12, .88),
+        new Deposit("ore_copper_small", 6, .10, .66), new Deposit("ore_gold", 2, .52, .90),
+        new Deposit("ore_redstone", 3, .56, .92), new Deposit("ore_lapis", 2, .30, .82),
+        new Deposit("ore_diamond_small", 2, .70, .94), new Deposit("ore_emerald", 1, .25, .85)
+    };
+
+    public static void place(WorldGenLevel level, ExpansionChunkGenerator generator, ChunkAccess chunk, ExpansionIsland island) {
+        if (island == null || generator.rootGeneration() != 24) return;
+        int minX = chunk.getPos().getMinBlockX(), minZ = chunk.getPos().getMinBlockZ();
+        // Density columns precede structures and vegetation. Cavities do not reset mineral depth:
+        // retain the full top-to-bottom envelope rather than using the nearest cave ceiling.
+        var column = generator.getBaseColumn(minX + 8, minZ + 8, level, generator.randomState(island));
+        int top = -1, bottom = -1;
+        for (int y = 1; y < 383; y++) if (column.getBlock(y).is(BlockTags.BASE_STONE_OVERWORLD)) {
+            if (bottom < 0) bottom = y;
+            top = y;
+        }
+        if (top - bottom < 24) return;
+        var registry = level.registryAccess().lookupOrThrow(Registries.FEATURE);
+        for (int index = 0; index < DEPOSITS.length; index++) {
+            Deposit deposit = DEPOSITS[index];
+            var feature = registry.getValue(Identifier.withDefaultNamespace(deposit.feature()));
+            if (feature == null) throw new IllegalStateException("Missing native ore " + deposit.feature());
+            var random = RandomSource.create(WoodlandGroveGeometry.seed(island.seed(), minX, index, minZ, 0x0280AE5L));
+            for (int attempt = 0; attempt < deposit.attempts(); attempt++) {
+                double depth = deposit.minDepth() + random.nextDouble() * (deposit.maxDepth() - deposit.minDepth());
+                int y = (int) Math.round(top - depth * (top - bottom));
+                // Largest selected native vein is 17 blocks (radius bound five). Its writes stay
+                // in the decorating chunk, including where neighbours are generated in another order.
+                var at = new BlockPos(minX + 5 + random.nextInt(6), y, minZ + 5 + random.nextInt(6));
+                if (level.getBlockState(at).is(BlockTags.BASE_STONE_OVERWORLD)) feature.place(level, generator, random, at);
+            }
+        }
+    }
+}

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

@@ -1,6 +1,7 @@
 package fr.koka.sanctuary.worldgen;
 
 import com.mojang.serialization.MapCodec;
+import com.mojang.serialization.Codec;
 import com.mojang.serialization.codecs.RecordCodecBuilder;
 import fr.koka.sanctuary.SanctuaryMod;
 import java.util.concurrent.ConcurrentHashMap;
@@ -10,7 +11,8 @@ import net.minecraft.world.level.levelgen.densityfunction.*;
 /** Capacity changes the envelope; all natural noise is still sampled at world coordinates. */
 public record PopulationIslandDensity(DensityFunction terrain, DensityFunction distortion,
         DensityFunction sculpt, DensityFunction detail, DensityFunction underside,
-        DensityFunction riftWarp, DensityFunction riftDetail, IslandCapacity capacity) implements DensityFunction {
+        DensityFunction riftWarp, DensityFunction riftDetail, IslandCapacity capacity,
+        DensityFunction caves28, DensityFunction ridges28, DensityFunction erosion28, boolean geology28) implements DensityFunction {
     public static final MapCodec<PopulationIslandDensity> CODEC = RecordCodecBuilder.mapCodec(instance -> instance.group(
         DensityFunction.CODEC.fieldOf("terrain").forGetter(PopulationIslandDensity::terrain),
         DensityFunction.CODEC.fieldOf("distortion").forGetter(PopulationIslandDensity::distortion),
@@ -19,36 +21,85 @@ public record PopulationIslandDensity(DensityFunction terrain, DensityFunction d
         DensityFunction.CODEC.fieldOf("underside").forGetter(PopulationIslandDensity::underside),
         DensityFunction.CODEC.fieldOf("rift_warp").forGetter(PopulationIslandDensity::riftWarp),
         DensityFunction.CODEC.fieldOf("rift_detail").forGetter(PopulationIslandDensity::riftDetail),
-        IslandCapacity.CODEC.optionalFieldOf("players", IslandCapacity.TWENTY).forGetter(PopulationIslandDensity::capacity)
+        IslandCapacity.CODEC.optionalFieldOf("players", IslandCapacity.TWENTY).forGetter(PopulationIslandDensity::capacity),
+        DensityFunction.CODEC.optionalFieldOf("caves_28", DensityFunctions.zero()).forGetter(PopulationIslandDensity::caves28),
+        DensityFunction.CODEC.optionalFieldOf("ridges_28", DensityFunctions.zero()).forGetter(PopulationIslandDensity::ridges28),
+        DensityFunction.CODEC.optionalFieldOf("erosion_28", DensityFunctions.zero()).forGetter(PopulationIslandDensity::erosion28),
+        Codec.BOOL.optionalFieldOf("geology_28", false).forGetter(PopulationIslandDensity::geology28)
     ).apply(instance, PopulationIslandDensity::new));
 
+    public PopulationIslandDensity(DensityFunction terrain, DensityFunction distortion,
+            DensityFunction sculpt, DensityFunction detail, DensityFunction underside,
+            DensityFunction riftWarp, DensityFunction riftDetail, IslandCapacity capacity) {
+        this(terrain, distortion, sculpt, detail, underside, riftWarp, riftDetail, capacity,
+            DensityFunctions.zero(), DensityFunctions.zero(), DensityFunctions.zero(), false);
+    }
+
     @Override public DensitySampler compileSampler(CompileContext context) {
         var raw = ExactInterpolationSampler.compileTerrain(terrain, context); var edge = distortion.compileSampler(context);
         var coarse = sculpt.compileSampler(context); var fine = detail.compileSampler(context);
         var bottom = underside.compileSampler(context); var warp = riftWarp.compileSampler(context);
         var fractureDetail = riftDetail.compileSampler(context);
+        var caves = geology28 ? caves28.compileSampler(context) : null;
+        var ridges = geology28 ? ridges28.compileSampler(context) : null;
+        var erosion = geology28 ? erosion28.compileSampler(context) : null;
         long seed = context.createRandom(SanctuaryMod.id("population_rifts_alpha10")).nextLong();
         var layouts = new ConcurrentHashMap<IslandCapacity.Region, RiftShape.Layout>();
         return new DensitySampler() {
+            private float terrainAt(SamplerContext sample, double x, double y, double z) {
+                int ix = (int) Math.floor(x), iy = (int) Math.floor(y), iz = (int) Math.floor(z);
+                double fx = x - ix, fy = y - iy, fz = z - iz;
+                double sum = 0;
+                // Trilinear sampling avoids integer snapping of the displaced native field.
+                for (int dz = 0; dz <= (fz == 0 ? 0 : 1); dz++)
+                    for (int dy = 0; dy <= (fy == 0 ? 0 : 1); dy++)
+                        for (int dx = 0; dx <= (fx == 0 ? 0 : 1); dx++) {
+                            double w = (dx == 0 ? 1 - fx : fx) * (dy == 0 ? 1 - fy : fy)
+                                * (dz == 0 ? 1 - fz : fz);
+                            sum += w * raw.sampleValue(sample, ix + dx, iy + dy, iz + dz);
+                        }
+                return (float) sum;
+            }
             @Override public float sampleValue(SamplerContext sample, int x, int y, int z) {
                 if (Math.hypot((double) x, z) >= capacity.terrainLimit() || y <= 0 || y >= 384) return -1;
+                float terrainValue;
+                double weight = geology28 ? CavesRelief28.deformationWeight(x, y, z, capacity.radius()) : 0;
+                if (weight > 0) {
+                    var shift = CavesRelief28.warp(weight,
+                        erosion.sampleValue(sample, x + 173, y - 59, z - 89),
+                        ridges.sampleValue(sample, x, y, z),
+                        erosion.sampleValue(sample, x - 211, y + 137, z + 307));
+                    terrainValue = terrainAt(sample, x - shift.x(), y - 64 - shift.y(), z - shift.z());
+                } else terrainValue = raw.sampleValue(sample, x, y - 64, z);
+                // Keep the island envelope at actual coordinates, independent from displaced rock.
                 int localY = y - 64;
-                float natural = PopulationIslandShape.raisedDensity(x, y, z, raw.sampleValue(sample, x, localY, z),
+                float natural = PopulationIslandShape.raisedDensity(x, y, z, terrainValue,
                     edge.sampleValue(sample, x, 0, z), coarse.sampleValue(sample, x, localY, z),
                     fine.sampleValue(sample, x, localY, z), bottom.sampleValue(sample, x, localY, z), 64, 384, capacity);
                 if (natural <= 0) return natural;
                 var region = capacity.regionAt(x, z);
                 var layout = layouts.computeIfAbsent(region, r -> RiftShape.layout(regionSeed(seed, r)));
                 int rx = x - region.originX(), rz = z - region.originZ();
-                if (!RiftShape.mayAffect(layout, rx, rz)) return natural;
-                return RiftShape.density(layout, rx, y, rz, natural,
-                    warp.sampleValue(sample, x, y, z), fractureDetail.sampleValue(sample, x, y, z));
+                boolean affects = geology28 ? RiftShape.mayAffect28(layout, rx, rz) : RiftShape.mayAffect(layout, rx, rz);
+                if (affects) natural = geology28
+                    ? RiftShape.density28(layout, rx, y, rz, natural,
+                        warp.sampleValue(sample, x, y, z), fractureDetail.sampleValue(sample, x, y, z))
+                    : RiftShape.density(layout, rx, y, rz, natural,
+                        warp.sampleValue(sample, x, y, z), fractureDetail.sampleValue(sample, x, y, z));
+                if (geology28 && natural > 0 && y > 40 && y < 232)
+                    natural = CavesRelief28.carve(natural, caves.sampleValue(sample, x, y - CavesRelief28.CAVE_OFFSET, z), y);
+                return natural;
             }
             @Override public void sampleVolume(SamplerContext sample, DensityBuffer buffer, DensityVolume volume) {
                 DensitySampler.sampleVolumeNaive(sample, buffer, volume, this);
             }
         };
     }
+    /** Native diagnostics can compile the exact accepted27 field without new adaptations. */
+    public PopulationIslandDensity legacy27() {
+        return new PopulationIslandDensity(terrain, distortion, sculpt, detail, underside, riftWarp, riftDetail,
+            capacity, DensityFunctions.zero(), DensityFunctions.zero(), DensityFunctions.zero(), false);
+    }
     public static long regionSeed(long seed, IslandCapacity.Region region) {
         long value = seed ^ ((long) region.x() << 32) ^ (region.z() & 0xffffffffL) ^ 0xA10CA7E1L;
         value = (value ^ (value >>> 30)) * 0xbf58476d1ce4e5b9L;
@@ -57,7 +108,8 @@ public record PopulationIslandDensity(DensityFunction terrain, DensityFunction d
     }
     @Override public DensityFunction rewriteChildren(DfRewriteRule rule) {
         return new PopulationIslandDensity(rule.rewrite(terrain), rule.rewrite(distortion), rule.rewrite(sculpt),
-            rule.rewrite(detail), rule.rewrite(underside), rule.rewrite(riftWarp), rule.rewrite(riftDetail), capacity);
+            rule.rewrite(detail), rule.rewrite(underside), rule.rewrite(riftWarp), rule.rewrite(riftDetail), capacity,
+            rule.rewrite(caves28), rule.rewrite(ridges28), rule.rewrite(erosion28), geology28);
     }
     @Override public Interval range() { return Interval.of(-1, 1); }
     @Override public int domainAxes() { return ALL_AXES; }

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

@@ -91,6 +91,55 @@ public final class RiftShape {
         return (float) Math.max(-1.0, terrain - erosion);
     }
 
+    /** Alpha28 fractures lean sideways, end within the mass and retain interrupted rock spans. */
+    public static boolean mayAffect28(Layout layout, int x, int z) {
+        double radius = Math.hypot((double) x, z);
+        if (radius <= INNER_UNTOUCHED_RADIUS || radius >= OUTER_UNTOUCHED_RADIUS) return false;
+        for (Rift rift : layout.rifts()) {
+            if (near28(rift.main(), x, z)) return true;
+            for (Segment branch : rift.branches()) if (near28(branch, x, z)) return true;
+        }
+        return false;
+    }
+
+    public static float density28(Layout layout, int x, int y, int z, float terrain, float warped, float detail) {
+        if (terrain <= 0 || y < 88 || y > 244 || !mayAffect28(layout, x, z)) return terrain;
+        double coarse = Math.clamp(warped, -1, 1), fine = Math.clamp(detail, -1, 1), cut = 0;
+        for (Rift rift : layout.rifts()) {
+            cut = Math.max(cut, erosion28(rift.main(), rift.id(), x, y, z, coarse, fine));
+            for (Segment branch : rift.branches())
+                cut = Math.max(cut, erosion28(branch, rift.id(), x, y, z, coarse, fine));
+        }
+        double radius = Math.hypot((double) x, z);
+        cut *= smoothstep((radius - INNER_UNTOUCHED_RADIUS) / 16)
+            * smoothstep((OUTER_UNTOUCHED_RADIUS - radius) / 20);
+        return (float) Math.max(-1, terrain - cut);
+    }
+
+    private static boolean near28(Segment segment, int x, int z) {
+        double rx = (double) x - segment.x(), rz = (double) z - segment.z();
+        return Math.abs(rx * segment.dx() + rz * segment.dz()) <= segment.halfLength() + 16
+            && Math.abs(-rx * segment.dz() + rz * segment.dx()) <= segment.bend() * 1.3 + 20;
+    }
+
+    private static double erosion28(Segment segment, long id, int x, int y, int z, double coarse, double fine) {
+        if (!near28(segment, x, z)) return 0;
+        double rx = x - segment.x(), rz = z - segment.z();
+        double along = rx * segment.dx() + rz * segment.dz();
+        double end = Math.clamp(along, -segment.halfLength(), segment.halfLength());
+        double centerY = 150 + unit(id + 41) * 32 + end * .12 + Math.sin(end / 29 + segment.phase()) * 7;
+        double halfHeight = 22 + unit(id + 42) * 14;
+        double vertical = smoothstep((halfHeight - Math.abs(y - centerY)) / 10);
+        if (vertical <= 0) return 0;
+        double lean = (y - centerY) * (.13 + unit(id + 43) * .07);
+        double sideways = -rx * segment.dz() + rz * segment.dx() - curve(segment, end) - lean - coarse * 1.05;
+        double width = Math.clamp(segment.halfWidth() + fine * .5 + coarse * .45, 2.2, 5.7);
+        double distance = Math.hypot(sideways, along - end);
+        double bridgeAt = (unit(id + 44) - .5) * segment.halfLength();
+        double bridge = smoothstep((Math.abs(end - bridgeAt) - 3) / 5);
+        return 2.1 * smoothstep((width + 1.6 - distance) / 2.6) * vertical * bridge;
+    }
+
     private static boolean near(Segment segment, int x, int z) {
         double rx = (double) x - segment.x(), rz = (double) z - segment.z();
         return Math.abs(rx * segment.dx() + rz * segment.dz()) <= segment.halfLength() + 10

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

@@ -183,7 +183,12 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
     public boolean intersectsExperimentalStructures(int minX, int minY, int minZ, int maxX, int maxY, int maxZ) {
         if (generation == 24) for (var site : aerialPlan24.sites()) {
             if (minX <= site.maxX() + 1 && maxX >= site.minX() - 1 && minZ <= site.maxZ() + 1 && maxZ >= site.minZ() - 1
-                    && minY <= site.maxY() + 1 && maxY >= (site.waterfall() ? 0 : site.minY() - 1)) return true;
+                    && minY <= site.maxY() + 1 && maxY >= site.minY() - 1) return true;
+            if (site.waterfall()) {
+                var flow = site.waterfallClaimBounds();
+                if (minX <= flow.maxX() && maxX >= flow.minX() && minZ <= flow.maxZ() && maxZ >= flow.minZ()
+                        && minY <= flow.maxY() && maxY >= flow.minY()) return true;
+            }
         }
         return (generation == 23 || generation == 24) && mineralSanctuary23.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ)
             || (generation == 17 || generation == 19 || generation == 20 || generation == 21 || generation == 22 || (generation == 23 || generation == 24)) && ruinsPlan17.intersectsProtection(minX, minY, minZ, maxX, maxY, maxZ)
@@ -210,6 +215,10 @@ public final class SanctuaryChunkGenerator extends ExpansionChunkGenerator {
             case "sanctuary:population_rocky_heath" -> "meadow";
             case "sanctuary:population_dark_grove" -> "dark_forest";
             case "sanctuary:population_bamboo_grove" -> "bamboo_jungle";
+            case "sanctuary:swamp27_caves" -> "swamp";
+            case "sanctuary:population_lush_caves" -> "lush_caves";
+            case "sanctuary:population_dripstone_caves" -> "dripstone_caves";
+            case "sanctuary:population_sulfur_depths" -> "sulfur_caves";
             default -> null;
         };
         return equivalent == null ? biome : registries.lookupOrThrow(Registries.BIOME).getOrThrow(

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/Swamp27Volumes.java

@@ -14,7 +14,7 @@ public final class Swamp27Volumes {
         // Broad, connected sectors change with height; finer noise softens their borders.
         double broad = noise(seed, x / 94.0, y / 48.0, z / 94.0);
         double detail = noise(seed ^ 0x7757A27L, x / 37.0, y / 31.0, z / 37.0);
-        return broad + detail * .22 > .04 + (1 - verticalEdge) * .7;
+        return broad + detail * .22 > .25 + (1 - verticalEdge) * .7;
     }
 
     private static double noise(long seed, double x, double y, double z) {

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/aerial/AerialPlanner24.java

@@ -15,6 +15,8 @@ import fr.koka.sanctuary.worldgen.aerial.AerialPlan24.Site;
 public final class AerialPlanner24 {
     public static final int MAX_ATTEMPTS_PER_SITE = 64;
     public static final int MAX_COLUMNS = 8192;
+    public static final int ARRIVAL_RADIUS = 96;
+    public static final int MIN_ISLET_GAP = 16;
     private AerialPlanner24() {}
     public interface Terrain {
         NoiseColumn column(int x, int z);
@@ -56,26 +58,67 @@ public final class AerialPlanner24 {
                 // Keep the four remaining bearings and seeded shapes; the former first sector is simply free.
                 double angle = initialAngle + (ordinal + 1) * (Math.PI * 2 / 5) + (unit(draw) - .5) * .9
                     + (attempt / 16) * .41;
-                Shore shore = shore(probe, angle, radius);
-                if (shore == null) continue;
                 int facing = (int) Math.floorMod(mix(draw), 4);
                 int worldWidth = facing % 2 == 0 ? width : depth, worldDepth = facing % 2 == 0 ? depth : width;
-                // The full claim remains outside initial terrain ownership, including corner chunks.
-                double distance = radius + 32 + Math.hypot(worldWidth, worldDepth) / 2 + 64 + (attempt % 4) * 20;
-                int cx = (int) Math.round(Math.cos(angle) * distance), cz = (int) Math.round(Math.sin(angle) * distance);
-                if (Math.hypot(cx - shore.x, cz - shore.z) > 500) continue;
-                int bottom = merchant ? Math.clamp(shore.y - 4 + (int) Math.floorMod(draw, 13), 180, 300)
-                    : Math.clamp(shore.y + 20 - bodyHeight / 2, 210, 320 - bodyHeight);
-                bottom = Math.min(bottom, 350 - height);
+                Shore shore;
+                int cx, cz, bottom;
+                if (merchant) {
+                    shore = shore(probe, angle, radius);
+                    if (shore == null) continue;
+                    // Start from the real edge, not the nominal island radius. The projected half-box
+                    // puts the complete hull 16–32 blocks out, even when the ship is rotated.
+                    double dx = Math.cos(angle), dz = Math.sin(angle);
+                    double offset = Math.abs(dx) * worldWidth / 2.0 + Math.abs(dz) * worldDepth / 2.0
+                        + 16 + (attempt % 3) * 8;
+                    cx = shore.x + (int) Math.round(dx * offset);
+                    cz = shore.z + (int) Math.round(dz * offset);
+                    // Native boarding deck is five blocks above the envelope's bottom.
+                    bottom = shore.y - 5 + (int) Math.floorMod(draw, 5);
+                } else {
+                    // Both mineral islands hover over Sanctuary, away from its natural arrival.
+                    double distance = radius * (.48 + .15 * unit(mix(draw ^ 0x28A1L)));
+                    cx = (int) Math.round(Math.cos(angle) * distance);
+                    cz = (int) Math.round(Math.sin(angle) * distance);
+                    int top = probe.surface(cx, cz);
+                    if (top < 120 || probe.terrain.reserved(cx, cz, top, top + 3)) continue;
+                    shore = new Shore(cx, top + 1, cz);
+                    int highest = top;
+                    for (int ox = -worldWidth / 2; ox <= worldWidth / 2; ox += 4)
+                        for (int oz = -worldDepth / 2; oz <= worldDepth / 2; oz += 4)
+                            highest = Math.max(highest, probe.highest(cx + ox, cz + oz));
+                    bottom = highest + MIN_ISLET_GAP + 1;
+                }
+                if (bottom < 32 || bottom + height > 350) continue;
                 var site = new Site(ids[ordinal], kinds[ordinal], cx - worldWidth / 2, bottom, cz - worldDepth / 2,
                     width, height, depth, facing, siteSeed, shore.x, shore.y, shore.z, ordinal == 2);
-                if (site.claimedChunks().stream().anyMatch(c -> claimed.contains(c.pack()))) continue;
-                boolean rootOverlap = site.claimedChunks().stream().anyMatch(c -> {
-                    int nearestX = Math.clamp(0, c.getMinBlockX(), c.getMaxBlockX());
-                    int nearestZ = Math.clamp(0, c.getMinBlockZ(), c.getMaxBlockZ());
-                    return Math.hypot(nearestX, nearestZ) <= radius + 32;
-                });
-                if (rootOverlap || !visible(probe, shore, cx, bottom + bodyHeight - 4, cz)) continue;
+                if (!outsideArrival(site) || site.claimedChunks().stream().anyMatch(c -> claimed.contains(c.pack()))) continue;
+                if (merchant) {
+                    double gap = shoreDistance(site);
+                    if (gap < 16 || gap > 48 || !clearShip(probe, site)) continue;
+                } else {
+                    // Certify every physical rock column, not only the coarse samples used to
+                    // choose a height. This may raise the whole unchanged island, never the ground.
+                    int highest = 0, supported = 0, count = 0;
+                    for (int x = 0; x < width; x++) for (int z = 0; z < depth; z++) {
+                        if (!isletColumn(site, x, z)) continue;
+                        int wx = site.worldX(x, z), wz = site.worldZ(x, z);
+                        highest = Math.max(highest, probe.highest(wx, wz));
+                        if (probe.surface(wx, wz) >= 120) supported++;
+                        count++;
+                    }
+                    if (supported * 4 < count * 3) continue;
+                    if (site.waterfall()) {
+                        var outlet = site.waterfallClaimBounds();
+                        for (int x = outlet.minX(); x <= outlet.maxX(); x++) for (int z = outlet.minZ(); z <= outlet.maxZ(); z++)
+                            highest = Math.max(highest, probe.highest(x, z));
+                    }
+                    bottom = Math.max(bottom, highest + MIN_ISLET_GAP + 1);
+                    if (bottom + height > 350) continue;
+                    site = new Site(site.id(), site.kind(), site.minX(), bottom, site.minZ(), width, height, depth,
+                        facing, siteSeed, shore.x, shore.y, shore.z, site.waterfall());
+                    if (!clearReservations(probe, site)) continue;
+                }
+                if (!visible(probe, shore, cx, bottom + bodyHeight - 4, cz)) continue;
                 accepted = site; break;
             }
             if (accepted == null) throw new IllegalStateException("aerial_sites_unavailable: could not place " + ids[ordinal] + " within the bounded search");
@@ -89,6 +132,39 @@ public final class AerialPlanner24 {
         return result;
     }
 
+    /** Horizontal distance from the saved land witness to the nearest point of the hull envelope. */
+    public static double shoreDistance(Site site) {
+        return Math.hypot(site.shoreX() - Math.clamp(site.shoreX(), site.minX(), site.maxX()),
+            site.shoreZ() - Math.clamp(site.shoreZ(), site.minZ(), site.maxZ()));
+    }
+    private static boolean outsideArrival(Site site) {
+        if (Math.hypot(Math.clamp(0, site.minX(), site.maxX()), Math.clamp(0, site.minZ(), site.maxZ())) < ARRIVAL_RADIUS) return false;
+        if (site.waterfall()) {
+            var box = site.waterfallClaimBounds();
+            if (Math.hypot(Math.clamp(0, box.minX(), box.maxX()), Math.clamp(0, box.minZ(), box.maxZ())) < ARRIVAL_RADIUS) return false;
+        }
+        return true;
+    }
+    private static boolean isletColumn(Site site, int x, int z) {
+        return AerialGeometry24.radial(site, x, z) <= 1
+            || site.waterfall() && Math.abs(x - site.width() / 2) <= 2 && z <= 6;
+    }
+    private static boolean clearShip(Probe probe, Site site) {
+        for (int x = site.minX(); x <= site.maxX(); x++) for (int z = site.minZ(); z <= site.maxZ(); z++)
+            if (probe.highest(x, z) >= site.minY() - 3 || probe.terrain.reserved(x, z, site.minY() - 1, site.maxY() + 1)) return false;
+        return true;
+    }
+    private static boolean clearReservations(Probe probe, Site site) {
+        for (int x = site.minX(); x <= site.maxX(); x++) for (int z = site.minZ(); z <= site.maxZ(); z++)
+            if (probe.terrain.reserved(x, z, site.minY() - 1, site.maxY() + 1)) return false;
+        if (site.waterfall()) {
+            var box = site.waterfallClaimBounds();
+            for (int x = box.minX(); x <= box.maxX(); x++) for (int z = box.minZ(); z <= box.maxZ(); z++)
+                if (probe.terrain.reserved(x, z, box.minY(), box.maxY())) return false;
+        }
+        return true;
+    }
+
     private static Shore shore(Probe probe, double angle, int radius) {
         double dx = Math.cos(angle), dz = Math.sin(angle);
         // An outside-in scan finds the outer shore, never an internal pond. Refine its edge to a block.
@@ -138,6 +214,11 @@ public final class AerialPlanner24 {
             for (int y = 382; y > 0; y--) if (column.getBlock(y).isSolid() && column.getBlock(y).getFluidState().isEmpty()) return y;
             return 0;
         }
+        int highest(int x, int z) {
+            var column = column(x, z); if (column == null) return 0;
+            for (int y = 382; y > 0; y--) if (!column.getBlock(y).isAir()) return y;
+            return 0;
+        }
         boolean solid(int x, int y, int z) {
             var column = column(x, z); return column != null && !column.getBlock(y).isAir();
         }

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/aerial/AerialStore24.java

@@ -95,13 +95,9 @@ public final class AerialStore24 {
 
     private static void validateExtent(AerialPlan24 plan, int diameter) throws IOException {
         if (diameter != 512 && diameter != 724 && diameter != 1024) throw new IOException("Unsupported aerial root size");
-        int radius = (diameter == 724 ? 395 : diameter / 2 + 32) + 32;
-        for (long packed : plan.claimsChunks()) {
-            var c = net.minecraft.world.level.ChunkPos.unpack(packed);
-            int x = Math.clamp(0, c.getMinBlockX(), c.getMaxBlockX());
-            int z = Math.clamp(0, c.getMinBlockZ(), c.getMaxBlockZ());
-            if (Math.hypot(x, z) <= radius) throw new IOException("Aerial claim overlaps initial terrain ownership");
-        }
+        // Aerial bodies may share X/Z with the initial island. Their vertical clearance is
+        // certified at creation; the immutable manifest preserves it on subsequent loads.
+        // Site/Plan constructors still validate finite height, dimensions, count and disjoint claims.
     }
     private static JsonObject encode(AerialPlan24 plan, long seed, int diameter) {
         var root = new JsonObject();

mods/sanctuary/src/main/java/fr/koka/sanctuary/worldgen/aerial/AerialStructures24.java

@@ -22,7 +22,7 @@ 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;
 
-/** Native starts for four immutable initial sites. Their void chunks need no terrain island owner. */
+/** Native starts for four immutable initial sites, in the void or above initial terrain. */
 public final class AerialStructures24 {
     public static final ResourceKey<Structure> MERCHANT_SHIP = key("aerial_merchant_ship");
     public static final ResourceKey<Structure> MINERAL_ISLET = key("aerial_mineral_islet");
@@ -67,7 +67,10 @@ public final class AerialStructures24 {
             if (previous != null && previous.isValid()) continue;
             var start = structure.generate(holder, level, registries, generator, generator.getBiomeSource(), sampler,
                 random, templates, origin.seed(), chunk.getPos(), previous == null ? 0 : previous.getReferences(),
-                chunk, structure.biomes()::contains);
+                // Only this explicit saved departure bypasses biome selection. Its complete
+                // geometry and clearance were certified by the aerial planner; the biome below
+                // may be forest, marsh or void. findGenerationPoint still requires this exact plan.
+                chunk, ignoredBiome -> sites.stream().anyMatch(site -> key(site).equals(key)));
             if (start.isValid()) manager.setStartForStructure(structure, start, chunk);
         }
     }

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/density_function/caves28_native.json

@@ -0,0 +1,58 @@
+{
+  "type": "minecraft:min",
+  "left": {
+    "type": "minecraft:max",
+    "left": {
+      "type": "minecraft:min",
+      "left": {
+        "type": "minecraft:min",
+        "left": {
+          "type": "minecraft:add",
+          "left": {
+            "type": "minecraft:mul",
+            "left": {
+              "type": "minecraft:square",
+              "input": {
+                "type": "minecraft:noise",
+                "noise": "minecraft:cave_layer",
+                "xz_scale": 1.0,
+                "y_scale": 8.0
+              }
+            },
+            "right": 4.0
+          },
+          "right": {
+            "type": "minecraft:clamp",
+            "input": {
+              "type": "minecraft:add",
+              "left": {
+                "type": "minecraft:noise",
+                "noise": "minecraft:cave_cheese",
+                "xz_scale": 1.0,
+                "y_scale": 0.6666666666666666
+              },
+              "right": 0.27
+            },
+            "max": 1.0,
+            "min": -1.0
+          }
+        },
+        "right": "minecraft:overworld/caves/entrances"
+      },
+      "right": {
+        "type": "minecraft:add",
+        "left": "minecraft:overworld/caves/spaghetti_2d",
+        "right": "minecraft:overworld/caves/spaghetti_roughness_function"
+      }
+    },
+    "right": {
+      "type": "minecraft:range_choice",
+      "input": "minecraft:overworld/caves/pillars",
+      "max_exclusive": 0.03,
+      "min_inclusive": -1000000.0,
+      "when_in_range": -1000000.0,
+      "when_out_of_range": "minecraft:overworld/caves/pillars"
+    }
+  },
+  "right": "minecraft:overworld/caves/noodle"
+}

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/density_function/population_10.json

@@ -49,5 +49,19 @@
     "noise": "sanctuary:rift_detail",
     "xz_scale": 1.0,
     "y_scale": 1.0
+  },
+  "geology_28": true,
+  "caves_28": "sanctuary:caves28_native",
+  "ridges_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:ridge",
+    "xz_scale": 1.0,
+    "y_scale": 1.0
+  },
+  "erosion_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:erosion",
+    "xz_scale": 2.0,
+    "y_scale": 2.0
   }
 }

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/density_function/population_20.json

@@ -49,5 +49,19 @@
     "noise": "sanctuary:rift_detail",
     "xz_scale": 1.0,
     "y_scale": 1.0
+  },
+  "geology_28": true,
+  "caves_28": "sanctuary:caves28_native",
+  "ridges_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:ridge",
+    "xz_scale": 1.0,
+    "y_scale": 1.0
+  },
+  "erosion_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:erosion",
+    "xz_scale": 2.0,
+    "y_scale": 2.0
   }
 }

mods/sanctuary/src/main/resources/data/sanctuary/worldgen/density_function/population_5.json

@@ -49,5 +49,19 @@
     "noise": "sanctuary:rift_detail",
     "xz_scale": 1.0,
     "y_scale": 1.0
+  },
+  "geology_28": true,
+  "caves_28": "sanctuary:caves28_native",
+  "ridges_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:ridge",
+    "xz_scale": 1.0,
+    "y_scale": 1.0
+  },
+  "erosion_28": {
+    "type": "minecraft:noise",
+    "noise": "minecraft:erosion",
+    "xz_scale": 2.0,
+    "y_scale": 2.0
   }
 }

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/CavesRelief28Smoke.java

@@ -0,0 +1,54 @@
+package fr.koka.sanctuary.worldgen;
+
+/** Adapters and finite fractures only. Native noise presence is checked separately in Minecraft. */
+public final class CavesRelief28Smoke {
+    public static void main(String[] args) {
+        for (int y = 0; y < 384; y++) {
+            require(CavesRelief28.deformationWeight(0, y, 0, 256) == 0, "arrival must not deform");
+            require(CavesRelief28.deformationWeight(256, y, 0, 256) == 0, "outer coast must not deform");
+            if (y <= 180) require(CavesRelief28.deformationWeight(128, y, 0, 256) == 0,
+                "accepted lower mass must not deform");
+        }
+        require(CavesRelief28.deformationWeight(128, 220, 0, 256)
+            < CavesRelief28.deformationWeight(128, 228, 0, 256), "3D deformation must have a smooth vertical envelope");
+        for (float v : new float[] {-10, -1, -.5F, 0, .5F, 1, 10}) {
+            var warp = CavesRelief28.warp(1, v, v, v);
+            var opposite = CavesRelief28.warp(1, -v, -v, -v);
+            require(Math.abs(warp.x()) <= 16 && Math.abs(warp.z()) <= 16 && Math.abs(warp.y()) <= 40,
+                "deformation must stay bounded in all three axes");
+            require(warp.x() == -opposite.x() && warp.y() == -opposite.y() && warp.z() == -opposite.z(),
+                "noise must permit equivalent uplift and subsidence, without positive bias");
+            var fixed = CavesRelief28.warp(0, v, v, v);
+            require(fixed.x() == 0 && fixed.y() == 0 && fixed.z() == 0, "zero envelope leaves coordinates unchanged");
+        }
+        require(CavesRelief28.warp(1, 0, .5F, 0).y() < CavesRelief28.warp(1, 0, .6F, 0).y(),
+            "deformation must not saturate into broad flat plateaus");
+        for (int y = 0; y < 384; y++) for (float cave : new float[] {-1, -.1F, .1F, 1, 64}) {
+            require(CavesRelief28.carve(-.3F, cave, y) == -.3F, "caves must never fill existing void");
+            require(CavesRelief28.carve(.7F, cave, y) <= .7F, "caves must only remove rock");
+            if (y <= 40 || y >= 232) require(CavesRelief28.carve(.7F, cave, y) == .7F, "bounded cave heights");
+        }
+        require(CavesRelief28.carve(.7F, -.1F, 140) < 0, "negative native cave must open solid interior");
+        for (long seed : new long[] {0, 42, 2026}) {
+            var layout = RiftShape.layout(seed);
+            int removed = 0, retained = 0;
+            for (int x = -216; x <= 216; x += 4) for (int z = -216; z <= 216; z += 4) {
+                require(RiftShape.density28(layout, x, 60, z, .7F, 0, 0) == .7F, "rift cannot cut lower boundary");
+                require(RiftShape.density28(layout, x, 260, z, .7F, 0, 0) == .7F, "rift cannot traverse upper surface");
+                int columnCut = 0;
+                for (int y = 88; y <= 244; y += 4) {
+                    float value = RiftShape.density28(layout, x, y, z, .7F, .2F, -.3F);
+                    require(value <= .7F, "rift cannot add material");
+                    if (value < 0) { removed++; columnCut++; } else retained++;
+                }
+                require(columnCut < 22, "fracture cannot cut the entire vertical island mass");
+            }
+            require(removed > 0 && retained > removed, "finite ravines must open passages and retain rock");
+            System.out.println("caves28 rifts seed=" + seed + " removed=" + removed + " retained=" + retained);
+        }
+        System.out.println("CavesRelief28Smoke: signed 3D deformation, native cut adapter and bounded ravines passed");
+    }
+    private static void require(boolean condition, String message) {
+        if (!condition) throw new AssertionError(message);
+    }
+}

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/aerial/Aerial24Smoke.java

@@ -48,12 +48,24 @@ public final class Aerial24Smoke {
                         && site.height() == site.rockHeight() + AerialPlan24.VEGETATION_HEADROOM,
                         "Vegetation adds eight blocks of headroom without enlarging the stone body");
                 double distance = Math.hypot(site.locator().getX() - site.shoreX(), site.locator().getZ() - site.shoreZ());
-                require(distance <= 512, "Every site has a nearby shore witness");
+                require(distance <= 512, "Every site has a nearby ground witness");
+                if (site.merchant()) {
+                    double gap = AerialPlanner24.shoreDistance(site);
+                    require(gap >= 16 && gap <= 48, "Complete ship envelope is 16–48 blocks from its actual shore");
+                    require(Math.abs(AerialGeometry24.entry(site).getY() - site.shoreY()) <= 4,
+                        "Boarding deck remains near the shore's walking height");
+                } else {
+                    require(root.ownsChunk(site.startChunkX(), site.startChunkZ()), "Mineral islets hover over the initial island");
+                    require(site.minY() - 240 - 1 >= AerialPlanner24.MIN_ISLET_GAP,
+                        "The unchanged rocky body has at least sixteen air blocks above the terrain");
+                }
+                require(Math.hypot(Math.clamp(0, site.minX(), site.maxX()), Math.clamp(0, site.minZ(), site.maxZ())) >= AerialPlanner24.ARRIVAL_RADIUS,
+                    "Aerial bodies preserve the natural arrival zone");
                 require(plan.atStartChunk(site.startChunkX(), site.startChunkZ()).contains(site), "Native departure belongs to its saved site");
                 for (var chunk : site.claimedChunks()) {
                     require(allClaims.add(chunk.pack()), "Site claims do not overlap");
                     require(site.ownsChunk(chunk.x(), chunk.z()) && plan.ownsChunk(chunk.x(), chunk.z()), "Claim query agrees with the immutable mask");
-                    require(!root.ownsChunk(chunk.x(), chunk.z()), "Claim does not replace initial island ownership");
+
                 }
                 var overlapping = new ExpansionIsland("overlap", "sanctuary", "east", "temperate", 64,
                     site.startChunkX() * 16, site.startChunkZ() * 16, 42, "natural", "reserved", 24);
@@ -109,7 +121,7 @@ public final class Aerial24Smoke {
             require(columns[0] <= AerialPlanner24.MAX_COLUMNS, "Reservations preserve the bounded terrain sampling budget");
             for (var site : replacement.sites())
                 require(!terrain.reserved(site.shoreX(), site.shoreZ(), site.shoreY() - 1, site.shoreY() + 2),
-                    "Every accepted shore stays outside planned root structures");
+                    "Every accepted ground witness stays outside planned root structures");
         }
     }
     private static AerialPlan24.Site rotate(AerialPlan24.Site site, int facing) {

mods/sanctuary/src/test/java/fr/koka/sanctuary/worldgen/aerial/AerialPersistence24Smoke.java

@@ -51,6 +51,9 @@ public final class AerialPersistence24Smoke {
             require(draws.get() == 1 && stored.plan().sites().size() == 4, "One complete initial plan is recorded");
             var journal = new ExpansionJournal(directory, SEED, 724, 24, stored.token());
             var root = ExpansionIsland.origin(724, SEED, 24);
+            require(stored.plan().sites().stream().filter(site -> site.kind() == Kind.MINERAL_ISLET)
+                .allMatch(site -> root.ownsChunk(site.startChunkX(), site.startChunkZ())),
+                "An immutable elevated islet may share initial terrain chunks without replacing root ownership");
             Path journalFile = directory.resolve(ExpansionJournal.FILE_NAME);
             byte[] pristineJournal = Files.readAllBytes(journalFile);
             require(JsonParser.parseString(Files.readString(journalFile)).getAsJsonObject().get("schema").getAsInt() == 2,
@@ -143,8 +146,8 @@ public final class AerialPersistence24Smoke {
         return new AerialPlan24(List.of(
             new Site("merchant_provisions", Kind.MERCHANT_PROVISIONS, 0, 235, 660, 11, 18, 28, 0, 2, 0, 240, 390, false),
             new Site("merchant_tools", Kind.MERCHANT_TOOLS, -740, 242, 0, 11, 18, 28, 0, 3, -390, 240, 0, false),
-            new Site("mineral_islet_water", Kind.MINERAL_ISLET, -450, 255, -650, 48, 36, 48, 0, 4, -200, 240, -330, true),
-            new Site("mineral_islet_dry", Kind.MINERAL_ISLET, 460, 260, -600, 56, 40, 56, 0, 5, 250, 240, -300, false)));
+            new Site("mineral_islet_water", Kind.MINERAL_ISLET, -180, 270, -160, 48, 36, 48, 0, 4, -156, 240, -136, true),
+            new Site("mineral_islet_dry", Kind.MINERAL_ISLET, 125, 270, -170, 56, 40, 56, 0, 5, 153, 240, -142, false)));
     }
     private static String digest(byte[] bytes) throws Exception { return HexFormat.of().formatHex(MessageDigest.getInstance("SHA-256").digest(bytes)); }
     private static void require(boolean value, String message) { if (!value) throw new AssertionError(message); }