Merged terrain generation updates

- Existing worlds retain generated terrain across generator updates
- New terrain blends at generation boundaries
- Cold generation and Studio startup improvements are integrated
- Terrain sampling validates active generator bounds and noise

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/CustomBiomeSource.java

@@ -17,6 +17,7 @@ import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisBiomeCustom;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisDimensionCarvingResolver;
+import art.arcane.iris.engine.platform.BukkitChunkGenerator;
 import art.arcane.iris.util.project.context.IrisContext;
 import art.arcane.volmlib.util.collection.KMap;
 import art.arcane.volmlib.util.math.RNG;
@@ -64,6 +65,7 @@ public class CustomBiomeSource extends BiomeSource {
 
     private final long seed;
     private final Engine engine;
+    private final BukkitChunkGenerator platformGenerator;
     private final Registry<Biome> biomeCustomRegistry;
     private final Registry<Biome> biomeRegistry;
     private final AtomicCache<RegistryAccess> registryAccess = new AtomicCache<>();
@@ -76,6 +78,9 @@ public class CustomBiomeSource extends BiomeSource {
 
     public CustomBiomeSource(long seed, Engine engine, World world) {
         this.engine = engine;
+        this.platformGenerator = world.getGenerator() instanceof BukkitChunkGenerator generator
+                ? generator
+                : null;
         this.seed = seed;
         this.biomeCustomRegistry = registry().lookup(Registries.BIOME).orElse(null);
         this.biomeRegistry = ((RegistryAccess) getFor(RegistryAccess.Frozen.class, ((CraftServer) Bukkit.getServer()).getHandle().getServer())).lookup(Registries.BIOME).orElse(null);
@@ -353,6 +358,9 @@ public class CustomBiomeSource extends BiomeSource {
             if (!isRuntimeAvailable()) {
                 return null;
             }
+            if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+                return fallbackBiome;
+            }
             runtimeBiomeState();
             int quartX = QuartPos.fromBlock(blockX);
             int quartZ = QuartPos.fromBlock(blockZ);
@@ -405,6 +413,9 @@ public class CustomBiomeSource extends BiomeSource {
     }
 
     private Holder<Biome> getStructureNoiseBiomeWithActiveGenerationLease(int x, int y, int z) {
+        if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+            return fallbackBiome;
+        }
         if (isGuaranteedSurfaceBiome(y)) {
             return getSurfaceStructureBiomeHolder(x, z);
         }
@@ -731,6 +742,9 @@ public class CustomBiomeSource extends BiomeSource {
             IrisDimensionCarvingResolver.State resolverState,
             boolean cacheable
     ) {
+        if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+            return fallbackBiome;
+        }
         RuntimeNoiseKey cacheKey = new RuntimeNoiseKey(
                 engine.getCacheID(), packNoiseKey(x, y, z));
         if (cacheable) {

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/IrisChunkGenerator.java

@@ -1,5 +1,10 @@
 package art.arcane.iris.core.nms.v26_2_R1;
 
+import art.arcane.iris.nativegen.NativeTransitionColumn;
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
+import java.util.Optional;
+import art.arcane.iris.nativegen.NativeGenerationWriteGuard;
+import java.util.function.LongPredicate;
 import art.arcane.iris.engine.DimensionStackContext;
 import art.arcane.iris.engine.DimensionStackLayout;
 import art.arcane.iris.engine.framework.Engine;
@@ -12,7 +17,12 @@ import art.arcane.iris.engine.framework.NativeStructureStartPlan;
 import art.arcane.iris.engine.framework.NativeStructureGenerationPolicy;
 import art.arcane.iris.engine.IrisEngine;
 import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import art.arcane.iris.engine.history.NativeTerrainReceipt;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import org.bukkit.NamespacedKey;
+import org.bukkit.persistence.PersistentDataType;
 import art.arcane.iris.engine.platform.BukkitChunkGenerator;
+import art.arcane.iris.engine.platform.studio.generators.JigsawStudioGenerator;
 import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisDimensionCarvingResolver;
 import art.arcane.iris.engine.object.IrisMaterialPalette;
@@ -112,7 +122,6 @@ import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.CancellationException;
 import java.util.concurrent.CompletableFuture;
@@ -122,7 +131,14 @@ import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.IntBinaryOperator;
 import java.util.function.Predicate;
 
-public class IrisChunkGenerator extends CustomChunkGenerator {
+public class IrisChunkGenerator extends CustomChunkGenerator implements LongPredicate {
+    private static final Set<Heightmap.Types> AUTHORING_HEIGHTMAPS = Set.of(
+            Heightmap.Types.WORLD_SURFACE_WG,
+            Heightmap.Types.OCEAN_FLOOR_WG,
+            Heightmap.Types.WORLD_SURFACE,
+            Heightmap.Types.OCEAN_FLOOR,
+            Heightmap.Types.MOTION_BLOCKING,
+            Heightmap.Types.MOTION_BLOCKING_NO_LEAVES);
     private static final WrappedField<ChunkGenerator, BiomeSource> BIOME_SOURCE;
     private static final WrappedReturningMethod<Heightmap, Object> SET_HEIGHT;
     private static final Runnable NO_OP = () -> {
@@ -413,6 +429,11 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
                     ));
             adjustGeneratedStructures(
                     registryAccess, access, previousStarts, configuredStarts, templateManager);
+            if (route != null) {
+                access.persistentDataContainer.set(new NamespacedKey("iris", "structure_activation"),
+                        PersistentDataType.LONG, route.activation().activationId());
+                access.markUnsaved();
+            }
         }
     }
 
@@ -716,6 +737,9 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
              GenerationHistoryRuntimeRouter.RuntimeRoute.RuntimeScope runtimeScope = openHistoryRuntimeScope(route);
              GenerationSessionLease lease = requireGenerationLease("bukkit_nms_build_surface");
              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+            if (!engine.getComplex().allowsMantleChunkWrite(chunkPos.x(), chunkPos.z())) {
+                return;
+            }
             delegate.buildSurface(regionlimitedworldaccess, structuremanager, randomstate, ichunkaccess);
         }
     }
@@ -729,6 +753,9 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
              GenerationHistoryRuntimeRouter.RuntimeRoute.RuntimeScope runtimeScope = openHistoryRuntimeScope(route);
              GenerationSessionLease lease = requireGenerationLease("bukkit_nms_apply_carvers");
              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+            if (!engine.getComplex().allowsMantleChunkWrite(chunkPos.x(), chunkPos.z())) {
+                return;
+            }
             delegate.applyCarvers(regionlimitedworldaccess, seed, randomstate, biomemanager, structuremanager, ichunkaccess);
         }
     }
@@ -766,6 +793,8 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
                         try (GenerationHistoryRuntimeRouter.RuntimeRoute.RuntimeScope runtimeScope =
                                      openHistoryRuntimeScope(route);
                              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+                            claimGeneratedSemantics(route, filled, engine.getMinHeight());
+                            persistNaturalTerrain(filled, route);
                             primeWorldgenHeightmaps(filled);
                             return filled;
                         }
@@ -783,6 +812,10 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
                     completion.completeExceptionally(completionFailure);
                 }
             });
+            lease.detachThread();
+            if (route != null) {
+                route.detachThread();
+            }
             return completion;
         } catch (RuntimeException | Error failure) {
             lease.close();
@@ -792,6 +825,19 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
         }
     }
 
+    private static void persistNaturalTerrain(ChunkAccess chunk, GenerationHistoryRuntimeRouter.RuntimeRoute route) {
+        if (route == null || route.naturalTerrain().isEmpty()) {
+            return;
+        }
+        try {
+            SavedTerrainChunk terrain = route.naturalTerrain().orElseThrow();
+            chunk.persistentDataContainer.set(new NamespacedKey("iris", "natural_terrain"), PersistentDataType.BYTE_ARRAY,
+                    NativeTerrainReceipt.encode(terrain, route.activation().activationId(), route.epoch().epochId()));
+        } catch (IOException failure) {
+            throw new IllegalStateException("Unable to persist natural terrain for chunk " + chunk.getPos(), failure);
+        }
+    }
+
     private static Throwable closeNoisePipelineResources(
             Throwable failure,
             GenerationSessionLease lease,
@@ -854,9 +900,17 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
     }
 
     private void primeWorldgenHeightmaps(ChunkAccess chunkAccess) {
+        if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+            primeAuthoringHeightmaps(chunkAccess);
+            return;
+        }
         WorldgenTerrainHeightmaps.primeTerrain(chunkAccess, worldgenSurfaceHeight(), worldgenFloorHeight());
     }
 
+    static void primeAuthoringHeightmaps(ChunkAccess chunkAccess) {
+        Heightmap.primeHeightmaps(chunkAccess, AUTHORING_HEIGHTMAPS);
+    }
+
     private IntBinaryOperator worldgenSurfaceHeight() {
         return (x, z) -> engine.getHeight(x, z, false) + runtimeMinY + 1;
     }
@@ -933,19 +987,27 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
              GenerationHistoryRuntimeRouter.RuntimeRoute.RuntimeScope runtimeScope = openHistoryRuntimeScope(route);
              GenerationSessionLease lease = requireGenerationLease("bukkit_nms_biome_decoration");
             IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
-            if (allowsRoutedDiscreteGeneration(ichunkaccess, ChunkStatus.FEATURES)) {
+            boolean flatStudioTerrain = platformGenerator != null && platformGenerator.usesFlatStudioTerrain();
-                // Bind-time equivalent for Bukkit: the table is built on the first decorated chunk, which is where a
+            if (!flatStudioTerrain && !ichunkaccess.getPersistedStatus().isOrAfter(ChunkStatus.FEATURES)) {
-                // feature-order cycle is reported once and degraded to features-off.
-                importedFeatures.prepare(generatoraccessseed);
-                addVanillaDecorations(generatoraccessseed, ichunkaccess, structuremanager);
                 placeVanillaStructures(generatoraccessseed, ichunkaccess, structuremanager);
-                // Vanilla's placed-feature pass, on THIS thread. The delegate is still called with
+            }
-                // addVanillaDecorations=false below, so the vanilla half never runs twice. Inert unless the
+            if (allowsRoutedDiscreteGeneration(ichunkaccess, ChunkStatus.FEATURES)
-                // dimension set importedFeatures.enabled.
+                    && NativeGenerationWriteGuard.allowsDecoration(engine, generatoraccessseed, chunkPos)) {
-                importedFeatures.run(generatoraccessseed, ichunkaccess, this);
+                if (!flatStudioTerrain) {
+                    // Bind-time equivalent for Bukkit: the table is built on the first decorated chunk, which is where a
+                    // feature-order cycle is reported once and degraded to features-off.
+                    importedFeatures.prepare(generatoraccessseed);
+                }
+                addVanillaDecorations(generatoraccessseed, ichunkaccess, structuremanager);
+                if (!flatStudioTerrain) {
+                    // Vanilla's placed-feature pass, on THIS thread. The delegate is still called with
+                    // addVanillaDecorations=false below, so the vanilla half never runs twice. Inert unless the
+                    // dimension set importedFeatures.enabled.
+                    importedFeatures.run(generatoraccessseed, ichunkaccess, this);
+                }
                 delegate.applyBiomeDecoration(generatoraccessseed, ichunkaccess, structuremanager, false);
             }
-            claimGeneratedSemantics(route, "bukkit_nms_biome_decoration");
+            claimGeneratedSemantics(route, ichunkaccess, engine.getMinHeight());
         }
     }
 
@@ -998,7 +1060,8 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
                     List<NativePlacement> resolvedPlacements = new ArrayList<>(starts.size());
                     for (StructureStart start : starts) {
                         BoundingBox footprint = start.getBoundingBox();
-                        if (!engine.getComplex().allowsNewGenerationFootprint(
+                        if (!isHistoricalStructureStart(world, start)
+                                && !engine.getComplex().allowsNewGenerationFootprint(
                                 footprint.minX(),
                                 footprint.minZ(),
                                 footprint.maxX(),
@@ -1098,6 +1161,20 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
         }
     }
 
+    private boolean isHistoricalStructureStart(WorldGenLevel world, StructureStart start) {
+        ChunkPos origin = start.getChunkPos();
+        if (!engine.getComplex().allowsMantleChunkWrite(origin.x(), origin.z())) {
+            return true;
+        }
+        ChunkAccess source = world.getChunk(origin.x(), origin.z(), ChunkStatus.EMPTY, false);
+        if (source == null) {
+            return false;
+        }
+        long activation = source.persistentDataContainer.getOrDefault(
+                new NamespacedKey("iris", "structure_activation"), PersistentDataType.LONG, 0L);
+        return NativeGenerationWriteGuard.isHistoricalStructure(engine, activation);
+    }
+
     private static String nativeStructureBatchContext(List<NativePlacementGroup> placementGroups) {
         if (placementGroups.isEmpty()) {
             return "<no resolved native structures>";
@@ -1219,6 +1296,9 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
             BlockPos blockPos = sectionPos.origin();
 
             primeWorldgenHeightmaps(chunkAccess);
+            if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+                return;
+            }
 
             Heightmap motion = chunkAccess.getOrCreateHeightmapUnprimed(Heightmap.Types.MOTION_BLOCKING);
             Heightmap motionNoLeaves = chunkAccess.getOrCreateHeightmapUnprimed(Heightmap.Types.MOTION_BLOCKING_NO_LEAVES);
@@ -1272,12 +1352,19 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
         }
     }
 
+    @Override
+    public boolean test(long packedChunk) {
+        return !engine.isClosing() && !engine.isClosed()
+                && engine.getComplex().allowsMantleChunkWrite(ChunkPos.getX(packedChunk), ChunkPos.getZ(packedChunk));
+    }
+
     private boolean allowsRoutedDiscreteGeneration(ChunkAccess chunk, ChunkStatus stage) {
         if (chunk.getPersistedStatus().isOrAfter(stage)) {
             return false;
         }
         ChunkPos chunkPos = chunk.getPos();
-        return engine.getComplex().allowsNewGenerationChunk(chunkPos.x(), chunkPos.z());
+        return NativeGenerationWriteGuard.allowsPendingStage(engine, chunk, stage)
+                || engine.getComplex().allowsNewGenerationChunk(chunkPos.x(), chunkPos.z());
     }
 
     private static WeightedList<MobSpawnSettings.SpawnerData> mergeSpawnTables(
@@ -1310,10 +1397,17 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
 
     @Override
     public int getBaseHeight(int i, int j, Heightmap.Types heightmap_type, LevelHeightAccessor levelheightaccessor, RandomState randomstate) {
+        if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+            return platformGenerator.getAuthoringBaseHeight();
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope route = openHistoryCoordinateScope(
                      i, j, "bukkit_nms_base_height");
              GenerationSessionLease lease = engine.acquireGenerationLease("bukkit_nms_base_height");
              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+            Optional<TerrainBoundarySignature> resolved = engine.getComplex().resolvedTerrainColumn(i, j);
+            if (resolved.isPresent()) {
+                return NativeTransitionColumn.height(resolved.get(), heightmap_type, levelheightaccessor);
+            }
             boolean ignoreFluid = !heightmap_type.isOpaque().test(Blocks.WATER.defaultBlockState());
             int height = engine.getDimensionStackContext() == null
                     ? engine.getHeight(i, j, ignoreFluid)
@@ -1327,10 +1421,27 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
 
     @Override
     public NoiseColumn getBaseColumn(int i, int j, LevelHeightAccessor levelheightaccessor, RandomState randomstate) {
+        if (platformGenerator != null && platformGenerator.usesFlatStudioTerrain()) {
+            BlockState[] column = new BlockState[levelheightaccessor.getHeight()];
+            int floorIndex = platformGenerator.getAuthoringFloorY() - levelheightaccessor.getMinY();
+            BlockState floor = platformGenerator.isJigsawStudioActive() && JigsawStudioGenerator.isLightFloor(i, j)
+                    ? Blocks.SMOOTH_STONE.defaultBlockState()
+                    : Blocks.POLISHED_DEEPSLATE.defaultBlockState();
+            for (int index = 0; index < column.length; index++) {
+                column[index] = index == floorIndex
+                        ? floor
+                        : Blocks.AIR.defaultBlockState();
+            }
+            return new NoiseColumn(levelheightaccessor.getMinY(), column);
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope route = openHistoryCoordinateScope(
                      i, j, "bukkit_nms_base_column");
              GenerationSessionLease lease = engine.acquireGenerationLease("bukkit_nms_base_column");
              IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+            Optional<TerrainBoundarySignature> resolved = engine.getComplex().resolvedTerrainColumn(i, j);
+            if (resolved.isPresent()) {
+                return NativeTransitionColumn.column(resolved.get(), levelheightaccessor);
+            }
             boolean dimensionStack = engine.getDimensionStackContext() != null;
             int block = dimensionStack
                     ? Engine.hostHeight(engine, i, j, true)
@@ -1412,16 +1523,20 @@ public class IrisChunkGenerator extends CustomChunkGenerator {
 
     private static void claimGeneratedSemantics(
             GenerationHistoryRuntimeRouter.RuntimeRoute route,
-            String operation
+            ChunkAccess chunk,
+            int minimumY
     ) {
         if (route == null) {
             return;
         }
         try {
-            route.claimGeneratedSemantics();
+            BlockPos.MutableBlockPos position = new BlockPos.MutableBlockPos();
+            route.claimGeneratedSemantics((x, y, z) -> {
+                BlockState state = chunk.getBlockState(position.set(x, minimumY + y, z));
+                return state.isAir() || state.liquid();
+            });
         } catch (IOException failure) {
-            throw new IllegalStateException("Iris " + operation
+            throw new IllegalStateException("Iris could not durably claim generated chunk semantics.", failure);
-                    + " could not durably claim generated chunk semantics.", failure);
         }
     }
 

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NMSBinding.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.core.nms.v26_2_R1;
 
+import art.arcane.iris.engine.history.SavedTerrainChunk;
 import ca.spottedleaf.moonrise.patches.chunk_system.io.MoonriseRegionFileIO;
 import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.ChunkHolderManager;
 import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.NewChunkHolder;
@@ -26,10 +27,8 @@ import art.arcane.iris.engine.platform.PlatformChunkGenerator;
 import art.arcane.iris.nativegen.NativeStructureFactory;
 import art.arcane.iris.nativegen.NativeStructureGenerationException;
 import art.arcane.iris.spi.PlatformStructureHooks.JigsawSourceMetadata;
-import art.arcane.iris.util.project.agent.Agent;
 import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.collection.KMap;
-import art.arcane.iris.util.common.format.C;
 import art.arcane.iris.util.project.hunk.Hunk;
 import art.arcane.iris.util.project.hunk.view.ChunkDataHunkHolder;
 import art.arcane.iris.spi.PlatformBlockState;
@@ -54,15 +53,6 @@ import art.arcane.volmlib.util.nbt.mca.palette.MCAWrappedPalettedContainer;
 import art.arcane.volmlib.util.nbt.tag.CompoundTag;
 import art.arcane.iris.util.common.scheduling.J;
 import it.unimi.dsi.fastutil.objects.Object2IntMap;
-import it.unimi.dsi.fastutil.shorts.ShortList;
-import net.bytebuddy.ByteBuddy;
-import net.bytebuddy.agent.builder.AgentBuilder;
-import net.bytebuddy.agent.builder.ResettableClassFileTransformer;
-import net.bytebuddy.description.type.TypeDescription;
-import net.bytebuddy.dynamic.DynamicType;
-import net.bytebuddy.utility.JavaModule;
-import net.bytebuddy.asm.Advice;
-import net.bytebuddy.matcher.ElementMatchers;
 import net.minecraft.core.BlockPos;
 import net.minecraft.core.Holder;
 import net.minecraft.core.IdMapper;
@@ -95,7 +85,6 @@ import net.minecraft.tags.TagKey;
 import net.minecraft.world.attribute.EnvironmentAttributes;
 import net.minecraft.world.entity.EntityType;
 import net.minecraft.world.item.component.CustomData;
-import net.minecraft.world.level.Level;
 import net.minecraft.world.level.biome.BiomeSource;
 import net.minecraft.world.level.biome.Biomes;
 import net.minecraft.world.level.block.Block;
@@ -108,7 +97,6 @@ import net.minecraft.world.level.chunk.ChunkAccess;
 import net.minecraft.world.level.chunk.ChunkGeneratorStructureState;
 import net.minecraft.world.level.chunk.LevelChunk;
 import net.minecraft.world.level.chunk.LevelChunkSection;
-import net.minecraft.world.level.chunk.ProtoChunk;
 import net.minecraft.world.level.chunk.status.ChunkStatus;
 import net.minecraft.world.level.chunk.status.WorldGenContext;
 import net.minecraft.world.level.dimension.LevelStem;
@@ -127,7 +115,6 @@ import net.minecraft.world.level.levelgen.feature.ConfiguredFeature;
 import net.minecraft.world.level.levelgen.feature.FallenTreeFeature;
 import net.minecraft.world.level.levelgen.feature.Feature;
 import net.minecraft.world.level.levelgen.feature.TreeFeature;
-import net.minecraft.world.level.storage.LevelStorageSource;
 import net.minecraft.world.level.levelgen.flat.FlatLayerInfo;
 import net.minecraft.world.level.levelgen.flat.FlatLevelGeneratorSettings;
 import org.bukkit.Bukkit;
@@ -159,10 +146,8 @@ import org.jetbrains.annotations.NotNull;
 import java.awt.Color;
 import java.io.File;
 import java.lang.reflect.Field;
-import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
-import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Iterator;
@@ -173,7 +158,6 @@ import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.Executor;
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 
 public class NMSBinding implements INMSBinding {
@@ -181,11 +165,7 @@ public class NMSBinding implements INMSBinding {
     private volatile DataVersion dataVersion;
     private final BlockData AIR = Material.AIR.createBlockData();
     private final AtomicCache<MCAIdMap<net.minecraft.world.level.biome.Biome>> biomeMapCache = new AtomicCache<>();
-    private final AtomicBoolean injected = new AtomicBoolean();
+    private final NmsWorldLifecycle worldLifecycle = new NmsWorldLifecycle();
-    private volatile ResettableClassFileTransformer levelStorageAccessTransformer;
-    private volatile ResettableClassFileTransformer serverLevelTransformer;
-    private volatile ResettableClassFileTransformer pluginClassLoaderTransformer;
-    private boolean pluginClassLoaderCloseDeferred;
     private final AtomicCache<MCAIdMapper<BlockState>> registryCache = new AtomicCache<>();
     private final AtomicCache<MCAPalette<BlockState>> globalCache = new AtomicCache<>();
     private final AtomicCache<RegistryAccess> registryAccess = new AtomicCache<>();
@@ -1131,6 +1111,17 @@ public class NMSBinding implements INMSBinding {
         }
     }
 
+    @Override
+    public CompletableFuture<Void> flushSavedTerrainCapture(World world) {
+        return NmsSavedTerrainCapture.flush(world);
+    }
+
+    @Override
+    public CompletableFuture<SavedTerrainChunk> captureSavedTerrainChunk(World world, int chunkX, int chunkZ,
+                                                                        int minimumY, int height) {
+        return NmsSavedTerrainCapture.capture(world, chunkX, chunkZ, minimumY, height);
+    }
+
     @Override
     public boolean saveAndUnloadChunk(World world, int x, int z) {
         try {
@@ -1279,9 +1270,9 @@ public class NMSBinding implements INMSBinding {
                 : null;
         boolean studioBootstrap = platformGenerator != null
                 && platformGenerator.isStudioEntryBootstrapActive();
-        boolean jigsawStudio = platformGenerator != null
+        boolean authoringStudio = platformGenerator != null
-                && platformGenerator.isJigsawStudioActive();
+                && platformGenerator.isAuthoringStudio();
-        if (jigsawStudio) {
+        if (authoringStudio) {
             requireIrisGenerator(generator);
             if (currentState.possibleStructureSets().isEmpty()) {
                 currentState.ensureStructuresGenerated();
@@ -1552,170 +1543,37 @@ public class NMSBinding implements INMSBinding {
 
     @Override
     public boolean injectBukkit() {
-        synchronized (injected) {
+        return worldLifecycle.injectBukkit();
-            if (injected.get()) {
-                return true;
-            }
-            try {
-                IrisLogging.info("Injecting Bukkit");
-                Agent.requireClassLoaderCloseDeferral();
-                Class<?> loaderCloseType = getClass().getClassLoader().getClass()
-                        .getMethod("close").getDeclaringClass();
-                PluginClassLoaderInjectionListener loaderListener = new PluginClassLoaderInjectionListener();
-                pluginClassLoaderTransformer = new AgentBuilder.Default()
-                        .disableClassFormatChanges()
-                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
-                        .with(AgentBuilder.RedefinitionStrategy.Listener.ErrorEscalating.FAIL_FAST)
-                        .with(loaderListener)
-                        .type(ElementMatchers.is(loaderCloseType))
-                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
-                                builder.visit(Advice.to(PluginClassLoaderCloseAdvice.class)
-                                        .on(ElementMatchers.named("close")
-                                                .and(ElementMatchers.takesArguments(0))
-                                                .and(ElementMatchers.returns(void.class)))))
-                        .installOn(Agent.getInstrumentation());
-                loaderListener.requireInstalled();
-                levelStorageAccessTransformer = new AgentBuilder.Default()
-                        .disableClassFormatChanges()
-                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
-                        .type(ElementMatchers.is(LevelStorageSource.LevelStorageAccess.class))
-                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
-                                builder.visit(Advice.to(LevelStorageAccessAdvice.class).on(ElementMatchers.isConstructor()
-                                        .and(ElementMatchers.takesArguments(4))
-                                        .and(ElementMatchers.takesArgument(0, LevelStorageSource.class))
-                                        .and(ElementMatchers.takesArgument(1, String.class))
-                                        .and(ElementMatchers.takesArgument(2, Path.class))
-                                        .and(ElementMatchers.takesArgument(3, ResourceKey.class)))))
-                        .installOn(Agent.getInstrumentation());
-                serverLevelTransformer = new AgentBuilder.Default()
-                        .disableClassFormatChanges()
-                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
-                        .type(ElementMatchers.is(ServerLevel.class))
-                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
-                                builder.visit(Advice.to(ServerLevelAdvice.class).on(ElementMatchers.isConstructor()
-                                        .and(ElementMatchers.takesArgument(0, MinecraftServer.class))
-                                        .and(ElementMatchers.takesArgument(5, LevelStem.class)))))
-                        .installOn(Agent.getInstrumentation());
-                ByteBuddy buddy = new ByteBuddy();
-                for (Class<?> clazz : List.of(ChunkAccess.class, ProtoChunk.class)) {
-                    buddy.redefine(clazz)
-                            .visit(Advice.to(ChunkAccessAdvice.class).on(ElementMatchers.isMethod().and(ElementMatchers.takesArguments(ShortList.class, int.class))))
-                            .make()
-                            .load(clazz.getClassLoader(), Agent.installed());
-                }
-
-                injected.set(true);
-                return true;
-            } catch (Throwable e) {
-                IrisLogging.reportError(C.RED + "Failed to inject Bukkit", e);
-                ResettableClassFileTransformer partialServerLevel = serverLevelTransformer;
-                ResettableClassFileTransformer partialStorageAccess = levelStorageAccessTransformer;
-                ResettableClassFileTransformer partialPluginClassLoader = pluginClassLoaderTransformer;
-                serverLevelTransformer = null;
-                levelStorageAccessTransformer = null;
-                pluginClassLoaderTransformer = null;
-                for (ResettableClassFileTransformer partial : new ResettableClassFileTransformer[]{
-                        partialServerLevel,
-                        partialStorageAccess,
-                        partialPluginClassLoader
-                }) {
-                    if (partial == null) {
-                        continue;
-                    }
-                    try {
-                        partial.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
-                    } catch (Throwable cleanupFailure) {
-                        IrisLogging.reportError("Failed to remove partial Bukkit lifecycle injection", cleanupFailure);
-                    }
-                }
-                return false;
-            }
-        }
     }
 
     @Override
     public void ensureServerLevelInjection() {
-        if (!injected.get())
+        worldLifecycle.ensureServerLevelInjection();
-            return;
-        try {
-            Agent.getInstrumentation().retransformClasses(
-                    LevelStorageSource.LevelStorageAccess.class,
-                    ServerLevel.class
-            );
-        } catch (Throwable e) {
-            IrisLogging.error(C.RED + "Failed to re-apply Bukkit world lifecycle injection");
-        }
     }
 
     @Override
     public void uninjectBukkit() {
-        synchronized (injected) {
+        worldLifecycle.uninjectBukkit();
-            ResettableClassFileTransformer activeServerLevel = serverLevelTransformer;
-            ResettableClassFileTransformer activeStorageAccess = levelStorageAccessTransformer;
-            serverLevelTransformer = null;
-            levelStorageAccessTransformer = null;
-            injected.set(false);
-            for (ResettableClassFileTransformer transformer : new ResettableClassFileTransformer[]{
-                    activeServerLevel,
-                    activeStorageAccess
-            }) {
-                if (transformer == null) {
-                    continue;
-                }
-                try {
-                    transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
-                } catch (Throwable e) {
-                    IrisLogging.reportError(C.RED + "Failed to remove Bukkit world lifecycle injection", e);
-                }
-            }
-        }
     }
 
     @Override
     public boolean isServerStopping() {
-        return ((CraftServer) Bukkit.getServer()).getServer().hasStopped();
+        return worldLifecycle.isServerStopping();
     }
 
     @Override
     public ServerShutdownBoundary createServerShutdownBoundary() {
-        MinecraftServer server = ((CraftServer) Bukkit.getServer()).getServer();
+        return worldLifecycle.createServerShutdownBoundary();
-        return new ServerShutdownBoundary(
-                () -> server.hasFullyShutdown,
-                server.getRunningThread()
-        );
     }
 
     @Override
     public void deferPluginClassLoaderClose() {
-        synchronized (injected) {
+        worldLifecycle.deferPluginClassLoaderClose();
-            if (pluginClassLoaderTransformer == null || pluginClassLoaderCloseDeferred) {
-                return;
-            }
-            Agent.retainClassLoader(getClass().getClassLoader());
-            pluginClassLoaderCloseDeferred = true;
-        }
     }
 
     @Override
     public void releasePluginClassLoaderClose() {
-        ResettableClassFileTransformer transformer;
+        worldLifecycle.releasePluginClassLoaderClose();
-        boolean releaseLoader;
-        synchronized (injected) {
-            transformer = pluginClassLoaderTransformer;
-            pluginClassLoaderTransformer = null;
-            releaseLoader = pluginClassLoaderCloseDeferred;
-            pluginClassLoaderCloseDeferred = false;
-        }
-        try {
-            if (transformer != null
-                    && !transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)) {
-                throw new IllegalStateException("Failed to remove Iris plugin class loader lifecycle injection");
-            }
-        } finally {
-            if (releaseLoader) {
-                Agent.releaseClassLoader(getClass().getClassLoader());
-            }
-        }
     }
 
     @Override
@@ -1761,220 +1619,4 @@ public class NMSBinding implements INMSBinding {
         settings.updateLayers();
         return new FlatLevelSource(settings);
     }
-
-    private static final class PluginClassLoaderInjectionListener extends AgentBuilder.Listener.Adapter {
-        private volatile boolean transformed;
-        private volatile Throwable failure;
-
-        @Override
-        public void onTransformation(TypeDescription type, ClassLoader loader, JavaModule module,
-                                     boolean loaded, DynamicType dynamicType) {
-            transformed = true;
-        }
-
-        @Override
-        public void onError(String typeName, ClassLoader loader, JavaModule module,
-                            boolean loaded, Throwable throwable) {
-            failure = throwable;
-        }
-
-        private void requireInstalled() {
-            if (!transformed || failure != null) {
-                throw new IllegalStateException("Iris plugin class loader lifecycle injection failed", failure);
-            }
-        }
-    }
-
-    private static class PluginClassLoaderCloseAdvice {
-        @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
-        static boolean enter(@Advice.This ClassLoader loader) throws ReflectiveOperationException {
-            Class<?> installer = Class.forName(
-                    "art.arcane.iris.util.project.agent.Installer", true, ClassLoader.getSystemClassLoader());
-            return Boolean.TRUE.equals(installer.getMethod("deferClassLoaderClose", ClassLoader.class)
-                    .invoke(null, loader));
-        }
-    }
-
-    private static class ChunkAccessAdvice {
-        @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
-        static boolean enter(@Advice.This ChunkAccess access, @Advice.Argument(1) int index) {
-            return index >= access.getPostProcessing().length;
-        }
-    }
-
-    private static class LevelStorageAccessAdvice {
-        @Advice.OnMethodEnter
-        static void enter(
-                @Advice.Argument(1) String levelId,
-                @Advice.Argument(value = 3, readOnly = false) ResourceKey<LevelStem> dimensionType
-        ) {
-            if (levelId == null || levelId.isBlank()) {
-                return;
-            }
-
-            ClassLoader pluginClassLoader;
-            Class<?> generatorType;
-            Class<?> stagingType;
-            try {
-                org.bukkit.plugin.Plugin irisPlugin = Bukkit.getPluginManager().getPlugin("Iris");
-                if (irisPlugin == null) {
-                    return;
-                }
-                pluginClassLoader = irisPlugin.getClass().getClassLoader();
-                generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
-                stagingType = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader);
-            } catch (Throwable ignored) {
-                return;
-            }
-
-            Object generator;
-            try {
-                generator = stagingType
-                        .getDeclaredMethod("peekStemGenerator", String.class)
-                        .invoke(null, levelId);
-            } catch (Throwable e) {
-                throw new RuntimeException("Iris failed to inspect the staged world generator",
-                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
-            }
-            if (generator == null || !generatorType.isInstance(generator)) {
-                return;
-            }
-
-            try {
-                Object target = generatorType.getMethod("getTarget").invoke(generator);
-                if (target == null) {
-                    throw new IllegalStateException("Iris generator has no engine target.");
-                }
-                Object world = target.getClass().getMethod("getWorld").invoke(target);
-                if (world == null) {
-                    throw new IllegalStateException("Iris generator target has no world identity.");
-                }
-                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
-                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
-                Identifier worldIdentifier = Identifier.parse(worldIdentity);
-                if (!"iris".equals(worldIdentifier.getNamespace())
-                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
-                    throw new IllegalStateException(
-                            "Iris generator has an unmanaged world identity: " + worldIdentity);
-                }
-                dimensionType = ResourceKey.create(Registries.LEVEL_STEM, worldIdentifier);
-            } catch (Throwable e) {
-                throw new RuntimeException("Iris failed to bind the staged world storage identity",
-                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
-            }
-        }
-    }
-
-    private static class ServerLevelAdvice {
-        @Advice.OnMethodEnter
-        static void enter(
-                @Advice.Argument(0) MinecraftServer server,
-                @Advice.Argument(value = 4, readOnly = false) ResourceKey<Level> dimensionKey,
-                @Advice.Argument(value = 5, readOnly = false) LevelStem levelStem,
-                @Advice.AllArguments Object[] constructorArguments
-        ) {
-            if (dimensionKey == null)
-                return;
-
-            // This advice is inlined into every ServerLevel construction on the server. Until a
-            // world is proven Iris-owned, every failure must fail OPEN (keep the vanilla stem):
-            // Iris being unloaded or half-loaded must never break other plugins' world creation.
-            String levelId;
-            ClassLoader pluginClassLoader;
-            Class<?> generatorType;
-            Class<?> stagingType;
-            try {
-                levelId = dimensionKey.identifier().getPath();
-                if (levelId == null || levelId.isBlank()) {
-                    return;
-                }
-
-                org.bukkit.plugin.Plugin irisPlugin = Bukkit.getPluginManager().getPlugin("Iris");
-                if (irisPlugin == null) {
-                    return;
-                }
-                pluginClassLoader = irisPlugin.getClass().getClassLoader();
-                generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
-                stagingType = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader);
-            } catch (Throwable ignored) {
-                // Iris absent or half-loaded: fail OPEN for a world we cannot prove ours.
-                return;
-            }
-
-            // From here Iris is present and its classes resolve; a failure resolving the
-            // staged generator must fail LOUD — silently handing a possibly-staged Iris world
-            // the vanilla stem corrupts generation.
-            ChunkGenerator gen = null;
-            try {
-                ChunkGenerator constructorGenerator = null;
-                for (Object argument : constructorArguments) {
-                    if (argument instanceof ChunkGenerator candidate) {
-                        constructorGenerator = candidate;
-                        break;
-                    }
-                }
-                Object generator = generatorType.isInstance(constructorGenerator) ? constructorGenerator : null;
-                if (generator == null) {
-                    generator = stagingType
-                            .getDeclaredMethod("consumeStemGenerator", String.class)
-                            .invoke(null, levelId);
-                }
-                if (generator instanceof ChunkGenerator owned && owned.getClass().getPackageName().startsWith("art.arcane.iris")) {
-                    gen = owned;
-                }
-            } catch (Throwable e) {
-                throw new RuntimeException("Iris failed to resolve the staged world generator",
-                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
-            }
-            if (gen == null) {
-                return;
-            }
-
-            // Past the ownership gate the world is Iris-owned; silently handing back the
-            // vanilla stem would corrupt generation, so failures from here rethrow.
-            try {
-                Object bindings = Class.forName("art.arcane.iris.core.nms.INMS", true, pluginClassLoader)
-                        .getDeclaredMethod("get")
-                        .invoke(null);
-                if (bindings == null) {
-                    throw new IllegalStateException("Iris failed to resolve an INMSBinding instance.");
-                }
-
-                java.lang.reflect.Method stemMethod = null;
-                for (java.lang.reflect.Method candidate : bindings.getClass().getMethods()) {
-                    if (candidate.getName().equals("createRuntimeLevelStem") && candidate.getParameterCount() == 2) {
-                        stemMethod = candidate;
-                        break;
-                    }
-                }
-                if (stemMethod == null) {
-                    throw new IllegalStateException("Iris binding is missing createRuntimeLevelStem.");
-                }
-                Object target = generatorType.getMethod("getTarget").invoke(gen);
-                if (target == null) {
-                    throw new IllegalStateException("Iris generator has no engine target.");
-                }
-                Object world = target.getClass().getMethod("getWorld").invoke(target);
-                if (world == null) {
-                    throw new IllegalStateException("Iris generator target has no world identity.");
-                }
-                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
-                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
-                Identifier worldIdentifier = Identifier.parse(worldIdentity);
-                if (!"iris".equals(worldIdentifier.getNamespace())
-                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
-                    throw new IllegalStateException(
-                            "Iris generator has an unmanaged world identity: " + worldIdentity);
-                }
-                Object resolvedStem = stemMethod.invoke(bindings, server.registryAccess(), gen);
-                if (!(resolvedStem instanceof LevelStem runtimeStem)) {
-                    throw new IllegalStateException("Iris runtime LevelStem binding returned " + (resolvedStem == null ? "null" : resolvedStem.getClass().getName()) + ".");
-                }
-                dimensionKey = ResourceKey.create(Registries.DIMENSION, worldIdentifier);
-                levelStem = runtimeStem;
-            } catch (Throwable e) {
-                throw new RuntimeException("Iris failed to replace the levelStem", e instanceof InvocationTargetException ex ? ex.getCause() : e);
-            }
-        }
-    }
 }

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NmsGenerationHooks.java

@@ -0,0 +1,61 @@
+package art.arcane.iris.core.nms.v26_2_R1;
+
+import art.arcane.iris.util.project.agent.Agent;
+import it.unimi.dsi.fastutil.shorts.ShortList;
+import net.bytebuddy.ByteBuddy;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.matcher.ElementMatchers;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ChunkGenerator;
+import net.minecraft.server.level.WorldGenRegion;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.ChunkPos;
+import java.util.function.LongPredicate;
+import net.minecraft.world.level.chunk.ProtoChunk;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+
+import java.util.List;
+
+final class NmsGenerationHooks {
+    private NmsGenerationHooks() {
+    }
+
+    static void install() {
+        ByteBuddy buddy = new ByteBuddy();
+        for (Class<?> clazz : List.of(ChunkAccess.class, ProtoChunk.class)) {
+            buddy.redefine(clazz)
+                    .visit(Advice.to(ChunkAccessAdvice.class).on(ElementMatchers.isMethod().and(ElementMatchers.takesArguments(ShortList.class, int.class))))
+                    .make()
+                    .load(clazz.getClassLoader(), Agent.installed());
+        }
+        buddy.redefine(WorldGenRegion.class)
+                .visit(Advice.to(WorldGenerationWriteAdvice.class).on(ElementMatchers.named("ensureCanWrite")
+                        .and(ElementMatchers.takesArguments(BlockPos.class))))
+                .make()
+                .load(WorldGenRegion.class.getClassLoader(), Agent.installed());
+    }
+
+    private static class WorldGenerationWriteAdvice {
+        @Advice.OnMethodExit
+        static void exit(@Advice.This WorldGenRegion region, @Advice.Argument(0) BlockPos position,
+                         @Advice.Return(readOnly = false) boolean allowed) {
+            if (!allowed) {
+                return;
+            }
+            ChunkGenerator generator = region.getLevel().getChunkSource().getGenerator();
+            if (generator instanceof LongPredicate predicate
+                    && generator.getClass().getName().equals("art.arcane.iris.core.nms.v26_2_R1.IrisChunkGenerator")
+                    && region.getChunk(position.getX() >> 4, position.getZ() >> 4)
+                    .getPersistedStatus().isOrAfter(ChunkStatus.FULL)) {
+                allowed = predicate.test(ChunkPos.pack(position.getX() >> 4, position.getZ() >> 4));
+            }
+        }
+    }
+
+    private static class ChunkAccessAdvice {
+        @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
+        static boolean enter(@Advice.This ChunkAccess access, @Advice.Argument(1) int index) {
+            return index >= access.getPostProcessing().length;
+        }
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NmsSavedTerrainCapture.java

@@ -0,0 +1,129 @@
+package art.arcane.iris.core.nms.v26_2_R1;
+
+import art.arcane.iris.engine.history.NativeTerrainReceipt;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.util.common.scheduling.J;
+import ca.spottedleaf.moonrise.common.PlatformHooks;
+import ca.spottedleaf.moonrise.patches.chunk_system.io.MoonriseRegionFileIO;
+import ca.spottedleaf.moonrise.patches.chunk_system.scheduling.NewChunkHolder;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.storage.SerializableChunkData;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.CraftWorld;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+
+final class NmsSavedTerrainCapture {
+    private NmsSavedTerrainCapture() {
+    }
+
+    static CompletableFuture<SavedTerrainChunk> capture(World world, int chunkX, int chunkZ, int minimumY, int height) {
+        ServerLevel level = ((CraftWorld) world).getHandle();
+        CompletableFuture<CompoundTag> snapshot = new CompletableFuture<>();
+        J.runRegionFuture(world, chunkX, chunkZ, () -> {
+            try {
+                NewChunkHolder holder = level.moonrise$getChunkTaskScheduler().chunkHolderManager.getChunkHolder(chunkX, chunkZ);
+                ChunkAccess chunk = holder == null ? null : holder.getCurrentChunk();
+                if (chunk == null) {
+                    snapshot.complete(null);
+                    return;
+                }
+                String status = BuiltInRegistries.CHUNK_STATUS.getKey(chunk.getPersistedStatus()).toString();
+                if (!SavedTerrainChunk.hasTerrain(status)) {
+                    throw new IOException("Native chunk " + chunkX + "," + chunkZ + " has no completed terrain at " + status);
+                }
+                snapshot.complete(saveSnapshot(level, chunk));
+            } catch (Throwable failure) {
+                snapshot.completeExceptionally(failure);
+            }
+        }).whenComplete((ignored, failure) -> {
+            if (failure != null) {
+                snapshot.completeExceptionally(failure);
+            }
+        });
+        return snapshot.thenApplyAsync(data -> {
+            try {
+                if (data == null) {
+                    return SavedTerrainChunk.read(world.getWorldFolder().toPath(), chunkX, chunkZ, minimumY, height);
+                }
+                ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+                try (DataOutputStream output = new DataOutputStream(bytes)) {
+                    NbtIo.write(data, output);
+                }
+                return SavedTerrainChunk.readNbt(bytes.toByteArray(), chunkX, chunkZ, minimumY, height);
+            } catch (IOException failure) {
+                throw new CompletionException(failure);
+            }
+        });
+    }
+
+    static CompletableFuture<Void> flush(World world) {
+        ServerLevel level = ((CraftWorld) world).getHandle();
+        List<NewChunkHolder> holders = level.moonrise$getChunkTaskScheduler().chunkHolderManager.getChunkHolders();
+        List<CompletableFuture<Checkpoint>> saves = new ArrayList<>(holders.size());
+        for (NewChunkHolder holder : holders) {
+            CompletableFuture<Checkpoint> saved = new CompletableFuture<>();
+            saves.add(saved);
+            J.runRegionFuture(world, holder.chunkX, holder.chunkZ, () -> {
+                try {
+                    ChunkAccess chunk = holder.getCurrentChunk();
+                    if (chunk == null || !chunk.isUnsaved()) {
+                        saved.complete(null);
+                        return;
+                    }
+                    CompoundTag data = saveSnapshot(level, chunk);
+                    byte[] receipt = data.getCompound("ChunkBukkitValues")
+                            .flatMap(values -> values.getByteArray(NativeTerrainReceipt.NBT_KEY)).orElse(null);
+                    saved.complete(new Checkpoint(holder.chunkX, holder.chunkZ,
+                            BuiltInRegistries.CHUNK_STATUS.getKey(chunk.getPersistedStatus()).toString(), receipt,
+                            data.getCompound("ChunkBukkitValues").map(values -> values.getLongOr(
+                                    NativeTerrainReceipt.STRUCTURE_ACTIVATION_KEY, 0)).orElse(0L)));
+                } catch (Throwable failure) {
+                    saved.completeExceptionally(failure);
+                }
+            }).whenComplete((ignored, failure) -> {
+                if (failure != null) {
+                    saved.completeExceptionally(failure);
+                }
+            });
+        }
+        return CompletableFuture.allOf(saves.toArray(CompletableFuture[]::new)).thenRunAsync(() -> {
+            try {
+                MoonriseRegionFileIO.flush(level, MoonriseRegionFileIO.RegionFileType.CHUNK_DATA);
+                MoonriseRegionFileIO.flushRegionStorages(level, MoonriseRegionFileIO.RegionFileType.CHUNK_DATA);
+                for (CompletableFuture<Checkpoint> future : saves) {
+                    Checkpoint saved = future.join();
+                    if (saved == null) {
+                        continue;
+                    }
+                    SavedTerrainChunk.verifyCheckpoint(world.getWorldFolder().toPath(), saved.chunkX(), saved.chunkZ(),
+                            saved.status(), saved.receipt(), saved.structureActivation());
+                }
+            } catch (IOException failure) {
+                throw new CompletionException(failure);
+            }
+        });
+    }
+
+    private static CompoundTag saveSnapshot(ServerLevel level, ChunkAccess chunk) {
+        SerializableChunkData snapshot = SerializableChunkData.copyOf(level, chunk);
+        PlatformHooks.get().chunkSyncSave(level, chunk, snapshot);
+        CompoundTag data = snapshot.write();
+        MoonriseRegionFileIO.scheduleSave(level, chunk.getPos().x(), chunk.getPos().z(), data,
+                MoonriseRegionFileIO.RegionFileType.CHUNK_DATA);
+        return data;
+    }
+
+    private record Checkpoint(int chunkX, int chunkZ, String status, byte[] receipt, long structureActivation) {
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NmsWorldLifecycle.java

@@ -0,0 +1,403 @@
+package art.arcane.iris.core.nms.v26_2_R1;
+
+import art.arcane.iris.core.nms.ServerShutdownBoundary;
+import art.arcane.iris.spi.IrisLogging;
+import art.arcane.iris.util.common.format.C;
+import art.arcane.iris.util.project.agent.Agent;
+import net.bytebuddy.agent.builder.AgentBuilder;
+import net.bytebuddy.agent.builder.ResettableClassFileTransformer;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.dynamic.DynamicType;
+import net.bytebuddy.matcher.ElementMatchers;
+import net.bytebuddy.utility.JavaModule;
+import net.minecraft.core.registries.Registries;
+import net.minecraft.resources.Identifier;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.Level;
+import net.minecraft.world.level.dimension.LevelStem;
+import net.minecraft.world.level.storage.LevelStorageSource;
+import org.bukkit.Bukkit;
+import org.bukkit.craftbukkit.CraftServer;
+import org.bukkit.generator.ChunkGenerator;
+import org.bukkit.plugin.Plugin;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.nio.file.Path;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+final class NmsWorldLifecycle {
+    private final AtomicBoolean injected = new AtomicBoolean();
+    private volatile ResettableClassFileTransformer levelStorageAccessTransformer;
+    private volatile ResettableClassFileTransformer serverLevelTransformer;
+    private volatile ResettableClassFileTransformer pluginClassLoaderTransformer;
+    private boolean pluginClassLoaderCloseDeferred;
+
+    public boolean injectBukkit() {
+        synchronized (injected) {
+            if (injected.get()) {
+                return true;
+            }
+            try {
+                IrisLogging.info("Injecting Bukkit");
+                Agent.requireClassLoaderCloseDeferral();
+                Class<?> loaderCloseType = getClass().getClassLoader().getClass()
+                        .getMethod("close").getDeclaringClass();
+                PluginClassLoaderInjectionListener loaderListener = new PluginClassLoaderInjectionListener();
+                pluginClassLoaderTransformer = new AgentBuilder.Default()
+                        .disableClassFormatChanges()
+                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
+                        .with(AgentBuilder.RedefinitionStrategy.Listener.ErrorEscalating.FAIL_FAST)
+                        .with(loaderListener)
+                        .type(ElementMatchers.is(loaderCloseType))
+                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
+                                builder.visit(Advice.to(PluginClassLoaderCloseAdvice.class)
+                                        .on(ElementMatchers.named("close")
+                                                .and(ElementMatchers.takesArguments(0))
+                                                .and(ElementMatchers.returns(void.class)))))
+                        .installOn(Agent.getInstrumentation());
+                loaderListener.requireInstalled();
+                levelStorageAccessTransformer = new AgentBuilder.Default()
+                        .disableClassFormatChanges()
+                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
+                        .type(ElementMatchers.is(LevelStorageSource.LevelStorageAccess.class))
+                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
+                                builder.visit(Advice.to(LevelStorageAccessAdvice.class).on(ElementMatchers.isConstructor()
+                                        .and(ElementMatchers.takesArguments(4))
+                                        .and(ElementMatchers.takesArgument(0, LevelStorageSource.class))
+                                        .and(ElementMatchers.takesArgument(1, String.class))
+                                        .and(ElementMatchers.takesArgument(2, Path.class))
+                                        .and(ElementMatchers.takesArgument(3, ResourceKey.class)))))
+                        .installOn(Agent.getInstrumentation());
+                serverLevelTransformer = new AgentBuilder.Default()
+                        .disableClassFormatChanges()
+                        .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
+                        .type(ElementMatchers.is(ServerLevel.class))
+                        .transform((builder, typeDescription, classLoader, module, protectionDomain) ->
+                                builder.visit(Advice.to(ServerLevelAdvice.class).on(ElementMatchers.isConstructor()
+                                        .and(ElementMatchers.takesArgument(0, MinecraftServer.class))
+                                        .and(ElementMatchers.takesArgument(5, LevelStem.class)))))
+                        .installOn(Agent.getInstrumentation());
+                NmsGenerationHooks.install();
+
+                injected.set(true);
+                return true;
+            } catch (Throwable e) {
+                IrisLogging.reportError(C.RED + "Failed to inject Bukkit", e);
+                ResettableClassFileTransformer partialServerLevel = serverLevelTransformer;
+                ResettableClassFileTransformer partialStorageAccess = levelStorageAccessTransformer;
+                ResettableClassFileTransformer partialPluginClassLoader = pluginClassLoaderTransformer;
+                serverLevelTransformer = null;
+                levelStorageAccessTransformer = null;
+                pluginClassLoaderTransformer = null;
+                for (ResettableClassFileTransformer partial : new ResettableClassFileTransformer[]{
+                        partialServerLevel,
+                        partialStorageAccess,
+                        partialPluginClassLoader
+                }) {
+                    if (partial == null) {
+                        continue;
+                    }
+                    try {
+                        partial.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
+                    } catch (Throwable cleanupFailure) {
+                        IrisLogging.reportError("Failed to remove partial Bukkit lifecycle injection", cleanupFailure);
+                    }
+                }
+                return false;
+            }
+        }
+    }
+
+    public void ensureServerLevelInjection() {
+        if (!injected.get()) {
+            throw new IllegalStateException("Iris world lifecycle injection is unavailable. Fix the Java Agent or Code Injection startup failure and restart before creating worlds.");
+        }
+        try {
+            Agent.getInstrumentation().retransformClasses(
+                    LevelStorageSource.LevelStorageAccess.class,
+                    ServerLevel.class
+            );
+        } catch (Throwable e) {
+            throw new IllegalStateException("Failed to re-apply Bukkit world lifecycle injection. World creation was stopped before loading the world.", e);
+        }
+    }
+
+    public void uninjectBukkit() {
+        synchronized (injected) {
+            ResettableClassFileTransformer activeServerLevel = serverLevelTransformer;
+            ResettableClassFileTransformer activeStorageAccess = levelStorageAccessTransformer;
+            serverLevelTransformer = null;
+            levelStorageAccessTransformer = null;
+            injected.set(false);
+            for (ResettableClassFileTransformer transformer : new ResettableClassFileTransformer[]{
+                    activeServerLevel,
+                    activeStorageAccess
+            }) {
+                if (transformer == null) {
+                    continue;
+                }
+                try {
+                    transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION);
+                } catch (Throwable e) {
+                    IrisLogging.reportError(C.RED + "Failed to remove Bukkit world lifecycle injection", e);
+                }
+            }
+        }
+    }
+
+    public boolean isServerStopping() {
+        return ((CraftServer) Bukkit.getServer()).getServer().hasStopped();
+    }
+
+    public ServerShutdownBoundary createServerShutdownBoundary() {
+        MinecraftServer server = ((CraftServer) Bukkit.getServer()).getServer();
+        return new ServerShutdownBoundary(
+                () -> server.hasFullyShutdown,
+                server.getRunningThread()
+        );
+    }
+
+    public void deferPluginClassLoaderClose() {
+        synchronized (injected) {
+            if (pluginClassLoaderTransformer == null || pluginClassLoaderCloseDeferred) {
+                return;
+            }
+            Agent.retainClassLoader(getClass().getClassLoader());
+            pluginClassLoaderCloseDeferred = true;
+        }
+    }
+
+    public void releasePluginClassLoaderClose() {
+        ResettableClassFileTransformer transformer;
+        boolean releaseLoader;
+        synchronized (injected) {
+            transformer = pluginClassLoaderTransformer;
+            pluginClassLoaderTransformer = null;
+            releaseLoader = pluginClassLoaderCloseDeferred;
+            pluginClassLoaderCloseDeferred = false;
+        }
+        try {
+            if (transformer != null
+                    && !transformer.reset(Agent.getInstrumentation(), AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)) {
+                throw new IllegalStateException("Failed to remove Iris plugin class loader lifecycle injection");
+            }
+        } finally {
+            if (releaseLoader) {
+                Agent.releaseClassLoader(getClass().getClassLoader());
+            }
+        }
+    }
+
+    private static final class PluginClassLoaderInjectionListener extends AgentBuilder.Listener.Adapter {
+        private volatile boolean transformed;
+        private volatile Throwable failure;
+
+        @Override
+        public void onTransformation(TypeDescription type, ClassLoader loader, JavaModule module,
+                                     boolean loaded, DynamicType dynamicType) {
+            transformed = true;
+        }
+
+        @Override
+        public void onError(String typeName, ClassLoader loader, JavaModule module,
+                            boolean loaded, Throwable throwable) {
+            failure = throwable;
+        }
+
+        private void requireInstalled() {
+            if (!transformed || failure != null) {
+                throw new IllegalStateException("Iris plugin class loader lifecycle injection failed", failure);
+            }
+        }
+    }
+
+    private static class PluginClassLoaderCloseAdvice {
+        @Advice.OnMethodEnter(skipOn = Advice.OnNonDefaultValue.class)
+        static boolean enter(@Advice.This ClassLoader loader) throws ReflectiveOperationException {
+            Class<?> installer = Class.forName(
+                    "art.arcane.iris.util.project.agent.Installer", true, ClassLoader.getSystemClassLoader());
+            return Boolean.TRUE.equals(installer.getMethod("deferClassLoaderClose", ClassLoader.class)
+                    .invoke(null, loader));
+        }
+    }
+
+    private static class LevelStorageAccessAdvice {
+        @Advice.OnMethodEnter
+        static void enter(
+                @Advice.Argument(1) String levelId,
+                @Advice.Argument(value = 3, readOnly = false) ResourceKey<LevelStem> dimensionType
+        ) {
+            if (levelId == null || levelId.isBlank()) {
+                return;
+            }
+
+            ClassLoader pluginClassLoader;
+            Class<?> generatorType;
+            Class<?> stagingType;
+            try {
+                Plugin irisPlugin = Bukkit.getPluginManager().getPlugin("Iris");
+                if (irisPlugin == null) {
+                    return;
+                }
+                pluginClassLoader = irisPlugin.getClass().getClassLoader();
+                generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
+                stagingType = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader);
+            } catch (Throwable ignored) {
+                return;
+            }
+
+            Object generator;
+            try {
+                generator = stagingType
+                        .getDeclaredMethod("peekStemGenerator", String.class)
+                        .invoke(null, levelId);
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to inspect the staged world generator",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+            if (generator == null || !generatorType.isInstance(generator)) {
+                return;
+            }
+
+            try {
+                Object target = generatorType.getMethod("getTarget").invoke(generator);
+                if (target == null) {
+                    throw new IllegalStateException("Iris generator has no engine target.");
+                }
+                Object world = target.getClass().getMethod("getWorld").invoke(target);
+                if (world == null) {
+                    throw new IllegalStateException("Iris generator target has no world identity.");
+                }
+                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
+                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
+                Identifier worldIdentifier = Identifier.parse(worldIdentity);
+                if (!"iris".equals(worldIdentifier.getNamespace())
+                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
+                    throw new IllegalStateException(
+                            "Iris generator has an unmanaged world identity: " + worldIdentity);
+                }
+                dimensionType = ResourceKey.create(Registries.LEVEL_STEM, worldIdentifier);
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to bind the staged world storage identity",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+        }
+    }
+
+    private static class ServerLevelAdvice {
+        @Advice.OnMethodEnter
+        static void enter(
+                @Advice.Argument(0) MinecraftServer server,
+                @Advice.Argument(value = 4, readOnly = false) ResourceKey<Level> dimensionKey,
+                @Advice.Argument(value = 5, readOnly = false) LevelStem levelStem,
+                @Advice.AllArguments Object[] constructorArguments
+        ) {
+            if (dimensionKey == null)
+                return;
+
+            // This advice is inlined into every ServerLevel construction on the server. Until a
+            // world is proven Iris-owned, every failure must fail OPEN (keep the vanilla stem):
+            // Iris being unloaded or half-loaded must never break other plugins' world creation.
+            String levelId;
+            ClassLoader pluginClassLoader;
+            Class<?> generatorType;
+            Class<?> stagingType;
+            try {
+                levelId = dimensionKey.identifier().getPath();
+                if (levelId == null || levelId.isBlank()) {
+                    return;
+                }
+
+                Plugin irisPlugin = Bukkit.getPluginManager().getPlugin("Iris");
+                if (irisPlugin == null) {
+                    return;
+                }
+                pluginClassLoader = irisPlugin.getClass().getClassLoader();
+                generatorType = Class.forName("art.arcane.iris.engine.platform.PlatformChunkGenerator", true, pluginClassLoader);
+                stagingType = Class.forName("art.arcane.iris.core.lifecycle.WorldLifecycleStaging", true, pluginClassLoader);
+            } catch (Throwable ignored) {
+                // Iris absent or half-loaded: fail OPEN for a world we cannot prove ours.
+                return;
+            }
+
+            // From here Iris is present and its classes resolve; a failure resolving the
+            // staged generator must fail LOUD — silently handing a possibly-staged Iris world
+            // the vanilla stem corrupts generation.
+            ChunkGenerator gen = null;
+            try {
+                ChunkGenerator constructorGenerator = null;
+                for (Object argument : constructorArguments) {
+                    if (argument instanceof ChunkGenerator candidate) {
+                        constructorGenerator = candidate;
+                        break;
+                    }
+                }
+                Object generator = generatorType.isInstance(constructorGenerator) ? constructorGenerator : null;
+                if (generator == null) {
+                    generator = stagingType
+                            .getDeclaredMethod("consumeStemGenerator", String.class)
+                            .invoke(null, levelId);
+                }
+                if (generator instanceof ChunkGenerator owned && owned.getClass().getPackageName().startsWith("art.arcane.iris")) {
+                    gen = owned;
+                }
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to resolve the staged world generator",
+                        e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+            if (gen == null) {
+                return;
+            }
+
+            // Past the ownership gate the world is Iris-owned; silently handing back the
+            // vanilla stem would corrupt generation, so failures from here rethrow.
+            try {
+                Object bindings = Class.forName("art.arcane.iris.core.nms.INMS", true, pluginClassLoader)
+                        .getDeclaredMethod("get")
+                        .invoke(null);
+                if (bindings == null) {
+                    throw new IllegalStateException("Iris failed to resolve an INMSBinding instance.");
+                }
+
+                Method stemMethod = null;
+                for (Method candidate : bindings.getClass().getMethods()) {
+                    if (candidate.getName().equals("createRuntimeLevelStem") && candidate.getParameterCount() == 2) {
+                        stemMethod = candidate;
+                        break;
+                    }
+                }
+                if (stemMethod == null) {
+                    throw new IllegalStateException("Iris binding is missing createRuntimeLevelStem.");
+                }
+                Object target = generatorType.getMethod("getTarget").invoke(gen);
+                if (target == null) {
+                    throw new IllegalStateException("Iris generator has no engine target.");
+                }
+                Object world = target.getClass().getMethod("getWorld").invoke(target);
+                if (world == null) {
+                    throw new IllegalStateException("Iris generator target has no world identity.");
+                }
+                Object rawIdentity = world.getClass().getMethod("identity").invoke(world);
+                String worldIdentity = rawIdentity == null ? "" : rawIdentity.toString().trim();
+                Identifier worldIdentifier = Identifier.parse(worldIdentity);
+                if (!"iris".equals(worldIdentifier.getNamespace())
+                        && !"minecraft".equals(worldIdentifier.getNamespace())) {
+                    throw new IllegalStateException(
+                            "Iris generator has an unmanaged world identity: " + worldIdentity);
+                }
+                Object resolvedStem = stemMethod.invoke(bindings, server.registryAccess(), gen);
+                if (!(resolvedStem instanceof LevelStem runtimeStem)) {
+                    throw new IllegalStateException("Iris runtime LevelStem binding returned " + (resolvedStem == null ? "null" : resolvedStem.getClass().getName()) + ".");
+                }
+                dimensionKey = ResourceKey.create(Registries.DIMENSION, worldIdentifier);
+                levelStem = runtimeStem;
+            } catch (Throwable e) {
+                throw new RuntimeException("Iris failed to replace the levelStem", e instanceof InvocationTargetException ex ? ex.getCause() : e);
+            }
+        }
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/CustomBiomeSourceStructureContractTest.java

@@ -24,6 +24,31 @@ public class CustomBiomeSourceStructureContractTest {
         Bootstrap.bootStrap();
     }
 
+    @Test
+    public void authoringBiomesBypassTerrainResolutionBeforeDestinationChunksGenerate() throws IOException {
+        String source = Files.readString(Path.of(System.getProperty("iris.customBiomeSource")));
+        int visibleStart = source.indexOf("private Holder<Biome> getVisibleNoiseBiomeWithActiveGenerationLease(");
+        int visibleEnd = source.indexOf("private boolean isBiomeCacheable(", visibleStart);
+        String visible = source.substring(visibleStart, visibleEnd);
+        int constantBiome = visible.indexOf("platformGenerator.usesFlatStudioTerrain()");
+        int terrainResolution = visible.indexOf("resolveVisibleBiomeHolder(");
+
+        assertTrue(source.contains("platformGenerator.usesFlatStudioTerrain()"));
+        assertTrue(constantBiome >= 0);
+        assertTrue(visible.indexOf("return fallbackBiome;", constantBiome) < terrainResolution);
+        assertTrue(terrainResolution > constantBiome);
+
+        int structureStart = source.indexOf("private Holder<Biome> getStructureNoiseBiomeWithActiveGenerationLease(");
+        int structureEnd = source.indexOf("boolean cacheable", structureStart);
+        assertTrue(source.substring(structureStart, structureEnd).contains("platformGenerator.usesFlatStudioTerrain()"));
+
+        String generator = Files.readString(Path.of(System.getProperty("iris.nmsChunkGeneratorSource")));
+        int createBiomes = generator.indexOf("public CompletableFuture<ChunkAccess> createBiomes(");
+        int buildSurface = generator.indexOf("public void buildSurface(", createBiomes);
+        assertTrue(generator.substring(createBiomes, buildSurface)
+                .contains("customBiomeSource.getVisibleNoiseBiomeWithActiveGenerationLease("));
+    }
+
     @Test
     public void nativeStructuresUseTerrainSafeDerivativeAtEveryBiomeBoundary() throws IOException {
         String source = Files.readString(Path.of(System.getProperty("iris.customBiomeSource")));

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/GenerationHistoryRoutingContractTest.java

@@ -43,6 +43,9 @@ public final class GenerationHistoryRoutingContractTest {
         assertBefore(noise, "openHistoryRoute(", "requireGenerationLease(");
         assertTrue(count(noise, "openHistoryRuntimeScope(route)") >= 2);
         assertBefore(noise, ".thenApply(filled ->", "pipeline.whenComplete(");
+        assertBefore(noise, "pipeline.whenComplete(", "lease.detachThread()");
+        assertBefore(noise, "lease.detachThread()", "route.detachThread()");
+        assertBefore(noise, "route.detachThread()", "return completion;");
         assertTrue(noise.contains("closeNoisePipelineResources(\n                        failure, lease, route, stage)"));
     }
 

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/IrisChunkGeneratorFailureContractTest.java

@@ -221,6 +221,55 @@ public class IrisChunkGeneratorFailureContractTest {
         assertTrue(source.contains("int minY = chunk.getMinY() + 1;"));
     }
 
+    @Test
+    public void authoringHeightmapStagesReturnBeforeAnyTerrainHeightResolver() throws IOException {
+        String source = Files.readString(Path.of(System.getProperty("iris.nmsChunkGeneratorSource")));
+        int primeStart = source.indexOf("private void primeWorldgenHeightmaps(");
+        int primeEnd = source.indexOf("private IntBinaryOperator worldgenSurfaceHeight()", primeStart);
+        String prime = source.substring(primeStart, primeEnd);
+        assertBefore(prime, "platformGenerator.usesFlatStudioTerrain()", "worldgenSurfaceHeight()");
+        assertBefore(prime, "primeAuthoringHeightmaps(chunkAccess);", "return;");
+        assertBefore(prime, "return;", "WorldgenTerrainHeightmaps.primeTerrain(");
+
+        int decorationStart = source.indexOf("public void addVanillaDecorations(");
+        int decorationEnd = source.indexOf("public void spawnOriginalMobs(", decorationStart);
+        String decorations = source.substring(decorationStart, decorationEnd);
+        assertBefore(decorations, "primeWorldgenHeightmaps(chunkAccess);", "platformGenerator.usesFlatStudioTerrain()");
+        assertBefore(decorations, "platformGenerator.usesFlatStudioTerrain()", "return;");
+        assertBefore(decorations, "return;", "engine.getHeight(");
+    }
+
+    @Test
+    public void authoringDecorationSkipsNativeFeaturesButRetainsHeightmapsAndBukkitPopulators() throws IOException {
+        String source = Files.readString(Path.of(System.getProperty("iris.nmsChunkGeneratorSource")));
+        String decoration = method(source,
+                "public void applyBiomeDecoration(WorldGenLevel generatoraccessseed, ChunkAccess ichunkaccess, StructureManager structuremanager, boolean vanilla)",
+                "public BiomeGenerationSettings getBiomeGenerationSettings");
+        int structuresGuard = decoration.indexOf("if (!flatStudioTerrain && !ichunkaccess.getPersistedStatus().isOrAfter(ChunkStatus.FEATURES))");
+        assertTrue(structuresGuard >= 0);
+        int structuresEnd = decoration.indexOf("\n            }", structuresGuard);
+        String structures = decoration.substring(structuresGuard, structuresEnd);
+        assertTrue(structures.contains("placeVanillaStructures(generatoraccessseed, ichunkaccess, structuremanager);"));
+        int preparationGuard = decoration.indexOf("if (!flatStudioTerrain)");
+        assertTrue(structuresEnd < preparationGuard);
+        assertTrue(decoration.indexOf("NativeGenerationWriteGuard.allowsDecoration") > structuresEnd);
+        int preparationEnd = decoration.indexOf("\n                }", preparationGuard);
+        String preparation = decoration.substring(preparationGuard, preparationEnd);
+        assertTrue(preparation.contains("importedFeatures.prepare(generatoraccessseed);"));
+
+        int placementGuard = decoration.indexOf("if (!flatStudioTerrain)", preparationEnd);
+        int placementEnd = decoration.indexOf("\n                }", placementGuard);
+        String placement = decoration.substring(placementGuard, placementEnd);
+        assertTrue(placement.contains("importedFeatures.run(generatoraccessseed, ichunkaccess, this);"));
+        int heightmaps = decoration.indexOf("addVanillaDecorations(generatoraccessseed, ichunkaccess, structuremanager);");
+        int populators = decoration.indexOf("delegate.applyBiomeDecoration(generatoraccessseed, ichunkaccess, structuremanager, false);");
+        assertTrue(heightmaps > preparationEnd && heightmaps < placementGuard);
+        assertTrue(populators > placementEnd);
+        assertTrue(decoration.indexOf("claimGeneratedSemantics(route,") > populators);
+        assertTrue(decoration.contains("requireGenerationStage(\"bukkit_nms_biome_decoration\")"));
+        assertTrue(decoration.contains("requireGenerationLease(\"bukkit_nms_biome_decoration\")"));
+    }
+
     @Test
     public void everyChunkUsesTheProductionGenerationStages() throws IOException {
         String source = Files.readString(Path.of(System.getProperty("iris.nmsChunkGeneratorSource")))

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NMSBindingDatapackStructureScopeTest.java

@@ -352,7 +352,7 @@ public class NMSBindingDatapackStructureScopeTest {
     }
 
     @Test
-    public void standardPublishesOneDeferredStateWhileJigsawPublishesInitializedEmptyState() throws IOException {
+    public void standardPublishesOneDeferredStateWhileAuthoringPublishesInitializedEmptyState() throws IOException {
         Path chunkGeneratorSource = Path.of(System.getProperty("iris.nmsChunkGeneratorSource"));
         String source = Files.readString(chunkGeneratorSource.resolveSibling("NMSBinding.java")).replace("\r\n", "\n");
         int methodStart = source.indexOf("public DatapackStructureScopeResult scopeDatapackStructures(");
@@ -365,8 +365,8 @@ public class NMSBindingDatapackStructureScopeTest {
         String method = source.substring(methodStart, methodEnd);
         int filteredState = method.indexOf("possibleSetsField.set(scopedState, selection.structureSets());");
         int jigsawMode = method.indexOf(
-                "boolean jigsawStudio = platformGenerator != null");
+                "boolean authoringStudio = platformGenerator != null");
-        int jigsawOnly = method.indexOf("if (jigsawStudio)");
+        int jigsawOnly = method.indexOf("if (authoringStudio)");
         int emptyCreation = method.indexOf("ChunkGeneratorStructureState bootstrapState = createStructureState(");
         int emptyFiltering = method.indexOf("bootstrapSetsField.set(bootstrapState, List.of());");
         int emptyInitialization = method.indexOf("bootstrapState.ensureStructuresGenerated();");

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NmsWorldLifecycleServerLevelAdviceContractTest.java

@@ -8,11 +8,11 @@ import java.nio.file.Path;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
-public class NMSBindingServerLevelAdviceContractTest {
+public class NmsWorldLifecycleServerLevelAdviceContractTest {
     @Test
     public void serverLevelAdviceSupportsCurrentSpigotAndPaperConstructorLayouts() throws Exception {
         String source = Files.readString(
-                Path.of(System.getProperty("iris.nmsBindingSource"))).replace("\r\n", "\n");
+                Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java")).replace("\r\n", "\n");
         String transformer = section(
                 source,
                 "public boolean injectBukkit()",
@@ -35,7 +35,7 @@ public class NMSBindingServerLevelAdviceContractTest {
     @Test
     public void currentSpigotStorageAccessReceivesManagedIdentityBeforeConstruction() throws Exception {
         String source = Files.readString(
-                Path.of(System.getProperty("iris.nmsBindingSource"))).replace("\r\n", "\n");
+                Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java")).replace("\r\n", "\n");
         String transformer = section(
                 source,
                 "public boolean injectBukkit()",
@@ -68,7 +68,7 @@ public class NMSBindingServerLevelAdviceContractTest {
     @Test
     public void ownedWorldPublishesItsManagedIdentityAndRuntimeStemTogether() throws Exception {
         String source = Files.readString(
-                Path.of(System.getProperty("iris.nmsBindingSource"))).replace("\r\n", "\n");
+                Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java")).replace("\r\n", "\n");
         String advice = section(
                 source,
                 "private static class ServerLevelAdvice",

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/NmsWorldLifecycleShutdownBoundaryContractTest.java

@@ -8,10 +8,10 @@ import java.nio.file.Path;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertFalse;
 
-public class NMSBindingShutdownBoundaryContractTest {
+public class NmsWorldLifecycleShutdownBoundaryContractTest {
     @Test
     public void shutdownClassificationUsesTheServerStopFlagInsteadOfPluginEnablement() throws Exception {
-        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")));
+        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java"));
         String stopping = section(source, "public boolean isServerStopping()", "public ServerShutdownBoundary createServerShutdownBoundary");
 
         assertTrue(stopping.contains("((CraftServer) Bukkit.getServer()).getServer().hasStopped()"));
@@ -21,10 +21,10 @@ public class NMSBindingShutdownBoundaryContractTest {
 
     @Test
     public void pluginLoaderGuardUsesSystemAgentIdentityAndIsRemovedAtRelease() throws Exception {
-        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")));
+        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java"));
         String injection = section(source, "public boolean injectBukkit()", "public void ensureServerLevelInjection()");
-        String guard = section(source, "private static class PluginClassLoaderCloseAdvice", "private static class ChunkAccessAdvice");
+        String guard = section(source, "private static class PluginClassLoaderCloseAdvice", "private static class LevelStorageAccessAdvice");
-        String release = section(source, "public void releasePluginClassLoaderClose()", "public KMap<Material, List<BlockProperty>> getBlockProperties");
+        String release = section(source, "public void releasePluginClassLoaderClose()", "private static final class PluginClassLoaderInjectionListener");
 
         assertTrue(injection.contains("Agent.requireClassLoaderCloseDeferral()"));
         assertTrue(injection.contains("getMethod(\"close\").getDeclaringClass()"));
@@ -40,8 +40,8 @@ public class NMSBindingShutdownBoundaryContractTest {
 
     @Test
     public void shutdownBoundaryUsesPaperFullyShutdownStateAndServerThread() throws Exception {
-        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource"))).replace("\r\n", "\n");
+        String source = Files.readString(Path.of(System.getProperty("iris.nmsBindingSource")).resolveSibling("NmsWorldLifecycle.java")).replace("\r\n", "\n");
-        String boundary = section(source, "public ServerShutdownBoundary createServerShutdownBoundary", "public KMap<Material, List<BlockProperty>> getBlockProperties");
+        String boundary = section(source, "public ServerShutdownBoundary createServerShutdownBoundary", "private static final class PluginClassLoaderInjectionListener");
 
         assertTrue(boundary.contains("new ServerShutdownBoundary("));
         assertTrue(boundary.contains("server.hasFullyShutdown"));

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/core/nms/v26_2_R1/WorldgenTerrainHeightmapsTest.java

@@ -64,6 +64,21 @@ public class WorldgenTerrainHeightmapsTest {
         Bootstrap.bootStrap();
     }
 
+    @Test
+    public void authoringHeightmapsReadPlacedObjectsAndFluidsWithoutTerrainResolvers() {
+        ProtoChunk chunk = terrainChunk(new ChunkPos(0, 0));
+
+        IrisChunkGenerator.primeAuthoringHeightmaps(chunk);
+
+        assertEquals(LAND_CANOPY_TOP, chunk.getHeight(Heightmap.Types.WORLD_SURFACE_WG, LAND_X, LAND_Z));
+        assertEquals(LAND_CANOPY_TOP, chunk.getHeight(Heightmap.Types.OCEAN_FLOOR_WG, LAND_X, LAND_Z));
+        assertEquals(LAND_CANOPY_TOP, chunk.getHeight(Heightmap.Types.MOTION_BLOCKING, LAND_X, LAND_Z));
+        assertEquals(LAND_TERRAIN_TOP + 6,
+                chunk.getHeight(Heightmap.Types.MOTION_BLOCKING_NO_LEAVES, LAND_X, LAND_Z));
+        assertEquals(OCEAN_FLUID_TOP, chunk.getHeight(Heightmap.Types.WORLD_SURFACE_WG, OCEAN_X, OCEAN_Z));
+        assertEquals(OCEAN_FLOOR_TOP, chunk.getHeight(Heightmap.Types.OCEAN_FLOOR_WG, OCEAN_X, OCEAN_Z));
+    }
+
     @Test
     public void primeTerrainWritesEngineSurfaceAndOceanFloorHeights() {
         ProtoChunk chunk = terrainChunk(new ChunkPos(0, 0));

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/nativegen/NativeGenerationWriteGuardTest.java

@@ -0,0 +1,79 @@
+package art.arcane.iris.nativegen;
+
+import art.arcane.iris.engine.IrisComplex;
+import art.arcane.iris.engine.IrisEngine;
+import art.arcane.iris.engine.history.GenerationActivation;
+import art.arcane.iris.engine.history.GenerationHistory;
+import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import java.util.Optional;
+import art.arcane.iris.engine.framework.Engine;
+import net.minecraft.SharedConstants;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public final class NativeGenerationWriteGuardTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void preTerrainSavedStampDistinguishesEarlierNativeStarts() {
+        IrisEngine engine = mock(IrisEngine.class);
+        GenerationHistoryRuntimeRouter router = mock(GenerationHistoryRuntimeRouter.class);
+        GenerationHistory history = mock(GenerationHistory.class);
+        GenerationActivation active = mock(GenerationActivation.class);
+        when(engine.getGenerationHistoryRuntimeRouter()).thenReturn(Optional.of(router));
+        when(router.history()).thenReturn(history);
+        when(history.activeActivation()).thenReturn(active);
+        when(active.activationId()).thenReturn(4L);
+        assertTrue(NativeGenerationWriteGuard.isHistoricalStructure(engine, 3));
+        assertFalse(NativeGenerationWriteGuard.isHistoricalStructure(engine, 0));
+        assertFalse(NativeGenerationWriteGuard.isHistoricalStructure(engine, 4));
+        assertFalse(NativeGenerationWriteGuard.isHistoricalStructure(engine, 5));
+    }
+
+    @Test
+    public void partialNeighborsMayFinishButCompletedHistoricalNeighborRejectsPass() {
+        Engine engine = mock(Engine.class);
+        IrisComplex complex = mock(IrisComplex.class);
+        when(engine.getComplex()).thenReturn(complex);
+        WorldGenLevel region = mock(WorldGenLevel.class);
+        ChunkAccess partial = mock(ChunkAccess.class);
+        when(partial.getPersistedStatus()).thenReturn(ChunkStatus.NOISE);
+        when(region.getChunk(anyInt(), anyInt())).thenReturn(partial);
+        assertTrue(NativeGenerationWriteGuard.allowsDecoration(engine, region, new ChunkPos(0, 0)));
+        ChunkAccess complete = mock(ChunkAccess.class);
+        when(complete.getPersistedStatus()).thenReturn(ChunkStatus.FULL);
+        when(region.getChunk(1, -1)).thenReturn(complete);
+        assertFalse(NativeGenerationWriteGuard.allowsDecoration(engine, region, new ChunkPos(0, 0)));
+    }
+
+    @Test
+    public void historicalNoiseMayFinishFeaturesButNeverReplaysNoiseOrCompletedStage() {
+        Engine engine = mock(Engine.class);
+        IrisComplex complex = mock(IrisComplex.class);
+        when(engine.getComplex()).thenReturn(complex);
+        ChunkAccess chunk = mock(ChunkAccess.class);
+        when(chunk.getPos()).thenReturn(new ChunkPos(-2, 3));
+        when(chunk.getPersistedStatus()).thenReturn(ChunkStatus.NOISE);
+        assertTrue(NativeGenerationWriteGuard.allowsPendingStage(engine, chunk, ChunkStatus.FEATURES));
+        assertFalse(NativeGenerationWriteGuard.allowsPendingStage(engine, chunk, ChunkStatus.NOISE));
+        when(chunk.getPersistedStatus()).thenReturn(ChunkStatus.FEATURES);
+        assertFalse(NativeGenerationWriteGuard.allowsPendingStage(engine, chunk, ChunkStatus.FEATURES));
+        when(chunk.getPersistedStatus()).thenReturn(ChunkStatus.FULL);
+        assertFalse(NativeGenerationWriteGuard.allowsPendingStage(engine, chunk, ChunkStatus.SPAWN));
+    }
+}

adapters/bukkit/nms/v26_2_R1/src/test/java/art/arcane/iris/nativegen/NativeTransitionColumnTest.java

@@ -0,0 +1,68 @@
+package art.arcane.iris.nativegen;
+
+import art.arcane.iris.engine.history.BoundaryColumnGeometry;
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Direction;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.block.RotatedPillarBlock;
+import net.minecraft.world.level.block.LiquidBlock;
+import net.minecraft.world.level.levelgen.Heightmap;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.OptionalInt;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+
+public final class NativeTransitionColumnTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void preservesNativePropertiesCavesAndFluids() {
+        NoiseColumn column = NativeTransitionColumn.column(signature("minecraft:oak_log[axis=x]"),
+                LevelHeightAccessor.create(-16, 32));
+        assertEquals(Direction.Axis.X, column.getBlock(-15).getValue(RotatedPillarBlock.AXIS));
+        assertTrue(column.getBlock(-14).is(Blocks.CAVE_AIR));
+        assertEquals(Integer.valueOf(3), column.getBlock(-13).getValue(LiquidBlock.LEVEL));
+        assertTrue(column.getBlock(0).isAir());
+    }
+
+    @Test
+    public void usesNativeHeightmapPredicatesForWaterAndOpenSpace() {
+        TerrainBoundarySignature signature = signature("minecraft:oak_log[axis=x]");
+        LevelHeightAccessor height = LevelHeightAccessor.create(-16, 32);
+        assertEquals(-12, NativeTransitionColumn.height(signature, Heightmap.Types.WORLD_SURFACE_WG, height));
+        assertEquals(-14, NativeTransitionColumn.height(signature, Heightmap.Types.OCEAN_FLOOR_WG, height));
+    }
+
+    @Test
+    public void rejectsUnknownSavedStatesInsteadOfReplacingTerrain() {
+        assertThrows(IllegalArgumentException.class, () -> NativeTransitionColumn.column(
+                signature("missing:removed_block"), LevelHeightAccessor.create(-16, 32)));
+    }
+
+    private static TerrainBoundarySignature signature(String solidState) {
+        BoundaryColumnGeometry geometry = BoundaryColumnGeometry.fromVoxels(-16, List.of(
+                new BoundaryColumnGeometry.Voxel("minecraft:stone", BoundaryColumnGeometry.Phase.SOLID, "", false),
+                new BoundaryColumnGeometry.Voxel(solidState, BoundaryColumnGeometry.Phase.SOLID, "", false),
+                new BoundaryColumnGeometry.Voxel("minecraft:cave_air", BoundaryColumnGeometry.Phase.AIR, "", false),
+                new BoundaryColumnGeometry.Voxel("minecraft:water[level=3]", BoundaryColumnGeometry.Phase.FLUID,
+                        "minecraft:water[level=3]", false)));
+        return new TerrainBoundarySignature(
+                new TerrainBoundarySignature.Column(0, 0, 3, 1, OptionalInt.of(3), OptionalInt.empty()),
+                new TerrainBoundarySignature.Samples(new TerrainBoundarySignature.VerticalLayout(-16, 4, 1),
+                        new TerrainBoundarySignature.BiomeEncoding(List.of("minecraft:plains"), new short[]{0})),
+                geometry);
+    }
+}

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/runtime/BukkitEnginePlatformHooks.java

@@ -23,6 +23,7 @@ import art.arcane.iris.core.ServerConfigurator;
 import art.arcane.iris.core.datapack.DatapackIngestService;
 import art.arcane.iris.core.events.IrisEngineHotloadEvent;
 import art.arcane.iris.core.gui.PregeneratorJob;
+import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.nms.INMS;
 import art.arcane.iris.core.project.IrisProject;
 import art.arcane.iris.core.project.IrisCodeWorkspace;
@@ -30,6 +31,9 @@ import art.arcane.iris.core.service.IrisApiEventSVC;
 import art.arcane.iris.core.tools.IrisToolbelt;
 import art.arcane.iris.core.tools.WorldMaintenance;
 import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+
+import java.util.concurrent.CompletableFuture;
 import art.arcane.iris.engine.framework.EngineMode;
 import art.arcane.iris.engine.framework.EnginePlatformHooks;
 import art.arcane.iris.engine.framework.NativeStructureVolume;
@@ -47,6 +51,16 @@ import org.bukkit.World;
 import org.bukkit.WorldBorder;
 
 public final class BukkitEnginePlatformHooks implements EnginePlatformHooks {
+    @Override
+    public CompletableFuture<Void> flushSavedTerrainCapture(Engine engine) {
+        return INMS.get().flushSavedTerrainCapture(BukkitWorldBinding.world(engine.getWorld()));
+    }
+
+    @Override
+    public CompletableFuture<SavedTerrainChunk> captureSavedTerrainChunk(Engine engine, int chunkX, int chunkZ) {
+        return BukkitSavedTerrainCapture.capture(engine, chunkX, chunkZ);
+    }
+
     @Override
     public KList<NativeStructureVolume> nativeStructureVolumes(Engine engine, int minX, int minZ, int maxX, int maxZ) {
         return INMS.get().nativeStructureVolumes(engine, minX, minZ, maxX, maxZ);
@@ -54,12 +68,17 @@ public final class BukkitEnginePlatformHooks implements EnginePlatformHooks {
 
     @Override
     public void refreshWorkspace(Engine engine) {
-        new IrisCodeWorkspace(new IrisProject(engine.getData().getDataFolder())).updateWorkspace();
+        new IrisCodeWorkspace(new IrisProject(engine.getPackSource().toFile())).updateWorkspace();
     }
 
     @Override
     public void refreshDatapackWorkspace(Engine engine) {
-        DatapackIngestService.refreshWorkspace(engine.getData());
+        IrisData data = IrisData.openRuntime(engine.getPackSource().toFile());
+        try {
+            DatapackIngestService.refreshWorkspace(data);
+        } finally {
+            data.close();
+        }
     }
 
     @Override

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/runtime/BukkitSavedTerrainCapture.java

@@ -0,0 +1,23 @@
+package art.arcane.iris.core.runtime;
+
+import art.arcane.iris.core.nms.INMS;
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.platform.bukkit.BukkitWorldBinding;
+import org.bukkit.World;
+
+import java.io.IOException;
+import java.util.concurrent.CompletableFuture;
+
+final class BukkitSavedTerrainCapture {
+    private BukkitSavedTerrainCapture() {
+    }
+
+    static CompletableFuture<SavedTerrainChunk> capture(Engine engine, int chunkX, int chunkZ) {
+        World world = BukkitWorldBinding.world(engine.getWorld());
+        if (world == null) {
+            return CompletableFuture.failedFuture(new IOException("The world is unavailable for terrain capture."));
+        }
+        return INMS.get().captureSavedTerrainChunk(world, chunkX, chunkZ, engine.getMinHeight(), engine.getHeight());
+    }
+}

adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/service/IrisProtocolService.java

@@ -192,7 +192,7 @@ public class IrisProtocolService implements IrisService, PluginMessageListener,
         World world = player.getWorld();
         Engine engine = engineFor(world);
         if (engine != null) {
-            protocol.sendDimensionStatus(sessionId, engine.getDimension().getLoadKey(), engine.getData().getDataFolder().getName(),
+            protocol.sendDimensionStatus(sessionId, engine.getDimension().getLoadKey(), engine.getPackSource().getFileName().toString(),
                     world.getSeed(), engine.getMinHeight(), engine.getMaxHeight(), true);
             return;
         }

adapters/fabric/build.gradle

@@ -26,7 +26,7 @@ plugins {
     alias(libs.plugins.shadow)
 }
 
-apply from: file('../../gradle/modded-generation-kernel-seals.gradle')
+apply from: file('../../gradle/modded-generation-build-revision.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }

adapters/forge/build.gradle

@@ -26,7 +26,7 @@ plugins {
     alias(libs.plugins.shadow)
 }
 
-apply from: file('../../gradle/modded-generation-kernel-seals.gradle')
+apply from: file('../../gradle/modded-generation-build-revision.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }

adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeGenerationWriteGuard.java

@@ -0,0 +1,46 @@
+package art.arcane.iris.nativegen;
+
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.IrisEngine;
+import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.status.ChunkPyramid;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+
+public final class NativeGenerationWriteGuard {
+    private NativeGenerationWriteGuard() {
+    }
+
+    public static boolean allowsDecoration(Engine engine, WorldGenLevel region, ChunkPos center) {
+        int radius = ChunkPyramid.GENERATION_PYRAMID.getStepTo(ChunkStatus.FEATURES).blockStateWriteRadius();
+        for (int offsetX = -radius; offsetX <= radius; offsetX++) {
+            for (int offsetZ = -radius; offsetZ <= radius; offsetZ++) {
+                int chunkX = Math.addExact(center.x(), offsetX);
+                int chunkZ = Math.addExact(center.z(), offsetZ);
+                ChunkAccess target = region.getChunk(chunkX, chunkZ);
+                if (target.getPersistedStatus().isOrAfter(ChunkStatus.FULL)
+                        && !engine.getComplex().allowsMantleChunkWrite(chunkX, chunkZ)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    public static boolean isHistoricalStructure(Engine engine, long activation) {
+        if (activation <= 0 || !(engine instanceof IrisEngine irisEngine)) {
+            return false;
+        }
+        GenerationHistoryRuntimeRouter router = irisEngine.getGenerationHistoryRuntimeRouter().orElse(null);
+        return router != null && activation < router.history().activeActivation().activationId();
+    }
+
+    public static boolean allowsPendingStage(Engine engine, ChunkAccess chunk, ChunkStatus stage) {
+        return stage.isOrAfter(ChunkStatus.FEATURES)
+                && chunk.getPersistedStatus().isOrAfter(ChunkStatus.NOISE)
+                && !chunk.getPersistedStatus().isOrAfter(stage)
+                && !engine.getComplex().allowsMantleChunkWrite(chunk.getPos().x(), chunk.getPos().z());
+    }
+}

adapters/minecraft-common/src/main/java/art/arcane/iris/nativegen/NativeTransitionColumn.java

@@ -0,0 +1,53 @@
+package art.arcane.iris.nativegen;
+
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
+import com.mojang.brigadier.StringReader;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import net.minecraft.commands.arguments.blocks.BlockStateParser;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.NoiseColumn;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.levelgen.Heightmap;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public final class NativeTransitionColumn {
+    private NativeTransitionColumn() {
+    }
+
+    public static NoiseColumn column(TerrainBoundarySignature signature, LevelHeightAccessor height) {
+        BlockState[] states = new BlockState[height.getHeight()];
+        Map<String, BlockState> palette = new HashMap<>();
+        for (int offset = 0; offset < states.length; offset++) {
+            String state = signature.geometry().voxelAt(height.getMinY() + offset).stateKey();
+            states[offset] = palette.computeIfAbsent(state, NativeTransitionColumn::parse);
+        }
+        return new NoiseColumn(height.getMinY(), states);
+    }
+
+    public static int height(TerrainBoundarySignature signature, Heightmap.Types type, LevelHeightAccessor height) {
+        Map<String, BlockState> palette = new HashMap<>();
+        for (int offset = height.getHeight() - 1; offset >= 0; offset--) {
+            String state = signature.geometry().voxelAt(height.getMinY() + offset).stateKey();
+            if (type.isOpaque().test(palette.computeIfAbsent(state, NativeTransitionColumn::parse))) {
+                return height.getMinY() + offset + 1;
+            }
+        }
+        return height.getMinY();
+    }
+
+    private static BlockState parse(String key) {
+        StringReader reader = new StringReader(key);
+        try {
+            BlockState state = BlockStateParser.parseForBlock(BuiltInRegistries.BLOCK, reader, false).blockState();
+            if (reader.canRead()) {
+                throw new IllegalArgumentException("Unexpected terrain block state suffix: " + reader.getRemaining());
+            }
+            return state;
+        } catch (CommandSyntaxException failure) {
+            throw new IllegalArgumentException("Saved terrain block state cannot be resolved: " + key, failure);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/IrisModdedChunkGenerator.java

@@ -18,6 +18,10 @@
 
 package art.arcane.iris.modded;
 
+import art.arcane.iris.nativegen.NativeTransitionColumn;
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
+import java.util.Optional;
+import art.arcane.iris.nativegen.NativeGenerationWriteGuard;
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.engine.IrisEngine;
@@ -1019,14 +1023,19 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
             generationEngine.generate(pos.getMinBlockX(), pos.getMinBlockZ(), blocks, biomes, false);
 
             writeBlocks(chunk, blocks, dimMinY, height);
+            if (route != null) {
+                BlockPos.MutableBlockPos position = new BlockPos.MutableBlockPos();
+                route.claimGeneratedSemantics((x, y, z) -> {
+                    BlockState state = chunk.getBlockState(position.set(x, dimMinY + y, z));
+                    return state.isAir() || state.liquid();
+                });
+            }
+            ModdedNativeTerrainReceipts.persist(chunk, route);
             writeTerrainHeightmaps(chunk, generationEngine, pos, height);
             Heightmap.primeHeightmaps(chunk, EnumSet.of(
                     Heightmap.Types.MOTION_BLOCKING,
                     Heightmap.Types.MOTION_BLOCKING_NO_LEAVES));
             ModdedWorldManager.enqueueGenerated(generationEngine, pos.x(), pos.z());
-            if (route != null) {
-                route.claimGeneratedSemantics();
-            }
             return chunk;
         } catch (GenerationSessionException e) {
             if (generationEngine.isClosing() || e.isExpectedTeardown()) {
@@ -1066,6 +1075,7 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
                 completion.completeExceptionally(completionFailure);
             }
         });
+        route.detachThread();
         return completion;
     }
 
@@ -1205,6 +1215,10 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
              GenerationHistoryRuntimeRouter.RuntimeRoute.RuntimeScope runtimeScope = openHistoryRuntimeScope(route);
              GenerationSessionLease lease = requireGenerationLease(current, "modded_biome_decoration");
              IrisContext.Scope ignored = IrisContext.open(current, lease.sessionId(), null)) {
+            if (chunk.getPersistedStatus().isOrAfter(ChunkStatus.FEATURES)) {
+                return;
+            }
+            nativeStructures.placeVanillaStructures(level, chunk, structureManager);
             if (!allowsRoutedDiscreteGeneration(
                     current,
                     route,
@@ -1214,8 +1228,10 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
             )) {
                 return;
             }
+            if (!NativeGenerationWriteGuard.allowsDecoration(current, level, chunkPos)) {
+                return;
+            }
             importedFeatures.prepare(current);
-            nativeStructures.placeVanillaStructures(level, chunk, structureManager);
             // Vanilla's placed-feature pass, on THIS thread and never on ModdedGenPool: the FEATURES chunk
             // step writes into the eight neighbouring chunks and is not parallel-safe. Inert unless the
             // dimension set importedFeatures.enabled.
@@ -1257,6 +1273,7 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
                     ));
             nativeStructures.adjustGeneratedStructures(
                     registryAccess, chunk, previousStarts, configuredStarts, current, templateManager);
+            ModdedNativeTerrainReceipts.persistStructureActivation(chunk, route);
         }
     }
 
@@ -1355,6 +1372,10 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
                      current, x, z, "modded_base_height");
              GenerationSessionLease lease = current.acquireGenerationLease("modded_base_height");
              IrisContext.Scope ignored = IrisContext.open(current, lease.sessionId(), null)) {
+            Optional<TerrainBoundarySignature> resolved = current.getComplex().resolvedTerrainColumn(x, z);
+            if (resolved.isPresent()) {
+                return NativeTransitionColumn.height(resolved.get(), type, heightAccessor);
+            }
             int height = current.getDimensionStackContext() == null
                     ? current.getHeight(x, z, ignoreFluid)
                     : Engine.hostHeight(current, x, z, ignoreFluid);
@@ -1367,12 +1388,16 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
     @Override
     public NoiseColumn getBaseColumn(int x, int z, LevelHeightAccessor heightAccessor, RandomState randomState) {
         int minY = heightAccessor.getMinY();
-        BlockState[] states = new BlockState[heightAccessor.getHeight()];
         Engine current = requireDataQueryEngine("base column");
         try (GenerationHistoryRuntimeRouter.CoordinateScope historyScope = openHistoryCoordinateScope(
                      current, x, z, "modded_base_column");
              GenerationSessionLease lease = current.acquireGenerationLease("modded_base_column");
              IrisContext.Scope ignored = IrisContext.open(current, lease.sessionId(), null)) {
+            Optional<TerrainBoundarySignature> resolved = current.getComplex().resolvedTerrainColumn(x, z);
+            if (resolved.isPresent()) {
+                return NativeTransitionColumn.column(resolved.get(), heightAccessor);
+            }
+            BlockState[] states = new BlockState[heightAccessor.getHeight()];
             BlockState airState = Blocks.AIR.defaultBlockState();
             boolean dimensionStack = current.getDimensionStackContext() != null;
             int surface = dimensionStack
@@ -1394,6 +1419,12 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
         }
     }
 
+    public boolean allowsNativeChunkWrite(int chunkX, int chunkZ) {
+        Engine current = engine;
+        return current == null || !current.isClosing() && !current.isClosed()
+                && current.getComplex().allowsMantleChunkWrite(chunkX, chunkZ);
+    }
+
     private boolean allowsRoutedDiscreteGeneration(
             Engine current,
             GenerationHistoryRuntimeRouter.RuntimeRoute route,
@@ -1407,7 +1438,8 @@ public final class IrisModdedChunkGenerator extends ChunkGenerator {
         if (route == null) {
             return allowsGenerationHistoryBypass(current);
         }
-        return current.getComplex().allowsNewGenerationChunk(chunkPos.x(), chunkPos.z());
+        return NativeGenerationWriteGuard.allowsPendingStage(current, chunk, stage)
+                || current.getComplex().allowsNewGenerationChunk(chunkPos.x(), chunkPos.z());
     }
 
     private void bindGenerationRuntimeRetirementListener(Engine current) {

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedForcedDatapack.java

@@ -362,13 +362,15 @@ public final class ModdedForcedDatapack {
         KList<String> presetIds = new KList<>();
         Path worldRoot = worldRootOrNull();
         Set<PackSelection> legacySelections = unadoptedSelections(worldRoot);
-        for (File pack : compilationPackRoots(worldRoot)) {
+        List<File> packRoots = compilationPackRoots(worldRoot);
+        for (File pack : packRoots) {
             PackStageContext context = packStageContext(pack.toPath(), legacySelections);
             if (stagePack(context, fixer, stagingDirectory, seenBiomes, presetIds)) {
                 packCount++;
             }
         }
 
+        IrisDatapackCompiler.installRetainedRegistrySources(packRoots, List.of(stagingDirectory.toFile()), fixer);
         writePackMeta(stagingDirectory);
         // Forge only: FML has no block-drops event Iris can use, so drops are routed through a global loot
         // modifier. NeoForge does not need one - IrisNeoForgeBootstrap listens to BlockDropsEvent and both
@@ -996,7 +998,7 @@ public final class ModdedForcedDatapack {
                 return currentSource;
             }
             PhysicalResourceKey key = new PhysicalResourceKey(registryKey, resourceKey);
-            return GenerationRegistryContractFactory.requireGeneratedSource(retainedContract, key, fixer);
+            return GenerationRegistryContractFactory.renderGeneratedSource(retainedContract, key, fixer);
         }
     }
 

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedNativeStructureStage.java

@@ -18,6 +18,10 @@
 
 package art.arcane.iris.modded;
 
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+
+import art.arcane.iris.nativegen.NativeGenerationWriteGuard;
+
 import art.arcane.iris.engine.DimensionStackContext;
 import art.arcane.iris.engine.DimensionStackLayout;
 import art.arcane.iris.engine.framework.Engine;
@@ -341,7 +345,8 @@ final class ModdedNativeStructureStage {
                     List<NativePlacement> resolvedPlacements = new ArrayList<>(starts.size());
                     for (StructureStart start : starts) {
                         BoundingBox footprint = start.getBoundingBox();
-                        if (!current.getComplex().allowsNewGenerationFootprint(
+                        if (!isHistoricalStructureStart(current, world, start)
+                                && !current.getComplex().allowsNewGenerationFootprint(
                                 footprint.minX(),
                                 footprint.minZ(),
                                 footprint.maxX(),
@@ -574,6 +579,16 @@ final class ModdedNativeStructureStage {
         return blockState;
     }
 
+    private boolean isHistoricalStructureStart(Engine current, WorldGenLevel world, StructureStart start) {
+        ChunkPos origin = start.getChunkPos();
+        if (!current.getComplex().allowsMantleChunkWrite(origin.x(), origin.z())) {
+            return true;
+        }
+        ChunkAccess source = world.getChunk(origin.x(), origin.z(), ChunkStatus.EMPTY, false);
+        return source != null && NativeGenerationWriteGuard.isHistoricalStructure(
+                current, ModdedNativeTerrainReceipts.structureActivation(source));
+    }
+
     private BoundingBox writableArea(ChunkAccess chunk) {
         ChunkPos chunkPos = chunk.getPos();
         int minX = chunkPos.getMinBlockX();

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedNativeTerrainReceipts.java

@@ -0,0 +1,53 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import art.arcane.iris.engine.history.NativeTerrainReceipt;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.ImposterProtoChunk;
+
+import java.io.IOException;
+
+public final class ModdedNativeTerrainReceipts {
+    private ModdedNativeTerrainReceipts() {
+    }
+
+    public static void persist(ChunkAccess chunk, GenerationHistoryRuntimeRouter.RuntimeRoute route) throws IOException {
+        if (route == null || route.naturalTerrain().isEmpty()) {
+            return;
+        }
+        set(chunk, NativeTerrainReceipt.encode(route.naturalTerrain().orElseThrow(),
+                route.activation().activationId(), route.epoch().epochId()));
+        chunk.markUnsaved();
+    }
+
+    public static long structureActivation(ChunkAccess chunk) {
+        return holder(chunk).iris$getStructureActivation();
+    }
+
+    public static void setStructureActivation(ChunkAccess chunk, long activation) {
+        holder(chunk).iris$setStructureActivation(activation);
+    }
+
+    public static void persistStructureActivation(ChunkAccess chunk, GenerationHistoryRuntimeRouter.RuntimeRoute route) {
+        if (route != null) {
+            setStructureActivation(chunk, route.activation().activationId());
+            chunk.markUnsaved();
+        }
+    }
+
+    public static byte[] get(ChunkAccess chunk) {
+        return holder(chunk).iris$getNaturalTerrain();
+    }
+
+    public static void set(ChunkAccess chunk, byte[] receipt) {
+        holder(chunk).iris$setNaturalTerrain(receipt);
+    }
+
+    private static NativeTerrainReceiptHolder holder(ChunkAccess chunk) {
+        ChunkAccess target = chunk instanceof ImposterProtoChunk imposter ? imposter.getWrapped() : chunk;
+        if (!(target instanceof NativeTerrainReceiptHolder holder)) {
+            throw new IllegalStateException("Native terrain receipt storage is unavailable for " + chunk.getPos());
+        }
+        return holder;
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedSavedTerrainCapture.java

@@ -0,0 +1,142 @@
+package art.arcane.iris.modded;
+
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.modded.mixin.ChunkMapTerrainReceiptAccess;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.nbt.NbtIo;
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ChunkMap;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.storage.SerializableChunkData;
+
+import java.io.ByteArrayOutputStream;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+
+public final class ModdedSavedTerrainCapture {
+    private ModdedSavedTerrainCapture() {
+    }
+
+    public static CompletableFuture<SavedTerrainChunk> capture(Engine engine, int chunkX, int chunkZ) {
+        ServerLevel level = requireLevel(engine);
+        CompletableFuture<CompoundTag> snapshot = new CompletableFuture<>();
+        runOwned(level, () -> {
+            try {
+                ChunkMap map = level.getChunkSource().chunkMap;
+                ChunkHolder holder = map.getUpdatingChunkIfPresent(ChunkPos.pack(chunkX, chunkZ));
+                ChunkAccess chunk = holder == null ? null : holder.getLatestChunk();
+                if (chunk == null) {
+                    map.read(new ChunkPos(chunkX, chunkZ)).whenComplete((data, failure) -> {
+                        if (failure != null) {
+                            snapshot.completeExceptionally(failure);
+                        } else {
+                            snapshot.complete(data.orElse(null));
+                        }
+                    });
+                    return;
+                }
+                String status = BuiltInRegistries.CHUNK_STATUS.getKey(chunk.getPersistedStatus()).toString();
+                if (!SavedTerrainChunk.hasTerrain(status)) {
+                    throw new IOException("Native chunk " + chunkX + "," + chunkZ + " has no terrain at " + status);
+                }
+                CompoundTag data = SerializableChunkData.copyOf(level, chunk).write();
+                if (chunk.isUnsaved()) {
+                    ((ChunkMapTerrainReceiptAccess) map).iris$saveTerrainCheckpoint(chunk);
+                }
+                snapshot.complete(data);
+            } catch (Throwable failure) {
+                snapshot.completeExceptionally(failure);
+            }
+        });
+        return snapshot.thenApplyAsync(data -> {
+            try {
+                if (data == null) {
+                    throw new IOException("Saved native chunk is unavailable: " + chunkX + "," + chunkZ);
+                }
+                ByteArrayOutputStream bytes = new ByteArrayOutputStream();
+                try (DataOutputStream output = new DataOutputStream(bytes)) {
+                    NbtIo.write(data, output);
+                }
+                return SavedTerrainChunk.readNbt(bytes.toByteArray(), chunkX, chunkZ, engine.getMinHeight(), engine.getHeight());
+            } catch (IOException failure) {
+                throw new CompletionException(failure);
+            }
+        });
+    }
+
+    public static CompletableFuture<Void> flush(Engine engine) {
+        ServerLevel level = requireLevel(engine);
+        CompletableFuture<Void> complete = new CompletableFuture<>();
+        runOwned(level, () -> {
+            try {
+                ChunkMap map = level.getChunkSource().chunkMap;
+                List<Checkpoint> checkpoints = new ArrayList<>();
+                for (ChunkHolder holder : ((ChunkMapTerrainReceiptAccess) map).iris$updatingChunks().values()) {
+                    ChunkAccess chunk = holder.getLatestChunk();
+                    if (chunk == null) {
+                        continue;
+                    }
+                    String status = BuiltInRegistries.CHUNK_STATUS.getKey(chunk.getPersistedStatus()).toString();
+                    if (!SavedTerrainChunk.hasTerrain(status)
+                            && ModdedNativeTerrainReceipts.structureActivation(chunk) == 0) {
+                        continue;
+                    }
+                    checkpoints.add(new Checkpoint(chunk.getPos().x(), chunk.getPos().z(), status,
+                            ModdedNativeTerrainReceipts.get(chunk), ModdedNativeTerrainReceipts.structureActivation(chunk)));
+                    if (chunk.isUnsaved()) {
+                        ((ChunkMapTerrainReceiptAccess) map).iris$saveTerrainCheckpoint(chunk);
+                    }
+                }
+                map.synchronize(true).thenRunAsync(() -> verifyCheckpoints(engine, checkpoints))
+                        .whenComplete((ignored, failure) -> {
+                            if (failure != null) {
+                                complete.completeExceptionally(failure);
+                            } else {
+                                complete.complete(null);
+                            }
+                        });
+            } catch (Throwable failure) {
+                complete.completeExceptionally(failure);
+            }
+        });
+        return complete;
+    }
+
+    private static void verifyCheckpoints(Engine engine, List<Checkpoint> checkpoints) {
+        try {
+            for (Checkpoint checkpoint : checkpoints) {
+                SavedTerrainChunk.verifyCheckpoint(engine.getWorld().worldFolder().toPath(),
+                        checkpoint.chunkX(), checkpoint.chunkZ(), checkpoint.status(), checkpoint.receipt(),
+                        checkpoint.structureActivation());
+            }
+        } catch (IOException failure) {
+            throw new CompletionException(failure);
+        }
+    }
+
+    private record Checkpoint(int chunkX, int chunkZ, String status, byte[] receipt, long structureActivation) {
+    }
+
+    private static ServerLevel requireLevel(Engine engine) {
+        if (!(engine.getWorld().platformWorld().nativeHandle() instanceof ServerLevel level)) {
+            throw new IllegalStateException("The level is unavailable for terrain capture.");
+        }
+        return level;
+    }
+
+    private static void runOwned(ServerLevel level, Runnable action) {
+        if (level.getServer().isSameThread()) {
+            action.run();
+        } else {
+            level.getServer().execute(action);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/ModdedWorldEngines.java

@@ -191,6 +191,8 @@ public final class ModdedWorldEngines {
             ModdedGenerationHistoryStorage.ActivePack opened
     ) throws IOException {
         GenerationHistory history = opened.history();
+        history.prepareCurrentGenerator(IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks());
+        opened = ModdedGenerationHistoryStorage.resolveActive(history);
         long openedActivationId = history.activeActivation().activationId();
         IrisEngine candidate = buildEngine(level, seed, opened);
         boolean ready = false;

adapters/modded-common/src/main/java/art/arcane/iris/modded/NativeTerrainReceiptHolder.java

@@ -0,0 +1,11 @@
+package art.arcane.iris.modded;
+
+public interface NativeTerrainReceiptHolder {
+    long iris$getStructureActivation();
+
+    void iris$setStructureActivation(long activation);
+
+    byte[] iris$getNaturalTerrain();
+
+    void iris$setNaturalTerrain(byte[] receipt);
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/command/ModdedPregenJob.java

@@ -25,6 +25,7 @@ import art.arcane.iris.core.pregenerator.PregenPerformanceProfile;
 import art.arcane.iris.core.pregenerator.PregenTask;
 import art.arcane.iris.core.pregenerator.PregeneratorMethod;
 import art.arcane.iris.core.pregenerator.cache.PregenCache;
+import art.arcane.iris.core.pregenerator.cache.PregenSavedChunkStatus;
 import art.arcane.iris.core.pregenerator.methods.CachedPregenMethod;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.volmlib.util.format.Form;
@@ -64,7 +65,9 @@ public final class ModdedPregenJob {
         ModdedPregenMethod moddedMethod = new ModdedPregenMethod(level, engine, sync);
         PregeneratorMethod method = moddedMethod;
         if (cached) {
-            method = new CachedPregenMethod(method, PregenCache.create(cacheDirectory(level)).sync(), task);
+            method = new CachedPregenMethod(new CachedPregenMethod.Configuration(method,
+                    PregenCache.create(cacheDirectory(level)).sync(), task,
+                    PregenSavedChunkStatus.fromWorld(engine.getWorld().worldFolder().toPath())));
         }
         ActivePregen active = new ActivePregen(engine, moddedMethod);
         ACTIVE.set(active);

adapters/modded-common/src/main/java/art/arcane/iris/modded/mixin/ChunkMapTerrainReceiptAccess.java

@@ -0,0 +1,18 @@
+package art.arcane.iris.modded.mixin;
+
+import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
+import net.minecraft.server.level.ChunkHolder;
+import net.minecraft.server.level.ChunkMap;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.gen.Accessor;
+import org.spongepowered.asm.mixin.gen.Invoker;
+
+@Mixin(ChunkMap.class)
+public interface ChunkMapTerrainReceiptAccess {
+    @Invoker("save")
+    boolean iris$saveTerrainCheckpoint(ChunkAccess chunk);
+
+    @Accessor("updatingChunkMap")
+    Long2ObjectLinkedOpenHashMap<ChunkHolder> iris$updatingChunks();
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/mixin/ChunkTerrainReceiptMixin.java

@@ -0,0 +1,37 @@
+package art.arcane.iris.modded.mixin;
+
+import art.arcane.iris.modded.NativeTerrainReceiptHolder;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+
+@Mixin(ChunkAccess.class)
+public abstract class ChunkTerrainReceiptMixin implements NativeTerrainReceiptHolder {
+    @Unique
+    private byte[] iris$naturalTerrain;
+    @Unique
+    private long iris$structureActivation;
+
+    @Override
+    public long iris$getStructureActivation() {
+        return iris$structureActivation;
+    }
+
+    @Override
+    public void iris$setStructureActivation(long activation) {
+        if (activation < 0) {
+            throw new IllegalArgumentException("Native structure activation cannot be negative");
+        }
+        iris$structureActivation = activation;
+    }
+
+    @Override
+    public byte[] iris$getNaturalTerrain() {
+        return iris$naturalTerrain == null ? null : iris$naturalTerrain.clone();
+    }
+
+    @Override
+    public void iris$setNaturalTerrain(byte[] receipt) {
+        iris$naturalTerrain = receipt == null ? null : receipt.clone();
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/mixin/LevelChunkTerrainReceiptMixin.java

@@ -0,0 +1,21 @@
+package art.arcane.iris.modded.mixin;
+
+import art.arcane.iris.modded.ModdedNativeTerrainReceipts;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.level.chunk.LevelChunk;
+import net.minecraft.world.level.chunk.ProtoChunk;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(LevelChunk.class)
+public abstract class LevelChunkTerrainReceiptMixin {
+    @Inject(method = "<init>(Lnet/minecraft/server/level/ServerLevel;Lnet/minecraft/world/level/chunk/ProtoChunk;Lnet/minecraft/world/level/chunk/LevelChunk$PostLoadProcessor;)V", at = @At("RETURN"))
+    private void iris$transferTerrain(ServerLevel level, ProtoChunk source, LevelChunk.PostLoadProcessor processor,
+                                      CallbackInfo callback) {
+        ModdedNativeTerrainReceipts.setStructureActivation((LevelChunk) (Object) this,
+                ModdedNativeTerrainReceipts.structureActivation(source));
+        ModdedNativeTerrainReceipts.set((LevelChunk) (Object) this, ModdedNativeTerrainReceipts.get(source));
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/mixin/SerializableTerrainReceiptMixin.java

@@ -0,0 +1,89 @@
+package art.arcane.iris.modded.mixin;
+
+import art.arcane.iris.engine.history.NativeTerrainReceipt;
+import art.arcane.iris.modded.ModdedNativeTerrainReceipts;
+import art.arcane.iris.modded.NativeTerrainReceiptHolder;
+import net.minecraft.nbt.CompoundTag;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.world.entity.ai.village.poi.PoiManager;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.LevelHeightAccessor;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.chunk.PalettedContainerFactory;
+import net.minecraft.world.level.chunk.ProtoChunk;
+import net.minecraft.world.level.chunk.storage.RegionStorageInfo;
+import net.minecraft.world.level.chunk.storage.SerializableChunkData;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(SerializableChunkData.class)
+public abstract class SerializableTerrainReceiptMixin implements NativeTerrainReceiptHolder {
+    @Unique
+    private byte[] iris$naturalTerrain;
+    @Unique
+    private long iris$structureActivation;
+
+    @Override
+    public long iris$getStructureActivation() {
+        return iris$structureActivation;
+    }
+
+    @Override
+    public void iris$setStructureActivation(long activation) {
+        if (activation < 0) {
+            throw new IllegalArgumentException("Native structure activation cannot be negative");
+        }
+        iris$structureActivation = activation;
+    }
+
+    @Override
+    public byte[] iris$getNaturalTerrain() {
+        return iris$naturalTerrain == null ? null : iris$naturalTerrain.clone();
+    }
+
+    @Override
+    public void iris$setNaturalTerrain(byte[] receipt) {
+        iris$naturalTerrain = receipt == null ? null : receipt.clone();
+    }
+
+    @Inject(method = "parse", at = @At("RETURN"))
+    private static void iris$parseTerrain(LevelHeightAccessor height, PalettedContainerFactory containers,
+                                          CompoundTag tag, CallbackInfoReturnable<SerializableChunkData> callback) {
+        SerializableChunkData parsed = callback.getReturnValue();
+        if (parsed != null) {
+            ((NativeTerrainReceiptHolder) (Object) parsed).iris$setStructureActivation(
+                    tag.getLongOr(NativeTerrainReceipt.STRUCTURE_ACTIVATION_KEY, 0));
+            ((NativeTerrainReceiptHolder) (Object) parsed).iris$setNaturalTerrain(
+                    tag.getByteArray(NativeTerrainReceipt.NBT_KEY).orElse(null));
+        }
+    }
+
+    @Inject(method = "copyOf", at = @At("RETURN"))
+    private static void iris$copyTerrain(ServerLevel level, ChunkAccess chunk,
+                                         CallbackInfoReturnable<SerializableChunkData> callback) {
+        ((NativeTerrainReceiptHolder) (Object) callback.getReturnValue()).iris$setStructureActivation(
+                ModdedNativeTerrainReceipts.structureActivation(chunk));
+        ((NativeTerrainReceiptHolder) (Object) callback.getReturnValue()).iris$setNaturalTerrain(
+                ModdedNativeTerrainReceipts.get(chunk));
+    }
+
+    @Inject(method = "read", at = @At("RETURN"))
+    private void iris$restoreTerrain(ServerLevel level, PoiManager points, RegionStorageInfo storage, ChunkPos position,
+                                     CallbackInfoReturnable<ProtoChunk> callback) {
+        ModdedNativeTerrainReceipts.set(callback.getReturnValue(), iris$naturalTerrain);
+        ModdedNativeTerrainReceipts.setStructureActivation(callback.getReturnValue(), iris$structureActivation);
+    }
+
+    @Inject(method = "write", at = @At("RETURN"))
+    private void iris$writeTerrain(CallbackInfoReturnable<CompoundTag> callback) {
+        if (iris$structureActivation > 0) {
+            callback.getReturnValue().putLong(NativeTerrainReceipt.STRUCTURE_ACTIVATION_KEY, iris$structureActivation);
+        }
+        if (iris$naturalTerrain != null) {
+            callback.getReturnValue().putByteArray(NativeTerrainReceipt.NBT_KEY, iris$naturalTerrain.clone());
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/mixin/WorldGenerationWriteGuardMixin.java

@@ -0,0 +1,25 @@
+package art.arcane.iris.modded.mixin;
+
+import art.arcane.iris.modded.IrisModdedChunkGenerator;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.WorldGenRegion;
+import net.minecraft.world.level.chunk.status.ChunkStatus;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
+
+@Mixin(WorldGenRegion.class)
+public abstract class WorldGenerationWriteGuardMixin {
+    @Inject(method = "ensureCanWrite", at = @At("RETURN"), cancellable = true)
+    private void iris$guardCompletedTerrain(BlockPos position, CallbackInfoReturnable<Boolean> result) {
+        WorldGenRegion region = (WorldGenRegion) (Object) this;
+        if (result.getReturnValue() && region.getLevel().getChunkSource().getGenerator()
+                instanceof IrisModdedChunkGenerator generator
+                && region.getChunk(position.getX() >> 4, position.getZ() >> 4)
+                .getPersistedStatus().isOrAfter(ChunkStatus.FULL)
+                && !generator.allowsNativeChunkWrite(position.getX() >> 4, position.getZ() >> 4)) {
+            result.setReturnValue(false);
+        }
+    }
+}

adapters/modded-common/src/main/java/art/arcane/iris/modded/service/ModdedStudioHotloadService.java

@@ -23,6 +23,10 @@ import art.arcane.iris.core.gui.PregeneratorJob;
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.tools.WorldMaintenance;
 import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.modded.ModdedSavedTerrainCapture;
+
+import java.util.concurrent.CompletableFuture;
 import art.arcane.iris.engine.framework.EnginePlatformHooks;
 import art.arcane.iris.engine.framework.NativeStructureVolume;
 import art.arcane.iris.engine.object.IrisDimension;
@@ -64,6 +68,16 @@ public final class ModdedStudioHotloadService implements ModdedTickableService,
     private volatile ExecutorService executor;
     private long lastPollAt;
 
+    @Override
+    public CompletableFuture<Void> flushSavedTerrainCapture(Engine engine) {
+        return ModdedSavedTerrainCapture.flush(engine);
+    }
+
+    @Override
+    public CompletableFuture<SavedTerrainChunk> captureSavedTerrainChunk(Engine engine, int chunkX, int chunkZ) {
+        return ModdedSavedTerrainCapture.capture(engine, chunkX, chunkZ);
+    }
+
     @Override
     public void onEnable() {
         if (executor != null) {

adapters/modded-common/src/main/resources/irisworldgen.entity.mixins.json

@@ -4,6 +4,11 @@
   "package": "art.arcane.iris.modded.mixin",
   "compatibilityLevel": "JAVA_21",
   "mixins": [
+    "WorldGenerationWriteGuardMixin",
+    "ChunkMapTerrainReceiptAccess",
+    "ChunkTerrainReceiptMixin",
+    "LevelChunkTerrainReceiptMixin",
+    "SerializableTerrainReceiptMixin",
     "EntityPersistenceMixin",
     "LivingEntityLootMixin",
     "MobAwarenessMixin",

adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedForcedDatapackTest.java

@@ -19,6 +19,16 @@
 package art.arcane.iris.modded;
 
 import art.arcane.volmlib.util.collection.KSet;
+import art.arcane.iris.core.nms.datapack.v1217.DataFixerV1217;
+import art.arcane.iris.engine.history.GenerationEpochContractFactory;
+import art.arcane.iris.engine.history.GenerationRegistryContract;
+import art.arcane.iris.engine.history.GenerationRegistryContractFactory;
+import art.arcane.iris.engine.object.IrisCustomBiomeAliasResolver;
+import art.arcane.iris.engine.object.IrisDimension;
+import art.arcane.iris.engine.object.IrisDimensionType;
+import art.arcane.iris.spi.PlatformGenerationRegistry;
+import java.lang.reflect.Constructor;
+import java.util.Set;
 import org.junit.Test;
 
 import java.io.IOException;
@@ -39,6 +49,33 @@ import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public class ModdedForcedDatapackTest {
+    @Test
+    public void retainedDimensionSourceRendersBeforeNativeRegistryExists() throws Exception {
+        DataFixerV1217 fixer = new DataFixerV1217();
+        IrisDimensionType type = new IrisDimension().getDimensionType();
+        String source = type.toJson(fixer);
+        GenerationRegistryContract.PhysicalResourceKey key = new GenerationRegistryContract.PhysicalResourceKey(
+                GenerationRegistryContractFactory.DIMENSION_TYPE_REGISTRY, "iris:test_type");
+        GenerationRegistryContract.GeneratedSource saved = new GenerationRegistryContract.GeneratedSource(
+                GenerationRegistryContractFactory.DIMENSION_TYPE_EFFECTIVE_SOURCE_SCHEMA,
+                GenerationEpochContractFactory.fingerprintDimensionType(type),
+                GenerationEpochContractFactory.dimensionTypeSemanticJson(type), "test-renderer",
+                GenerationRegistryContractFactory.fingerprintDefinition(
+                        key, PlatformGenerationRegistry.Definition.exactJson(source), "generated"), source);
+        GenerationRegistryContract contract = GenerationRegistryContract.fromDefinitionsAndGeneratedSources(
+                Map.of(key, GenerationRegistryContractFactory.fingerprintGeneratedSemantic(key, saved)),
+                Map.of(key, saved));
+        Class<?> stageType = Class.forName(ModdedForcedDatapack.class.getName() + "$PackStageContext");
+        Constructor<?> constructor = stageType.getDeclaredConstructor(Path.class, String.class, String.class,
+                String.class, boolean.class, boolean.class, boolean.class, Set.class, GenerationRegistryContract.class);
+        constructor.setAccessible(true);
+        IrisCustomBiomeAliasResolver resolver = (IrisCustomBiomeAliasResolver) constructor.newInstance(
+                Path.of("retained"), "test", "test", "iris:test_type", false, false, true, Set.of(), contract);
+        assertEquals(source, resolver.generatedSource(key.registryKey(), key.resourceKey(), "{}", fixer));
+        assertThrows(IOException.class, () -> resolver.generatedSource(
+                key.registryKey(), "iris:missing_type", "{}", fixer));
+    }
+
     @Test
     public void packScopedIdsCannotCollideAndHaveReadableLabels() {
         String first = ModdedWorldgenIds.presetRef("overworld", "overworld");

adapters/modded-common/src/test/java/art/arcane/iris/modded/ModdedGenerationHistoryRoutingContractTest.java

@@ -25,7 +25,15 @@ public class ModdedGenerationHistoryRoutingContractTest {
         assertTrue(createHistoryEngine.contains("IrisBoundarySignatureSampler.INSTANCE"));
         assertTrue(createHistoryEngine.contains("getGenerationTransitionWidthBlocks()"));
         assertTrue(createHistoryEngine.contains("router.preloadActiveRuntimes();"));
-        assertBefore(createHistoryEngine, "close(candidate);", "ModdedGenerationHistoryStorage.resolveActive(history)");
+        assertBefore(createHistoryEngine, "history.prepareCurrentGenerator(",
+                "opened = ModdedGenerationHistoryStorage.resolveActive(history)");
+        assertBefore(createHistoryEngine, "opened = ModdedGenerationHistoryStorage.resolveActive(history)",
+                "IrisEngine candidate = buildEngine(level, seed, opened)");
+        String promoted = method(createHistoryEngine,
+                "if (history.activeActivation().activationId() != openedActivationId)");
+        assertBefore(promoted, "close(candidate);", "ModdedGenerationHistoryStorage.resolveActive(history)");
+        assertBefore(promoted, "ModdedGenerationHistoryStorage.resolveActive(history)",
+                "candidate = buildEngine(level, seed, promoted)");
         assertTrue(createHistoryEngine.contains("GenerationHistoryRuntimeRouter.attach("));
         assertTrue(buildEngine.contains("active.packRoot().toFile()"));
         assertTrue(buildEngine.contains("history.paths().activationMantleRoot(activation.activationId())"));
@@ -84,10 +92,16 @@ public class ModdedGenerationHistoryRoutingContractTest {
         assertTrue(fill.contains("generateTerrain(chunk, generationEngine, pos, air, route)"));
         assertTrue(fill.contains("return closeRouteOnCompletion(pipeline, route);"));
         assertTrue(terrain.contains("openHistoryRuntimeScope(route)"));
-        assertBefore(terrain, "generationEngine.generate(", "route.claimGeneratedSemantics();");
+        assertBefore(terrain, "generationEngine.generate(", "writeBlocks(chunk, blocks, dimMinY, height)");
-        assertBefore(terrain, "route.claimGeneratedSemantics();", "return chunk;");
+        assertBefore(terrain, "writeBlocks(chunk, blocks, dimMinY, height)", "route.claimGeneratedSemantics(");
+        assertTrue(terrain.contains("chunk.getBlockState(position.set(x, dimMinY + y, z))"));
+        assertTrue(terrain.contains("state.isAir() || state.liquid()"));
+        assertBefore(terrain, "route.claimGeneratedSemantics(", "ModdedNativeTerrainReceipts.persist(chunk, route)");
+        assertBefore(terrain, "ModdedNativeTerrainReceipts.persist(chunk, route)", "return chunk;");
         assertTrue(completion.contains("pipeline.whenComplete("));
         assertTrue(completion.contains("route.close();"));
+        assertBefore(completion, "pipeline.whenComplete(", "route.detachThread()");
+        assertBefore(completion, "route.detachThread()", "return completion;");
     }
 
     @Test
@@ -108,7 +122,7 @@ public class ModdedGenerationHistoryRoutingContractTest {
     }
 
     @Test
-    public void discreteStagesResumeIncompleteHistoricalChunksAndRejectTransitionOwnership() throws IOException {
+    public void pendingNativeStagesPreserveSavedStartsAndGuardNewFeatureFootprints() throws IOException {
         String generator = source("IrisModdedChunkGenerator.java");
         String discrete = method(generator, "private boolean allowsRoutedDiscreteGeneration(");
         String decoration = method(generator, "public void applyBiomeDecoration(");
@@ -117,19 +131,28 @@ public class ModdedGenerationHistoryRoutingContractTest {
         String nativeStage = source("ModdedNativeStructureStage.java");
         String adjust = method(nativeStage, "void adjustGeneratedStructures(");
         String place = method(nativeStage, "void placeVanillaStructures(");
+        String savedStart = method(nativeStage, "private boolean isHistoricalStructureStart(");
 
         assertTrue(discrete.contains("chunk.getPersistedStatus().isOrAfter(stage)"));
         assertFalse(discrete.contains("router.history().activeActivation().activationId()"));
         assertFalse(discrete.contains("return true;"));
         assertTrue(discrete.contains("allowsNewGenerationChunk("));
+        assertTrue(discrete.contains("NativeGenerationWriteGuard.allowsPendingStage(current, chunk, stage)"));
         assertTrue(decoration.contains("ChunkStatus.FEATURES"));
         assertTrue(structures.contains("ChunkStatus.STRUCTURE_STARTS"));
         assertTrue(mobs.contains("ChunkStatus.SPAWN"));
-        assertBefore(decoration, "allowsRoutedDiscreteGeneration(", "nativeStructures.placeVanillaStructures(");
+        assertBefore(decoration, "chunk.getPersistedStatus().isOrAfter(ChunkStatus.FEATURES)",
+                "nativeStructures.placeVanillaStructures(");
+        assertBefore(decoration, "nativeStructures.placeVanillaStructures(", "allowsRoutedDiscreteGeneration(");
+        assertBefore(decoration, "allowsRoutedDiscreteGeneration(", "importedFeatures.run(");
+        assertBefore(decoration, "NativeGenerationWriteGuard.allowsDecoration(", "importedFeatures.run(");
         assertBefore(structures, "allowsRoutedDiscreteGeneration(", "super.createStructures(");
         assertBefore(mobs, "allowsRoutedDiscreteGeneration(", "NaturalSpawner.spawnMobsForChunkGeneration(");
         assertBefore(adjust, "allowsNewGenerationFootprint(", "recordWorldCheckStructureShift(");
-        assertTrue(place.contains("allowsNewGenerationFootprint("));
+        assertBefore(place, "!isHistoricalStructureStart(current, world, start)", "allowsNewGenerationFootprint(");
+        assertTrue(savedStart.contains("world.getChunk(origin.x(), origin.z(), ChunkStatus.EMPTY, false)"));
+        assertTrue(savedStart.contains("ModdedNativeTerrainReceipts.structureActivation(source)"));
+        assertBefore(structures, "super.createStructures(", "ModdedNativeTerrainReceipts.persistStructureActivation(");
     }
 
     private static void assertRuntimeRoute(String source, String signature) {

adapters/neoforge/build.gradle

@@ -26,7 +26,7 @@ plugins {
     alias(libs.plugins.shadow)
 }
 
-apply from: file('../../gradle/modded-generation-kernel-seals.gradle')
+apply from: file('../../gradle/modded-generation-build-revision.gradle')
 
 Properties rootProperties = new Properties()
 file('../../gradle.properties').withInputStream { InputStream stream -> rootProperties.load(stream) }

build.gradle

@@ -72,7 +72,7 @@ String fabricArtifactName = irisArtifactName('Fabric', "${minecraftVersion}+${lo
 String forgeArtifactName = irisArtifactName('Forge', "${minecraftVersion}+${loaderDisplayVersion(forgeVersion)}")
 String neoForgeArtifactName = irisArtifactName('NeoForge', "${minecraftVersion}+${loaderDisplayVersion(neoForgeVersion)}")
 File pluginOutDirectory = layout.projectDirectory.dir('../PluginOuts').asFile
-long maximumBukkitArtifactBytes = 7_500_000L
+long maximumBukkitArtifactBytes = 8_000_000L
 apply plugin: ApiGenerator
 
 // Where `buildAll` drops the per-platform jars for a local test server. Use the approved sibling
@@ -113,6 +113,7 @@ nmsBindings.each { key, value ->
             compileOnly(rootProject.libs.annotations)
             compileOnly(rootProject.libs.byteBuddy.core)
             testImplementation('junit:junit:4.13.2')
+            testImplementation('org.mockito:mockito-core:5.23.0')
             testImplementation(project(':core'))
             testCompileOnly(volmLibCoordinate) {
                 transitive = false
@@ -427,7 +428,7 @@ tasks.named('neoforgeJar').configure {
 
 List<String> commonModdedArtifactEntries = [
     'META-INF/iris/generation-kernels/catalog.tsv',
-    'META-INF/iris/generation-kernels/abi-1.seal',
+    'META-INF/iris/generation-kernels/abi-1.revision',
     'art/arcane/iris/engine/IrisEngine.class',
     'art/arcane/iris/spi/IrisPlatform.class',
     'art/arcane/volmlib/util/mantle/io/Lz4IOWorkerCodecSupport.class',
@@ -533,7 +534,7 @@ tasks.register('verifyModdedArtifacts') {
 // them, so a shadowJar exclude that drops one is silent until a server hits that path.
 List<String> requiredBukkitArtifactEntries = [
     'META-INF/iris/generation-kernels/catalog.tsv',
-    'META-INF/iris/generation-kernels/abi-1.seal',
+    'META-INF/iris/generation-kernels/abi-1.revision',
     'plugin.yml',
     'paper-plugin.yml',
     'slimjar.dat',

buildSrc/src/main/java/art/arcane/iris/buildtools/GenerationBuildRevision.java

@@ -24,18 +24,18 @@ import java.util.stream.Stream;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
-public final class GenerationKernelSeal {
+public final class GenerationBuildRevision {
-    public static final String FORMAT = "iris-generation-kernel-seal-v1";
+    public static final String FORMAT = "iris-generation-build-revision-v1";
     private static final Pattern HASH = Pattern.compile("[0-9a-f]{64}");
-    private static final long MAXIMUM_SEAL_BYTES = 8L * 1024L * 1024L;
+    private static final long MAXIMUM_REVISION_BYTES = 8L * 1024L * 1024L;
     private static final int MAXIMUM_ENTRIES = 30_000;
 
-    private GenerationKernelSeal() {
+    private GenerationBuildRevision() {
     }
 
     public static void main(String[] arguments) throws IOException {
         if (arguments.length < 4 || arguments.length % 2 != 0 || !arguments[0].equals("verify-dependencies")) {
-            throw new IllegalArgumentException("Expected verify-dependencies <seal> <identity> <artifact> pairs.");
+            throw new IllegalArgumentException("Expected verify-dependencies <revision> <identity> <artifact> pairs.");
         }
         Map<String, Path> dependencies = new TreeMap<>();
         for (int index = 2; index < arguments.length; index += 2) {
@@ -46,8 +46,8 @@ public final class GenerationKernelSeal {
         verifyDependencySubset(Path.of(arguments[1]), dependencies);
     }
 
-    public static void verifyDependencySubset(Path seal, Map<String, Path> dependencies) throws IOException {
+    public static void verifyDependencySubset(Path revision, Map<String, Path> dependencies) throws IOException {
-        SourceManifest expected = read(seal);
+        SourceManifest expected = read(revision);
         for (Map.Entry<String, String> dependency : dependencyHashes(dependencies).entrySet()) {
             if (!Objects.equals(expected.dependencies().get(dependency.getKey()), dependency.getValue())) {
                 throw new IOException("Resolved platform dependency does not match generation ABI " + expected.abi()
@@ -75,7 +75,7 @@ public final class GenerationKernelSeal {
             AlgorithmVersion algorithms = new AlgorithmVersion(positive(current[2]), positive(current[3]));
             SourceManifest selected = manifests.get(currentAbi);
             if (selected == null || !selected.algorithms().contains(algorithms)) {
-                throw new IllegalArgumentException("Current generation version has no matching sealed factory.");
+                throw new IllegalArgumentException("Current generation version has no matching build factory.");
             }
             TreeSet<Integer> registered = new TreeSet<>();
             int previous = 0;
@@ -92,7 +92,7 @@ public final class GenerationKernelSeal {
                 registered.add(abi);
             }
             if (!registered.equals(manifests.keySet())) {
-                throw new IllegalArgumentException("Kernel catalog must register exactly the retained sealed kernels.");
+                throw new IllegalArgumentException("Kernel catalog must register exactly the packaged kernels.");
             }
         } catch (IllegalArgumentException failure) {
             throw new IOException("Invalid generation kernel catalog.", failure);
@@ -116,33 +116,32 @@ public final class GenerationKernelSeal {
                 sourceHashes, dependencyHashes(dependencies));
     }
 
-    public static void verify(Path repository, Path seal, Map<String, Path> dependencies) throws IOException {
+    public static void verifySnapshot(Path repository, Path revision, Map<String, Path> dependencies) throws IOException {
-        SourceManifest expected = read(seal);
+        SourceManifest expected = read(revision);
         SourceManifest actual = capture(new CaptureOptions(repository, expected.abi(), expected.factoryClass(), expected.algorithms(),
                 expected.roots(), expected.exclusions()), dependencies);
         List<String> failures = new ArrayList<>();
         differences("source", expected.sources(), actual.sources(), failures);
         differences("dependency", expected.dependencies(), actual.dependencies(), failures);
         if (!failures.isEmpty()) {
-            throw new IOException("Generation ABI " + expected.abi() + " no longer matches its sealed implementation:\n"
+            throw new IOException("Generation build inputs changed after revision capture:\n"
-                    + String.join("\n", failures)
+                    + String.join("\n", failures));
-                    + "\nRetain this kernel's implementation and add a separately versioned kernel for changed generation.");
         }
     }
 
-    public static void writeNew(Path destination, SourceManifest manifest) throws IOException {
+    public static void write(Path destination, SourceManifest manifest) throws IOException {
         Files.createDirectories(destination.toAbsolutePath().getParent());
         Files.writeString(destination, encode(manifest), StandardCharsets.UTF_8,
-                StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE);
+                StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.WRITE);
     }
 
     public static SourceManifest read(Path path) throws IOException {
-        if (!Files.isRegularFile(path, LinkOption.NOFOLLOW_LINKS) || Files.size(path) > MAXIMUM_SEAL_BYTES) {
+        if (!Files.isRegularFile(path, LinkOption.NOFOLLOW_LINKS) || Files.size(path) > MAXIMUM_REVISION_BYTES) {
-            throw new IOException("Missing or oversized generation kernel seal: " + path);
+            throw new IOException("Missing or oversized generation build revision: " + path);
         }
         List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
         if (lines.size() < 4 || !FORMAT.equals(lines.getFirst()) || lines.size() > MAXIMUM_ENTRIES) {
-            throw new IOException("Invalid generation kernel seal: " + path);
+            throw new IOException("Invalid generation build revision: " + path);
         }
         int abi = 0;
         String factory = null;
@@ -155,7 +154,7 @@ public final class GenerationKernelSeal {
             for (int index = 1; index < lines.size(); index++) {
                 String[] entry = lines.get(index).split("\t", -1);
                 if (entry.length < 2 || entry.length > 3) {
-                    throw new IllegalArgumentException("Invalid seal entry.");
+                    throw new IllegalArgumentException("Invalid revision entry.");
                 }
                 switch (entry[0]) {
                     case "abi" -> {
@@ -180,16 +179,16 @@ public final class GenerationKernelSeal {
                     case "exclude" -> addPath(exclusions, entry);
                     case "source" -> addHash(sources, entry, true);
                     case "dependency" -> addHash(dependencies, entry, false);
-                    default -> throw new IllegalArgumentException("Unknown generation kernel seal entry.");
+                    default -> throw new IllegalArgumentException("Unknown generation build revision entry.");
                 }
             }
             SourceManifest manifest = new SourceManifest(abi, factory, algorithms, roots, exclusions, sources, dependencies);
             if (!Files.readString(path, StandardCharsets.UTF_8).equals(encode(manifest))) {
-                throw new IllegalArgumentException("Generation kernel seal is not canonical.");
+                throw new IllegalArgumentException("Generation build revision is not canonical.");
             }
             return manifest;
         } catch (RuntimeException failure) {
-            throw new IOException("Invalid generation kernel seal: " + path, failure);
+            throw new IOException("Invalid generation build revision: " + path, failure);
         }
     }
 
@@ -352,11 +351,11 @@ public final class GenerationKernelSeal {
 
     private static void addHash(Map<String, String> hashes, String[] entry, boolean path) {
         if (entry.length != 3 || !HASH.matcher(entry[2]).matches()) {
-            throw new IllegalArgumentException("Invalid sealed hash.");
+            throw new IllegalArgumentException("Invalid revision hash.");
         }
         String key = path ? relative(entry[1]) : token(entry[1]);
         if (hashes.putIfAbsent(key, entry[2]) != null) {
-            throw new IllegalArgumentException("Duplicate sealed entry.");
+            throw new IllegalArgumentException("Duplicate revision entry.");
         }
     }
 
@@ -377,9 +376,9 @@ public final class GenerationKernelSeal {
     }
 
     private static String token(String value) {
-        String required = Objects.requireNonNull(value, "seal token");
+        String required = Objects.requireNonNull(value, "revision token");
         if (required.isBlank() || required.chars().anyMatch(Character::isWhitespace)) {
-            throw new IllegalArgumentException("Invalid generation seal token.");
+            throw new IllegalArgumentException("Invalid generation revision token.");
         }
         return required;
     }
@@ -442,7 +441,7 @@ public final class GenerationKernelSeal {
             sources = Map.copyOf(sources);
             dependencies = Map.copyOf(dependencies);
             if (sources.isEmpty() || dependencies.isEmpty() || sources.size() + dependencies.size() > MAXIMUM_ENTRIES) {
-                throw new IllegalArgumentException("Invalid generation kernel seal entry count.");
+                throw new IllegalArgumentException("Invalid generation build revision entry count.");
             }
         }
     }

buildSrc/src/main/java/art/arcane/iris/buildtools/GenerationRevisionScope.java

@@ -0,0 +1,57 @@
+package art.arcane.iris.buildtools;
+
+import java.nio.file.Path;
+import java.util.List;
+
+public final class GenerationRevisionScope {
+    private static final List<String> SOURCE_ROOTS = List.of(
+            "lombok.config",
+            "core/agent/build.gradle",
+            "core/agent/src/main/java",
+            "core/src/main/java",
+            "spi/src/main/java",
+            "adapters/bukkit/plugin/src/main/java",
+            "adapters/bukkit/nms/v26_2_R1/src/main/java",
+            "adapters/minecraft-common/src/main/java",
+            "adapters/modded-common/src/main/java",
+            "adapters/client-common/src/main/java",
+            "adapters/fabric/src/main/java",
+            "adapters/forge/src/main/java",
+            "adapters/neoforge/src/main/java"
+    );
+    private static final List<String> OPERATIONAL_EXCLUSIONS = List.of(
+            "core/src/main/java/art/arcane/iris/engine/EngineDiagnostics.java",
+            "core/src/main/java/art/arcane/iris/engine/EngineMetricsReport.java",
+            "core/src/main/java/art/arcane/iris/core/IrisStartupValidation.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/IrisSafeguard.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/Mode.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/task/Task.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/task/Tasks.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/task/Diagnostic.java",
+            "core/src/main/java/art/arcane/iris/core/safeguard/task/ValueWithDiagnostics.java",
+            "core/src/main/java/art/arcane/iris/core/splash/IrisSplashRenderer.java",
+            "adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/NmsWorldLifecycle.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandDeveloper.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandPregen.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandIris.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandJigsaw.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandStudio.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandObject.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/PaperCommandRegistrar.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandPack.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandStructure.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandWhat.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandFind.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandEdit.java",
+            "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/CommandDatapack.java"
+    );
+
+    private GenerationRevisionScope() {
+    }
+
+    public static GenerationBuildRevision.CaptureOptions current(Path repository) {
+        return new GenerationBuildRevision.CaptureOptions(repository, 1,
+                "art.arcane.iris.engine.history.GenerationKernelV1",
+                List.of(new GenerationBuildRevision.AlgorithmVersion(1, 1)), SOURCE_ROOTS, OPERATIONAL_EXCLUSIONS);
+    }
+}

buildSrc/src/test/java/GenerationBuildRevisionTest.java

@@ -1,4 +1,4 @@
-import art.arcane.iris.buildtools.GenerationKernelSeal;
+import art.arcane.iris.buildtools.GenerationBuildRevision;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
@@ -17,20 +17,20 @@ import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
-public class GenerationKernelSealTest {
+public class GenerationBuildRevisionTest {
     @Rule
     public final TemporaryFolder temporary = new TemporaryFolder();
 
     @Test
     public void verifiesUnchangedSourceAndCanonicalDependencyContents() throws Exception {
         Fixture fixture = fixture();
-        GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies());
+        GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
-        String original = GenerationKernelSeal.artifactHash(fixture.dependency());
+        String original = GenerationBuildRevision.artifactHash(fixture.dependency());
         artifact(fixture.dependency(), "same code", "another version", 1_700_000_000_000L);
-        assertEquals(original, GenerationKernelSeal.artifactHash(fixture.dependency()));
+        assertEquals(original, GenerationBuildRevision.artifactHash(fixture.dependency()));
-        GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies());
+        GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
-        assertEquals(GenerationKernelSeal.fingerprint(GenerationKernelSeal.read(fixture.seal())),
+        assertEquals(GenerationBuildRevision.fingerprint(GenerationBuildRevision.read(fixture.revision())),
-                GenerationKernelSeal.fingerprint(GenerationKernelSeal.capture(fixture.options(), fixture.dependencies())));
+                GenerationBuildRevision.fingerprint(GenerationBuildRevision.capture(fixture.options(), fixture.dependencies())));
     }
 
     @Test
@@ -39,120 +39,118 @@ public class GenerationKernelSealTest {
         Path source = fixture.root().resolve("generation/Noise.java");
         Files.writeString(source, "class Noise { int value = 2; }");
         assertTrue(assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()))
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()))
                 .getMessage().contains("source changed"));
         Files.writeString(source, "class Noise { int value = 1; }");
         Path added = fixture.root().resolve("generation/Added.java");
         Files.writeString(added, "class Added {}");
         assertTrue(assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()))
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()))
                 .getMessage().contains("source added"));
         Files.delete(added);
         Files.delete(source);
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()));
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()));
     }
 
     @Test
     public void rejectsChangedAddedAndDeletedDependencies() throws Exception {
         Fixture fixture = fixture();
-        String original = GenerationKernelSeal.artifactHash(fixture.dependency());
+        String original = GenerationBuildRevision.artifactHash(fixture.dependency());
         artifact(fixture.dependency(), "changed code", "same version", 0L);
-        assertNotEquals(original, GenerationKernelSeal.artifactHash(fixture.dependency()));
+        assertNotEquals(original, GenerationBuildRevision.artifactHash(fixture.dependency()));
         assertTrue(assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()))
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()))
                 .getMessage().contains("dependency changed"));
         artifact(fixture.dependency(), "same code", "same version", 0L);
-        assertThrows(IOException.class, () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(),
+        assertThrows(IOException.class, () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(),
                 Map.of("math", fixture.dependency(), "new-math", fixture.dependency())));
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), Map.of()));
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), Map.of()));
     }
 
     @Test
     public void rejectsMultiReleaseManifestChanges() throws Exception {
         Fixture fixture = fixture();
-        String original = GenerationKernelSeal.artifactHash(fixture.dependency());
+        String original = GenerationBuildRevision.artifactHash(fixture.dependency());
         artifact(fixture.dependency(), "same code", "same version\r\nMulti-Release: true", 0L);
-        assertNotEquals(original, GenerationKernelSeal.artifactHash(fixture.dependency()));
+        assertNotEquals(original, GenerationBuildRevision.artifactHash(fixture.dependency()));
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()));
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()));
     }
 
     @Test
     public void rejectsAgentEntrypointAndCapabilityChanges() throws Exception {
         Fixture fixture = fixture();
-        String original = GenerationKernelSeal.artifactHash(fixture.dependency());
+        String original = GenerationBuildRevision.artifactHash(fixture.dependency());
         for (String attribute : List.of("Agent-Class", "Premain-Class", "Launcher-Agent-Class", "Boot-Class-Path",
                 "Can-Redefine-Classes", "Can-Retransform-Classes", "Can-Set-Native-Method-Prefix")) {
             artifact(fixture.dependency(), "same code", "same version\r\n" + attribute + ": changed", 0L);
-            assertNotEquals(attribute, original, GenerationKernelSeal.artifactHash(fixture.dependency()));
+            assertNotEquals(attribute, original, GenerationBuildRevision.artifactHash(fixture.dependency()));
             assertThrows(IOException.class,
-                    () -> GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies()));
+                    () -> GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies()));
         }
     }
 
     @Test
-    public void sealsExplicitAgentBuildInputsAndExecutableSources() throws Exception {
+    public void capturesExplicitAgentBuildInputsAndExecutableSources() throws Exception {
         Fixture fixture = fixture();
         Path agentSource = fixture.root().resolve("agent/src/main/java/Installer.java");
         Path agentBuild = fixture.root().resolve("agent/build.gradle");
         Files.createDirectories(agentSource.getParent());
         Files.writeString(agentSource, "class Installer {}");
         Files.writeString(agentBuild, "plugins { id 'java' }");
-        GenerationKernelSeal.CaptureOptions options = new GenerationKernelSeal.CaptureOptions(
+        GenerationBuildRevision.CaptureOptions options = new GenerationBuildRevision.CaptureOptions(
-                fixture.root(), 1, "example.KernelV1", List.of(new GenerationKernelSeal.AlgorithmVersion(1, 1)),
+                fixture.root(), 1, "example.KernelV1", List.of(new GenerationBuildRevision.AlgorithmVersion(1, 1)),
                 List.of("generation", "agent/build.gradle", "agent/src/main/java"), List.of("generation/kernels"));
-        Path seal = fixture.root().resolve("agent.seal");
+        Path revision = fixture.root().resolve("agent.revision");
-        GenerationKernelSeal.writeNew(seal, GenerationKernelSeal.capture(options, fixture.dependencies()));
+        GenerationBuildRevision.write(revision, GenerationBuildRevision.capture(options, fixture.dependencies()));
-        GenerationKernelSeal.verify(fixture.root(), seal, fixture.dependencies());
+        GenerationBuildRevision.verifySnapshot(fixture.root(), revision, fixture.dependencies());
         Files.writeString(agentBuild, "plugins { id 'application' }");
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), seal, fixture.dependencies()));
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), revision, fixture.dependencies()));
         Files.writeString(agentBuild, "plugins { id 'java' }");
         Files.writeString(agentSource, "class Installer { boolean defers; }");
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verify(fixture.root(), seal, fixture.dependencies()));
+                () -> GenerationBuildRevision.verifySnapshot(fixture.root(), revision, fixture.dependencies()));
     }
 
     @Test
     public void checksTheActualPlatformDependencySubset() throws Exception {
         Fixture fixture = fixture();
-        GenerationKernelSeal.verifyDependencySubset(fixture.seal(), fixture.dependencies());
+        GenerationBuildRevision.verifyDependencySubset(fixture.revision(), fixture.dependencies());
-        assertThrows(IOException.class, () -> GenerationKernelSeal.verifyDependencySubset(fixture.seal(),
+        assertThrows(IOException.class, () -> GenerationBuildRevision.verifyDependencySubset(fixture.revision(),
                 Map.of("unknown-library", fixture.dependency())));
         artifact(fixture.dependency(), "platform override", "same version", 0L);
         assertThrows(IOException.class,
-                () -> GenerationKernelSeal.verifyDependencySubset(fixture.seal(), fixture.dependencies()));
+                () -> GenerationBuildRevision.verifyDependencySubset(fixture.revision(), fixture.dependencies()));
     }
 
     @Test
-    public void catalogCannotSelectAnUnsealedAlgorithmTuple() throws Exception {
+    public void catalogRequiresAPackagedAlgorithmTuple() throws Exception {
         Fixture fixture = fixture();
         Path catalog = fixture.root().resolve("catalog.tsv");
         Files.writeString(catalog, "iris-generation-kernel-catalog-v1\ncurrent\t1\t1\t1\nkernel\t1\n");
-        Map<Integer, GenerationKernelSeal.SourceManifest> manifests = Map.of(1, GenerationKernelSeal.read(fixture.seal()));
+        Map<Integer, GenerationBuildRevision.SourceManifest> manifests = Map.of(1, GenerationBuildRevision.read(fixture.revision()));
-        GenerationKernelSeal.verifyCatalog(catalog, manifests);
+        GenerationBuildRevision.verifyCatalog(catalog, manifests);
         Files.writeString(catalog, "iris-generation-kernel-catalog-v1\ncurrent\t1\t2\t1\nkernel\t1\n");
-        assertThrows(IOException.class, () -> GenerationKernelSeal.verifyCatalog(catalog, manifests));
+        assertThrows(IOException.class, () -> GenerationBuildRevision.verifyCatalog(catalog, manifests));
         Files.writeString(catalog, "iris-generation-kernel-catalog-v1\ncurrent\t1\t1\t1\nkernel\t1\nkernel\t2\n");
-        assertThrows(IOException.class, () -> GenerationKernelSeal.verifyCatalog(catalog, manifests));
+        assertThrows(IOException.class, () -> GenerationBuildRevision.verifyCatalog(catalog, manifests));
     }
 
     @Test
-    public void permitsSeparatelyScopedFutureKernelsWithoutChangingRetainedSeal() throws Exception {
+    public void recapturesChangedGenerationWithoutChangingAbi() throws Exception {
         Fixture fixture = fixture();
-        Path future = fixture.root().resolve("generation/kernels/v2/NewMath.java");
+        String original = GenerationBuildRevision.fingerprint(GenerationBuildRevision.read(fixture.revision()));
-        Files.createDirectories(future.getParent());
+        Files.writeString(fixture.root().resolve("generation/Noise.java"), "class Noise { int value = 9; }");
-        Files.writeString(future, "class NewMath {}");
+        artifact(fixture.dependency(), "new generation code", "new version", 0L);
-        GenerationKernelSeal.verify(fixture.root(), fixture.seal(), fixture.dependencies());
+        GenerationBuildRevision.SourceManifest next = GenerationBuildRevision.capture(fixture.options(), fixture.dependencies());
-        GenerationKernelSeal.SourceManifest next = GenerationKernelSeal.capture(new GenerationKernelSeal.CaptureOptions(
+        GenerationBuildRevision.write(fixture.revision(), next);
-                fixture.root(), 2, "example.KernelV2", List.of(new GenerationKernelSeal.AlgorithmVersion(2, 3)),
+        GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
-                List.of("generation/kernels/v2"), List.of()), fixture.dependencies());
+        assertEquals(1, next.abi());
-        assertNotEquals(GenerationKernelSeal.fingerprint(next),
+        assertNotEquals(original, GenerationBuildRevision.fingerprint(next));
-                GenerationKernelSeal.fingerprint(GenerationKernelSeal.read(fixture.seal())));
+        assertEquals(next, GenerationBuildRevision.read(fixture.revision()));
-        assertThrows(IOException.class,
-                () -> GenerationKernelSeal.writeNew(fixture.seal(), next));
     }
 
     private Fixture fixture() throws Exception {
@@ -161,13 +159,13 @@ public class GenerationKernelSealTest {
         Files.writeString(root.resolve("generation/Noise.java"), "class Noise { int value = 1; }");
         Path dependency = root.resolve("math.jar");
         artifact(dependency, "same code", "same version", 0L);
-        GenerationKernelSeal.CaptureOptions options = new GenerationKernelSeal.CaptureOptions(
+        GenerationBuildRevision.CaptureOptions options = new GenerationBuildRevision.CaptureOptions(
-                root, 1, "example.KernelV1", List.of(new GenerationKernelSeal.AlgorithmVersion(1, 1)),
+                root, 1, "example.KernelV1", List.of(new GenerationBuildRevision.AlgorithmVersion(1, 1)),
                 List.of("generation"), List.of("generation/kernels"));
-        Path seal = root.resolve("abi-1.seal");
+        Path revision = root.resolve("abi-1.revision");
         Map<String, Path> dependencies = Map.of("math", dependency);
-        GenerationKernelSeal.writeNew(seal, GenerationKernelSeal.capture(options, dependencies));
+        GenerationBuildRevision.write(revision, GenerationBuildRevision.capture(options, dependencies));
-        return new Fixture(root, seal, dependency, dependencies, options);
+        return new Fixture(root, revision, dependency, dependencies, options);
     }
 
     private static void artifact(Path path, String content, String version, long timestamp) throws IOException {
@@ -186,7 +184,7 @@ public class GenerationKernelSealTest {
         }
     }
 
-    private record Fixture(Path root, Path seal, Path dependency, Map<String, Path> dependencies,
+    private record Fixture(Path root, Path revision, Path dependency, Map<String, Path> dependencies,
-                           GenerationKernelSeal.CaptureOptions options) {
+                           GenerationBuildRevision.CaptureOptions options) {
     }
 }

buildSrc/src/test/java/GenerationRevisionScopeTest.java

@@ -0,0 +1,163 @@
+import art.arcane.iris.buildtools.GenerationRevisionScope;
+import art.arcane.iris.buildtools.GenerationBuildRevision;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Map;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipOutputStream;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+
+public class GenerationRevisionScopeTest {
+    private static final String ENGINE_ROOT = "core/src/main/java/art/arcane/iris/engine/";
+    private static final String NMS_ROOT = "adapters/bukkit/nms/v26_2_R1/src/main/java/art/arcane/iris/core/nms/v26_2_R1/";
+    private static final String COMMAND_ROOT = "adapters/bukkit/plugin/src/main/java/art/arcane/iris/core/commands/";
+
+    @Rule
+    public final TemporaryFolder temporary = new TemporaryFolder();
+
+    @Test
+    public void operationalChangesPreserveTheGenerationFingerprint() throws Exception {
+        Fixture fixture = fixture();
+        String original = GenerationBuildRevision.fingerprint(GenerationBuildRevision.read(fixture.revision()));
+        for (String exclusion : fixture.options().exclusions()) {
+            if (!exclusion.endsWith(".java")) {
+                continue;
+            }
+            Path operationalSource = fixture.root().resolve(exclusion);
+            write(operationalSource, "class Operational { String message = \"updated\"; }");
+            GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
+            assertEquals(exclusion, original, GenerationBuildRevision.fingerprint(
+                    GenerationBuildRevision.capture(fixture.options(), fixture.dependencies())));
+            Files.delete(operationalSource);
+            GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
+        }
+    }
+
+    @Test
+    public void generationChangesProduceANewBuildRevision() throws Exception {
+        Fixture fixture = fixture();
+        for (String relative : generationSources()) {
+            Path source = fixture.root().resolve(relative);
+            Files.writeString(source, "class Generation { int sample = 2; }");
+            GenerationBuildRevision.SourceManifest changed = GenerationBuildRevision.capture(fixture.options(), fixture.dependencies());
+            assertNotEquals(relative, GenerationBuildRevision.fingerprint(GenerationBuildRevision.read(fixture.revision())),
+                    GenerationBuildRevision.fingerprint(changed));
+            GenerationBuildRevision.write(fixture.revision(), changed);
+            GenerationBuildRevision.verifySnapshot(fixture.root(), fixture.revision(), fixture.dependencies());
+            Files.writeString(source, "class Generation { int sample = 1; }");
+            GenerationBuildRevision.write(fixture.revision(), GenerationBuildRevision.capture(fixture.options(), fixture.dependencies()));
+        }
+    }
+
+    @Test
+    public void newSourcesChangeRevisionAcrossPlatforms() throws Exception {
+        Fixture fixture = fixture();
+        for (String root : fixture.options().roots()) {
+            if (!root.endsWith("/java")) {
+                continue;
+            }
+            assertNewSourceChangesRevision(fixture, root + "/NewSource.java");
+        }
+        assertNewSourceChangesRevision(fixture, ENGINE_ROOT + "NewDiagnostics.java");
+        assertNewSourceChangesRevision(fixture, NMS_ROOT + "NmsWorldLifecycleHelper.java");
+        assertNewSourceChangesRevision(fixture, COMMAND_ROOT + "NewCommand.java");
+        assertNewSourceChangesRevision(fixture, "core/src/main/java/art/arcane/iris/core/safeguard/task/NewTask.java");
+    }
+
+    @Test
+    public void onlyExplicitOperationalFilesAreExcluded() throws Exception {
+        Fixture fixture = fixture();
+        List<String> directoryExclusions = fixture.options().exclusions().stream()
+                .filter(path -> !path.endsWith(".java"))
+                .toList();
+        assertTrue(directoryExclusions.isEmpty());
+        GenerationBuildRevision.SourceManifest manifest = GenerationBuildRevision.read(fixture.revision());
+        for (String relative : generationSources()) {
+            assertTrue(relative, manifest.sources().containsKey(relative));
+        }
+        assertFalse(manifest.sources().containsKey(ENGINE_ROOT + "EngineDiagnostics.java"));
+        assertFalse(manifest.sources().containsKey(NMS_ROOT + "NmsWorldLifecycle.java"));
+        assertFalse(manifest.sources().containsKey(COMMAND_ROOT + "CommandIris.java"));
+    }
+
+    private static void assertNewSourceChangesRevision(Fixture fixture, String relative) throws IOException {
+        Path source = fixture.root().resolve(relative);
+        write(source, "class NewSource {}");
+        GenerationBuildRevision.SourceManifest changed = GenerationBuildRevision.capture(fixture.options(), fixture.dependencies());
+        assertTrue(changed.sources().containsKey(relative));
+        assertNotEquals(GenerationBuildRevision.fingerprint(GenerationBuildRevision.read(fixture.revision())),
+                GenerationBuildRevision.fingerprint(changed));
+        Files.delete(source);
+    }
+
+    private Fixture fixture() throws Exception {
+        Path root = temporary.newFolder().toPath();
+        GenerationBuildRevision.CaptureOptions options = GenerationRevisionScope.current(root);
+        for (String scope : options.roots()) {
+            Path path = root.resolve(scope);
+            if (scope.endsWith("/java")) {
+                Files.createDirectories(path);
+            } else {
+                write(path, "build input");
+            }
+        }
+        for (String relative : generationSources()) {
+            write(root.resolve(relative), "class Generation { int sample = 1; }");
+        }
+        for (String exclusion : options.exclusions()) {
+            if (exclusion.endsWith(".java")) {
+                write(root.resolve(exclusion), "class Operational {}");
+            }
+        }
+        Path dependency = root.resolve("dependency.jar");
+        try (ZipOutputStream output = new ZipOutputStream(Files.newOutputStream(dependency))) {
+            output.putNextEntry(new ZipEntry("generation/Math.class"));
+            output.write("generation dependency".getBytes(StandardCharsets.UTF_8));
+            output.closeEntry();
+        }
+        Map<String, Path> dependencies = Map.of("volmlib", dependency);
+        Path revision = root.resolve("abi-1.revision");
+        GenerationBuildRevision.write(revision, GenerationBuildRevision.capture(options, dependencies));
+        return new Fixture(root, revision, options, dependencies);
+    }
+
+    private static List<String> generationSources() {
+        return List.of(
+                ENGINE_ROOT + "IrisEngine.java",
+                ENGINE_ROOT + "IrisComplex.java",
+                ENGINE_ROOT + "IrisEngineMantle.java",
+                ENGINE_ROOT + "EngineRuntimeBuilder.java",
+                ENGINE_ROOT + "history/GenerationKernelV1.java",
+                ENGINE_ROOT + "object/IrisDimension.java",
+                ENGINE_ROOT + "mode/ModeOverworld.java",
+                "core/src/main/java/art/arcane/iris/core/loader/IrisData.java",
+                "core/src/main/java/art/arcane/iris/core/IrisSettings.java",
+                "core/agent/src/main/java/GenerationTransformer.java",
+                NMS_ROOT + "NmsGenerationHooks.java",
+                NMS_ROOT + "NmsGenerationRegistry.java",
+                NMS_ROOT + "NMSBinding.java",
+                "spi/src/main/java/art/arcane/iris/spi/PlatformGenerationRegistry.java",
+                "adapters/modded-common/src/main/java/art/arcane/iris/modded/IrisModdedChunkGenerator.java"
+        );
+    }
+
+    private static void write(Path path, String content) throws IOException {
+        Files.createDirectories(path.getParent());
+        Files.writeString(path, content);
+    }
+
+    private record Fixture(Path root, Path revision, GenerationBuildRevision.CaptureOptions options,
+                           Map<String, Path> dependencies) {
+    }
+}

buildSrc/src/test/java/JarCompactorTest.java

@@ -63,7 +63,7 @@ public class JarCompactorTest {
             writeEntry(output, "META-INF/MANIFEST.MF", "Manifest-Version: 1.0\r\nMulti-Release: true\r\n\r\n"
                     .getBytes(StandardCharsets.UTF_8));
             writeEntry(output, "JarCompactorTest.class", classResource.readAllBytes());
-            writeEntry(output, "META-INF/iris/generation-kernels/abi-1.seal", "registry fixture".getBytes(StandardCharsets.UTF_8));
+            writeEntry(output, "META-INF/iris/generation-kernels/abi-1.revision", "registry fixture".getBytes(StandardCharsets.UTF_8));
             writeEntry(output, "example/caf\u00e9.txt", "unicode name".getBytes(StandardCharsets.UTF_8));
             for (int index = 0; index < 100; index++) {
                 writeEntry(output, "example/item-" + index + ".txt", ("value-" + index).getBytes(StandardCharsets.UTF_8));

core/build.gradle

@@ -522,4 +522,4 @@ tasks.named('check').configure {
     dependsOn('bukkitPurityRatchet')
 }
 
-apply from: rootProject.file('gradle/generation-kernel-seals.gradle')
+apply from: rootProject.file('gradle/generation-build-revision.gradle')

core/src/main/java/art/arcane/iris/core/IrisDatapackCompiler.java

@@ -22,6 +22,11 @@ import art.arcane.iris.spi.IrisLogging;
 import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.collection.KSet;
 
+import com.google.gson.JsonObject;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParser;
+
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
@@ -53,7 +58,7 @@ import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
 public final class IrisDatapackCompiler {
-    private static final int INPUT_FINGERPRINT_SCHEMA = 3;
+    private static final int INPUT_FINGERPRINT_SCHEMA = 4;
     private static final int INPUT_BUFFER_BYTES = 64 * 1024;
     private static final int WORLD_PACK_SCAN_DEPTH = 8;
     private static final Pattern REGISTRY_KEY_PATTERN = Pattern.compile("[a-z0-9_.-]+:[a-z0-9/._-]+");
@@ -177,6 +182,9 @@ public final class IrisDatapackCompiler {
                 }
             }
         }
+        for (GenerationRegistryContract contract : retainedRegistryContracts(packRoots)) {
+            updateDigestString(digest, contract.fingerprint());
+        }
         return HexFormat.of().formatHex(digest.digest());
     }
 
@@ -220,6 +228,14 @@ public final class IrisDatapackCompiler {
                 data.close();
             }
         }
+        for (GenerationRegistryContract contract : retainedRegistryContracts(packRoots)) {
+            for (PhysicalResourceKey key : contract.generatedSources().keySet()) {
+                putRegistryRequirement(requirements, registryPath(key) + "/" + key.resourceKey(),
+                        fingerprintContent(GenerationRegistryContractFactory.renderGeneratedSource(contract, key, fixer)));
+            }
+            contract.biomeTags().forEach((biome, tags) ->
+                    biomeTags.computeIfAbsent(biome, ignored -> new TreeSet<>()).addAll(tags));
+        }
         addBiomeTagRequirements(requirements, biomeTags);
         return Map.copyOf(requirements);
     }
@@ -494,11 +510,111 @@ public final class IrisDatapackCompiler {
         }
 
         IrisDimension.writeShared(datapackRoots, height, adjustVanillaHeight);
+        installRetainedRegistrySources(packRoots, datapackRoots, fixer);
         installLevelStemBindings(normalizedBindings, dimensions, datapackRoots);
         validateOutputs(datapackRoots, dimensionCount, normalizedBindings.size());
         return new CompilationResult(packCount, dimensionCount, countBiomes(biomes));
     }
 
+    public static void installRetainedRegistrySources(List<File> packRoots, Collection<File> datapackRoots,
+                                                     IDataFixer fixer) throws IOException {
+        Map<PhysicalResourceKey, String> sources = new TreeMap<>();
+        Map<String, Set<String>> tags = new TreeMap<>();
+        for (GenerationRegistryContract contract : retainedRegistryContracts(packRoots)) {
+            for (PhysicalResourceKey key : contract.generatedSources().keySet()) {
+                String source = GenerationRegistryContractFactory.renderGeneratedSource(contract, key, fixer);
+                String previous = sources.putIfAbsent(key, source);
+                if (previous != null && !JsonParser.parseString(previous).equals(JsonParser.parseString(source))) {
+                    throw new IOException("Conflicting retained registry source for " + key);
+                }
+            }
+            contract.biomeTags().forEach((biome, memberships) -> {
+                for (String tag : memberships) {
+                    tags.computeIfAbsent(tag, ignored -> new TreeSet<>()).add(biome);
+                }
+            });
+        }
+        for (File root : datapackRoots) {
+            for (Map.Entry<PhysicalResourceKey, String> entry : sources.entrySet()) {
+                Path output = registryOutput(root.toPath(), registryPath(entry.getKey()), entry.getKey().resourceKey());
+                if (Files.exists(output)) {
+                    String previous = Files.readString(output, StandardCharsets.UTF_8);
+                    if (!JsonParser.parseString(previous).equals(JsonParser.parseString(entry.getValue()))) {
+                        throw new IOException("Conflicting retained registry output at " + output);
+                    }
+                    continue;
+                }
+                Files.createDirectories(output.getParent());
+                Files.writeString(output, entry.getValue(), StandardCharsets.UTF_8);
+            }
+            for (Map.Entry<String, Set<String>> entry : tags.entrySet()) {
+                writeRetainedBiomeTag(registryOutput(root.toPath(), "tags/worldgen/biome", entry.getKey()), entry.getValue());
+            }
+        }
+    }
+
+    private static void writeRetainedBiomeTag(Path output, Set<String> biomes) throws IOException {
+        Set<String> merged = new TreeSet<>(biomes);
+        if (Files.exists(output)) {
+            JsonObject existing = JsonParser.parseString(Files.readString(output, StandardCharsets.UTF_8)).getAsJsonObject();
+            for (JsonElement value : existing.getAsJsonArray("values")) {
+                merged.add(value.getAsString());
+            }
+        }
+        JsonArray values = new JsonArray();
+        merged.forEach(values::add);
+        JsonObject tag = new JsonObject();
+        tag.addProperty("replace", false);
+        tag.add("values", values);
+        Files.createDirectories(output.getParent());
+        Files.writeString(output, tag.toString(), StandardCharsets.UTF_8);
+    }
+
+    private static Path registryOutput(Path root, String registryPath, String resourceKey) throws IOException {
+        int separator = resourceKey.indexOf(':');
+        Path directory = root.toAbsolutePath().normalize().resolve("data")
+                .resolve(resourceKey.substring(0, separator)).resolve(registryPath);
+        Path output = directory.resolve(resourceKey.substring(separator + 1) + ".json").normalize();
+        if (!output.startsWith(directory)) {
+            throw new IOException("Unsafe retained registry resource key " + resourceKey);
+        }
+        return output;
+    }
+
+    private static String registryPath(PhysicalResourceKey key) {
+        return key.registryKey().substring(key.registryKey().indexOf(':') + 1);
+    }
+
+    private static List<GenerationRegistryContract> retainedRegistryContracts(List<File> packRoots) throws IOException {
+        Map<String, GenerationRegistryContract> contracts = new TreeMap<>();
+        Set<Path> loadedWorlds = new LinkedHashSet<>();
+        for (File pack : packRoots) {
+            Path dimensionRoot = historyDimensionRoot(pack.toPath());
+            if (dimensionRoot == null || !loadedWorlds.add(dimensionRoot)) {
+                continue;
+            }
+            for (GenerationEpoch epoch : GenerationHistory.open(dimensionRoot).manifest().epochs()) {
+                contracts.putIfAbsent(epoch.registryContract().fingerprint(), epoch.registryContract());
+            }
+        }
+        return List.copyOf(contracts.values());
+    }
+
+    private static Path historyDimensionRoot(Path packRoot) {
+        Path pack = packRoot.toAbsolutePath().normalize();
+        Path epoch = pack.getParent();
+        Path epochs = epoch == null ? null : epoch.getParent();
+        Path generation = epochs == null ? null : epochs.getParent();
+        Path iris = generation == null ? null : generation.getParent();
+        if (iris == null || iris.getParent() == null || !"pack".equals(pack.getFileName().toString())
+                || !"epochs".equals(epochs.getFileName().toString())
+                || !"generation".equals(generation.getFileName().toString())
+                || !"iris".equals(iris.getFileName().toString())) {
+            return null;
+        }
+        return iris.getParent();
+    }
+
     private static void installLevelStemBindings(
             List<IrisGeneratorBinding> bindings,
             Map<String, List<DimensionCandidate>> dimensions,
@@ -648,11 +764,9 @@ public final class IrisDatapackCompiler {
                 && (Files.exists(generationRoot, LinkOption.NOFOLLOW_LINKS)
                 || Files.isSymbolicLink(generationRoot))) {
             GenerationHistory history = GenerationHistory.open(worldRoot);
-            for (GenerationEpoch epoch : history.manifest().epochs()) {
+            candidates.add(history.activePackRoot());
-                Path retainedPack = history.paths().packRoot(epoch.epochId());
+            if (history.pendingActivation().isPresent()) {
-                if (hasDimensions(retainedPack)) {
+                candidates.add(history.packRoot(history.pendingActivation().orElseThrow().activationId()));
-                    candidates.add(retainedPack);
-                }
             }
             return true;
         }

core/src/main/java/art/arcane/iris/core/IrisStartupValidation.java

@@ -10,25 +10,50 @@ public final class IrisStartupValidation {
     }
 
     public static synchronized void begin() {
-        snapshot = new Snapshot(true, ValidationState.PENDING, ValidationState.PENDING, List.of(), List.of());
+        snapshot = new Snapshot(true, ValidationState.PENDING, ValidationState.PENDING, List.of(), List.of(), ValidationState.DISABLED, "");
     }
 
     public static synchronized void disable() {
         snapshot = Snapshot.disabled();
     }
 
+    public static synchronized void beginRuntimeValidation() {
+        if (!snapshot.enforced()) {
+            return;
+        }
+        snapshot = new Snapshot(true, snapshot.datapacks(), snapshot.packs(),
+                snapshot.datapackFailures(), snapshot.packFailures(), ValidationState.PENDING, "");
+    }
+
+    public static synchronized void markRuntimeReady() {
+        if (!snapshot.enforced()) {
+            return;
+        }
+        snapshot = new Snapshot(true, snapshot.datapacks(), snapshot.packs(),
+                snapshot.datapackFailures(), snapshot.packFailures(), ValidationState.READY, "");
+    }
+
+    public static synchronized void markRuntimeInvalid(String failure) {
+        if (!snapshot.enforced()) {
+            return;
+        }
+        snapshot = new Snapshot(true, snapshot.datapacks(), snapshot.packs(),
+                snapshot.datapackFailures(), snapshot.packFailures(), ValidationState.INVALID,
+                normalizeFailure(failure, "Iris runtime injection failed. Resolve the startup errors and restart the server."));
+    }
+
     public static synchronized void beginDatapackValidation() {
         if (!snapshot.enforced() || snapshot.datapacks() == ValidationState.RESTART_REQUIRED) {
             return;
         }
-        snapshot = new Snapshot(true, ValidationState.PENDING, snapshot.packs(), List.of(), snapshot.packFailures());
+        snapshot = new Snapshot(true, ValidationState.PENDING, snapshot.packs(), List.of(), snapshot.packFailures(), snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static synchronized void markDatapacksReady() {
         if (!snapshot.enforced() || snapshot.datapacks() == ValidationState.RESTART_REQUIRED) {
             return;
         }
-        snapshot = new Snapshot(true, ValidationState.READY, snapshot.packs(), List.of(), snapshot.packFailures());
+        snapshot = new Snapshot(true, ValidationState.READY, snapshot.packs(), List.of(), snapshot.packFailures(), snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static synchronized void markDatapacksInvalid(String failure) {
@@ -40,7 +65,7 @@ public final class IrisStartupValidation {
                 ValidationState.INVALID,
                 snapshot.packs(),
                 List.of(normalizeFailure(failure, "External datapack validation failed.")),
-                snapshot.packFailures());
+                snapshot.packFailures(), snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static synchronized void requireRestart(String reason) {
@@ -52,14 +77,14 @@ public final class IrisStartupValidation {
                 ValidationState.RESTART_REQUIRED,
                 snapshot.packs(),
                 List.of(normalizeFailure(reason, "A restart is required to load validated datapacks.")),
-                snapshot.packFailures());
+                snapshot.packFailures(), snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static synchronized void markPacksReady() {
         if (!snapshot.enforced()) {
             return;
         }
-        snapshot = new Snapshot(true, snapshot.datapacks(), ValidationState.READY, snapshot.datapackFailures(), List.of());
+        snapshot = new Snapshot(true, snapshot.datapacks(), ValidationState.READY, snapshot.datapackFailures(), List.of(), snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static synchronized void markPacksInvalid(List<String> failures) {
@@ -72,7 +97,7 @@ public final class IrisStartupValidation {
                 .map(failure -> normalizeFailure(failure, "Iris dimension-pack validation failed."))
                 .toList();
         snapshot = new Snapshot(true, snapshot.datapacks(), ValidationState.INVALID,
-                snapshot.datapackFailures(), normalized);
+                snapshot.datapackFailures(), normalized, snapshot.runtime(), snapshot.runtimeFailure());
     }
 
     public static boolean isReady() {
@@ -92,6 +117,7 @@ public final class IrisStartupValidation {
         Snapshot current = snapshot;
         if (force
                 && current.enforced()
+                && isRuntimeReady(current)
                 && current.datapacks() == ValidationState.RESTART_REQUIRED
                 && current.packs() == ValidationState.READY) {
             return Optional.empty();
@@ -103,6 +129,11 @@ public final class IrisStartupValidation {
         if (!current.enforced() || isReady(current)) {
             return Optional.empty();
         }
+        if (!isRuntimeReady(current)) {
+            return Optional.of(current.runtime() == ValidationState.INVALID
+                    ? current.runtimeFailure()
+                    : "Iris is still validating runtime injection.");
+        }
         if (current.datapacks() == ValidationState.RESTART_REQUIRED) {
             return Optional.of(firstFailure(current.datapackFailures(),
                     "Iris installed validated datapacks and requires a restart before the server is safe."));
@@ -131,6 +162,7 @@ public final class IrisStartupValidation {
     public static void requireWorldReplacementStagingReady() {
         Snapshot current = snapshot;
         if (current.enforced()
+                && isRuntimeReady(current)
                 && current.datapacks() == ValidationState.RESTART_REQUIRED
                 && current.packs() == ValidationState.READY) {
             return;
@@ -150,9 +182,14 @@ public final class IrisStartupValidation {
         return failures == null || failures.isEmpty() ? fallback : failures.getFirst();
     }
 
+    private static boolean isRuntimeReady(Snapshot current) {
+        return current.runtime() == ValidationState.DISABLED || current.runtime() == ValidationState.READY;
+    }
+
     private static boolean isReady(Snapshot current) {
         return !current.enforced()
-                || current.datapacks() == ValidationState.READY
+                || isRuntimeReady(current)
+                && current.datapacks() == ValidationState.READY
                 && current.packs() == ValidationState.READY;
     }
 
@@ -169,7 +206,9 @@ public final class IrisStartupValidation {
             ValidationState datapacks,
             ValidationState packs,
             List<String> datapackFailures,
-            List<String> packFailures
+            List<String> packFailures,
+            ValidationState runtime,
+            String runtimeFailure
     ) {
         Snapshot {
             datapackFailures = List.copyOf(datapackFailures);
@@ -177,7 +216,7 @@ public final class IrisStartupValidation {
         }
 
         private static Snapshot disabled() {
-            return new Snapshot(false, ValidationState.DISABLED, ValidationState.DISABLED, List.of(), List.of());
+            return new Snapshot(false, ValidationState.DISABLED, ValidationState.DISABLED, List.of(), List.of(), ValidationState.DISABLED, "");
         }
     }
 }

core/src/main/java/art/arcane/iris/core/gui/ImageMapStudioGUI.java

@@ -143,7 +143,7 @@ public final class ImageMapStudioGUI {
 
     private ImageMapStudioGUI(Engine engine) {
         this.engine = Objects.requireNonNull(engine, "Image Map Studio engine");
-        this.packFolder = engine.getData().getDataFolder();
+        this.packFolder = engine.getPackSource().toFile();
         this.dimensionKey = engine.getDimension().getLoadKey();
         this.boundary = engine.getDimension().getWorldBoundary() == null
                 ? null
@@ -163,7 +163,6 @@ public final class ImageMapStudioGUI {
     }
 
     static void reloadActiveEngine(Engine engine) {
-        engine.getData().getImageMapLoader().clearCache();
         engine.hotloadSilently();
     }
 
@@ -431,9 +430,14 @@ public final class ImageMapStudioGUI {
     }
 
     private void refreshPresets() {
-        String[] keys = engine.getData().getImageMapLoader().getPossibleKeys();
+        IrisData data = IrisData.openRuntime(packFolder);
-        Arrays.sort(keys);
+        try {
-        presetPicker.setModel(new DefaultComboBoxModel<>(keys));
+            String[] keys = data.getImageMapLoader().getPossibleKeys();
+            Arrays.sort(keys);
+            presetPicker.setModel(new DefaultComboBoxModel<>(keys));
+        } finally {
+            data.close();
+        }
     }
 
     private void loadPreset(String key) {

core/src/main/java/art/arcane/iris/core/lifecycle/BukkitPublicBackend.java

@@ -32,9 +32,8 @@ final class BukkitPublicBackend implements WorldLifecycleBackend {
             WorldLifecycleStaging.stageStemGenerator(request.worldName(), request.generator());
         }
 
-        INMS.get().ensureServerLevelInjection();
-
         try {
+            INMS.get().ensureServerLevelInjection();
             World world = creator.createWorld();
             return CompletableFuture.completedFuture(world);
         } catch (Throwable e) {

core/src/main/java/art/arcane/iris/core/loader/IrisData.java

@@ -189,6 +189,26 @@ public class IrisData implements ExclusionStrategy, TypeAdapterFactory {
         return Optional.ofNullable(dataLoaders.get(dataFolder));
     }
 
+    public static void invalidateLoadedAuthoringResources(File source) {
+        Path requested = dataFolderIdentity(Objects.requireNonNull(source, "authoring pack source"));
+        for (Map.Entry<File, IrisData> entry : dataLoaders.entrySet()) {
+            if (dataFolderIdentity(entry.getKey()).equals(requested)) {
+                entry.getValue().invalidateAuthoringResources();
+            }
+        }
+    }
+
+    private synchronized void invalidateAuthoringResources() {
+        if (generationRegistryContract != null) {
+            throw new IllegalStateException("Cannot invalidate an immutable generation pack as an authoring source.");
+        }
+        dump();
+        clearLists();
+        generationPackFingerprint = null;
+        contentGate = null;
+        dimensionCustomBiomeResourceKeys.clear();
+    }
+
     public String customBiomeResourceKey(IrisDimension dimension, IrisBiomeCustom customBiome) {
         IrisDimension requiredDimension = Objects.requireNonNull(dimension, "dimension");
         IrisBiomeCustom requiredBiome = Objects.requireNonNull(customBiome, "customBiome");

core/src/main/java/art/arcane/iris/core/nms/INMSBinding.java

@@ -18,6 +18,8 @@
 
 package art.arcane.iris.core.nms;
 
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import java.util.concurrent.CompletableFuture;
 import art.arcane.iris.core.datapack.DatapackStructureScopeIndex;
 import art.arcane.iris.engine.object.IrisImportedStructureControl;
 import art.arcane.iris.core.lifecycle.WorldLifecycleCaller;
@@ -57,9 +59,19 @@ import org.bukkit.inventory.ItemStack;
 import java.awt.Color;
 import java.util.List;
 import java.util.Set;
-import java.util.concurrent.CompletableFuture;
 
 public interface INMSBinding {
+    default CompletableFuture<Void> flushSavedTerrainCapture(World world) {
+        return CompletableFuture.failedFuture(new UnsupportedOperationException(
+                "Native saved terrain checkpoints are unavailable."));
+    }
+
+    default CompletableFuture<SavedTerrainChunk> captureSavedTerrainChunk(
+            World world, int chunkX, int chunkZ, int minimumY, int height) {
+        return CompletableFuture.failedFuture(new UnsupportedOperationException(
+                "Native saved terrain capture is unavailable."));
+    }
+
     default PlatformGenerationRegistry generationRegistry() {
         throw new UnsupportedOperationException(
                 "The active NMS binding does not expose generation registry definitions."

core/src/main/java/art/arcane/iris/core/pack/PackStructurePlacementValidator.java

@@ -110,6 +110,11 @@ final class PackStructurePlacementValidator {
                         continue;
                     }
                     if (hasNativeStructures) {
+                        Object anchor = placement.opt("anchor");
+                        if (anchor != null && anchor != JSONObject.NULL && !"LEGACY".equals(anchor)) {
+                            blockingErrors.add(placementPath
+                                    + ".anchor must be omitted, null, or LEGACY for nativeStructures.");
+                        }
                         validateNativeStructures(
                                 placementPath, nativeStructures,
                                 registries.structures(), registries.jigsaws(),

core/src/main/java/art/arcane/iris/core/pregenerator/IrisPregenerator.java

@@ -203,7 +203,7 @@ public class IrisPregenerator {
         // fires — leaving a phantom job that suppresses spawns and blocks future pregens.
         try {
             init();
-            task.iterateAllChunks((_a, _b) -> totalChunks.incrementAndGet());
+            totalChunks.set(task.chunkCount());
             long startedAt = M.ms();
             startTime.set(startedAt);
             rateTracker.reset(startedAt, generated.get());
@@ -211,7 +211,6 @@ public class IrisPregenerator {
             historyLastCached.set(cached.get());
             historyLastMillis.set(startedAt);
             ticker.start();
-            checkRegions();
             int[] regionBounds = task.regionBounds();
             generator.onRegionBounds(regionBounds[0], regionBounds[1], regionBounds[2], regionBounds[3]);
             generator.onPregenStart(task.getCenter().getX(), task.getCenter().getZ());
@@ -280,10 +279,6 @@ public class IrisPregenerator {
                 + "] chunks/s";
     }
 
-    private void checkRegions() {
-        task.iterateRegions(this::checkRegion);
-    }
-
     private void init() {
         generator.init();
     }
@@ -413,9 +408,6 @@ public class IrisPregenerator {
             }
 
             generatedRegions.add(pos);
-            // No checkRegions() here: re-spiraling every region after every completed region
-            // was O(regions^2) dead work on the submitter thread (result discarded, and the
-            // only side effect was CachedPregenMethod faulting plates against eviction).
         }
     }
 
@@ -437,14 +429,6 @@ public class IrisPregenerator {
         MantleHeapPressure.requestPanicReclaim();
     }
 
-    private void checkRegion(int x, int z) {
-        if (generatedRegions.contains(new Position2(x, z))) {
-            return;
-        }
-
-        generator.supportsRegions(x, z, listener);
-    }
-
     public long getFailedChunks() {
         return failed.get();
     }

core/src/main/java/art/arcane/iris/core/pregenerator/PregenPerformanceProfile.java

@@ -21,22 +21,15 @@ package art.arcane.iris.core.pregenerator;
 import art.arcane.iris.core.IrisSettings;
 import art.arcane.iris.engine.IrisComplex;
 import art.arcane.iris.engine.framework.Engine;
-import art.arcane.iris.engine.framework.MeteredCache;
-import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.platform.PlatformChunkGenerator;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.util.common.parallel.MultiBurst;
 import art.arcane.iris.util.project.stream.ProceduralStream;
 import art.arcane.iris.util.project.stream.utility.CachedDoubleStream2D;
-import art.arcane.iris.util.project.stream.utility.CachedStream2D;
 
-import java.util.concurrent.TimeUnit;
+import java.util.Objects;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 public final class PregenPerformanceProfile {
-    private static final long HOTLOAD_ACQUISITION_TIMEOUT_SECONDS = 30L;
-    private static final AtomicBoolean JVM_HINT_LOGGED = new AtomicBoolean(false);
-
     private PregenPerformanceProfile() {
     }
 
@@ -44,7 +37,6 @@ public final class PregenPerformanceProfile {
         IrisSettings.IrisSettingsPerformance performance = IrisSettings.get().getPerformance();
         int previousNoiseCacheSize = performance.getNoiseCacheSize();
         int targetNoiseCacheSize = Math.max(previousNoiseCacheSize, 4_096);
-        boolean fastCacheEnabledBefore = Boolean.getBoolean("iris.cache.fast");
         boolean changed = false;
 
         if (targetNoiseCacheSize != previousNoiseCacheSize) {
@@ -52,73 +44,41 @@ public final class PregenPerformanceProfile {
             changed = true;
         }
 
-        if (!fastCacheEnabledBefore) {
-            System.setProperty("iris.cache.fast", "true");
-            changed = true;
-        }
         if (MultiBurst.burst.raiseParallelism(pregenBurstParallelism(Runtime.getRuntime().availableProcessors()))) {
             changed = true;
         }
 
-        if (JVM_HINT_LOGGED.compareAndSet(false, true) && !fastCacheEnabledBefore) {
-            IrisLogging.info("For startup-wide cache-fast coverage, set JVM argument: -Diris.cache.fast=true");
-        }
-
         return changed;
     }
 
     public static void apply(Engine engine) {
         apply();
-        if (!prepareNoiseCacheInPlace(engine)) {
+        if (engine != null) {
-            engine.hotloadComplex();
+            prepareNoiseCacheInPlace(engine);
-            logApplied();
+            IrisLogging.info("Pregen profile applied: noiseCacheSize="
+                    + IrisSettings.get().getPerformance().getNoiseCacheSize());
         }
     }
 
     public static void applyToGenerator(PlatformChunkGenerator generator) {
-        apply();
+        apply(generator == null ? null : generator.getEngine());
-        Engine engine = generator == null ? null : generator.getEngine();
-        if (!prepareNoiseCacheInPlace(engine)) {
-            generator.hotloadComplexAsync(HOTLOAD_ACQUISITION_TIMEOUT_SECONDS, TimeUnit.SECONDS).join();
-            logApplied();
-        }
     }
 
     static int pregenBurstParallelism(int availableProcessors) {
         return Math.max(4, availableProcessors * 2);
     }
 
-    private static boolean prepareNoiseCacheInPlace(Engine engine) {
+    private static void prepareNoiseCacheInPlace(Engine engine) {
-        if (engine == null) {
+        IrisComplex complex = Objects.requireNonNull(engine.getComplex(), "Pregeneration requires an active biome complex");
-            return true;
-        }
-        IrisComplex complex = engine.getComplex();
-        if (complex == null) {
-            return false;
-        }
-        ProceduralStream<IrisBiome> caveBiomeStream = complex.getCaveBiomeStream();
-        if (!(caveBiomeStream instanceof CachedStream2D<?> cachedStream) || !cachedStream.usesFastCache()) {
-            return false;
-        }
         int configuredChunks = IrisSettings.get().getPerformance().getNoiseCacheSize();
-        if (!resizeNoiseCache(complex.getNaturalHeightStream(), configuredChunks)) {
+        resizeNoiseCache(complex.getNaturalHeightStream(), configuredChunks);
-            return false;
+        resizeNoiseCache(complex.getRawHeightStream(), configuredChunks);
-        }
-        return resizeNoiseCache(complex.getHeightStream(), configuredChunks);
     }
 
-    private static boolean resizeNoiseCache(ProceduralStream<Double> stream, int configuredChunks) {
+    private static void resizeNoiseCache(ProceduralStream<Double> stream, int configuredChunks) {
-        if (stream instanceof CachedDoubleStream2D cachedStream) {
+        if (!(stream instanceof CachedDoubleStream2D cachedStream)) {
-            cachedStream.setMaximumChunks(configuredChunks);
+            throw new IllegalStateException("Pregeneration requires a mutable double terrain cache");
-            return true;
         }
-        if (!(stream instanceof MeteredCache cache)) {
+        cachedStream.setMaximumChunks(configuredChunks);
-            return false;
-        }
-        return cache.getMaxSize() == (long) configuredChunks * 256L;
-    }
-
-    private static void logApplied() {
-        IrisLogging.info("Pregen profile applied: noiseCacheSize=" + IrisSettings.get().getPerformance().getNoiseCacheSize() + " iris.cache.fast=" + Boolean.getBoolean("iris.cache.fast"));
     }
 }

core/src/main/java/art/arcane/iris/core/pregenerator/PregenTask.java

@@ -215,6 +215,11 @@ public class PregenTask {
         return new int[]{bound.minX(), bound.minZ(), bound.maxX(), bound.maxZ()};
     }
 
+    public long chunkCount() {
+        Bound bound = bounds.chunk();
+        return (long) bound.sizeX() * bound.sizeZ();
+    }
+
     @FunctionalInterface
     public interface InterleavedChunkConsumer {
         boolean on(int regionX, int regionZ, int chunkX, int chunkZ, boolean firstChunkInRegion, boolean lastChunkInRegion);

core/src/main/java/art/arcane/iris/core/pregenerator/cache/PregenSavedChunkStatus.java

@@ -0,0 +1,72 @@
+package art.arcane.iris.core.pregenerator.cache;
+
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.BitSet;
+import java.util.LinkedHashMap;
+import java.util.Objects;
+
+public final class PregenSavedChunkStatus {
+    private static final int MAXIMUM_REGIONS = 256;
+
+    private final StatusReader reader;
+    private final LinkedHashMap<Long, RegionStatus> regions = new LinkedHashMap<>(16, 0.75f, true);
+
+    public PregenSavedChunkStatus(StatusReader reader) {
+        this.reader = Objects.requireNonNull(reader);
+    }
+
+    public static PregenSavedChunkStatus fromWorld(Path dimensionRoot) {
+        Path root = Objects.requireNonNull(dimensionRoot).toAbsolutePath().normalize();
+        return new PregenSavedChunkStatus((x, z) -> readFull(root, x, z));
+    }
+
+    public synchronized boolean isFull(int chunkX, int chunkZ) {
+        long key = ((long) (chunkX >> 5) << 32) | ((chunkZ >> 5) & 0xffffffffL);
+        RegionStatus status = regions.get(key);
+        if (status == null) {
+            status = new RegionStatus(new BitSet(1024), new BitSet(1024));
+            regions.put(key, status);
+            if (regions.size() > MAXIMUM_REGIONS) {
+                regions.remove(regions.keySet().iterator().next());
+            }
+        }
+        int index = ((chunkZ & 31) << 5) | (chunkX & 31);
+        if (!status.checked().get(index)) {
+            try {
+                status.full().set(index, reader.isFull(chunkX, chunkZ));
+                status.checked().set(index);
+            } catch (IOException failure) {
+                throw new UncheckedIOException("Cannot verify saved pregeneration chunk " + chunkX + "," + chunkZ, failure);
+            }
+        }
+        return status.full().get(index);
+    }
+
+    private static boolean readFull(Path root, int chunkX, int chunkZ) throws IOException {
+        Path region = root.resolve("region/r." + (chunkX >> 5) + "." + (chunkZ >> 5) + ".mca");
+        if (Files.notExists(region)) {
+            return false;
+        }
+        try (RandomAccessFile input = new RandomAccessFile(region.toFile(), "r")) {
+            input.seek((long) (((chunkZ & 31) << 5) | (chunkX & 31)) * Integer.BYTES);
+            if (input.readInt() == 0) {
+                return false;
+            }
+        }
+        return SavedTerrainChunk.isComplete(SavedTerrainChunk.readStatus(root, chunkX, chunkZ));
+    }
+
+    @FunctionalInterface
+    public interface StatusReader {
+        boolean isFull(int chunkX, int chunkZ) throws IOException;
+    }
+
+    private record RegionStatus(BitSet checked, BitSet full) {
+    }
+}

core/src/main/java/art/arcane/iris/core/pregenerator/methods/CachedPregenMethod.java

@@ -4,19 +4,22 @@ import art.arcane.iris.core.pregenerator.PregenListener;
 import art.arcane.iris.core.pregenerator.PregenTask;
 import art.arcane.iris.core.pregenerator.PregeneratorMethod;
 import art.arcane.iris.core.pregenerator.cache.PregenCache;
+import art.arcane.iris.core.pregenerator.cache.PregenSavedChunkStatus;
 import art.arcane.volmlib.util.mantle.runtime.Mantle;
 
 public class CachedPregenMethod implements PregeneratorMethod {
     private final PregeneratorMethod method;
     private final PregenCache cache;
     private final PregenTask task;
+    private final PregenSavedChunkStatus savedStatus;
     private volatile PregenListener wrappedSource;
     private volatile PregenListener wrappedListener;
 
-    public CachedPregenMethod(PregeneratorMethod method, PregenCache cache, PregenTask task) {
+    public CachedPregenMethod(Configuration configuration) {
-        this.method = method;
+        this.method = configuration.method();
-        this.cache = cache.sync();
+        this.cache = configuration.cache().sync();
-        this.task = task;
+        this.task = configuration.task();
+        this.savedStatus = configuration.savedStatus();
     }
 
     @Override
@@ -26,7 +29,6 @@ public class CachedPregenMethod implements PregeneratorMethod {
 
     @Override
     public void close() {
-        cache.write();
         method.close();
         cache.write();
     }
@@ -39,12 +41,12 @@ public class CachedPregenMethod implements PregeneratorMethod {
 
     @Override
     public boolean supportsRegions(int x, int z, PregenListener listener) {
-        return cache.isRegionCached(x, z) || method.supportsRegions(x, z, listener);
+        return isSavedRegionCached(x, z) || method.supportsRegions(x, z, listener);
     }
 
     @Override
     public String getMethod(int x, int z) {
-        if (cache.isRegionCached(x, z)) {
+        if (isSavedRegionCached(x, z)) {
             return "Cached";
         }
         return method.getMethod(x, z);
@@ -52,7 +54,7 @@ public class CachedPregenMethod implements PregeneratorMethod {
 
     @Override
     public void generateRegion(int x, int z, PregenListener listener) {
-        if (cache.isRegionCached(x, z)) {
+        if (isSavedRegionCached(x, z)) {
             listener.onRegionGenerated(x, z);
             task.iterateChunks(x, z, (cX, cZ) -> {
                 listener.onChunkGenerated(cX, cZ, true);
@@ -60,13 +62,16 @@ public class CachedPregenMethod implements PregeneratorMethod {
             });
             return;
         }
-        method.generateRegion(x, z, listener);
+        if (!method.supportsRegions(x, z, listener)) {
-        cache.cacheRegion(x, z);
+            task.iterateChunks(x, z, (chunkX, chunkZ) -> generateChunk(chunkX, chunkZ, listener));
+            return;
+        }
+        method.generateRegion(x, z, cachingListener(listener));
     }
 
     @Override
     public void generateChunk(int x, int z, PregenListener listener) {
-        if (cache.isChunkCached(x, z)) {
+        if (cache.isChunkCached(x, z) && savedStatus.isFull(x, z)) {
             listener.onChunkGenerated(x, z, true);
             listener.onChunkCleaned(x, z);
             return;
@@ -74,6 +79,20 @@ public class CachedPregenMethod implements PregeneratorMethod {
         method.generateChunk(x, z, cachingListener(listener));
     }
 
+    private boolean isSavedRegionCached(int x, int z) {
+        if (!cache.isRegionCached(x, z)) {
+            return false;
+        }
+        for (int localX = 0; localX < 32; localX++) {
+            for (int localZ = 0; localZ < 32; localZ++) {
+                if (!savedStatus.isFull((x << 5) + localX, (z << 5) + localZ)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
     private PregenListener cachingListener(PregenListener listener) {
         PregenListener source = wrappedSource;
         PregenListener wrapped = wrappedListener;
@@ -185,6 +204,10 @@ public class CachedPregenMethod implements PregeneratorMethod {
         method.onRegionSubmitted(regionX, regionZ);
     }
 
+    public record Configuration(PregeneratorMethod method, PregenCache cache, PregenTask task,
+                                PregenSavedChunkStatus savedStatus) {
+    }
+
     @Override
     public Mantle getMantle() {
         return method.getMantle();

core/src/main/java/art/arcane/iris/core/runtime/StudioOpenCoordinator.java

@@ -952,7 +952,7 @@ public final class StudioOpenCoordinator {
         }
 
         public boolean prepareGeneratorState() {
-            return this != JIGSAW;
+            return this == STANDARD || this == FORCED_STANDARD;
         }
 
         public IrisCreator.DatapackPreparation datapackPreparation() {

core/src/main/java/art/arcane/iris/core/safeguard/IrisSafeguard.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.core.safeguard;
 
+import art.arcane.iris.core.IrisStartupValidation;
 import art.arcane.iris.core.safeguard.task.Diagnostic;
 import art.arcane.iris.core.safeguard.task.Task;
 import art.arcane.iris.core.safeguard.task.Tasks;
@@ -24,6 +25,7 @@ public final class IrisSafeguard {
     }
 
     public static void execute() {
+        IrisStartupValidation.beginRuntimeValidation();
         List<Task> tasks = Tasks.getTasks();
         LinkedHashMap<Task, ValueWithDiagnostics<Mode>> resultValues = new LinkedHashMap<>(tasks.size());
         LinkedHashMap<String, String> contextValues = new LinkedHashMap<>(tasks.size());
@@ -36,9 +38,13 @@ public final class IrisSafeguard {
             try {
                 result = task.run();
             } catch (Throwable e) {
+                boolean injectionFailure = "injection".equals(task.getId());
+                if (injectionFailure) {
+                    IrisStartupValidation.markRuntimeInvalid("Iris runtime injection failed. Resolve the startup errors and restart the server.");
+                }
                 IrisLogging.reportError(e);
                 result = new ValueWithDiagnostics<>(
-                        Mode.WARNING,
+                        injectionFailure ? Mode.UNSTABLE : Mode.WARNING,
                         new Diagnostic(Diagnostic.Logger.ERROR, "Error while running task " + task.getId(), e)
                 );
             }

core/src/main/java/art/arcane/iris/core/safeguard/task/Tasks.java

@@ -1,6 +1,7 @@
 package art.arcane.iris.core.safeguard.task;
 
 import art.arcane.iris.BuildConstants;
+import art.arcane.iris.core.IrisStartupValidation;
 import art.arcane.iris.platform.bukkit.BukkitPlatform;
 import art.arcane.iris.core.IrisWorlds;
 import art.arcane.iris.core.IrisWorldStorage;
@@ -119,18 +120,22 @@ public final class Tasks {
 
     private static final Task INJECTION = Task.of("injection", () -> {
         if (!Agent.install()) {
+            IrisStartupValidation.markRuntimeInvalid("Iris Java agent is unavailable. Add -javaagent:"
+                    + Agent.AGENT_JAR.getPath() + " to the JVM arguments before -jar and restart the server.");
             return withDiagnostics(Mode.UNSTABLE,
                     Diagnostic.Logger.ERROR.create("Java Agent"),
-                    Diagnostic.Logger.ERROR.create("- Please enable dynamic agent loading by adding -XX:+EnableDynamicAgentLoading to your jvm arguments."),
+                    Diagnostic.Logger.ERROR.create("- Add -javaagent:" + Agent.AGENT_JAR.getPath() + " before -jar in your startup command and restart the server."),
-                    Diagnostic.Logger.ERROR.create("- or add the jvm argument -javaagent:" + Agent.AGENT_JAR.getPath()));
+                    Diagnostic.Logger.ERROR.create("- Dynamic attachment requires -XX:+EnableDynamicAgentLoading and a host that permits JVM attachment."));
         }
 
         if (!INMS.get().injectBukkit()) {
+            IrisStartupValidation.markRuntimeInvalid("Iris runtime injection failed. Resolve the startup errors and restart the server.");
             return withDiagnostics(Mode.UNSTABLE,
                     Diagnostic.Logger.ERROR.create("Code Injection"),
                     Diagnostic.Logger.ERROR.create("- Failed to inject code. Please contact support"));
         }
 
+        IrisStartupValidation.markRuntimeReady();
         return withDiagnostics(Mode.STABLE);
     });
 

core/src/main/java/art/arcane/iris/core/service/ObjectStudioSaveService.java

@@ -91,7 +91,7 @@ public class ObjectStudioSaveService implements IrisService {
 
         Map<String, File> objectsDirs = new ConcurrentHashMap<>();
         for (Map.Entry<String, IrisData> e : sources.entrySet()) {
-            File dir = resolveObjectsDir(e.getValue());
+            File dir = resolveObjectsDir(e.getValue(), engine);
             if (dir != null) {
                 objectsDirs.put(e.getKey(), dir);
             }
@@ -200,9 +200,13 @@ public class ObjectStudioSaveService implements IrisService {
         return false;
     }
 
-    private static File resolveObjectsDir(IrisData data) {
+    static File resolveObjectsDir(IrisData data, Engine engine) {
         File root = data.getDataFolder();
         if (root == null) return null;
+        if (root.toPath().toAbsolutePath().normalize().equals(
+                engine.getData().getDataFolder().toPath().toAbsolutePath().normalize())) {
+            root = engine.getPackSource().toFile();
+        }
         File objects = new File(root, "objects");
         if (!objects.exists()) {
             objects.mkdirs();

core/src/main/java/art/arcane/iris/core/structure/StructureIndexService.java

@@ -21,8 +21,6 @@ package art.arcane.iris.core.structure;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.core.loader.IrisData;
-import art.arcane.iris.core.loader.ResourceLoader;
-import art.arcane.iris.engine.object.IrisStructure;
 import com.google.gson.GsonBuilder;
 
 import java.io.File;
@@ -38,8 +36,6 @@ import java.util.concurrent.ConcurrentHashMap;
 
 public final class StructureIndexService {
     private static final String INDEX_PATH = ".iris/structure-index.json";
-    private static final String LEGACY_INDEX_PATH = "structures/structure-index.json";
-    private static final String LEGACY_INDEX_KEY = "structure-index";
     private static final Set<String> GENERATED = ConcurrentHashMap.newKeySet();
 
     private StructureIndexService() {
@@ -66,7 +62,6 @@ public final class StructureIndexService {
     }
 
     public static File write(IrisData data) {
-        removeLegacyIndex(data);
         List<String> structures = IrisPlatforms.get().structureHooks().structureKeys();
         List<String> sets = IrisPlatforms.get().structureHooks().structureSetKeys();
 
@@ -93,7 +88,6 @@ public final class StructureIndexService {
         List<String> iris = new ArrayList<>();
         if (data.getStructureLoader() != null) {
             Collections.addAll(iris, data.getStructureLoader().getPossibleKeys());
-            iris.removeIf(LEGACY_INDEX_KEY::equals);
         }
 
         Collections.sort(vanilla);
@@ -138,22 +132,4 @@ public final class StructureIndexService {
         return new File(dataFolder, INDEX_PATH);
     }
 
-    static File legacyIndexFile(File dataFolder) {
-        return new File(dataFolder, LEGACY_INDEX_PATH);
-    }
-
-    static void removeLegacyIndex(IrisData data) {
-        File legacyFile = legacyIndexFile(data.getDataFolder());
-        try {
-            Files.deleteIfExists(legacyFile.toPath());
-            ResourceLoader<IrisStructure> structureLoader = data.getStructureLoader();
-            if (structureLoader != null) {
-                structureLoader.getLoadCache().invalidate(LEGACY_INDEX_KEY);
-                structureLoader.clearList();
-            }
-        } catch (Throwable e) {
-            IrisLogging.reportError("Failed to remove legacy structure index '"
-                    + legacyFile.getAbsolutePath() + "'", e);
-        }
-    }
 }

core/src/main/java/art/arcane/iris/core/tools/IrisCreator.java

@@ -118,9 +118,9 @@ public class IrisCreator {
      */
     private String name = "irisworld";
     /**
-     * Studio mode makes the engine hotloadable and uses the dimension in
+     * Studio mode snapshots edits from your Iris/packs folder into generation history.
-     * your Iris/packs folder instead of copying the dimension files into
+     * Existing chunks retain their generation while new chunks use accepted edits.
-     * the world itself. Studio worlds are deleted when they are unloaded.
+     * Studio worlds are deleted when they are unloaded.
      */
     private boolean studio = false;
     /**
@@ -260,18 +260,15 @@ public class IrisCreator {
                         + "Restart the server, then run the command again.");
             }
 
-            IrisDimension installedDimension = resolvedDimension;
+            reportCreationProgress(creationReporter, 0.26D, "prepare_world_pack");
-            if (!studio() || benchmark) {
+            StudioSVC studioService = IrisServices.get(StudioSVC.class);
-                reportCreationProgress(creationReporter, 0.26D, "prepare_world_pack");
+            IrisDimension installedDimension = benchmark && !studio
-                StudioSVC studioService = IrisServices.get(StudioSVC.class);
+                    ? studioService.installIntoTransientWorld(sender, resolvedDimension, dimensionRoot)
-                installedDimension = benchmark
+                    : studioService.installIntoWorld(sender, resolvedDimension, dimensionRoot, seed);
-                        ? studioService.installIntoTransientWorld(sender, resolvedDimension, dimensionRoot)
+            if (installedDimension == null) {
-                        : studioService.installIntoWorld(sender, resolvedDimension, dimensionRoot, seed);
+                throw new IrisException("Failed to install dimension pack for " + dimension());
-                if (installedDimension == null) {
-                    throw new IrisException("Failed to install dimension pack for " + dimension());
-                }
-                dimension = installedDimension.getLoadKey();
             }
+            dimension = installedDimension.getLoadKey();
             if (studio()) {
                 IrisRuntimeSchedulerMode runtimeSchedulerMode = IrisRuntimeSchedulerMode.resolve(IrisSettings.get().getPregen());
                 IrisLogging.debug("Studio create scheduling: mode=" + runtimeSchedulerMode.name().toLowerCase(Locale.ROOT)
@@ -285,6 +282,7 @@ public class IrisCreator {
             long generatorPrepareStart = System.nanoTime();
             WorldCreator wc = new IrisWorldCreator()
                     .dimension(installedDimension)
+                    .studioPackSource(resolvedDimension.getLoader().getDataFolder())
                     .name(name)
                     .seed(seed)
                     .studio(studio)

core/src/main/java/art/arcane/iris/core/tools/IrisToolbelt.java

@@ -33,6 +33,7 @@ import art.arcane.iris.core.pregenerator.PregenPerformanceProfile;
 import art.arcane.iris.core.pregenerator.PregenTask;
 import art.arcane.iris.core.pregenerator.PregeneratorMethod;
 import art.arcane.iris.core.pregenerator.cache.PregenCache;
+import art.arcane.iris.core.pregenerator.cache.PregenSavedChunkStatus;
 import art.arcane.iris.core.pack.PackDirectoryResolver;
 import art.arcane.iris.core.pack.PackDownloader;
 import art.arcane.iris.core.project.IrisProject;
@@ -316,7 +317,8 @@ public class IrisToolbelt {
             useCachedWrapper = runtimeSchedulerMode != IrisRuntimeSchedulerMode.FOLIA;
         }
         PregeneratorMethod activeMethod = useCachedWrapper
-                ? new CachedPregenMethod(method, resolvePregenCache(engine.getWorld()), task)
+                ? new CachedPregenMethod(new CachedPregenMethod.Configuration(method, resolvePregenCache(engine.getWorld()), task,
+                        PregenSavedChunkStatus.fromWorld(engine.getWorld().worldFolder().toPath())))
                 : method;
         return new PregeneratorJob(new PregeneratorJob.Configuration(
                 task,

core/src/main/java/art/arcane/iris/core/tools/IrisWorldCreator.java

@@ -33,6 +33,7 @@ import org.bukkit.generator.ChunkGenerator;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Objects;
 
 public class IrisWorldCreator {
     private String name;
@@ -41,6 +42,7 @@ public class IrisWorldCreator {
     private IrisDimension dimension;
     private long seed = 1337;
     private boolean persistent;
+    private File studioPackSource;
 
     public IrisWorldCreator() {
 
@@ -83,6 +85,11 @@ public class IrisWorldCreator {
         return this;
     }
 
+    public IrisWorldCreator studioPackSource(File source) {
+        this.studioPackSource = Objects.requireNonNull(source, "Studio authoring source");
+        return this;
+    }
+
     public WorldCreator create() {
         IrisDimension dim = dimension == null ? IrisData.loadAnyDimension(dimensionName, null) : dimension;
         NamespacedKey worldKey = IrisWorldStorage.keyFromName(name);
@@ -102,13 +109,13 @@ public class IrisWorldCreator {
                 .seed(seed)
                 .worldFolder(worldFolder)
                 .build();
-        GenerationHistory generationHistory = persistent
+        GenerationHistory generationHistory = persistent || studio
                 ? requireGenerationHistory(w.worldFolder(), seed)
                 : null;
-        File packRoot = generationHistory != null
+        File packRoot = studio
+                ? Objects.requireNonNull(studioPackSource, "Studio authoring source")
+                : generationHistory != null
                 ? requireActivePack(generationHistory)
-                : studio
-                ? dim.getLoader().getDataFolder()
                 : new File(w.worldFolder(), "iris/pack");
         ChunkGenerator g = new BukkitChunkGenerator(
                 w,

core/src/main/java/art/arcane/iris/engine/EngineDiagnostics.java

@@ -0,0 +1,63 @@
+package art.arcane.iris.engine;
+
+import art.arcane.iris.core.compat.PackCompatReport;
+import art.arcane.iris.core.pack.PackValidationResult;
+import art.arcane.iris.core.pack.PackValidationRegistry;
+import art.arcane.iris.spi.IrisLogging;
+import art.arcane.iris.spi.IrisPlatforms;
+
+import java.io.File;
+import java.util.Locale;
+import java.util.concurrent.TimeUnit;
+
+final class EngineDiagnostics {
+    private final IrisEngine engine;
+
+    EngineDiagnostics(IrisEngine engine) {
+        this.engine = engine;
+    }
+
+    /**
+     * One line per engine naming what this pack cannot generate on the running Minecraft version. The published
+     * validation result is complete (validation force-loads the whole pack), so it is preferred; an unvalidated pack
+     * falls back to what this engine has gated while building its runtime (dimension, regions, biomes). Never throws:
+     * a report failure must not take an otherwise working world down with it.
+     */
+    void logPackCompatSummary() {
+        try {
+            File folder = engine.getData().getDataFolder();
+            // Runtime data comes from an immutable snapshot; the dimension key identifies the pack.
+            String pack = engine.getDimension().getLoadKey();
+            String world = engine.getTarget().getWorld().name();
+            String version = IrisPlatforms.isBound() ? IrisPlatforms.get().minecraftVersion() : null;
+            PackValidationResult published = PackValidationRegistry.get(folder.toPath());
+            if (published == null) {
+                published = PackValidationRegistry.get(folder.getName());
+            }
+            PackCompatReport report = published != null && !published.getCompatFindings().isEmpty()
+                    ? PackCompatReport.of(published.getCompatFindings())
+                    : engine.getData().getCompatReport();
+            if (!report.isEmpty()) {
+                IrisLogging.info("World '" + world + "' pack '" + pack + "' " + report.summaryLine(version));
+            }
+            if (engine.getDimension().isCompatExcluded()) {
+                IrisLogging.error("World '" + world + "' pack '" + pack + "' cannot generate on Minecraft "
+                        + (version == null || version.isBlank() ? "unknown" : version));
+            }
+        } catch (Throwable e) {
+            IrisLogging.debug("Pack compat summary failed: " + e.getMessage());
+        }
+    }
+
+    void logStudioInitializationPhase(String phase, long startedAtNanos, boolean skipped) {
+        if (!engine.isStudio()) {
+            return;
+        }
+        IrisLogging.info("[Studio engine timing] world=%s kind=%s phase=%s duration=%dms skipped=%s",
+                engine.getTarget().getWorld().name(),
+                engine.getInitializationMode().name().toLowerCase(Locale.ROOT),
+                phase,
+                TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startedAtNanos),
+                Boolean.toString(skipped));
+    }
+}

core/src/main/java/art/arcane/iris/engine/EngineHotloader.java

@@ -19,6 +19,7 @@
 package art.arcane.iris.engine;
 
 import art.arcane.iris.core.loader.IrisData;
+import art.arcane.iris.core.IrisSettings;
 import art.arcane.iris.core.protocol.IrisProtocolServer;
 import art.arcane.iris.engine.GenerationRuntime.BiomeMaxes;
 import art.arcane.iris.engine.EngineRuntimeBuilder.RuntimeAssembly;
@@ -27,6 +28,10 @@ import art.arcane.iris.engine.framework.EngineTarget;
 import art.arcane.iris.engine.framework.IrisStructureLocator;
 import art.arcane.iris.engine.framework.StructureReachability;
 import art.arcane.iris.engine.object.IrisDimension;
+import art.arcane.iris.engine.history.GenerationHistory;
+import art.arcane.iris.engine.history.IrisBoundarySignatureSampler;
+import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import art.arcane.iris.engine.history.GenerationManifest;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.spi.IrisServices;
 import art.arcane.iris.util.project.context.IrisContext;
@@ -34,12 +39,13 @@ import art.arcane.iris.util.project.context.IrisContext;
 import static art.arcane.iris.engine.EngineShutdownSequence.runCleanup;
 
 /**
- * Performs the two supported live reload transitions for an {@link IrisEngine}: a full pack hotload
+ * Reloads mutable engine runtimes and publishes immutable Studio generation activations.
- * and a biome-complex-only rebuild. Both run entirely under the engine lifecycle lock, seal and
+ * Studio transitions drain sessions outside the lifecycle lock before freezing chunk ownership.
- * drain generation before swapping anything, and roll the previous runtime back on failure.
+ * Failures before publication preserve the previous runtime; durable publication failures stop generation.
  */
 final class EngineHotloader {
     private final IrisEngine engine;
+    private final Object studioTransitionLock = new Object();
 
     EngineHotloader(IrisEngine engine) {
         this.engine = engine;
@@ -51,6 +57,10 @@ final class EngineHotloader {
     }
 
     void hotloadComplex() {
+        if (engine.isStudio() && engine.getGenerationHistoryRuntimeRouter().isPresent()) {
+            hotloadSilently();
+            return;
+        }
         synchronized (engine.lifecycleLock) {
             engine.requireRunning("rebuild the biome complex");
             requireMutableGenerationRuntime("rebuild the biome complex");
@@ -114,6 +124,11 @@ final class EngineHotloader {
     }
 
     void hotloadSilently() {
+        GenerationHistoryRuntimeRouter router = engine.getGenerationHistoryRuntimeRouter().orElse(null);
+        if (engine.isStudio() && router != null) {
+            hotloadStudio(router);
+            return;
+        }
         synchronized (engine.lifecycleLock) {
             engine.requireRunning("hotload");
             requireMutableGenerationRuntime("hotload");
@@ -192,6 +207,95 @@ final class EngineHotloader {
         }
     }
 
+    private void hotloadStudio(GenerationHistoryRuntimeRouter router) {
+        synchronized (studioTransitionLock) {
+            EngineRuntime previous = null;
+            GenerationManifest previousManifest = router.history().manifest();
+            GenerationHistoryRuntimeRouter.StudioCutover cutover = null;
+            StudioGenerationUpdate update = null;
+            boolean backgroundAdmissionClosed = false;
+            try {
+                engine.requireRunning("hotload the Studio pack");
+                GenerationHistory history = router.history();
+                update = StudioGenerationUpdate.prepare(engine, history);
+                if (update == null) {
+                    return;
+                }
+                engine.awaitNativeStructureBootstrap("Studio generation cutover");
+                engine.backgroundTasks.closeBackgroundTaskAdmission();
+                backgroundAdmissionClosed = true;
+                engine.backgroundTasks.drainBackgroundTasks("Studio generation cutover")
+                        .requireComplete("Studio generation cutover");
+                cutover = router.beginStudioCutover(IrisEngine.SESSION_DRAIN_TIMEOUT_MILLIS);
+                synchronized (engine.lifecycleLock) {
+                    engine.requireRunning("prepare the Studio pack cutover");
+                    previous = engine.runtime;
+                    engine.studioGenerationTransition = true;
+                    engine.lifecycleState = LifecycleState.HOTLOADING;
+                }
+                engine.sealForTransition("Studio generation cutover", false);
+                IrisBoundarySignatureSampler.checkpoint(engine);
+                synchronized (engine.lifecycleLock) {
+                    if (engine.lifecycleState != LifecycleState.HOTLOADING || engine.runtime != previous) {
+                        throw new IllegalStateException("Studio engine changed while its generation cutover was draining.");
+                    }
+                    engine.prepareRuntimeHotload();
+                    history.stageUpdate(update.source(), update.fingerprint(), update.dimensionContract(),
+                            update.registryContract(), IrisSettings.get().getGenerator().getGenerationTransitionWidthBlocks());
+                    cutover.promotePending();
+                    IrisStructureLocator.invalidate(engine);
+                    StructureReachability.invalidate(engine);
+                    engine.runtimeBuilder.refreshStudioRuntimeServices();
+                    engine.getPrefetchSaveStarted().set(false);
+                    engine.getEngineData().getStatistics().hotloaded();
+                    engine.getPlatformHooks().applyWorldBoundary(engine);
+                }
+                broadcastStudioHotload(false, "");
+            } catch (Throwable failure) {
+                if (previous != null) {
+                    synchronized (engine.lifecycleLock) {
+                        if (engine.lifecycleState == LifecycleState.HOTLOADING
+                                || engine.lifecycleState == LifecycleState.RUNNING) {
+                            boolean unchanged = false;
+                            try {
+                                unchanged = router.history().manifest() == previousManifest;
+                            } catch (Throwable historyFailure) {
+                                failure.addSuppressed(historyFailure);
+                            }
+                            if (unchanged) {
+                                engine.runtimeBuilder.restoreRuntimeAfterFailedTransition(previous);
+                            } else {
+                                engine.lifecycleState = LifecycleState.FAILED;
+                                engine.getClosing().set(true);
+                                engine.backgroundTasks.closeBackgroundTaskAdmission();
+                            }
+                        }
+                    }
+                } else if (backgroundAdmissionClosed && engine.lifecycleState == LifecycleState.RUNNING
+                        && !engine.getClosing().get()) {
+                    engine.backgroundTasks.openBackgroundTaskAdmission();
+                }
+                IrisLogging.reportError("Studio generation update failed for '" + engine.getWorld().name() + "'.", failure);
+                broadcastStudioHotload(true, failure.getClass().getSimpleName() + ": " + failure.getMessage());
+                throw EngineShutdownSequence.propagate(failure);
+            } finally {
+                synchronized (engine.lifecycleLock) {
+                    engine.studioGenerationTransition = false;
+                }
+                if (cutover != null) {
+                    cutover.close();
+                }
+                if (update != null) {
+                    try {
+                        update.close();
+                    } catch (Throwable cleanupFailure) {
+                        IrisLogging.reportError("Failed to remove the staged Studio pack after its update.", cleanupFailure);
+                    }
+                }
+            }
+        }
+    }
+
     private void requireMutableGenerationRuntime(String operation) {
         if (engine.getGenerationHistoryRuntimeRouter().isPresent()) {
             throw new IllegalStateException("Cannot " + operation
@@ -210,7 +314,7 @@ final class EngineHotloader {
             if (protocolServer == null) {
                 return;
             }
-            String packKey = engine.getData().getDataFolder().getName();
+            String packKey = engine.getPackSource().getFileName().toString();
             protocolServer.broadcastStudioHotload(packKey, 0, failed, message);
         } catch (Throwable broadcastFailure) {
             IrisLogging.error("Iris studio hotload broadcast failed: " + broadcastFailure.getClass().getSimpleName()

core/src/main/java/art/arcane/iris/engine/EngineRuntimeBuilder.java

@@ -248,6 +248,39 @@ final class EngineRuntimeBuilder {
         IrisLogging.debug("Engine Setup Complete " + next.generation().cacheId());
     }
 
+    void refreshStudioRuntimeServices() {
+        EngineRuntime previous = requireRuntime("refresh Studio runtime services");
+        EngineEffects effects = null;
+        EngineWorldManager worldManager = null;
+        try {
+            effects = Objects.requireNonNull(IrisServices.get(EngineEffectsProvider.class).create(engine),
+                    "Studio engine effects");
+            worldManager = Objects.requireNonNull(IrisServices.get(EngineWorldManagerProvider.class).create(engine),
+                    "Studio world manager");
+        } catch (Throwable failure) {
+            if (effects != null) {
+                EngineEffects createdEffects = effects;
+                EngineShutdownSequence.runCleanup(failure, createdEffects::close);
+            }
+            throw propagate(failure);
+        }
+        EngineRuntime next = new EngineRuntime(previous.generation(), effects, worldManager);
+        Throwable retirementFailure = EngineShutdownSequence.runCleanup(null, previous.worldManager()::close);
+        retirementFailure = EngineShutdownSequence.runCleanup(retirementFailure, previous.effects()::close);
+        if (retirementFailure != null) {
+            retirementFailure = EngineShutdownSequence.runCleanup(retirementFailure, worldManager::close);
+            retirementFailure = EngineShutdownSequence.runCleanup(retirementFailure, effects::close);
+            throw new IllegalStateException("Failed to retire Studio runtime services.", retirementFailure);
+        }
+        engine.runtime = next;
+        worldManager.start();
+        engine.getGenerationSessions().activateNextSession();
+        engine.lifecycleState = LifecycleState.RUNNING;
+        engine.getClosing().set(false);
+        engine.backgroundTasks.openBackgroundTaskAdmission();
+        scheduleRuntimeTasks(next);
+    }
+
     private void scheduleRuntimeTasks(EngineRuntime engineRuntime) {
         schedulePackHash(engineRuntime.generation());
         try {

core/src/main/java/art/arcane/iris/engine/IrisComplex.java

@@ -18,6 +18,7 @@
 
 package art.arcane.iris.engine;
 
+
 import art.arcane.iris.core.IrisSettings;
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.loader.IrisRegistrant;
@@ -25,6 +26,7 @@ import art.arcane.iris.engine.data.cache.Cache;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.history.GenerationBlend;
 import art.arcane.iris.engine.history.TransitionGenerationPlan;
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
 import art.arcane.iris.engine.hydrology.HydrologyColumnLayer;
 import art.arcane.iris.engine.hydrology.HydrologyColumnSample;
 import art.arcane.iris.engine.hydrology.HydrologyFeatureType;
@@ -38,6 +40,9 @@ import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisDecorationPart;
 import art.arcane.iris.engine.object.IrisDecorator;
 import art.arcane.iris.engine.object.IrisGenerator;
+import art.arcane.iris.engine.object.IrisGeneratorStyle;
+import art.arcane.iris.engine.object.IrisDimension;
+import art.arcane.iris.util.project.context.IrisContext;
 import art.arcane.iris.engine.object.IrisInterpolator;
 import art.arcane.iris.engine.object.IrisMaterialPalette;
 import art.arcane.iris.engine.object.IrisRegion;
@@ -67,6 +72,7 @@ import lombok.Getter;
 import lombok.ToString;
 
 import java.io.File;
+import java.lang.ref.WeakReference;
 import java.util.Arrays;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -79,6 +85,7 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
+import java.util.OptionalInt;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.atomic.AtomicLong;
@@ -133,6 +140,8 @@ public class IrisComplex implements DataProvider {
     private ProceduralStream<IrisBiome> seaBiomeStream;
     private ProceduralStream<IrisBiome> shoreBiomeStream;
     private ProceduralStream<IrisBiome> baseBiomeStream;
+    @Getter(AccessLevel.NONE)
+    private final transient boolean reuseNaturalBaseBiome;
     private ProceduralStream<UUID> baseBiomeIDStream;
     private ProceduralStream<IrisBiome> naturalTrueBiomeStream;
     private ProceduralStream<IrisBiome> unblendedNaturalTrueBiomeStream;
@@ -140,6 +149,8 @@ public class IrisComplex implements DataProvider {
     private ProceduralStream<PlatformBiome> trueBiomeDerivativeStream;
     private ProceduralStream<Double> naturalHeightStream;
     private ProceduralStream<Double> unblendedNaturalHeightStream;
+    private final ResolvedTerrainProvider resolvedTerrain;
+    private ProceduralStream<Double> placementHeightStream;
     private ProceduralStream<Double> heightStream;
     private ProceduralStream<Integer> roundedHeighteightStream;
     private ProceduralStream<Double> maxHeightStream;
@@ -188,6 +199,7 @@ public class IrisComplex implements DataProvider {
 
     IrisComplex(Engine engine, boolean simple, TransitionGenerationPlan transitionGenerationPlan) {
         this.transitionGenerationPlan = transitionGenerationPlan;
+        this.resolvedTerrain = new ResolvedTerrainProvider(engine);
         int cacheSize = noiseCacheSize(engine, IrisSettings.get().getPerformance().getNoiseCacheSize());
         IrisBiome emptyBiome = new IrisBiome().setInferredType(InferredType.CAVE);
         UUID focusUUID = UUID.nameUUIDFromBytes("focus".getBytes());
@@ -228,6 +240,7 @@ public class IrisComplex implements DataProvider {
             }
             imageMapRuntime.getMappedBiomes().forEach(this::registerGenerators);
         }
+        reuseNaturalBaseBiome = hasFixedNaturalBiomeNoise(engine.getDimension(), generatorBiomes);
         inferredBiomeStreams = compileInferredBiomeStreams(
                 preparedRegions,
                 (region, inferredType) -> compileInferredBiomeStream(engine, region, inferredType, emptyBiome)
@@ -314,11 +327,7 @@ public class IrisComplex implements DataProvider {
                 (x, z) -> sampleUnblendedNaturalTerrainHeight(engine, x, z),
                 Interpolated.DOUBLE
         ).cache2DDouble("unblendedNaturalHeightStream", engine, cacheSize);
-        naturalHeightStream = transitionGenerationPlan == null ? unblendedNaturalHeightStream
+        naturalHeightStream = unblendedNaturalHeightStream;
-                : unblendedNaturalHeightStream.convertAware2D((newHeight, x, z) -> blendNaturalTerrainHeight(
-                        newHeight,
-                        transitionGenerationPlan.terrainSampleAt(blockCoordinate(x), blockCoordinate(z))))
-                .cache2DDouble("naturalHeightStream", engine, cacheSize);
         naturalTrueBiomeStream = focusBiome != null ? ProceduralStream.of((x, y) -> focusBiome, Interpolated.of(a -> 0D,
                         b -> focusBiome))
                 .cache2D("naturalTrueBiomeStream-focus", engine, cacheSize) : naturalHeightStream
@@ -355,10 +364,11 @@ public class IrisComplex implements DataProvider {
         }
         heightStream = ProceduralStream.ofDouble((x, z) -> resolveHydrologyTerrainHeight(x, z))
                 .cache2DDouble("heightStream", engine, cacheSize);
-        roundedHeighteightStream = heightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
+        placementHeightStream = ProceduralStream.ofDouble(this::samplePlacementHeight);
+        roundedHeighteightStream = placementHeightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
                 .round();
-        slopeStream = heightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
+        slopeStream = placementHeightStream.contextInjecting(engine, (c, x, z) -> c.getHeight().getDouble(x, z))
-                .slope(3).cache2DDouble("slopeStream", engine, cacheSize);
+                .slope(3);
         naturalSlopeStream = naturalHeightStream.slope(3).cache2DDouble("naturalSlopeStream", engine, cacheSize);
         trueBiomeStream = focusBiome != null ? ProceduralStream.of((x, y) -> focusBiome, Interpolated.of(a -> 0D,
                         b -> focusBiome))
@@ -480,14 +490,7 @@ public class IrisComplex implements DataProvider {
     }
 
     private double sampleNaturalTerrainHeight(Engine engine, double x, double z) {
-        double newHeight = sampleUnblendedNaturalTerrainHeight(engine, x, z);
+        return sampleUnblendedNaturalTerrainHeight(engine, x, z);
-        if (transitionGenerationPlan == null) {
-            return newHeight;
-        }
-        TransitionGenerationPlan.TerrainSample sample = transitionGenerationPlan.terrainSampleAt(
-                blockCoordinate(x),
-                blockCoordinate(z));
-        return blendNaturalTerrainHeight(newHeight, sample);
     }
 
     private double sampleUnblendedNaturalTerrainHeight(Engine engine, double x, double z) {
@@ -495,20 +498,6 @@ public class IrisComplex implements DataProvider {
         return imageMapRuntime.sampleTerrainHeight(x, z, proceduralHeight);
     }
 
-    static double blendNaturalTerrainHeight(
-            double newHeight,
-            TransitionGenerationPlan.TerrainSample sample
-    ) {
-        Objects.requireNonNull(sample, "terrain transition sample");
-        if (sample.newEpochWeight() == 1D || !sample.hasHistoricalSignature()) {
-            return newHeight;
-        }
-        double historicalHeight = sample.nearestSignature().fluidHeight().isPresent()
-                ? sample.historicalOceanFloorHeight()
-                : sample.historicalSurfaceHeight();
-        return GenerationBlend.interpolate(historicalHeight, newHeight, sample.newEpochWeight());
-    }
-
     static double calculateNaturalSlope(double naturalHeight, double easternHeight, double southernHeight) {
         double deltaX = easternHeight - naturalHeight;
         double deltaZ = southernHeight - naturalHeight;
@@ -519,16 +508,19 @@ public class IrisComplex implements DataProvider {
             InferredType inferredType,
             IrisRegion region,
             double naturalHeight,
-            double x,
+            int x,
-            double z
+            int z
     ) {
         IrisBiome mapped = imageMapRuntime.sampleBiome(x, z);
         if (mapped != null) {
             return mapped;
         }
-        IrisBiome baseBiome = implode(sampleInferredBiome(region, inferredType, x, z), x, z);
+        IrisContext context = IrisContext.get();
+        IrisBiome baseBiome = reuseNaturalBaseBiome && (context == null || context.getChunkContext() == null)
+                ? baseBiomeStream.get(x, z)
+                : implode(sampleInferredBiome(region, inferredType, x, z), (double) x, (double) z);
         IrisBiome resolved = resolveNaturalSurfaceBiome(naturalHeight, baseBiome, region, x, z);
-        return resolved == baseBiome ? baseBiome : implode(resolved, x, z);
+        return resolved == baseBiome ? baseBiome : implode(resolved, (double) x, (double) z);
     }
 
     private IrisBiome resolveNaturalSurfaceBiome(
@@ -808,6 +800,9 @@ public class IrisComplex implements DataProvider {
             int naturalHeight,
             double hydrologyWeight
     ) {
+        if (layer.feature().type().isUnderground() || layer.feature().type().isDeepFluid()) {
+            return layer;
+        }
         return new HydrologyColumnLayer(
                 layer.feature(),
                 GenerationBlend.interpolateHeight(naturalHeight, layer.bedY(), hydrologyWeight),
@@ -847,6 +842,42 @@ public class IrisComplex implements DataProvider {
                 || hydrologyRuntime.isPlanned(x, z);
     }
 
+    public ProceduralStream<Double> getRawHeightStream() {
+        return heightStream;
+    }
+
+    public ProceduralStream<Double> getHeightStream() {
+        return placementHeightStream;
+    }
+
+    public Optional<TerrainBoundarySignature> resolvedTerrainColumn(int blockX, int blockZ) {
+        if (transitionGenerationPlan == null || isNaturalTerrainContext()
+                || !transitionGenerationPlan.hasTransitionAtChunk(blockX >> 4, blockZ >> 4)) {
+            return Optional.empty();
+        }
+        return Optional.of(resolvedTerrain.column(blockX, blockZ));
+    }
+
+    public OptionalInt resolvedTerrainHeight(int blockX, int blockZ, boolean ignoreFluid) {
+        if (transitionGenerationPlan == null || isNaturalTerrainContext()
+                || !transitionGenerationPlan.hasTransitionAtChunk(blockX >> 4, blockZ >> 4)) {
+            return OptionalInt.empty();
+        }
+        return OptionalInt.of(resolvedTerrain.height(blockX, blockZ, ignoreFluid));
+    }
+
+    boolean isNaturalTerrainContext() {
+        IrisContext context = IrisContext.get();
+        return context != null && context.getChunkContext() != null
+                && context.getChunkContext().getComplex() == this
+                && context.getChunkContext().isNaturalTerrain();
+    }
+
+    private double samplePlacementHeight(double x, double z) {
+        OptionalInt resolved = resolvedTerrainHeight(blockCoordinate(x), blockCoordinate(z), true);
+        return resolved.isPresent() ? resolved.getAsInt() : heightStream.getDouble(x, z);
+    }
+
     public boolean isHistoricalChunk(int chunkX, int chunkZ) {
         return transitionGenerationPlan != null
                 && transitionGenerationPlan.boundary().isHistoricalChunk(chunkX, chunkZ);
@@ -1370,9 +1401,25 @@ public class IrisComplex implements DataProvider {
         if (generators.length == 0) {
             return 0D;
         }
+        if (!Double.isFinite(low) || !Double.isFinite(high)) {
+            throw new IllegalStateException("Terrain generator bounds were not finite at " + x + "," + z
+                    + " (generator=" + generators[0].getLoadKey() + ", bounds=" + low + ".." + high + ").");
+        }
         double height = 0D;
+        if (low == high) {
+            for (int i = 0; i < generators.length; i++) {
+                height += low;
+            }
+            return height / generators.length;
+        }
         for (IrisGenerator generator : generators) {
-            height += M.lerp(low, high, generator.getHeight(x, z, seed));
+            double noise = generator.getHeight(x, z, seed);
+            if (!Double.isFinite(noise)) {
+                throw new IllegalStateException("Terrain generator noise was not finite at " + x + "," + z
+                        + " (generator=" + generator.getLoadKey() + ", noise=" + noise
+                        + ", bounds=" + low + ".." + high + ").");
+            }
+            height += M.lerp(low, high, noise);
         }
         return height / generators.length;
     }
@@ -1455,9 +1502,34 @@ public class IrisComplex implements DataProvider {
         CNG childCell = b.getChildrenGenerator(rng, 123, b.getChildShrinkFactor());
         ChildSelectionPlan childSelectionPlan = resolveChildSelectionPlan(b);
         IrisBiome biome = childSelectionPlan.select(childCell, x, z).withInferredType(b.getInferredType());
+        if (biome == b && hasFixedNoise(b.getChildStyle())) {
+            return biome;
+        }
         return implode(biome, x, z, max - 1);
     }
 
+    static boolean hasFixedNaturalBiomeNoise(IrisDimension dimension, Iterable<IrisBiome> biomes) {
+        if (!hasFixedNoise(dimension.getRegionStyle()) || !hasFixedNoise(dimension.getContinentalStyle())
+                || !hasFixedNoise(dimension.getLandBiomeStyle()) || !hasFixedNoise(dimension.getSeaBiomeStyle())) {
+            return false;
+        }
+        for (IrisBiome biome : biomes) {
+            if (!biome.getChildren().isEmpty() && !hasFixedNoise(biome.getChildStyle())) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static boolean hasFixedNoise(IrisGeneratorStyle style) {
+        for (IrisGeneratorStyle current = style; current != null; current = current.getFracture()) {
+            if (current.getExpression() != null) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     private ChildSelectionPlan resolveChildSelectionPlan(IrisBiome biome) {
         ChildSelectionPlan cachedPlan = childSelectionPlans.get(biome);
         if (cachedPlan != null) {
@@ -1517,14 +1589,15 @@ public class IrisComplex implements DataProvider {
     /**
      * Reusable per-thread bounds provider. Holds the biome memo and the lazily computed generator
      * bounds for one sampleBoundsRaw pass so the pass allocates nothing; {@link #bind}
-     * resets both, giving each pass the same empty-scratch semantics a fresh allocation had.
+     * resets generator bounds while retaining bounded coordinate samples for the same biome stream.
      * <p>
      * Single threaded and non reentrant by contract, matching the thread local sample caches in
      * IrisInterpolation that this provider is invoked through. If a nested pass ever does appear,
      * {@link #isInUse()} makes the caller fall back to a freshly allocated sampler.
      */
     private static final class BoundsSampler implements NoiseBoundsProvider {
-        private final CoordinateBiomeCache sampleCache = new CoordinateBiomeCache(64);
+        private final CoordinateBiomeCache sampleCache = new CoordinateBiomeCache(4096);
+        private WeakReference<ProceduralStream<IrisBiome>> sampleSource = new WeakReference<>(null);
         private final IdentityHashMap<IrisBiome, GeneratorBounds> localBounds = new IdentityHashMap<>(8);
         private IrisComplex complex;
         private Engine engine;
@@ -1542,7 +1615,10 @@ public class IrisComplex implements DataProvider {
             this.generators = generators;
             this.cachedBounds = cachedBounds;
             this.inUse = true;
-            sampleCache.clear();
+            if (sampleSource.get() != complex.baseBiomeStream) {
+                sampleCache.clear();
+                sampleSource = new WeakReference<>(complex.baseBiomeStream);
+            }
 
             if (!localBounds.isEmpty()) {
                 localBounds.clear();
@@ -1585,73 +1661,40 @@ public class IrisComplex implements DataProvider {
     }
 
     /**
-     * Open addressed biome memo keyed on the packed coordinate bits, replacing a linear scan that was
+     * Bounded biome memo keyed on the packed coordinate bits, replacing a linear scan that was
      * quadratic in the number of columns a wide starcast touches. Single threaded by contract.
      */
     private static final class CoordinateBiomeCache {
-        private long[] xBits;
+        private final long[] xBits;
-        private long[] zBits;
+        private final long[] zBits;
-        private IrisBiome[] values;
+        private final IrisBiome[] values;
-        private byte[] states;
+        private final int mask;
-        private int mask;
-        private int resizeThreshold;
-        private int size;
 
-        private CoordinateBiomeCache(int initialCapacity) {
+        private CoordinateBiomeCache(int capacity) {
-            int minimumCapacity = Math.max(8, initialCapacity);
+            xBits = new long[capacity];
-            int tableSize = tableSizeFor((minimumCapacity << 1) + minimumCapacity);
+            zBits = new long[capacity];
-            xBits = new long[tableSize];
+            values = new IrisBiome[capacity];
-            zBits = new long[tableSize];
+            mask = capacity - 1;
-            values = new IrisBiome[tableSize];
-            states = new byte[tableSize];
-            mask = tableSize - 1;
-            resizeThreshold = Math.max(1, (tableSize * 3) >> 2);
-            size = 0;
         }
 
         private void clear() {
-            if (size == 0) {
+            Arrays.fill(values, null);
-                return;
-            }
-
-            Arrays.fill(states, (byte) 0);
-            size = 0;
         }
 
         private IrisBiome get(double x, double z) {
-            int slot = findSlot(Double.doubleToLongBits(x), Double.doubleToLongBits(z));
+            long xb = Double.doubleToLongBits(x);
-            return states[slot] == 0 ? null : values[slot];
+            long zb = Double.doubleToLongBits(z);
+            int slot = mix(xb, zb) & mask;
+            return xBits[slot] == xb && zBits[slot] == zb ? values[slot] : null;
         }
 
         private void put(double x, double z, IrisBiome biome) {
             long xb = Double.doubleToLongBits(x);
             long zb = Double.doubleToLongBits(z);
-            int slot = findSlot(xb, zb);
+            int slot = mix(xb, zb) & mask;
-            boolean occupied = states[slot] != 0;
             xBits[slot] = xb;
             zBits[slot] = zb;
             values[slot] = biome;
-            states[slot] = 1;
-
-            if (occupied) {
-                return;
-            }
-
-            size++;
-            if (size >= resizeThreshold) {
-                grow();
-            }
-        }
-
-        private int findSlot(long xb, long zb) {
-            int slot = mix(xb, zb) & mask;
-            while (states[slot] != 0) {
-                if (xBits[slot] == xb && zBits[slot] == zb) {
-                    break;
-                }
-                slot = (slot + 1) & mask;
-            }
-            return slot;
         }
 
         private int mix(long xb, long zb) {
@@ -1662,49 +1705,6 @@ public class IrisComplex implements DataProvider {
             hash ^= (hash >>> 33);
             return (int) hash;
         }
-
-        private void grow() {
-            long[] previousXBits = xBits;
-            long[] previousZBits = zBits;
-            IrisBiome[] previousValues = values;
-            byte[] previousStates = states;
-
-            int nextLength = previousXBits.length << 1;
-            xBits = new long[nextLength];
-            zBits = new long[nextLength];
-            values = new IrisBiome[nextLength];
-            states = new byte[nextLength];
-            mask = nextLength - 1;
-            resizeThreshold = Math.max(1, (nextLength * 3) >> 2);
-            size = 0;
-
-            for (int i = 0; i < previousStates.length; i++) {
-                if (previousStates[i] == 0) {
-                    continue;
-                }
-
-                int slot = findSlot(previousXBits[i], previousZBits[i]);
-                xBits[slot] = previousXBits[i];
-                zBits[slot] = previousZBits[i];
-                values[slot] = previousValues[i];
-                states[slot] = 1;
-                size++;
-            }
-        }
-
-        private int tableSizeFor(int value) {
-            int n = value - 1;
-            n |= n >>> 1;
-            n |= n >>> 2;
-            n |= n >>> 4;
-            n |= n >>> 8;
-            n |= n >>> 16;
-            int tableSize = n + 1;
-            if (tableSize < 8) {
-                return 8;
-            }
-            return tableSize;
-        }
     }
 
     static final class ChildSelectionPlan {
@@ -1783,6 +1783,7 @@ public class IrisComplex implements DataProvider {
     }
 
     public void close() {
+        resolvedTerrain.clear();
         if (hydrologyRuntime != null) {
             hydrologyRuntime.close();
         }

core/src/main/java/art/arcane/iris/engine/IrisEngine.java

@@ -37,6 +37,7 @@ import art.arcane.iris.engine.framework.GenerationSessionManager;
 import art.arcane.iris.engine.history.GenerationBoundarySignatureSampler;
 import art.arcane.iris.engine.history.GenerationHistory;
 import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import art.arcane.iris.engine.history.ChunkGenerationSemantics;
 import art.arcane.iris.engine.history.GenerationKernelRegistry;
 import art.arcane.iris.engine.history.TransitionGenerationPlan;
 import art.arcane.iris.engine.framework.SeedManager;
@@ -46,10 +47,7 @@ import art.arcane.iris.engine.object.IrisDimension;
 import art.arcane.iris.engine.object.IrisDimensionCarvingResolver;
 import art.arcane.iris.engine.object.IrisEngineData;
 import art.arcane.iris.engine.object.IrisRegion;
-import art.arcane.iris.core.compat.PackCompatReport;
 import art.arcane.iris.core.pack.PackValidationCache;
-import art.arcane.iris.core.pack.PackValidationResult;
-import art.arcane.iris.core.pack.PackValidationRegistry;
 import art.arcane.iris.spi.IrisLogging;
 import com.google.common.util.concurrent.AtomicDouble;
 import art.arcane.iris.spi.IrisPlatforms;
@@ -78,20 +76,17 @@ import lombok.Data;
 import lombok.Getter;
 import lombok.Setter;
 
-import java.io.File;
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
-import java.util.Locale;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.CopyOnWriteArraySet;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
@@ -118,6 +113,11 @@ public class IrisEngine implements Engine {
     private final EngineMetrics metrics;
     private final CompletableFuture<Void> generationCacheWarm;
     private final boolean studio;
+    @Setter(AccessLevel.NONE)
+    private volatile Path studioGenerationSource;
+    @Getter(AccessLevel.NONE)
+    @Setter(AccessLevel.NONE)
+    boolean studioGenerationTransition;
     private final AtomicRollingSequence wallClock;
     @Getter(AccessLevel.NONE)
     @Setter(AccessLevel.NONE)
@@ -163,6 +163,9 @@ public class IrisEngine implements Engine {
     @Getter(AccessLevel.NONE)
     @Setter(AccessLevel.NONE)
     final EngineMetricsReport metricsReport = new EngineMetricsReport(this);
+    @Getter(AccessLevel.NONE)
+    @Setter(AccessLevel.NONE)
+    private final EngineDiagnostics diagnostics = new EngineDiagnostics(this);
     private final AtomicBoolean cleaning;
     private final ChronoLatch cleanLatch;
     private final SeedManager seedManager;
@@ -267,7 +270,7 @@ public class IrisEngine implements Engine {
         this.initialKernelVersion = Objects.requireNonNull(kernelVersion, "generation kernel version");
         this.initialTransitionPlan = transitionPlan;
         this.platformHooks = IrisServices.get(EnginePlatformHooks.class);
-        this.generationSessions = new GenerationSessionManager();
+        this.generationSessions = new GenerationSessionManager(requiredMode.studio());
         this.closing = new AtomicBoolean(true);
         this.nativeStructureVolumeQueriesEnabled = new AtomicBoolean(!requiredMode.studio());
         this.lifecycleState = LifecycleState.INITIALIZING;
@@ -313,7 +316,7 @@ public class IrisEngine implements Engine {
             String studioCacheIdentity = currentStudioCacheIdentity();
             getData().loadPrefetch(this);
             IrisLogging.debug("[IrisEngine timing] loadPrefetch=" + (M.ms() - _t0) + "ms");
-            logStudioInitializationPhase("load_prefetch", phaseStartedAt, false);
+            diagnostics.logStudioInitializationPhase("load_prefetch", phaseStartedAt, false);
             try {
                 StructureIndexService.writeOnce(getData());
             } catch (Throwable e) {
@@ -326,8 +329,8 @@ public class IrisEngine implements Engine {
             enableStableStudioCache(initialRuntime, studioCacheIdentity);
             runtimeBuilder.publishRuntime(initialRuntime, null);
             IrisLogging.debug("[IrisEngine timing] setupEngine total=" + (M.ms() - _t0) + "ms");
-            logPackCompatSummary();
+            diagnostics.logPackCompatSummary();
-            logStudioInitializationPhase("build_runtime", phaseStartedAt, false);
+            diagnostics.logStudioInitializationPhase("build_runtime", phaseStartedAt, false);
             phaseStartedAt = System.nanoTime();
             if (requiredMode.warmGenerationCaches()) {
                 if (requiredMode.studio()) {
@@ -337,7 +340,7 @@ public class IrisEngine implements Engine {
                 }
             } else {
                 generationCacheWarm.complete(null);
-                logStudioInitializationPhase("generation_cache_warm", phaseStartedAt, true);
+                diagnostics.logStudioInitializationPhase("generation_cache_warm", phaseStartedAt, true);
             }
             EngineTickRegistry.registerTicking(this);
         } catch (Throwable e) {
@@ -347,38 +350,6 @@ public class IrisEngine implements Engine {
         IrisLogging.debug("Engine Initialized " + getCacheID());
     }
 
-    /**
-     * One line per engine naming what this pack cannot generate on the running Minecraft version. The published
-     * validation result is complete (validation force-loads the whole pack), so it is preferred; an unvalidated pack
-     * falls back to what this engine has gated while building its runtime (dimension, regions, biomes). Never throws:
-     * a report failure must not take an otherwise working world down with it.
-     */
-    private void logPackCompatSummary() {
-        try {
-            File folder = getData().getDataFolder();
-            // A world engine reads its snapshot copy under <world>/iris/pack, so the dimension key is the pack's name.
-            String pack = getDimension().getLoadKey();
-            String world = target.getWorld().name();
-            String version = IrisPlatforms.isBound() ? IrisPlatforms.get().minecraftVersion() : null;
-            PackValidationResult published = PackValidationRegistry.get(folder.toPath());
-            if (published == null) {
-                published = PackValidationRegistry.get(folder.getName());
-            }
-            PackCompatReport report = published != null && !published.getCompatFindings().isEmpty()
-                    ? PackCompatReport.of(published.getCompatFindings())
-                    : getData().getCompatReport();
-            if (!report.isEmpty()) {
-                IrisLogging.info("World '" + world + "' pack '" + pack + "' " + report.summaryLine(version));
-            }
-            if (getDimension().isCompatExcluded()) {
-                IrisLogging.error("World '" + world + "' pack '" + pack + "' cannot generate on Minecraft "
-                        + (version == null || version.isBlank() ? "unknown" : version));
-            }
-        } catch (Throwable e) {
-            IrisLogging.debug("Pack compat summary failed: " + e.getMessage());
-        }
-    }
-
     public void awaitGenerationCacheWarm() {
         if (generationCacheWarm.isDone() && !generationCacheWarm.isCompletedExceptionally()) {
             return;
@@ -394,18 +365,6 @@ public class IrisEngine implements Engine {
         return !generationCacheWarm.isDone();
     }
 
-    private void logStudioInitializationPhase(String phase, long startedAtNanos, boolean skipped) {
-        if (!studio) {
-            return;
-        }
-        IrisLogging.info("[Studio engine timing] world=%s kind=%s phase=%s duration=%dms skipped=%s",
-                target.getWorld().name(),
-                initializationMode.name().toLowerCase(Locale.ROOT),
-                phase,
-                TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startedAtNanos),
-                Boolean.toString(skipped));
-    }
-
     private String currentStudioCacheIdentity() {
         if (initializationMode != InitializationMode.STUDIO || !IrisPlatforms.isBound()) {
             return "";
@@ -447,6 +406,36 @@ public class IrisEngine implements Engine {
         return packRoot.resolve(".iris").resolve("studio-hydrology");
     }
 
+    public void startStudioEntryHydrology(int blockX, int blockZ) {
+        GenerationRuntimeBinding binding = getActiveGenerationRuntimeBinding();
+        if (!backgroundTasks.scheduleTrackedTask(() -> prepareStudioEntryHydrology(binding, blockX, blockZ))) {
+            throw new IllegalStateException("Iris background task admission closed before Studio entry preparation.");
+        }
+    }
+
+    private void prepareStudioEntryHydrology(GenerationRuntimeBinding binding, int blockX, int blockZ) {
+        if (closing.get()) {
+            return;
+        }
+        GenerationSessionLease lease;
+        try {
+            lease = acquireGenerationLease("studio_entry_hydrology");
+        } catch (GenerationSessionException failure) {
+            if (closing.get()) {
+                return;
+            }
+            throw new IllegalStateException("Studio entry hydrology preparation could not acquire its generation session.", failure);
+        }
+        try (lease;
+             GenerationRuntimeScope runtimeScope = generationRuntimeScopes.open(binding);
+             IrisContext.Scope context = IrisContext.open(this, lease.sessionId(), null)) {
+            getComplex().getHydrologyRuntime().prepareChunkColumns(blockX, blockZ);
+        } catch (Exception failure) {
+            throw new IllegalStateException("Studio entry hydrology preparation failed at "
+                    + blockX + "," + blockZ + ".", failure);
+        }
+    }
+
     private void startGenerationCacheWarm(long phaseStartedAtNanos) {
         if (!backgroundTasks.scheduleTrackedTask(() -> warmGenerationCaches(phaseStartedAtNanos))) {
             throw new IllegalStateException("Iris background task admission closed before generation cache warming.");
@@ -469,7 +458,7 @@ public class IrisEngine implements Engine {
             throw new IllegalStateException("Generation cache warming failed.", failure);
         } finally {
             IrisLogging.debug("[IrisEngine timing] cache warm total=" + (M.ms() - startedAtMillis) + "ms");
-            logStudioInitializationPhase("generation_cache_warm", phaseStartedAtNanos, false);
+            diagnostics.logStudioInitializationPhase("generation_cache_warm", phaseStartedAtNanos, false);
         }
     }
 
@@ -575,6 +564,9 @@ public class IrisEngine implements Engine {
     @BlockCoordinates
     @Override
     public IrisBiome getCaveBiome(int x, int z) {
+        if (usesScopedNaturalTerrain()) {
+            return Engine.super.getCaveBiome(x, z);
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope ignored =
                      openGenerationHistoryCoordinateScopeUnchecked(x, z, "resolve a cave biome")) {
             return Engine.super.getCaveBiome(x, z);
@@ -595,6 +587,9 @@ public class IrisEngine implements Engine {
             int z,
             IrisDimensionCarvingResolver.State state
     ) {
+        if (usesScopedNaturalTerrain()) {
+            return Engine.super.getCaveBiome(x, y, z, state);
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope ignored =
                      openGenerationHistoryCoordinateScopeUnchecked(x, z, "resolve a vertical cave biome")) {
             return Engine.super.getCaveBiome(x, y, z, state);
@@ -604,6 +599,9 @@ public class IrisEngine implements Engine {
     @BlockCoordinates
     @Override
     public IrisBiome getSurfaceBiome(int x, int z) {
+        if (usesScopedNaturalTerrain()) {
+            return Engine.super.getSurfaceBiome(x, z);
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope ignored =
                      openGenerationHistoryCoordinateScopeUnchecked(x, z, "resolve a surface biome")) {
             return Engine.super.getSurfaceBiome(x, z);
@@ -637,6 +635,10 @@ public class IrisEngine implements Engine {
     @ChunkCoordinates
     @Override
     public Set<String> getObjectsAt(int x, int z) {
+        Optional<ChunkGenerationSemantics> recorded = recordedChunkSemantics(x, z);
+        if (recorded.isPresent()) {
+            return recorded.get().objectKeys();
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope ignored =
                      openGenerationHistoryCoordinateScopeUnchecked(x << 4, z << 4, "resolve chunk objects")) {
             return getMantle().getObjectComponent().guess(x, z);
@@ -646,6 +648,15 @@ public class IrisEngine implements Engine {
     @ChunkCoordinates
     @Override
     public Set<Pair<String, BlockPos>> getPOIsAt(int chunkX, int chunkZ) {
+        Optional<ChunkGenerationSemantics> recorded = recordedChunkSemantics(chunkX, chunkZ);
+        if (recorded.isPresent()) {
+            Set<Pair<String, BlockPos>> points = new HashSet<>();
+            for (ChunkGenerationSemantics.PointOfInterest point : recorded.get().pointsOfInterest()) {
+                ChunkGenerationSemantics.BlockPosition position = point.position();
+                points.add(new Pair<>(point.key(), new BlockPos(position.x(), position.y(), position.z())));
+            }
+            return points;
+        }
         try (GenerationHistoryRuntimeRouter.CoordinateScope ignored =
                      openGenerationHistoryCoordinateScopeUnchecked(
                              chunkX << 4, chunkZ << 4, "resolve chunk points of interest")) {
@@ -654,11 +665,19 @@ public class IrisEngine implements Engine {
                     chunkX,
                     chunkZ,
                     MatterStructurePOI.class,
-                    (x, y, z, data) -> pois.add(new Pair<>(data.getType(), new BlockPos(x, y, z))));
+                    (x, y, z, data) -> pois.add(new Pair<>(data.getType(), new BlockPos(
+                            Math.addExact(Math.multiplyExact(chunkX, 16), x), y,
+                            Math.addExact(Math.multiplyExact(chunkZ, 16), z)))));
             return pois;
         }
     }
 
+    private Optional<ChunkGenerationSemantics> recordedChunkSemantics(int chunkX, int chunkZ) {
+        GenerationHistoryRuntimeRouter router = getGenerationHistoryRuntimeRouter().orElse(null);
+        return router == null ? Optional.empty()
+                : router.history().semantics(chunkX, chunkZ).filter(ChunkGenerationSemantics::sealed);
+    }
+
     private void warmupChunk(int x, int z) {
         for (int i = 0; i < 16; i++) {
             for (int j = 0; j < 16; j++) {
@@ -675,6 +694,30 @@ public class IrisEngine implements Engine {
         hotloader.hotload();
     }
 
+    public void configureStudioGenerationSource(Path source) {
+        if (!studio) {
+            throw new IllegalStateException("An authoring pack source requires a Studio engine.");
+        }
+        Path required = Objects.requireNonNull(source, "Studio generation source").toAbsolutePath().normalize();
+        synchronized (lifecycleLock) {
+            requireRunning("configure the Studio authoring pack");
+            if (studioGenerationSource != null && !studioGenerationSource.equals(required)) {
+                throw new IllegalStateException("The Studio authoring pack is already configured.");
+            }
+            studioGenerationSource = required;
+        }
+    }
+
+    public Path getStudioGenerationSource() {
+        return Objects.requireNonNull(studioGenerationSource, "Studio authoring pack is not configured");
+    }
+
+    @Override
+    public Path getPackSource() {
+        Path source = studioGenerationSource;
+        return source == null ? getData().getDataFolder().toPath() : source;
+    }
+
     public void hotloadComplex() {
         hotloader.hotloadComplex();
     }
@@ -827,6 +870,10 @@ public class IrisEngine implements Engine {
         return generationRuntimeScopes.current() != null;
     }
 
+    private boolean usesScopedNaturalTerrain() {
+        return hasGenerationRuntimeScope() && getComplex().isNaturalTerrainContext();
+    }
+
     private GenerationHistoryRuntimeRouter.CoordinateScope openGenerationHistoryCoordinateScopeUnchecked(
             int blockX,
             int blockZ,
@@ -956,7 +1003,7 @@ public class IrisEngine implements Engine {
         EngineTarget requiredTarget = Objects.requireNonNull(runtimeTarget, "detached generation target");
         Path requiredMantleStorageDirectory = IrisEngineMantle.normalizeStorageDirectory(mantleStorageDirectory);
         synchronized (lifecycleLock) {
-            requireRunning("build a detached generation runtime");
+            requireGenerationRuntimeMutation("build a detached generation runtime");
             GenerationRuntime active = runtime.generation();
             if (requiredTarget.getWorld() != active.target().getWorld()) {
                 throw new IllegalArgumentException("Detached generation runtime must target this Iris world.");
@@ -1066,7 +1113,7 @@ public class IrisEngine implements Engine {
     public void setDefaultGenerationRuntime(GenerationRuntimeBinding binding) {
         GenerationRuntimeBinding required = Objects.requireNonNull(binding, "generation runtime binding");
         synchronized (lifecycleLock) {
-            requireRunning("select the default generation runtime");
+            requireGenerationRuntimeMutation("select the default generation runtime");
             if (required.engine != this) {
                 throw new IllegalArgumentException("Generation runtime binding belongs to a different Iris engine.");
             }
@@ -1439,6 +1486,14 @@ public class IrisEngine implements Engine {
         }
     }
 
+    private void requireGenerationRuntimeMutation(String operation) {
+        if (!closed && studio && studioGenerationTransition && lifecycleState == LifecycleState.HOTLOADING
+                && generationHistoryRuntimeRouter != null) {
+            return;
+        }
+        requireRunning(operation);
+    }
+
     private boolean EngineSafe() {
         // Todo: this has potential if done right
         int EngineMCVersion = getEngineData().getStatistics().getMCVersion();
@@ -1466,6 +1521,7 @@ public class IrisEngine implements Engine {
     public enum InitializationMode {
         RUNTIME(false, true),
         STUDIO(true, true),
+        OBJECT_STUDIO(true, false),
         JIGSAW_STUDIO(true, false);
 
         private final boolean studio;

core/src/main/java/art/arcane/iris/engine/ResolvedTerrainProvider.java

@@ -0,0 +1,240 @@
+package art.arcane.iris.engine;
+
+import art.arcane.iris.engine.actuator.IrisTransitionGeometryActuator;
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.framework.EngineMode;
+import art.arcane.iris.engine.history.BoundaryColumnGeometry;
+import art.arcane.iris.engine.history.GenerationHistoryRuntimeRouter;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.engine.history.TerrainBoundarySignature;
+import art.arcane.iris.engine.history.TransitionGenerationPlan;
+import art.arcane.iris.engine.history.TransitionFluidContainment;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformBiome;
+import art.arcane.iris.spi.PlatformBlockState;
+import art.arcane.iris.spi.PlatformRegistries;
+import art.arcane.iris.util.project.context.ChunkContext;
+import art.arcane.iris.util.project.context.IrisContext;
+import art.arcane.iris.util.project.hunk.Hunk;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class ResolvedTerrainProvider {
+    private static final int MAXIMUM_CACHED_CHUNKS = 64;
+    private static final int MAXIMUM_HEIGHT_CHUNKS = 4_096;
+
+    private final Engine engine;
+    private final LinkedHashMap<Long, SavedTerrainChunk> completed = new LinkedHashMap<>(64, 0.75F, true);
+    private final ConcurrentHashMap<Long, CompletableFuture<SavedTerrainChunk>> pending = new ConcurrentHashMap<>();
+    private final LinkedHashMap<Long, SavedTerrainChunk> rawCompleted = new LinkedHashMap<>(64, 0.75F, true);
+    private final ConcurrentHashMap<Long, CompletableFuture<SavedTerrainChunk>> rawPending = new ConcurrentHashMap<>();
+    private final LinkedHashMap<Long, int[]> heights = new LinkedHashMap<>(64, 0.75F, true);
+
+    public ResolvedTerrainProvider(Engine engine) {
+        this.engine = engine;
+    }
+
+    public TerrainBoundarySignature column(int blockX, int blockZ) {
+        return resolve(blockX >> 4, blockZ >> 4).column(blockX, blockZ);
+    }
+
+    public int height(int blockX, int blockZ, boolean ignoreFluid) {
+        long key = chunkKey(blockX >> 4, blockZ >> 4);
+        synchronized (heights) {
+            int[] cached = heights.get(key);
+            if (cached != null) {
+                return cached[(ignoreFluid ? 256 : 0) + (blockX & 15) * 16 + (blockZ & 15)];
+            }
+        }
+        TerrainBoundarySignature column = resolve(blockX >> 4, blockZ >> 4).column(blockX, blockZ);
+        return ignoreFluid ? column.oceanFloorHeight() : column.surfaceHeight();
+    }
+
+    public void generate(EngineMode mode, int x, int z, Hunk<PlatformBlockState> blocks,
+                         Hunk<PlatformBiome> biomes, boolean multicore, ChunkContext context) {
+        SavedTerrainChunk terrain;
+        if (context.getComplex().getTransitionGenerationPlan() != null
+                && context.getComplex().getTransitionGenerationPlan().hasTransitionAtChunk(x >> 4, z >> 4)) {
+            terrain = resolve(x >> 4, z >> 4);
+            copy(terrain, blocks, biomes, context);
+        } else {
+            mode.generateTerrain(x, z, blocks, biomes, multicore, context);
+            terrain = capture(x, z, blocks, biomes, context, true);
+        }
+        if (engine instanceof IrisEngine irisEngine) {
+            GenerationHistoryRuntimeRouter router = irisEngine.getGenerationHistoryRuntimeRouter().orElse(null);
+            if (router != null) {
+                router.recordNaturalTerrain(terrain.boundaryOnly());
+            }
+        }
+    }
+
+    public void clear() {
+        synchronized (completed) {
+            completed.clear();
+        }
+        synchronized (rawCompleted) {
+            rawCompleted.clear();
+        }
+        synchronized (heights) {
+            heights.clear();
+        }
+    }
+
+    private SavedTerrainChunk resolve(int chunkX, int chunkZ) {
+        return resolve(chunkX, chunkZ, false);
+    }
+
+    private SavedTerrainChunk resolve(int chunkX, int chunkZ, boolean raw) {
+        LinkedHashMap<Long, SavedTerrainChunk> cache = raw ? rawCompleted : completed;
+        ConcurrentHashMap<Long, CompletableFuture<SavedTerrainChunk>> loads = raw ? rawPending : pending;
+        long key = chunkKey(chunkX, chunkZ);
+        synchronized (cache) {
+            SavedTerrainChunk cached = cache.get(key);
+            if (cached != null) {
+                return cached;
+            }
+        }
+        CompletableFuture<SavedTerrainChunk> result = new CompletableFuture<>();
+        CompletableFuture<SavedTerrainChunk> existing = loads.putIfAbsent(key, result);
+        if (existing != null) {
+            return existing.join();
+        }
+        try {
+            synchronized (cache) {
+                SavedTerrainChunk published = cache.get(key);
+                if (published != null) {
+                    result.complete(published);
+                    return published;
+                }
+            }
+            SavedTerrainChunk terrain = raw ? compute(chunkX, chunkZ) : contain(chunkX, chunkZ);
+            if (!raw) {
+                cacheHeights(key, terrain);
+            }
+            synchronized (cache) {
+                cache.put(key, terrain);
+                while (cache.size() > MAXIMUM_CACHED_CHUNKS) {
+                    cache.pollFirstEntry();
+                }
+            }
+            result.complete(terrain);
+            return terrain;
+        } catch (RuntimeException | Error failure) {
+            result.completeExceptionally(failure);
+            throw failure;
+        } finally {
+            loads.remove(key, result);
+        }
+    }
+
+    private static long chunkKey(int chunkX, int chunkZ) {
+        return ((long) chunkX << 32) | (chunkZ & 0xffffffffL);
+    }
+
+    private void cacheHeights(long key, SavedTerrainChunk terrain) {
+        int[] values = new int[512];
+        for (int x = 0; x < 16; x++) {
+            for (int z = 0; z < 16; z++) {
+                TerrainBoundarySignature column = terrain.column((terrain.chunkX() << 4) + x,
+                        (terrain.chunkZ() << 4) + z);
+                int index = x * 16 + z;
+                values[index] = column.surfaceHeight();
+                values[256 + index] = column.oceanFloorHeight();
+            }
+        }
+        synchronized (heights) {
+            heights.put(key, values);
+            while (heights.size() > MAXIMUM_HEIGHT_CHUNKS) {
+                heights.pollFirstEntry();
+            }
+        }
+    }
+
+    private SavedTerrainChunk contain(int chunkX, int chunkZ) {
+        SavedTerrainChunk raw = resolve(chunkX, chunkZ, true);
+        TransitionGenerationPlan plan = engine.getComplex().getTransitionGenerationPlan();
+        if (plan == null || !plan.hasTransitionAtChunk(chunkX, chunkZ)) {
+            return raw;
+        }
+        try {
+            return TransitionFluidContainment.contain(raw, plan, (x, z) -> rawColumn(plan, raw, x, z));
+        } catch (IOException failure) {
+            throw new IllegalStateException("Unable to contain transition fluids at " + chunkX + "," + chunkZ, failure);
+        }
+    }
+
+    private BoundaryColumnGeometry rawColumn(TransitionGenerationPlan plan, SavedTerrainChunk current, int x, int z)
+            throws IOException {
+        if (plan.isHistoricalBlock(x, z)) {
+            BoundaryColumnGeometry geometry = plan.terrainSignatures().signatureAt(x, z)
+                    .orElseThrow(() -> new IOException("Missing saved terrain boundary column at " + x + "," + z))
+                    .geometry();
+            if (geometry.minimumY() != engine.getMinHeight() || geometry.height() != engine.getHeight()) {
+                throw new IOException("Saved terrain boundary column has the wrong vertical layout at " + x + "," + z);
+            }
+            return geometry;
+        }
+        return (x >> 4) == current.chunkX() && (z >> 4) == current.chunkZ()
+                ? current.column(x, z).geometry() : resolve(x >> 4, z >> 4, true).column(x, z).geometry();
+    }
+
+    private SavedTerrainChunk compute(int chunkX, int chunkZ) {
+        int x = Math.multiplyExact(chunkX, 16);
+        int z = Math.multiplyExact(chunkZ, 16);
+        try (GenerationHistoryRuntimeRouter.CoordinateScope runtimeScope = engine instanceof IrisEngine irisEngine
+                ? irisEngine.openGenerationHistoryCoordinateScope(x, z) : null) {
+            IrisContext active = IrisContext.get();
+            long sessionId = active == null ? 0L : active.getGenerationSessionId();
+            ChunkContext context = new ChunkContext(x, z, engine.getComplex(), sessionId, true,
+                ChunkContext.PrefillPlan.NATURAL_TERRAIN, engine.getMetrics(), engine.getDimensionStackContext());
+            context.beginSpeculativeTerrain();
+            Hunk<PlatformBlockState> blocks = Hunk.newArrayHunk(16, engine.getHeight(), 16);
+            Hunk<PlatformBiome> biomes = Hunk.newArrayHunk(16, engine.getHeight(), 16);
+            try (IrisContext.Scope ignored = IrisContext.open(engine, sessionId, context)) {
+                engine.getMode().generateTerrain(x, z, blocks, biomes, false, context);
+                return capture(x, z, blocks, biomes, context, false);
+            }
+        } catch (IOException failure) {
+            throw new IllegalStateException("Unable to scope natural terrain at " + chunkX + "," + chunkZ, failure);
+        }
+    }
+
+    private SavedTerrainChunk capture(int x, int z, Hunk<PlatformBlockState> blocks,
+                                      Hunk<PlatformBiome> biomes, ChunkContext context, boolean boundaryOnly) {
+        try {
+            return IrisTransitionGeometryActuator.capture(x, z, blocks, biomes, engine.getMinHeight(), context, boundaryOnly);
+        } catch (IOException failure) {
+            throw new IllegalStateException("Unable to capture natural terrain at " + (x >> 4) + "," + (z >> 4), failure);
+        }
+    }
+
+    private static void copy(SavedTerrainChunk terrain, Hunk<PlatformBlockState> blocks,
+                             Hunk<PlatformBiome> biomes, ChunkContext context) {
+        PlatformRegistries registries = IrisPlatforms.get().registries();
+        Map<String, PlatformBlockState> states = new HashMap<>();
+        Map<String, PlatformBiome> physicalBiomes = new HashMap<>();
+        for (int x = 0; x < 16; x++) {
+            for (int z = 0; z < 16; z++) {
+                TerrainBoundarySignature column = terrain.column((terrain.chunkX() << 4) + x, (terrain.chunkZ() << 4) + z);
+                BoundaryColumnGeometry geometry = column.geometry();
+                for (int offset = 0; offset < blocks.getHeight(); offset++) {
+                    String stateKey = geometry.voxelAt(geometry.minimumY() + offset).stateKey();
+                    PlatformBlockState state = states.computeIfAbsent(stateKey, registries::blockOrNull);
+                    if (state == null) {
+                        throw new IllegalStateException("Resolved terrain requires unavailable block state " + stateKey);
+                    }
+                    blocks.setRaw(x, offset, z, state);
+                    String biomeKey = column.biomeAtSample(offset / 4);
+                    biomes.setRaw(x, offset, z, physicalBiomes.computeIfAbsent(biomeKey, registries::biome));
+                }
+                context.setTerrainHeight(x, z, column.oceanFloorHeight());
+            }
+        }
+    }
+}

core/src/main/java/art/arcane/iris/engine/StudioGenerationUpdate.java

@@ -0,0 +1,88 @@
+package art.arcane.iris.engine;
+
+import art.arcane.iris.core.loader.IrisData;
+import art.arcane.iris.core.pack.PackValidationResult;
+import art.arcane.iris.core.pack.PackValidator;
+import art.arcane.iris.core.pack.AtomicDirectoryPublisher;
+import art.arcane.iris.engine.history.GenerationEpoch;
+import art.arcane.iris.engine.history.GenerationEpochContractFactory;
+import art.arcane.iris.engine.history.GenerationHistory;
+import art.arcane.iris.engine.history.GenerationPackFingerprint;
+import art.arcane.iris.engine.history.GenerationPackRepository;
+import art.arcane.iris.engine.history.GenerationRegistryContract;
+import art.arcane.iris.engine.history.GenerationRegistryContractFactory;
+import art.arcane.iris.engine.object.IrisDimension;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.nio.file.Files;
+import java.util.List;
+
+record StudioGenerationUpdate(
+        Path stagingRoot,
+        Path source,
+        String fingerprint,
+        GenerationEpoch.DimensionContract dimensionContract,
+        GenerationRegistryContract registryContract
+) implements AutoCloseable {
+    static StudioGenerationUpdate prepare(IrisEngine engine, GenerationHistory history) throws IOException {
+        Path source = engine.getStudioGenerationSource();
+        IrisData.invalidateLoadedAuthoringResources(source.toFile());
+        String fingerprint = GenerationPackFingerprint.compute(source, GenerationPackFingerprint.CURRENT_VERSION);
+        GenerationEpoch active = history.activeEpoch();
+        if (active.packFingerprintVersion() == GenerationPackFingerprint.CURRENT_VERSION
+                && fingerprint.equals(active.packFingerprint())) {
+            return null;
+        }
+        Path stagingRoot = Files.createTempDirectory(history.paths().generationRoot(), ".studio-");
+        Path snapshot = stagingRoot.resolve(source.getFileName());
+        try {
+            GenerationPackRepository.copyPackTree(source, snapshot);
+            if (!fingerprint.equals(GenerationPackFingerprint.compute(snapshot, GenerationPackFingerprint.CURRENT_VERSION))) {
+                throw new IOException("Studio pack changed while its update snapshot was being captured.");
+            }
+            return prepareSnapshot(engine, history, stagingRoot, snapshot, fingerprint);
+        } catch (Throwable failure) {
+            try {
+                AtomicDirectoryPublisher.deleteTree(stagingRoot);
+            } catch (IOException cleanupFailure) {
+                failure.addSuppressed(cleanupFailure);
+            }
+            throw failure;
+        }
+    }
+
+    private static StudioGenerationUpdate prepareSnapshot(IrisEngine engine, GenerationHistory history,
+                                                           Path stagingRoot, Path source, String fingerprint)
+            throws IOException {
+        GenerationEpoch active = history.activeEpoch();
+        PackValidationResult validation = PackValidator.validate(source.toFile());
+        if (!validation.isLoadable()) {
+            throw new IOException("Studio pack update is invalid: " + String.join("; ", validation.getBlockingErrors()));
+        }
+        IrisData data = IrisData.openRuntime(source.toFile());
+        try {
+            IrisDimension replacement = data.getDimensionLoader().load(active.dimensionContract().dimensionKey());
+            if (replacement == null) {
+                throw new IOException("Studio pack update is missing dimension '"
+                        + active.dimensionContract().dimensionKey() + "'.");
+            }
+            engine.getPlatformHooks().validateDimensionHotload(engine, replacement);
+            GenerationEpoch.DimensionContract contract = GenerationEpochContractFactory.create(
+                    replacement, replacement.getLoadKey(), active.dimensionContract().dimensionTypeKey());
+            if (!active.dimensionContract().hasSameLayout(contract)) {
+                throw new IOException("Studio pack update changes the world's immutable dimension layout.");
+            }
+            GenerationRegistryContract registry = GenerationRegistryContractFactory.create(data, replacement, fingerprint);
+            registry.requireDefinitionsAvailableIn(GenerationRegistryContractFactory.captureRequiredDefinitions(List.of(registry)));
+            return new StudioGenerationUpdate(stagingRoot, source, fingerprint, contract, registry);
+        } finally {
+            data.close();
+        }
+    }
+
+    @Override
+    public void close() throws IOException {
+        AtomicDirectoryPublisher.deleteTree(stagingRoot);
+    }
+}

core/src/main/java/art/arcane/iris/engine/UpperDimensionContext.java

@@ -20,8 +20,6 @@ package art.arcane.iris.engine;
 
 import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.engine.framework.Engine;
-import art.arcane.iris.engine.history.GenerationBlend;
-import art.arcane.iris.engine.history.TransitionGenerationPlan;
 import art.arcane.iris.engine.image.IrisImageMapRuntime;
 import art.arcane.iris.engine.object.IrisBiome;
 import art.arcane.iris.engine.object.IrisDimension;
@@ -33,16 +31,12 @@ import art.arcane.iris.util.project.stream.ProceduralStream;
 public class UpperDimensionContext implements DataProvider {
     private final DimensionTerrainContext terrainContext;
     private final ProceduralStream<Double> lowerHeightStream;
-    private final ProceduralStream<Double> unblendedLowerHeightStream;
-    private final TransitionGenerationPlan transitionPlan;
     private final CeilingLayout ceilingLayout;
 
     private UpperDimensionContext(DimensionTerrainContext terrainContext, Engine engine) {
         this.terrainContext = terrainContext;
         IrisComplex complex = engine.getComplex();
         lowerHeightStream = complex.getHeightStream();
-        unblendedLowerHeightStream = complex.getUnblendedNaturalHeightStream();
-        transitionPlan = complex.getTransitionGenerationPlan();
         ceilingLayout = new CeilingLayout(engine.getHeight(), engine.getDimension().getUpperDimensionGap());
     }
 
@@ -103,18 +97,6 @@ public class UpperDimensionContext implements DataProvider {
                 0D,
                 Math.min(ceilingLayout.height() - 1D, terrainContext.getNormalTerrainHeight(x, z))
         );
-        if (transitionPlan != null) {
-            TransitionGenerationPlan.TerrainSample sample = transitionPlan.terrainSampleAt(x, z);
-            if (sample.newEpochWeight() < 1D && sample.hasHistoricalSignature()) {
-                int targetLowerSurfaceY = (int) Math.min(
-                        ceilingLayout.height(),
-                        Math.round(unblendedLowerHeightStream.getDouble(x, z))
-                );
-                int targetSurfaceY = effectiveSurfaceY(depth, ceilingLayout, targetLowerSurfaceY);
-                double targetDepth = Math.max(0D, ceilingLayout.height() - 1D - targetSurfaceY);
-                depth = blendCeilingDepth(targetDepth, sample);
-            }
-        }
         int lowerSurfaceY = (int) Math.min(
                 ceilingLayout.height(),
                 Math.round(lowerHeightStream.getDouble(x, z))
@@ -122,14 +104,6 @@ public class UpperDimensionContext implements DataProvider {
         return effectiveSurfaceY(depth, ceilingLayout, lowerSurfaceY);
     }
 
-    static double blendCeilingDepth(double newDepth, TransitionGenerationPlan.TerrainSample sample) {
-        if (sample.newEpochWeight() == 1D || !sample.hasHistoricalSignature()) {
-            return newDepth;
-        }
-        return GenerationBlend.interpolate(
-                sample.historicalUpperCeilingDepth(), newDepth, sample.newEpochWeight());
-    }
-
     static int effectiveSurfaceY(double depth, CeilingLayout layout, int lowerSurfaceY) {
         long mirroredSurface = layout.height() - 1L - Math.round(depth);
         long gapSurface = (long) lowerSurfaceY + layout.minimumGap();

core/src/main/java/art/arcane/iris/engine/actuator/IrisBiomeActuator.java

@@ -36,6 +36,7 @@ import art.arcane.iris.util.project.hunk.Hunk;
 import art.arcane.volmlib.util.collection.KMap;
 import art.arcane.volmlib.util.documentation.BlockCoordinates;
 import art.arcane.volmlib.util.mantle.runtime.Mantle;
+import art.arcane.volmlib.util.mantle.runtime.MantleChunk;
 import art.arcane.volmlib.util.math.RNG;
 import art.arcane.volmlib.util.matter.Matter;
 import art.arcane.volmlib.util.matter.MatterBiomeInject;
@@ -65,7 +66,7 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
         int depth = h.getDepth();
         int height = h.getHeight();
         Engine engine = getEngine();
-        Mantle<Matter> mantle = engine.getMantle().getMantle();
+        Mantle<Matter> mantle = context.isSpeculativeTerrain() ? null : engine.getMantle().getMantle();
         ChunkedDataCache<IrisBiome> biomeCache = context.getBiome();
         IrisComplex complex = context.getComplex();
         DimensionStackContext dimensionStackContext = engine.getDimensionStackContext();
@@ -74,21 +75,6 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
             for (int zf = 0; zf < depth; zf++) {
                 int worldX = x + xf;
                 int worldZ = z + zf;
-                if (!complex.allowsNewDiscreteContentAt(worldX, worldZ)) {
-                    writeHistoricalColumn(
-                            h,
-                            mantle,
-                            xf,
-                            zf,
-                            worldX,
-                            worldZ,
-                            height,
-                            engine,
-                            complex
-                    );
-                    continue;
-                }
-
                 IrisBiome biome = biomeCache.get(xf, zf);
                 ResolvedBiome resolved = resolve(biomeKey(
                         biome,
@@ -117,11 +103,39 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
                             context.getDimensionStackLayout(xf, zf)
                     );
                 }
+                writeHistoricalColumn(h, mantle, xf, zf, worldX, worldZ, height, engine, complex);
             }
         }
         engine.getMetrics().getBiome().put(p.getMilliseconds());
     }
 
+    public static void publishNaturalMetadata(Engine engine, int x, int z, Hunk<PlatformBiome> biomes,
+                                               ChunkContext context) {
+        if (context.isSpeculativeTerrain() || !context.getComplex().allowsMantleChunkWrite(x >> 4, z >> 4)) {
+            return;
+        }
+        Mantle<Matter> mantle = engine.getMantle().getMantle();
+        MantleChunk<Matter> chunk = mantle.getChunk(x >> 4, z >> 4).use();
+        try {
+            synchronized (chunk) {
+                IrisDimensionStackActuator.clearNaturalMetadata(chunk, context, biomes.getHeight());
+                chunk.deleteSlices(MatterBiomeInject.class);
+                for (int localX = 0; localX < biomes.getWidth(); localX += 4) {
+                    for (int localZ = 0; localZ < biomes.getDepth(); localZ += 4) {
+                        for (int y = 0; y < biomes.getHeight(); y += 4) {
+                            PlatformBiome biome = biomes.getRaw(localX, y, localZ);
+                            if (biome != null) {
+                                mantle.set(x + localX, y, z + localZ, BiomeInjectMatter.get(biome.key()));
+                            }
+                        }
+                    }
+                }
+            }
+        } finally {
+            chunk.release();
+        }
+    }
+
     private void writeHistoricalColumn(
             Hunk<PlatformBiome> output,
             Mantle<Matter> mantle,
@@ -137,14 +151,17 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
         if (transitionPlan == null) {
             return;
         }
-        TransitionGenerationPlan.TerrainSample sample = transitionPlan.terrainSampleAt(worldX, worldZ);
+        TransitionGenerationPlan.TerrainSample terrainSample = transitionPlan.terrainSampleAt(worldX, worldZ);
+        if (terrainSample.newEpochWeight() == 1D) {
+            return;
+        }
         int minimumWorldY = engine.getMinHeight();
-        String activeKey = sample.historicalPhysicalBiomeKeyAt(minimumWorldY).orElse(null);
+        String activeKey = transitionPlan.historicalPhysicalBiomeKeyAt(worldX, minimumWorldY, worldZ, terrainSample).orElse(null);
         int rangeStart = 0;
         for (int internalY = 1; internalY <= height; internalY++) {
             String nextKey = internalY == height
                     ? null
-                    : sample.historicalPhysicalBiomeKeyAt(minimumWorldY + internalY).orElse(null);
+                    : transitionPlan.historicalPhysicalBiomeKeyAt(worldX, minimumWorldY + internalY, worldZ, terrainSample).orElse(null);
             if (Objects.equals(activeKey, nextKey)) {
                 continue;
             }
@@ -179,7 +196,9 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
         if (resolved.biome() != null) {
             output.set(localX, 0, localZ, localX, height - 1, localZ, resolved.biome());
         }
-        mantle.set(worldX, 0, worldZ, resolved.matter());
+        if (mantle != null) {
+            mantle.set(worldX, 0, worldZ, resolved.matter());
+        }
     }
 
     private void applyDimensionStackBiomes(
@@ -256,7 +275,9 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
         if (minimumY > maximumY) {
             return;
         }
-        clearBiomeMatterRange(mantle, worldX, worldZ, minimumY, maximumY);
+        if (mantle != null) {
+            clearBiomeMatterRange(mantle, worldX, worldZ, minimumY, maximumY);
+        }
         if (resolved.biome() != null) {
             output.set(
                     localX,
@@ -268,7 +289,7 @@ public class IrisBiomeActuator extends EngineAssignedActuator<PlatformBiome> {
                     resolved.biome()
             );
         }
-        if (resolved.matter() != null) {
+        if (mantle != null && resolved.matter() != null) {
             mantle.set(worldX, minimumY, worldZ, resolved.matter());
         }
     }

core/src/main/java/art/arcane/iris/engine/actuator/IrisDimensionStackActuator.java

@@ -33,6 +33,7 @@ import art.arcane.iris.util.common.data.B;
 import art.arcane.iris.util.project.context.ChunkContext;
 import art.arcane.iris.util.project.hunk.Hunk;
 import art.arcane.iris.util.project.matter.TileWrapper;
+import art.arcane.iris.util.project.matter.PreObjectMatterCell;
 import art.arcane.volmlib.util.collection.KList;
 import art.arcane.volmlib.util.documentation.BlockCoordinates;
 import art.arcane.volmlib.util.mantle.runtime.MantleChunk;
@@ -81,8 +82,8 @@ public final class IrisDimensionStackActuator extends EngineAssignedActuator<Pla
         if (getEngine().getDimensionStackContext() == null) {
             return;
         }
-        MantleChunk<Matter> mantleChunk = getEngine().getMantle().getMantle()
+        MantleChunk<Matter> mantleChunk = context.isSpeculativeTerrain() ? null
-                .getChunk(x >> 4, z >> 4).use();
+                : getEngine().getMantle().getMantle().getChunk(x >> 4, z >> 4).use();
         try {
             MetadataCleaner metadata = new MetadataCleaner(mantleChunk, blocks.getHeight());
             for (int localX = 0; localX < blocks.getWidth(); localX++) {
@@ -100,7 +101,26 @@ public final class IrisDimensionStackActuator extends EngineAssignedActuator<Pla
                 }
             }
         } finally {
-            mantleChunk.release();
+            if (mantleChunk != null) {
+                mantleChunk.release();
+            }
+        }
+    }
+
+    public static void clearNaturalMetadata(MantleChunk<Matter> chunk, ChunkContext context, int height) {
+        MetadataCleaner metadata = new MetadataCleaner(chunk, height);
+        for (int x = 0; x < 16; x++) {
+            for (int z = 0; z < 16; z++) {
+                DimensionStackLayout layout = context.getDimensionStackLayout(x, z);
+                if (layout == null) {
+                    continue;
+                }
+                for (int y = 0; y < height; y++) {
+                    if (layout.isHostFeatureProtectedY(y)) {
+                        metadata.clear(x, y, z);
+                    }
+                }
+            }
         }
     }
 
@@ -229,17 +249,46 @@ public final class IrisDimensionStackActuator extends EngineAssignedActuator<Pla
         }
 
         void clear(int x, int y, int z) {
-            int sectionIndex = y >> 4;
+            if (chunk == null) {
-            List<MatterSlice<?>> slices = slicesBySection[sectionIndex];
+                return;
-            if (slices == null) {
-                slices = resolveSlices(sectionIndex);
-                slicesBySection[sectionIndex] = slices;
             }
-            for (MatterSlice<?> slice : slices) {
+            synchronized (chunk) {
-                slice.set(x, y & 15, z, null);
+                int sectionIndex = y >> 4;
+                captureNaturalFacts(sectionIndex, x, y & 15, z);
+                List<MatterSlice<?>> slices = slicesBySection[sectionIndex];
+                if (slices == null) {
+                    slices = resolveSlices(sectionIndex);
+                    slicesBySection[sectionIndex] = slices;
+                }
+                for (MatterSlice<?> slice : slices) {
+                    slice.set(x, y & 15, z, null);
+                }
             }
         }
 
+        private void captureNaturalFacts(int sectionIndex, int x, int y, int z) {
+            Matter section = chunk.get(sectionIndex);
+            if (section == null) {
+                return;
+            }
+            MatterSlice<MatterCavern> caverns = section.getSlice(MatterCavern.class);
+            MatterSlice<HydrologyCaveCell> hydrology = section.getSlice(HydrologyCaveCell.class);
+            MatterCavern cavern = caverns == null ? null : caverns.get(x, y, z);
+            HydrologyCaveCell cell = hydrology == null ? null : hydrology.get(x, y, z);
+            if (cavern == null && cell == null) {
+                return;
+            }
+            MatterSlice<PreObjectMatterCell> journal = section.slice(PreObjectMatterCell.class);
+            PreObjectMatterCell previous = journal.get(x, y, z);
+            if (cavern != null) {
+                previous = previous == null ? PreObjectMatterCell.cavern(cavern) : previous.captureCavern(cavern);
+            }
+            if (cell != null) {
+                previous = previous == null ? PreObjectMatterCell.hydrology(cell) : previous.captureHydrology(cell);
+            }
+            journal.set(x, y, z, previous);
+        }
+
         private List<MatterSlice<?>> resolveSlices(int sectionIndex) {
             Matter section = chunk.get(sectionIndex);
             if (section == null) {

core/src/main/java/art/arcane/iris/engine/actuator/IrisTransitionGeometryActuator.java

@@ -0,0 +1,157 @@
+package art.arcane.iris.engine.actuator;
+
+import art.arcane.iris.engine.framework.Engine;
+import art.arcane.iris.engine.framework.EngineAssignedComponent;
+import art.arcane.iris.engine.framework.EngineStage;
+import art.arcane.iris.engine.history.BoundaryColumnGeometry;
+import art.arcane.iris.engine.history.BoundaryGeometryInfluence;
+import art.arcane.iris.engine.history.GenerationBlend;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+import art.arcane.iris.engine.history.TransitionGenerationPlan;
+import art.arcane.iris.engine.history.TransitionGeometryBlender;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformBiome;
+import art.arcane.iris.spi.PlatformBlockState;
+import art.arcane.iris.spi.PlatformRegistries;
+import art.arcane.iris.util.project.context.ChunkContext;
+import art.arcane.iris.util.project.hunk.Hunk;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.IdentityHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.OptionalInt;
+
+public final class IrisTransitionGeometryActuator extends EngineAssignedComponent implements EngineStage {
+    public IrisTransitionGeometryActuator(Engine engine) {
+        super(engine, "Terrain Transition");
+    }
+
+    @Override
+    public void close() {
+        super.close();
+    }
+
+    @Override
+    public void generate(int x, int z, Hunk<PlatformBlockState> blocks, Hunk<PlatformBiome> biomes,
+                         boolean multicore, ChunkContext context) {
+        TransitionGenerationPlan plan = context.getComplex().getTransitionGenerationPlan();
+        if (plan == null || !plan.hasTransitionAtChunk(x >> 4, z >> 4)) {
+            return;
+        }
+        GeometrySource source = new GeometrySource(blocks, biomes, getEngine().getMinHeight(), context);
+        if (plan != null && plan.hasTransitionAtChunk(x >> 4, z >> 4)) {
+            blendGeometry(x, z, blocks, context, source, plan);
+        }
+    }
+
+    public static SavedTerrainChunk capture(int x, int z, Hunk<PlatformBlockState> blocks,
+                                             Hunk<PlatformBiome> biomes, int minimumY,
+                                             ChunkContext context, boolean boundaryOnly) throws IOException {
+        GeometrySource source = new GeometrySource(blocks, biomes, minimumY, context);
+        return boundaryOnly
+                ? SavedTerrainChunk.captureBoundary(x >> 4, z >> 4, minimumY, blocks.getHeight(), "minecraft:noise", source)
+                : SavedTerrainChunk.capture(x >> 4, z >> 4, minimumY, blocks.getHeight(), "minecraft:noise", source);
+    }
+
+    private void blendGeometry(int x, int z, Hunk<PlatformBlockState> blocks, ChunkContext context,
+                               GeometrySource source, TransitionGenerationPlan plan) {
+        PlatformRegistries registries = IrisPlatforms.get().registries();
+        Map<String, PlatformBlockState> resolved = new HashMap<>();
+        for (int localX = 0; localX < blocks.getWidth(); localX++) {
+            for (int localZ = 0; localZ < blocks.getDepth(); localZ++) {
+                BoundaryGeometryInfluence influence = plan.geometryAt(x + localX, z + localZ);
+                if (influence.newTerrainWeight() == 1D || influence.contributions().isEmpty()) {
+                    continue;
+                }
+                BoundaryColumnGeometry current = source.column(localX, localZ);
+                BoundaryColumnGeometry blended = TransitionGeometryBlender.blendColumn(
+                        influence, x + localX, z + localZ, current);
+                if (blended == current) {
+                    continue;
+                }
+                double expectedFloor = GenerationBlend.interpolate(
+                        plan.terrainSampleAt(x + localX, z + localZ).historicalOceanFloorHeight(),
+                        context.getRoundedHeight(localX, localZ), influence.newTerrainWeight());
+                int floor = blended.surfaceOffsetNear(expectedFloor);
+                List<BoundaryColumnGeometry.Voxel> voxels = blended.voxels();
+                for (int offset = 0; offset < voxels.size(); offset++) {
+                    BoundaryColumnGeometry.Voxel voxel = voxels.get(offset);
+                    PlatformBlockState existing = blocks.getRaw(localX, offset, localZ);
+                    if (existing != null && existing.key().equals(voxel.stateKey())) {
+                        continue;
+                    }
+                    PlatformBlockState replacement = resolved.computeIfAbsent(voxel.stateKey(), registries::blockOrNull);
+                    if (replacement == null) {
+                        throw new IllegalStateException("Terrain boundary requires unavailable block state " + voxel.stateKey());
+                    }
+                    blocks.setRaw(localX, offset, localZ, replacement);
+                }
+                context.setTerrainHeight(localX, localZ, floor);
+            }
+        }
+    }
+
+    private static final class GeometrySource implements SavedTerrainChunk.VoxelSource {
+        private final Hunk<PlatformBlockState> blocks;
+        private final Hunk<PlatformBiome> biomes;
+        private final int minimumY;
+        private final ChunkContext context;
+        private final Map<PlatformBlockState, BoundaryColumnGeometry.Voxel> voxels = new IdentityHashMap<>();
+
+        private GeometrySource(Hunk<PlatformBlockState> blocks, Hunk<PlatformBiome> biomes, int minimumY, ChunkContext context) {
+            this.blocks = blocks;
+            this.biomes = biomes;
+            this.minimumY = minimumY;
+            this.context = context;
+        }
+
+        @Override
+        public BoundaryColumnGeometry.Voxel voxel(int localX, int worldY, int localZ) {
+            PlatformBlockState state = blocks.getRaw(localX, worldY - minimumY, localZ);
+            if (state == null) {
+                state = IrisPlatforms.get().registries().air();
+            }
+            return voxels.computeIfAbsent(state, GeometrySource::encode);
+        }
+
+        @Override
+        public OptionalInt groundSurface(int localX, int localZ) {
+            return OptionalInt.of(Math.max(0, Math.min(blocks.getHeight() - 1, context.getRoundedHeight(localX, localZ))));
+        }
+
+        @Override
+        public String biome(int localX, int worldY, int localZ) throws IOException {
+            PlatformBiome biome = biomes.getRaw(localX, worldY - minimumY, localZ);
+            if (biome == null) {
+                throw new IOException("Natural terrain has no physical biome at " + localX + "," + worldY + "," + localZ);
+            }
+            return biome.key();
+        }
+
+        private BoundaryColumnGeometry column(int localX, int localZ) {
+            ArrayList<BoundaryColumnGeometry.Voxel> values = new ArrayList<>(blocks.getHeight());
+            for (int offset = 0; offset < blocks.getHeight(); offset++) {
+                values.add(voxel(localX, minimumY + offset, localZ));
+            }
+            return BoundaryColumnGeometry.fromVoxels(minimumY, values);
+        }
+
+        private static BoundaryColumnGeometry.Voxel encode(PlatformBlockState state) {
+            boolean custom = state.isCustom();
+            PlatformBlockState nativeState = state.placementBaseState();
+            if (nativeState != null) {
+                state = nativeState;
+            }
+            BoundaryColumnGeometry.Phase phase = state.isAir() ? BoundaryColumnGeometry.Phase.AIR
+                    : state.isFluid() ? BoundaryColumnGeometry.Phase.FLUID : BoundaryColumnGeometry.Phase.SOLID;
+            String fluidKey = state.isFluid() ? state.key()
+                    : state.isWaterLogged() ? "minecraft:water[level=0]" : "";
+            boolean protectedContent = custom || state.isDecorant() || state.isFoliage() || state.isTreeBlock()
+                    || state.hasTileEntity();
+            return new BoundaryColumnGeometry.Voxel(state.key(), phase, fluidKey, protectedContent);
+        }
+    }
+}

core/src/main/java/art/arcane/iris/engine/decorator/IrisShoreLineDecorator.java

@@ -40,17 +40,16 @@ public class IrisShoreLineDecorator extends IrisEngineDecorator {
     @Override
     public void decorate(int x, int z, int realX, int realX1, int realX_1, int realZ, int realZ1, int realZ_1,
                          Hunk<PlatformBlockState> data, IrisBiome biome, int height, int max) {
-        double localFluidHeight = getComplex().getRiverWaterSurfaceStream().get(realX, realZ);
+        double localFluidHeight = getEngine().getMantle().getFluidHeight(realX, realZ);
         if (height != Math.round(localFluidHeight)) {
             return;
         }
 
         ProceduralStream<Double> heightStream = getComplex().getHeightStream();
-        ProceduralStream<Double> fluidStream = getComplex().getRiverWaterSurfaceStream();
+        if (Math.round(heightStream.get(realX1, realZ)) >= getEngine().getMantle().getFluidHeight(realX1, realZ)
-        if (Math.round(heightStream.get(realX1, realZ)) >= Math.round(fluidStream.get(realX1, realZ))
+                && Math.round(heightStream.get(realX_1, realZ)) >= getEngine().getMantle().getFluidHeight(realX_1, realZ)
-                && Math.round(heightStream.get(realX_1, realZ)) >= Math.round(fluidStream.get(realX_1, realZ))
+                && Math.round(heightStream.get(realX, realZ1)) >= getEngine().getMantle().getFluidHeight(realX, realZ1)
-                && Math.round(heightStream.get(realX, realZ1)) >= Math.round(fluidStream.get(realX, realZ1))
+                && Math.round(heightStream.get(realX, realZ_1)) >= getEngine().getMantle().getFluidHeight(realX, realZ_1)) {
-                && Math.round(heightStream.get(realX, realZ_1)) >= Math.round(fluidStream.get(realX, realZ_1))) {
             return;
         }
 

core/src/main/java/art/arcane/iris/engine/decorator/IrisSurfaceDecorator.java

@@ -60,7 +60,7 @@ public class IrisSurfaceDecorator extends IrisEngineDecorator {
     @BlockCoordinates
     public void decorate(int x, int z, int realX, int realX1, int realX_1, int realZ, int realZ1, int realZ_1,
                          Hunk<PlatformBlockState> data, IrisBiome biome, InferredType inferredType, int height, int max) {
-        int fluidHeight = (int) Math.round(getComplex().getRiverWaterSurfaceStream().get(realX, realZ));
+        int fluidHeight = getEngine().getMantle().getFluidHeight(realX, realZ);
         if (inferredType == InferredType.SHORE && height < fluidHeight) {
             return;
         }

core/src/main/java/art/arcane/iris/engine/framework/Engine.java

@@ -19,6 +19,7 @@
 package art.arcane.iris.engine.framework;
 
 
+
 import art.arcane.iris.core.IrisSettings;
 import art.arcane.iris.engine.framework.render.RenderType;
 import art.arcane.iris.engine.framework.render.Renderer;
@@ -75,6 +76,9 @@ import art.arcane.iris.util.project.stream.ProceduralStream;
 import org.jetbrains.annotations.Nullable;
 
 import java.awt.Color;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.OptionalInt;
 import java.util.Locale;
 import java.util.Set;
 import java.util.UUID;
@@ -166,12 +170,7 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
         if (context != null && context.getEngine() == this && context.getGenerationSessionId() != 0L) {
             return generationSessions.continueSession(operation, context.getGenerationSessionId());
         }
-        if (isClosing() || isClosed()) {
+        return generationSessions.acquireForEngine(this, operation);
-            throw new GenerationSessionException("Generation session rejected new work for " + operation
-                    + " while the Iris engine is closing.", isClosed());
-        }
-
-        return generationSessions.acquire(operation);
     }
 
     default long getGenerationSessionId() {
@@ -238,6 +237,8 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
         return getTarget().getData();
     }
 
+    Path getPackSource();
+
     default IrisWorld getWorld() {
         return getTarget().getWorld();
     }
@@ -448,6 +449,10 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
 
     @BlockCoordinates
     default int getHeight(int x, int z, boolean ignoreFluid) {
+        OptionalInt resolved = getComplex().resolvedTerrainHeight(x, z, ignoreFluid);
+        if (resolved.isPresent()) {
+            return resolved.getAsInt();
+        }
         DimensionStackContext dimensionStackContext = getDimensionStackContext();
         if (dimensionStackContext != null) {
             return ignoreFluid

core/src/main/java/art/arcane/iris/engine/framework/EngineLifecycleTasks.java

@@ -3,6 +3,7 @@ package art.arcane.iris.engine.framework;
 import art.arcane.iris.util.project.context.IrisContext;
 
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Supplier;
 
 public final class EngineLifecycleTasks {
@@ -13,10 +14,16 @@ public final class EngineLifecycleTasks {
         Objects.requireNonNull(engine);
         Objects.requireNonNull(operation);
         Objects.requireNonNull(task);
-        try (GenerationSessionLease lease = engine.acquireGenerationLease(operation);
+        try {
-             IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+            Optional<GenerationSessionLease> admitted = tryAcquire(engine, operation);
-            task.run();
+            if (admitted.isEmpty()) {
-            return true;
+                return false;
+            }
+            try (GenerationSessionLease lease = admitted.get();
+                 IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+                task.run();
+                return true;
+            }
         } catch (GenerationSessionException exception) {
             if (engine.isClosing() || engine.isClosed() || exception.isExpectedTeardown()) {
                 return false;
@@ -27,9 +34,17 @@ public final class EngineLifecycleTasks {
 
     public static <T> T call(Engine engine, String operation, Supplier<T> task, T unavailable) {
         Objects.requireNonNull(task);
-        try (GenerationSessionLease lease = engine.acquireGenerationLease(operation);
+        Objects.requireNonNull(engine);
-             IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+        Objects.requireNonNull(operation);
-            return task.get();
+        try {
+            Optional<GenerationSessionLease> admitted = tryAcquire(engine, operation);
+            if (admitted.isEmpty()) {
+                return unavailable;
+            }
+            try (GenerationSessionLease lease = admitted.get();
+                 IrisContext.Scope ignored = IrisContext.open(engine, lease.sessionId(), null)) {
+                return task.get();
+            }
         } catch (GenerationSessionException exception) {
             if (engine.isClosing() || engine.isClosed() || exception.isExpectedTeardown()) {
                 return unavailable;
@@ -37,4 +52,11 @@ public final class EngineLifecycleTasks {
             throw new IllegalStateException("Iris lifecycle rejected " + operation + ".", exception);
         }
     }
+
+    private static Optional<GenerationSessionLease> tryAcquire(Engine engine, String operation)
+            throws GenerationSessionException {
+        GenerationSessionManager sessions = engine.getGenerationSessions();
+        return sessions == null ? Optional.of(GenerationSessionLease.noop())
+                : sessions.tryAcquireForEngine(engine, operation);
+    }
 }

core/src/main/java/art/arcane/iris/engine/framework/EngineMode.java

@@ -19,6 +19,8 @@
 package art.arcane.iris.engine.framework;
 
 import art.arcane.iris.engine.IrisComplex;
+import art.arcane.iris.engine.actuator.IrisBiomeActuator;
+import art.arcane.volmlib.util.collection.KList;
 import art.arcane.iris.engine.IrisEngine;
 import art.arcane.iris.engine.mantle.EngineMantle;
 import art.arcane.iris.util.project.context.ChunkContext;
@@ -31,6 +33,21 @@ import art.arcane.iris.spi.PlatformBiome;
 import art.arcane.iris.spi.PlatformBlockState;
 
 public interface EngineMode extends Staged {
+    KList<EngineStage> getTerrainStages();
+
+    void registerTerrainStage(EngineStage stage);
+
+    EngineStage getTransitionStage();
+
+    default void generateTerrain(int x, int z, Hunk<PlatformBlockState> blocks, Hunk<PlatformBiome> biomes,
+                                 boolean multicore, ChunkContext context) {
+        context.setTerrainBiomeOutput(biomes);
+        for (EngineStage stage : getTerrainStages()) {
+            stage.generate(x, z, blocks, biomes, multicore, context);
+        }
+        getTransitionStage().generate(x, z, blocks, biomes, multicore, context);
+    }
+
     void close();
 
     Engine getEngine();
@@ -159,8 +176,12 @@ public interface EngineMode extends Staged {
         return getEngine().getMantle();
     }
 
-    default void generateMatter(int x, int z, boolean multicore, ChunkContext context) {
+    default void generateTerrainMatter(int x, int z, boolean multicore, ChunkContext context) {
-        getMantle().generateMatter(x, z, multicore, context);
+        getMantle().generateTerrainMatter(x, z, multicore, context);
+    }
+
+    default void generateContentMatter(int x, int z, boolean multicore, ChunkContext context) {
+        getMantle().generateContentMatter(x, z, multicore, context);
     }
 
     @BlockCoordinates
@@ -180,6 +201,9 @@ public interface EngineMode extends Staged {
 
         EngineStage[] stages = getStages().toArray(new EngineStage[0]);
         try (IrisContext.Scope chunkScope = IrisContext.open(getEngine(), generationSessionId, ctx)) {
+            getComplex().getResolvedTerrain().generate(this, x, z, blocks, biomes, multicore, ctx);
+            IrisBiomeActuator.publishNaturalMetadata(getEngine(), x, z, biomes, ctx);
+            ctx.beginContent();
             for (EngineStage i : stages) {
                 i.generate(x, z, blocks, biomes, multicore, ctx);
             }

core/src/main/java/art/arcane/iris/engine/framework/EnginePlatformHooks.java

@@ -19,10 +19,23 @@
 package art.arcane.iris.engine.framework;
 
 import art.arcane.iris.engine.object.IrisDimension;
+import art.arcane.iris.engine.history.SavedTerrainChunk;
+
+import java.util.concurrent.CompletableFuture;
 import art.arcane.iris.engine.mantle.MantleComponent;
 import art.arcane.volmlib.util.collection.KList;
 
 public interface EnginePlatformHooks {
+    default CompletableFuture<Void> flushSavedTerrainCapture(Engine engine) {
+        return CompletableFuture.failedFuture(new UnsupportedOperationException(
+                "This platform does not support saved terrain checkpoints."));
+    }
+
+    default CompletableFuture<SavedTerrainChunk> captureSavedTerrainChunk(Engine engine, int chunkX, int chunkZ) {
+        return CompletableFuture.failedFuture(new UnsupportedOperationException(
+                "This platform does not support saved terrain boundary capture."));
+    }
+
     /**
      * World-space piece bounds of every native structure that will generate inside the given XZ rect. Platforms
      * without native structures return no volumes, which keeps the object veto free on those platforms.

core/src/main/java/art/arcane/iris/engine/framework/GenerationSessionLease.java

@@ -1,17 +1,20 @@
 package art.arcane.iris.engine.framework;
 
 public final class GenerationSessionLease implements AutoCloseable {
-    private static final GenerationSessionLease NOOP = new GenerationSessionLease(null, null, 0L);
+    private static final GenerationSessionLease NOOP = new GenerationSessionLease(null, null, 0L, null);
 
     private final GenerationSessionManager manager;
     private final GenerationSessionManager.GenerationSessionState state;
     private final long sessionId;
+    private final GenerationTransitionGate.Participation participation;
     private boolean released;
 
-    GenerationSessionLease(GenerationSessionManager manager, GenerationSessionManager.GenerationSessionState state, long sessionId) {
+    GenerationSessionLease(GenerationSessionManager manager, GenerationSessionManager.GenerationSessionState state,
+                           long sessionId, GenerationTransitionGate.Participation participation) {
         this.manager = manager;
         this.state = state;
         this.sessionId = sessionId;
+        this.participation = participation;
         this.released = false;
     }
 
@@ -23,6 +26,12 @@ public final class GenerationSessionLease implements AutoCloseable {
         return sessionId;
     }
 
+    public void detachThread() {
+        if (participation != null) {
+            participation.detachThread();
+        }
+    }
+
     @Override
     public void close() {
         if (released || state == null) {
@@ -30,6 +39,10 @@ public final class GenerationSessionLease implements AutoCloseable {
         }
 
         released = true;
-        manager.releaseLease(state);
+        try {
+            manager.releaseLease(state);
+        } finally {
+            participation.close();
+        }
     }
 }

core/src/main/java/art/arcane/iris/engine/framework/GenerationSessionManager.java

@@ -1,22 +1,94 @@
 package art.arcane.iris.engine.framework;
 
+import art.arcane.iris.util.project.context.IrisContext;
+
+import java.util.Optional;
+
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.CancellationException;
 
 public final class GenerationSessionManager {
     private final AtomicLong sessionSequence;
     private final AtomicReference<GenerationSessionState> current;
     private final Object drainMonitor;
+    private final GenerationTransitionGate transitionGate;
 
     public GenerationSessionManager() {
+        this(false);
+    }
+
+    public GenerationSessionManager(boolean studioTransitions) {
+        this.transitionGate = new GenerationTransitionGate(studioTransitions);
         this.sessionSequence = new AtomicLong(0L);
         this.current = new AtomicReference<>(new GenerationSessionState(nextSessionId(), new AtomicBoolean(true), new AtomicInteger(0), new AtomicBoolean(false), new AtomicReference<>(null)));
         this.drainMonitor = new Object();
     }
 
     public GenerationSessionLease acquire(String operation) throws GenerationSessionException {
+        GenerationTransitionGate.Participation participation = transitionGate.enter();
+        try {
+            return acquireAdmitted(operation, participation);
+        } catch (Throwable failure) {
+            participation.close();
+            throw failure;
+        }
+    }
+
+    public GenerationTransitionGate transitionGate() {
+        return transitionGate;
+    }
+
+    public GenerationSessionLease acquireForEngine(Engine engine, String operation) throws GenerationSessionException {
+        GenerationTransitionGate.Participation participation;
+        try {
+            participation = transitionGate.enter();
+        } catch (CancellationException cancellation) {
+            GenerationSessionException failure = new GenerationSessionException(
+                    "Generation session cancelled while waiting to run " + operation + ".",
+                    engine.isClosing() || engine.isClosed());
+            failure.initCause(cancellation);
+            throw failure;
+        }
+        try {
+            if (engine.isClosing() || engine.isClosed()) {
+                throw new GenerationSessionException("Generation session rejected new work for " + operation
+                        + " while the Iris engine is closing.", engine.isClosed());
+            }
+            return acquireAdmitted(operation, participation);
+        } catch (Throwable failure) {
+            participation.close();
+            throw failure;
+        }
+    }
+
+    public Optional<GenerationSessionLease> tryAcquireForEngine(Engine engine, String operation)
+            throws GenerationSessionException {
+        Optional<GenerationTransitionGate.Participation> entered = transitionGate.tryEnter();
+        if (entered.isEmpty()) {
+            return Optional.empty();
+        }
+        GenerationTransitionGate.Participation participation = entered.get();
+        try {
+            if (engine.isClosing() || engine.isClosed()) {
+                throw new GenerationSessionException("Generation session rejected new work for " + operation
+                        + " while the Iris engine is closing.", engine.isClosed());
+            }
+            IrisContext context = IrisContext.get();
+            return Optional.of(context != null && context.getEngine() == engine && context.getGenerationSessionId() != 0L
+                    ? continueAdmittedSession(operation, context.getGenerationSessionId(), participation)
+                    : acquireAdmitted(operation, participation));
+        } catch (Throwable failure) {
+            participation.close();
+            throw failure;
+        }
+    }
+
+    private GenerationSessionLease acquireAdmitted(String operation,
+                                                   GenerationTransitionGate.Participation participation)
+            throws GenerationSessionException {
         while (true) {
             GenerationSessionState state = current.get();
             if (state == null || !state.accepting().get()) {
@@ -34,11 +106,23 @@ public final class GenerationSessionManager {
                 throw rejected(operation, state);
             }
 
-            return new GenerationSessionLease(this, state, state.sessionId());
+            return new GenerationSessionLease(this, state, state.sessionId(), participation);
         }
     }
 
     public GenerationSessionLease continueSession(String operation, long sessionId) throws GenerationSessionException {
+        GenerationTransitionGate.Participation participation = transitionGate.continueAdmittedWork();
+        try {
+            return continueAdmittedSession(operation, sessionId, participation);
+        } catch (Throwable failure) {
+            participation.close();
+            throw failure;
+        }
+    }
+
+    private GenerationSessionLease continueAdmittedSession(String operation, long sessionId,
+                                                           GenerationTransitionGate.Participation participation)
+            throws GenerationSessionException {
         while (true) {
             GenerationSessionState state = current.get();
             if (state == null || state.sessionId() != sessionId) {
@@ -51,7 +135,7 @@ public final class GenerationSessionManager {
                 continue;
             }
 
-            return new GenerationSessionLease(this, state, state.sessionId());
+            return new GenerationSessionLease(this, state, state.sessionId(), participation);
         }
     }
 

core/src/main/java/art/arcane/iris/engine/framework/GenerationTransitionGate.java

@@ -0,0 +1,200 @@
+package art.arcane.iris.engine.framework;
+
+import java.util.IdentityHashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.CancellationException;
+import java.util.concurrent.TimeUnit;
+
+public final class GenerationTransitionGate {
+    private final boolean enabled;
+    private final Participation noop = new Participation(null);
+    private final Map<Thread, Integer> participants = new IdentityHashMap<>();
+    private int active;
+    private int waitingTransitions;
+    private Thread transitionOwner;
+
+    public GenerationTransitionGate(boolean enabled) {
+        this.enabled = enabled;
+    }
+
+    public Participation enter() {
+        if (!enabled) {
+            return noop;
+        }
+        synchronized (this) {
+            return enter(false);
+        }
+    }
+
+    public Optional<Participation> tryEnter() {
+        if (!enabled) {
+            return Optional.of(noop);
+        }
+        synchronized (this) {
+            Thread owner = Thread.currentThread();
+            return blocked(owner, false) ? Optional.empty() : Optional.of(admit(owner));
+        }
+    }
+
+    Participation continueAdmittedWork() {
+        if (!enabled) {
+            return noop;
+        }
+        synchronized (this) {
+            return enter(true);
+        }
+    }
+
+    private Participation enter(boolean continuation) {
+        Thread owner = Thread.currentThread();
+        while (blocked(owner, continuation)) {
+            awaitChange();
+        }
+        return admit(owner);
+    }
+
+    private boolean blocked(Thread owner, boolean continuation) {
+        return transitionOwner != null && transitionOwner != owner
+                || waitingTransitions > 0 && transitionOwner != owner
+                && !participants.containsKey(owner) && !(continuation && active > 0);
+    }
+
+    private Participation admit(Thread owner) {
+        active++;
+        participants.merge(owner, 1, Integer::sum);
+        return new Participation(owner);
+    }
+
+    public synchronized Transition beginTransition(long timeoutMillis) {
+        if (!enabled) {
+            throw new IllegalStateException("Live generation transitions are disabled for this engine.");
+        }
+        if (timeoutMillis < 1L) {
+            throw new IllegalArgumentException("Generation transition timeout must be positive.");
+        }
+        Thread owner = Thread.currentThread();
+        if (participants.containsKey(owner) || transitionOwner == owner) {
+            throw new IllegalStateException("Cannot reload generation from inside an active generation operation.");
+        }
+        waitingTransitions++;
+        long deadline = System.nanoTime() + TimeUnit.MILLISECONDS.toNanos(timeoutMillis);
+        try {
+            while (transitionOwner != null || active > 0) {
+                long remaining = deadline - System.nanoTime();
+                if (remaining <= 0L) {
+                    throw new IllegalStateException("Timed out draining generation for a Studio update after "
+                            + timeoutMillis + "ms; active operations=" + active + ".");
+                }
+                try {
+                    TimeUnit.NANOSECONDS.timedWait(this, remaining);
+                } catch (InterruptedException failure) {
+                    Thread.currentThread().interrupt();
+                    throw new IllegalStateException("Interrupted while draining generation for a Studio update.", failure);
+                }
+            }
+            transitionOwner = owner;
+            return new Transition(owner);
+        } finally {
+            waitingTransitions--;
+            notifyAll();
+        }
+    }
+
+    private void awaitChange() {
+        try {
+            wait();
+        } catch (InterruptedException failure) {
+            Thread.currentThread().interrupt();
+            CancellationException cancellation = new CancellationException(
+                    "Interrupted while waiting for generation admission.");
+            cancellation.initCause(failure);
+            throw cancellation;
+        }
+    }
+
+    public final class Participation implements AutoCloseable {
+        private final Thread owner;
+        private boolean closed;
+        private boolean attached = true;
+
+        private Participation(Thread owner) {
+            this.owner = owner;
+        }
+
+        public Participation attach() {
+            if (owner == null) {
+                return this;
+            }
+            synchronized (GenerationTransitionGate.this) {
+                if (closed) {
+                    throw new IllegalStateException("Generation participation has already ended.");
+                }
+                return enter(true);
+            }
+        }
+
+        public void detachThread() {
+            if (owner == null) {
+                return;
+            }
+            synchronized (GenerationTransitionGate.this) {
+                if (!closed && attached) {
+                    detach();
+                }
+            }
+        }
+
+        private void detach() {
+            int depth = participants.get(owner);
+            if (depth == 1) {
+                participants.remove(owner);
+            } else {
+                participants.put(owner, depth - 1);
+            }
+            attached = false;
+        }
+
+        @Override
+        public void close() {
+            if (owner == null) {
+                return;
+            }
+            synchronized (GenerationTransitionGate.this) {
+                if (closed) {
+                    return;
+                }
+                closed = true;
+                if (attached) {
+                    detach();
+                }
+                active--;
+                GenerationTransitionGate.this.notifyAll();
+            }
+        }
+    }
+
+    public final class Transition implements AutoCloseable {
+        private final Thread owner;
+        private boolean closed;
+
+        private Transition(Thread owner) {
+            this.owner = owner;
+        }
+
+        @Override
+        public void close() {
+            synchronized (GenerationTransitionGate.this) {
+                if (closed) {
+                    return;
+                }
+                if (Thread.currentThread() != owner || transitionOwner != owner) {
+                    throw new IllegalStateException("Generation transition belongs to another thread.");
+                }
+                closed = true;
+                transitionOwner = null;
+                GenerationTransitionGate.this.notifyAll();
+            }
+        }
+    }
+}

core/src/main/java/art/arcane/iris/engine/framework/IrisEngineMode.java

@@ -19,15 +19,20 @@
 package art.arcane.iris.engine.framework;
 
 import art.arcane.volmlib.util.collection.KList;
+import art.arcane.iris.engine.actuator.IrisTransitionGeometryActuator;
 
 public abstract class IrisEngineMode implements EngineMode {
     private final Engine engine;
+    private final EngineStage transitionStage;
     private final KList<EngineStage> stages;
+    private final KList<EngineStage> terrainStages;
     private boolean closed;
 
     public IrisEngineMode(Engine engine) {
         this.engine = engine;
+        this.transitionStage = new IrisTransitionGeometryActuator(engine);
         this.stages = new KList<>();
+        this.terrainStages = new KList<>();
         this.closed = false;
     }
 
@@ -39,6 +44,9 @@ public abstract class IrisEngineMode implements EngineMode {
 
         closed = true;
         dump();
+        terrainStages.forEach(EngineStage::close);
+        terrainStages.clear();
+        transitionStage.close();
     }
 
     @Override
@@ -51,6 +59,21 @@ public abstract class IrisEngineMode implements EngineMode {
         return stages;
     }
 
+    @Override
+    public EngineStage getTransitionStage() {
+        return transitionStage;
+    }
+
+    @Override
+    public KList<EngineStage> getTerrainStages() {
+        return terrainStages;
+    }
+
+    @Override
+    public void registerTerrainStage(EngineStage stage) {
+        terrainStages.add(stage);
+    }
+
     @Override
     public void registerStage(EngineStage stage) {
         stages.add(stage);

core/src/main/java/art/arcane/iris/engine/history/BoundaryColumnGeometry.java

@@ -0,0 +1,258 @@
+package art.arcane.iris.engine.history;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.TreeSet;
+
+public final class BoundaryColumnGeometry {
+    public static final int MAXIMUM_HEIGHT = 65_536;
+    private static final Comparator<Voxel> VOXEL_ORDER = Comparator.comparing(Voxel::stateKey)
+            .thenComparing(Voxel::phase)
+            .thenComparing(Voxel::fluidStateKey)
+            .thenComparing(Voxel::protectedContent);
+    private static final Voxel AIR = new Voxel("minecraft:air", Phase.AIR, "", false);
+    private static final BoundaryColumnGeometry EMPTY = new BoundaryColumnGeometry(0, List.of(), new int[0], new short[0]);
+
+    private final int minimumY;
+    private final List<Voxel> palette;
+    private final int[] runEnds;
+    private final short[] paletteIndices;
+
+    public BoundaryColumnGeometry(int minimumY, List<Voxel> palette, int[] runEnds, short[] paletteIndices) {
+        this.minimumY = minimumY;
+        this.palette = List.copyOf(Objects.requireNonNull(palette, "Geometry palette"));
+        this.runEnds = Objects.requireNonNull(runEnds, "Geometry run ends").clone();
+        this.paletteIndices = Objects.requireNonNull(paletteIndices, "Geometry palette indices").clone();
+        validate();
+    }
+
+    public static BoundaryColumnGeometry empty() {
+        return EMPTY;
+    }
+
+    public static BoundaryColumnGeometry fromVoxels(int minimumY, List<Voxel> voxels) {
+        Objects.requireNonNull(voxels, "Geometry voxels");
+        if (voxels.size() > MAXIMUM_HEIGHT) {
+            throw new IllegalArgumentException("Geometry column exceeds maximum height");
+        }
+        TreeSet<Voxel> used = new TreeSet<>(VOXEL_ORDER);
+        Voxel previous = null;
+        for (Voxel voxel : voxels) {
+            if (previous == null || !previous.equals(voxel)) {
+                used.add(voxel);
+                previous = voxel;
+            }
+        }
+        List<Voxel> palette = List.copyOf(used);
+        Map<Voxel, Short> indices = new HashMap<>(palette.size());
+        for (int index = 0; index < palette.size(); index++) {
+            if (index > Short.MAX_VALUE) {
+                throw new IllegalArgumentException("Geometry palette exceeds compact index capacity");
+            }
+            indices.put(palette.get(index), (short) index);
+        }
+        int[] ends = new int[voxels.size()];
+        short[] values = new short[voxels.size()];
+        int runCount = 0;
+        previous = null;
+        for (int offset = 0; offset < voxels.size(); offset++) {
+            Voxel voxel = voxels.get(offset);
+            if (previous == null || !previous.equals(voxel)) {
+                values[runCount++] = indices.get(voxel);
+                previous = voxel;
+            }
+            ends[runCount - 1] = offset + 1;
+        }
+        return new BoundaryColumnGeometry(minimumY, palette,
+                Arrays.copyOf(ends, runCount), Arrays.copyOf(values, runCount));
+    }
+
+    public int minimumY() {
+        return minimumY;
+    }
+
+    public int height() {
+        return runEnds.length == 0 ? 0 : runEnds[runEnds.length - 1];
+    }
+
+    public List<Voxel> palette() {
+        return palette;
+    }
+
+    public int[] runEnds() {
+        return runEnds.clone();
+    }
+
+    public short[] paletteIndices() {
+        return paletteIndices.clone();
+    }
+
+    public Voxel voxelAt(int worldY) {
+        long offset = (long) worldY - minimumY;
+        if (offset < 0 || offset >= height()) {
+            return AIR;
+        }
+        return palette.get(paletteIndices[runAt((int) offset)]);
+    }
+
+    public boolean isEnclosedOpenAt(int worldY) {
+        long offset = (long) worldY - minimumY;
+        if (offset < 0 || offset >= height() || voxelAt(worldY).phase() == Phase.SOLID) {
+            return false;
+        }
+        return hasSolidAbove(worldY);
+    }
+
+    public boolean hasSolidAbove(int worldY) {
+        long offset = (long) worldY - minimumY;
+        if (offset >= height() - 1L) {
+            return false;
+        }
+        int startRun = offset < 0 ? 0 : runAt((int) offset);
+        for (int run = startRun; run < runEnds.length; run++) {
+            if (runEnds[run] <= offset + 1L) {
+                continue;
+            }
+            if (palette.get(paletteIndices[run]).phase() == Phase.SOLID) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public List<Voxel> voxels() {
+        ArrayList<Voxel> values = new ArrayList<>(height());
+        int start = 0;
+        for (int run = 0; run < runEnds.length; run++) {
+            Voxel value = palette.get(paletteIndices[run]);
+            for (int offset = start; offset < runEnds[run]; offset++) {
+                values.add(value);
+            }
+            start = runEnds[run];
+        }
+        return List.copyOf(values);
+    }
+
+    public int surfaceOffsetNear(double expectedOffset) {
+        if (!Double.isFinite(expectedOffset) || height() == 0) {
+            throw new IllegalArgumentException("A surface reference requires finite height and nonempty geometry");
+        }
+        int nearest = -1;
+        double nearestDistance = Double.POSITIVE_INFINITY;
+        for (int offset = 0; offset + 1 < height(); offset++) {
+            Voxel current = voxelAt(minimumY + offset);
+            Voxel above = voxelAt(minimumY + offset + 1);
+            if (current.phase() != Phase.SOLID || current.protectedContent()
+                    || above.phase() == Phase.SOLID && !above.protectedContent()) {
+                continue;
+            }
+            double distance = Math.abs(offset - expectedOffset);
+            if (distance < nearestDistance) {
+                nearest = offset;
+                nearestDistance = distance;
+            }
+        }
+        if (nearest >= 0) {
+            return nearest;
+        }
+        for (int offset = height() - 1; offset >= 0; offset--) {
+            Voxel current = voxelAt(minimumY + offset);
+            if (current.phase() == Phase.SOLID && !current.protectedContent()) {
+                return offset;
+            }
+        }
+        return 0;
+    }
+
+    public double[] solidDistances() {
+        return phaseDistances(Phase.SOLID);
+    }
+
+    public double[] fluidDistances() {
+        return phaseDistances(Phase.FLUID);
+    }
+
+    private double[] phaseDistances(Phase phase) {
+        int height = height();
+        double[] distances = new double[height];
+        boolean[] solid = new boolean[height];
+        int start = 0;
+        for (int run = 0; run < runEnds.length; run++) {
+            Voxel value = palette.get(paletteIndices[run]);
+            boolean occupied = value.phase() == phase && !value.protectedContent();
+            Arrays.fill(solid, start, runEnds[run], occupied);
+            start = runEnds[run];
+        }
+        double distance = height + 0.5D;
+        for (int offset = 0; offset < height; offset++) {
+            distance = offset > 0 && solid[offset] != solid[offset - 1] ? 0.5D : distance + 1D;
+            distances[offset] = distance;
+        }
+        distance = height + 0.5D;
+        for (int offset = height - 1; offset >= 0; offset--) {
+            distance = offset + 1 < height && solid[offset] != solid[offset + 1] ? 0.5D : distance + 1D;
+            distances[offset] = Math.min(distances[offset], distance) * (solid[offset] ? 1D : -1D);
+        }
+        return distances;
+    }
+
+    @Override
+    public boolean equals(Object compared) {
+        return this == compared || compared instanceof BoundaryColumnGeometry other
+                && minimumY == other.minimumY && palette.equals(other.palette)
+                && Arrays.equals(runEnds, other.runEnds) && Arrays.equals(paletteIndices, other.paletteIndices);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(minimumY, palette, Arrays.hashCode(runEnds), Arrays.hashCode(paletteIndices));
+    }
+
+    private int runAt(int offset) {
+        int index = Arrays.binarySearch(runEnds, offset + 1);
+        return index >= 0 ? index : -index - 1;
+    }
+
+    private void validate() {
+        if (palette.size() > Short.MAX_VALUE + 1 || runEnds.length > MAXIMUM_HEIGHT
+                || runEnds.length != paletteIndices.length) {
+            throw new IllegalArgumentException("Invalid compact geometry sizes");
+        }
+        int previousEnd = 0;
+        for (int run = 0; run < runEnds.length; run++) {
+            if (runEnds[run] <= previousEnd || runEnds[run] > MAXIMUM_HEIGHT
+                    || paletteIndices[run] < 0 || paletteIndices[run] >= palette.size()) {
+                throw new IllegalArgumentException("Invalid compact geometry run");
+            }
+            previousEnd = runEnds[run];
+        }
+        if (height() > 0) {
+            Math.toIntExact((long) minimumY + height() - 1L);
+        }
+    }
+
+    public enum Phase {
+        AIR,
+        SOLID,
+        FLUID
+    }
+
+    public record Voxel(String stateKey, Phase phase, String fluidStateKey, boolean protectedContent) {
+        public Voxel {
+            Objects.requireNonNull(stateKey, "Block state key");
+            Objects.requireNonNull(phase, "Voxel phase");
+            Objects.requireNonNull(fluidStateKey, "Fluid state key");
+            if (stateKey.isBlank()) {
+                throw new IllegalArgumentException("Block state key cannot be blank");
+            }
+            if (phase == Phase.FLUID && fluidStateKey.isBlank()) {
+                throw new IllegalArgumentException("Fluid voxels require a fluid state key");
+            }
+        }
+    }
+}

core/src/main/java/art/arcane/iris/engine/history/BoundaryGeometryInfluence.java

@@ -0,0 +1,41 @@
+package art.arcane.iris.engine.history;
+
+import java.util.List;
+import java.util.Objects;
+
+public record BoundaryGeometryInfluence(double newTerrainWeight, double openingWeight, List<Contribution> contributions) {
+    private static final BoundaryGeometryInfluence NONE = new BoundaryGeometryInfluence(1D, 1D, List.of());
+
+    public BoundaryGeometryInfluence {
+        if (!Double.isFinite(newTerrainWeight) || newTerrainWeight < 0D || newTerrainWeight > 1D) {
+            throw new IllegalArgumentException("Geometry blend weight must be between zero and one");
+        }
+        if (!Double.isFinite(openingWeight) || openingWeight < 0D || openingWeight > 1D) {
+            throw new IllegalArgumentException("Opening blend weight must be between zero and one");
+        }
+        contributions = List.copyOf(contributions);
+        double total = 0D;
+        for (Contribution contribution : contributions) {
+            total += contribution.weight();
+        }
+        if (!contributions.isEmpty() && Math.abs(total - 1D) > 1E-9D) {
+            throw new IllegalArgumentException("Geometry contribution weights must sum to one");
+        }
+    }
+
+    public static BoundaryGeometryInfluence none() {
+        return NONE;
+    }
+
+    public record Contribution(BoundaryColumnGeometry geometry, double weight) {
+        public Contribution {
+            Objects.requireNonNull(geometry, "Historical geometry");
+            if (geometry.height() == 0) {
+                throw new IllegalArgumentException("Historical boundary geometry is missing");
+            }
+            if (!Double.isFinite(weight) || weight <= 0D || weight > 1D) {
+                throw new IllegalArgumentException("Geometry contribution weight must be positive and at most one");
+            }
+        }
+    }
+}

core/src/main/java/art/arcane/iris/engine/history/ChunkGenerationOwnership.java

@@ -8,6 +8,7 @@ import java.nio.file.Files;
 import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.nio.file.attribute.BasicFileAttributes;
+import java.util.Set;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Comparator;
@@ -184,6 +185,34 @@ public final class ChunkGenerationOwnership {
         }
     }
 
+    public int discardUnstoredClaims(WorldChunkInventory stored, Set<Long> activationIds) throws IOException {
+        Objects.requireNonNull(stored, "stored chunks");
+        Set<Long> selected = Set.copyOf(activationIds);
+        for (long activation : selected) {
+            requireActivation(activation);
+        }
+        lock.writeLock().lock();
+        try {
+            int removed = 0;
+            for (long regionKey : orderedRegionKeys()) {
+                RegionGenerationOwnership region = loadExistingRegion(regionX(regionKey), regionZ(regionKey));
+                if (region == null) {
+                    continue;
+                }
+                int count = region.discardUnstoredClaims(stored, selected);
+                if (count > 0) {
+                    region.persist(directory);
+                    explicitChunkCount -= count;
+                    regionAssignmentCounts.put(regionKey, region.assignmentCount());
+                    removed += count;
+                }
+            }
+            return removed;
+        } finally {
+            lock.writeLock().unlock();
+        }
+    }
+
     public int persist() throws IOException {
         lock.writeLock().lock();
         try {

core/src/main/java/art/arcane/iris/engine/history/ChunkGenerationSemantics.java

@@ -6,11 +6,9 @@ import java.nio.charset.StandardCharsets;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Comparator;
-import java.util.Locale;
 import java.util.Objects;
 import java.util.Set;
 import java.util.TreeSet;
-import java.util.regex.Pattern;
 
 public final class ChunkGenerationSemantics {
     static final int MAX_KEY_BYTES = 1_024;
@@ -18,12 +16,15 @@ public final class ChunkGenerationSemantics {
     static final int MAX_RIVER_FEATURES = 16_384;
     static final int MAX_STRUCTURES = 4_096;
 
-    private static final Pattern RESOURCE_KEY_PATTERN = Pattern.compile("[a-z0-9_][a-z0-9._:/#@-]*");
     private static final Comparator<StructureOccurrence> STRUCTURE_COMPARATOR = Comparator
             .comparing(StructureOccurrence::key)
             .thenComparingInt(occurrence -> occurrence.position().x())
             .thenComparingInt(occurrence -> occurrence.position().z())
             .thenComparingInt(occurrence -> occurrence.position().y());
+    private static final Comparator<PointOfInterest> POI_COMPARATOR = Comparator.comparing(PointOfInterest::key)
+            .thenComparingInt(point -> point.position().x())
+            .thenComparingInt(point -> point.position().z())
+            .thenComparingInt(point -> point.position().y());
     private static final Comparator<RiverFeatureOccurrence> RIVER_FEATURE_COMPARATOR = Comparator
             .comparing(RiverFeatureOccurrence::profileKey)
             .thenComparing(RiverFeatureOccurrence::type)
@@ -43,6 +44,7 @@ public final class ChunkGenerationSemantics {
     private final Set<String> objectKeys;
     private final Set<RiverFeatureOccurrence> riverFeatures;
     private final Set<StructureOccurrence> structures;
+    private final Set<PointOfInterest> pointsOfInterest;
 
     private ChunkGenerationSemantics(Builder builder) {
         chunkX = builder.chunkX;
@@ -56,6 +58,7 @@ public final class ChunkGenerationSemantics {
         objectKeys = immutableKeys(builder.objectKeys, "object");
         riverFeatures = immutableRiverFeatures(builder.riverFeatures);
         structures = immutableStructures(builder.structures);
+        pointsOfInterest = immutablePoints(builder.pointsOfInterest);
     }
 
     public static Builder builder(int chunkX, int chunkZ, long activationId) {
@@ -102,6 +105,10 @@ public final class ChunkGenerationSemantics {
         return riverFeatures;
     }
 
+    public Set<PointOfInterest> pointsOfInterest() {
+        return pointsOfInterest;
+    }
+
     public Set<StructureOccurrence> structures() {
         return structures;
     }
@@ -129,7 +136,8 @@ public final class ChunkGenerationSemantics {
                 || !riverProfileKeys.containsAll(requiredUpdate.riverProfileKeys)
                 || !objectKeys.containsAll(requiredUpdate.objectKeys)
                 || !riverFeatures.containsAll(requiredUpdate.riverFeatures)
-                || !structures.containsAll(requiredUpdate.structures);
+                || !structures.containsAll(requiredUpdate.structures)
+                || !pointsOfInterest.containsAll(requiredUpdate.pointsOfInterest);
         if (sealed && addsFacts) {
             throw new IllegalStateException(
                     "Chunk " + chunkX + "," + chunkZ + " has sealed generation semantics"
@@ -153,7 +161,9 @@ public final class ChunkGenerationSemantics {
                 .addRiverFeatures(riverFeatures)
                 .addRiverFeatures(requiredUpdate.riverFeatures)
                 .addStructures(structures)
-                .addStructures(requiredUpdate.structures);
+                .addStructures(requiredUpdate.structures)
+                .addPointsOfInterest(pointsOfInterest)
+                .addPointsOfInterest(requiredUpdate.pointsOfInterest);
         if (sealed || requiredUpdate.sealed) {
             merged.seal();
         }
@@ -178,7 +188,8 @@ public final class ChunkGenerationSemantics {
                 && riverProfileKeys.equals(semantics.riverProfileKeys)
                 && objectKeys.equals(semantics.objectKeys)
                 && riverFeatures.equals(semantics.riverFeatures)
-                && structures.equals(semantics.structures);
+                && structures.equals(semantics.structures)
+                && pointsOfInterest.equals(semantics.pointsOfInterest);
     }
 
     @Override
@@ -194,7 +205,8 @@ public final class ChunkGenerationSemantics {
                 riverProfileKeys,
                 objectKeys,
                 riverFeatures,
-                structures
+                structures,
+                pointsOfInterest
         );
     }
 
@@ -230,11 +242,11 @@ public final class ChunkGenerationSemantics {
         if (!requiredKey.equals(requiredKey.trim())) {
             throw new IllegalArgumentException("Generation semantic resource keys must not contain surrounding whitespace: " + requiredKey);
         }
-        if (!requiredKey.equals(requiredKey.toLowerCase(Locale.ROOT))) {
+        for (int index = 0; index < requiredKey.length(); index++) {
-            throw new IllegalArgumentException("Generation semantic resource keys must be lowercase: " + requiredKey);
+            char character = requiredKey.charAt(index);
-        }
+            if (character == '\\' || Character.isISOControl(character)) {
-        if (!RESOURCE_KEY_PATTERN.matcher(requiredKey).matches()) {
+                throw new IllegalArgumentException("Generation semantic resource key contains an invalid character");
-            throw new IllegalArgumentException("Generation semantic resource key is not normalized: " + requiredKey);
+            }
         }
         if (requiredKey.getBytes(StandardCharsets.UTF_8).length > MAX_KEY_BYTES) {
             throw new IllegalArgumentException("Generation semantic resource key is too long");
@@ -283,6 +295,28 @@ public final class ChunkGenerationSemantics {
         return Collections.unmodifiableSet(validated);
     }
 
+    private static Set<PointOfInterest> immutablePoints(Collection<PointOfInterest> points) {
+        if (points.size() > MAX_STRUCTURES) {
+            throw new IllegalArgumentException("A chunk contains too many points of interest");
+        }
+        TreeSet<PointOfInterest> copy = new TreeSet<>(POI_COMPARATOR);
+        for (PointOfInterest point : points) {
+            copy.add(Objects.requireNonNull(point, "point of interest"));
+        }
+        return Collections.unmodifiableSet(copy);
+    }
+
+    static Comparator<PointOfInterest> pointComparator() {
+        return POI_COMPARATOR;
+    }
+
+    public record PointOfInterest(String key, BlockPosition position) {
+        public PointOfInterest {
+            key = requireResourceKey(key);
+            position = Objects.requireNonNull(position, "position");
+        }
+    }
+
     public record BlockPosition(int x, int y, int z) {
     }
 
@@ -317,6 +351,7 @@ public final class ChunkGenerationSemantics {
         private final Set<String> objectKeys;
         private final Set<RiverFeatureOccurrence> riverFeatures;
         private final Set<StructureOccurrence> structures;
+        private final Set<PointOfInterest> pointsOfInterest;
         private boolean sealed;
 
         private Builder(int chunkX, int chunkZ, long activationId) {
@@ -333,6 +368,7 @@ public final class ChunkGenerationSemantics {
             objectKeys = new TreeSet<>();
             riverFeatures = new TreeSet<>(RIVER_FEATURE_COMPARATOR);
             structures = new TreeSet<>(STRUCTURE_COMPARATOR);
+            pointsOfInterest = new TreeSet<>(POI_COMPARATOR);
         }
 
         public Builder addSurfaceBiome(String key) {
@@ -450,6 +486,22 @@ public final class ChunkGenerationSemantics {
             return this;
         }
 
+        public Builder addPointOfInterest(PointOfInterest point) {
+            Objects.requireNonNull(point, "point of interest");
+            if (pointsOfInterest.size() >= MAX_STRUCTURES && !pointsOfInterest.contains(point)) {
+                throw new IllegalArgumentException("A chunk contains too many points of interest");
+            }
+            pointsOfInterest.add(point);
+            return this;
+        }
+
+        public Builder addPointsOfInterest(Collection<PointOfInterest> points) {
+            for (PointOfInterest point : points) {
+                addPointOfInterest(point);
+            }
+            return this;
+        }
+
         public Builder seal() {
             sealed = true;
             return this;

core/src/main/java/art/arcane/iris/engine/history/DiskBoundaryCapture.java

@@ -0,0 +1,44 @@
+package art.arcane.iris.engine.history;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Objects;
+
+public final class DiskBoundaryCapture implements TerrainBoundarySignatureStore.SignatureSampler {
+    private static final int MAXIMUM_CACHED_CHUNKS = 32;
+
+    private final Path dimensionRoot;
+    private final int minimumY;
+    private final int height;
+    private final LinkedHashMap<Long, SavedTerrainChunk> chunks = new LinkedHashMap<>(32, 0.75F, true);
+
+    public DiskBoundaryCapture(Path dimensionRoot, int minimumY, int height) {
+        this.dimensionRoot = Objects.requireNonNull(dimensionRoot, "dimension root");
+        this.minimumY = minimumY;
+        this.height = height;
+    }
+
+    @Override
+    public TerrainBoundarySignature sample(int blockX, int blockZ) throws IOException {
+        int chunkX = Math.floorDiv(blockX, 16);
+        int chunkZ = Math.floorDiv(blockZ, 16);
+        long key = ChunkGenerationOwnership.packChunk(chunkX, chunkZ);
+        SavedTerrainChunk chunk = chunks.get(key);
+        if (chunk == null) {
+            chunk = SavedTerrainChunk.read(dimensionRoot, chunkX, chunkZ, minimumY, height);
+            chunks.put(key, chunk);
+            if (chunks.size() > MAXIMUM_CACHED_CHUNKS) {
+                Map.Entry<Long, SavedTerrainChunk> oldest = chunks.firstEntry();
+                chunks.remove(oldest.getKey());
+            }
+        }
+        return chunk.column(blockX, blockZ);
+    }
+
+    @Override
+    public void close() {
+        chunks.clear();
+    }
+}

core/src/main/java/art/arcane/iris/engine/history/GenerationBlend.java

@@ -58,6 +58,23 @@ public final class GenerationBlend {
         return (int) Math.round(historicalHeight + ((double) newHeight - historicalHeight) * newEpochWeight);
     }
 
+    public static boolean usesHistoricalMaterial(int blockX, int blockY, int blockZ, double newWeight) {
+        validateWeight(newWeight);
+        if (newWeight == 0D) {
+            return true;
+        }
+        if (newWeight == 1D) {
+            return false;
+        }
+        long hash = Math.floorDiv(blockX, 8) * 341873128712L
+                ^ Math.floorDiv(blockY, 8) * 132897987541L
+                ^ Math.floorDiv(blockZ, 8) * 42317861L;
+        hash = (hash ^ (hash >>> 30)) * 0xbf58476d1ce4e5b9L;
+        hash = (hash ^ (hash >>> 27)) * 0x94d049bb133111ebL;
+        hash ^= hash >>> 31;
+        return newWeight < (hash >>> 11) * 0x1.0p-53;
+    }
+
     private static void validateWeight(double weight) {
         if (!Double.isFinite(weight) || weight < 0D || weight > 1D) {
             throw new IllegalArgumentException("Blend weight must be finite and between zero and one");

core/src/main/java/art/arcane/iris/engine/history/GenerationBoundarySignatureSampler.java

@@ -7,4 +7,8 @@ import java.io.IOException;
 @FunctionalInterface
 public interface GenerationBoundarySignatureSampler {
     TerrainBoundarySignature sample(IrisEngine engine, int blockX, int blockZ) throws IOException;
+
+    default TerrainBoundarySignatureStore.SignatureSampler open(IrisEngine engine) throws IOException {
+        return (blockX, blockZ) -> sample(engine, blockX, blockZ);
+    }
 }

core/src/main/java/art/arcane/iris/engine/history/GenerationBoundaryStore.java

@@ -632,13 +632,16 @@ public final class GenerationBoundaryStore {
         }
 
         @Override
-        public synchronized boolean contains(int chunkX, int chunkZ) throws IOException {
+        public boolean contains(int chunkX, int chunkZ) throws IOException {
             long regionKey = packRegion(chunkX >> 5, chunkZ >> 5);
             String hash = shardHashes.get(regionKey);
             if (hash == null) {
                 return false;
             }
-            byte[] mask = load(regionKey, hash);
+            byte[] mask;
+            synchronized (this) {
+                mask = load(regionKey, hash);
+            }
             int localIndex = (Math.floorMod(chunkZ, REGION_SIDE) << 5)
                     | Math.floorMod(chunkX, REGION_SIDE);
             return (mask[localIndex >>> 3] & (1 << (localIndex & 7))) != 0;

core/src/main/java/art/arcane/iris/engine/history/GenerationBuildRevision.java

@@ -11,31 +11,31 @@ import java.util.List;
 import java.util.Objects;
 import java.util.regex.Pattern;
 
-final class GenerationKernelSourceSeal {
+final class GenerationBuildRevision {
     private static final int MAXIMUM_BYTES = 8 * 1024 * 1024;
     private static final Pattern SHA256 = Pattern.compile("[0-9a-f]{64}");
 
-    private GenerationKernelSourceSeal() {
+    private GenerationBuildRevision() {
     }
 
     static String requireFingerprint(int abi, Class<?> factory) {
         Descriptor descriptor = load(abi);
         if (!descriptor.factoryClass().equals(factory.getName())) {
-            throw new IllegalStateException("Generation ABI " + abi + " is sealed for " + descriptor.factoryClass() + ".");
+            throw new IllegalStateException("Generation ABI " + abi + " declares factory " + descriptor.factoryClass() + ".");
         }
         return descriptor.fingerprint();
     }
 
     static Descriptor load(int abi) {
-        String resource = "/META-INF/iris/generation-kernels/abi-" + abi + ".seal";
+        String resource = "/META-INF/iris/generation-kernels/abi-" + abi + ".revision";
-        try (InputStream input = GenerationKernelSourceSeal.class.getResourceAsStream(resource)) {
+        try (InputStream input = GenerationBuildRevision.class.getResourceAsStream(resource)) {
             if (input == null) {
-                throw new IOException("Missing generation kernel source seal " + resource + ".");
+                throw new IOException("Missing generation kernel build revision " + resource + ".");
             }
             byte[] bytes = input.readNBytes(MAXIMUM_BYTES + 1);
             String[] lines = new String(bytes, StandardCharsets.UTF_8).split("\n", -1);
             if (lines.length < 4 || !lines[2].startsWith("factory\t")) {
-                throw new IOException("Generation kernel seal has no factory identity.");
+                throw new IOException("Generation build revision has no factory identity.");
             }
             String factoryClass = lines[2].substring("factory\t".length());
             if (!factoryClass.matches("[A-Za-z_$][A-Za-z0-9_$]*(\\.[A-Za-z_$][A-Za-z0-9_$]*)+")) {
@@ -52,7 +52,7 @@ final class GenerationKernelSourceSeal {
             }
             return new Descriptor(abi, factoryClass, List.copyOf(algorithms), fingerprint);
         } catch (IOException failure) {
-            throw new IllegalStateException("Cannot load sealed Iris generation ABI " + abi + ".", failure);
+            throw new IllegalStateException("Cannot load Iris generation build revision for ABI " + abi + ".", failure);
         }
     }
 
@@ -60,13 +60,13 @@ final class GenerationKernelSourceSeal {
         Objects.requireNonNull(factoryClass, "factoryClass");
         Objects.requireNonNull(bytes, "bytes");
         if (abi < 1 || bytes.length == 0 || bytes.length > MAXIMUM_BYTES) {
-            throw new IOException("Invalid generation kernel seal size or ABI.");
+            throw new IOException("Invalid generation build revision size or ABI.");
         }
         String source = new String(bytes, StandardCharsets.UTF_8);
-        String prefix = "iris-generation-kernel-seal-v1\nabi\t" + abi + "\nfactory\t" + factoryClass + "\n";
+        String prefix = "iris-generation-build-revision-v1\nabi\t" + abi + "\nfactory\t" + factoryClass + "\n";
         if (!source.startsWith(prefix) || !source.endsWith("\n") || source.indexOf('\r') >= 0
                 || !source.contains("\nsource\t") || !source.contains("\ndependency\t")) {
-            throw new IOException("Generation kernel seal does not match ABI " + abi + " and factory " + factoryClass + ".");
+            throw new IOException("Generation build revision does not match ABI " + abi + " and factory " + factoryClass + ".");
         }
         requireCanonicalEntries(source.substring(prefix.length()));
         try {
@@ -79,7 +79,7 @@ final class GenerationKernelSourceSeal {
     private static void requireCanonicalEntries(String source) throws IOException {
         String[] entries = source.split("\n", -1);
         if (entries.length > 30_000) {
-            throw new IOException("Generation kernel seal has too many entries.");
+            throw new IOException("Generation build revision has too many entries.");
         }
         int previousType = -1;
         String previousKey = "";
@@ -92,7 +92,7 @@ final class GenerationKernelSourceSeal {
             if (fields[0].equals("algorithm")) {
                 if (previousType != -1 || fields.length != 3 || !fields[1].matches("[1-9][0-9]{0,8}")
                         || !fields[2].matches("[1-9][0-9]{0,8}")) {
-                    throw new IOException("Generation kernel seal contains an invalid algorithm version.");
+                    throw new IOException("Generation build revision contains an invalid algorithm version.");
                 }
                 int rng = Integer.parseInt(fields[1]);
                 int seed = Integer.parseInt(fields[2]);
@@ -116,14 +116,14 @@ final class GenerationKernelSourceSeal {
                     || fields[1].chars().anyMatch(Character::isWhitespace)
                     || (type == previousType && fields[1].compareTo(previousKey) <= 0)
                     || (type >= 2 && !SHA256.matcher(fields[2]).matches())) {
-                throw new IOException("Generation kernel seal contains an invalid or noncanonical entry.");
+                throw new IOException("Generation build revision contains an invalid or noncanonical entry.");
             }
             previousType = type;
             previousKey = fields[1];
             hasScope |= type == 0;
         }
         if (!hasScope || !hasAlgorithm) {
-            throw new IOException("Generation kernel seal has no source scope or algorithm version.");
+            throw new IOException("Generation build revision has no source scope or algorithm version.");
         }
     }
 

core/src/main/java/art/arcane/iris/engine/history/GenerationEpoch.java

@@ -346,15 +346,10 @@ public final class GenerationEpoch {
             return dimensionKey.equals(other.dimensionKey)
                     && dimensionTypeKey.equals(other.dimensionTypeKey)
                     && environment.equals(other.environment)
-                    && generationMode.equals(other.generationMode)
-                    && internalFluidHeight == other.internalFluidHeight
                     && minHeight == other.minHeight
                     && height == other.height
                     && logicalHeight == other.logicalHeight
                     && Double.compare(coordinateScale, other.coordinateScale) == 0
-                    && upperTerrainEnabled == other.upperTerrainEnabled
-                    && upperDimensionKey.equals(other.upperDimensionKey)
-                    && upperDimensionGap == other.upperDimensionGap
                     && dimensionTypeFingerprintSchema == other.dimensionTypeFingerprintSchema
                     && dimensionTypeFingerprint.equals(other.dimensionTypeFingerprint);
         }

core/src/main/java/art/arcane/iris/engine/history/GenerationFindCatalog.java

@@ -1,23 +1,16 @@
 package art.arcane.iris.engine.history;
 
-import art.arcane.iris.core.loader.IrisData;
 import art.arcane.iris.core.loader.IrisRegistrant;
 import art.arcane.iris.engine.IrisEngine;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.engine.object.IrisBiome;
-import art.arcane.iris.engine.object.IrisDimension;
-import art.arcane.iris.engine.object.IrisObjectPlacement;
 import art.arcane.iris.engine.object.IrisRegion;
-import art.arcane.iris.engine.object.IrisStructurePlacement;
 import art.arcane.volmlib.util.collection.KList;
 
 import java.io.IOException;
 import java.io.UncheckedIOException;
-import java.nio.file.Path;
-import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
-import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.WeakHashMap;
@@ -55,7 +48,7 @@ public final class GenerationFindCatalog {
     }
 
     public static boolean hasObjectPlacement(Engine engine, String key) {
-        return engine.hasObjectPlacement(key) || retained(engine).objects.contains(normalizeObjectKey(key));
+        return engine.hasObjectPlacement(key) || containsKey(retained(engine).objects, normalizeObjectKey(key));
     }
 
     public static KList<String> retainedStructureKeys(Engine engine) {
@@ -63,7 +56,7 @@ public final class GenerationFindCatalog {
     }
 
     public static boolean hasRetainedStructurePlacement(Engine engine, String key) {
-        return retained(engine).structures.contains(normalizeKey(key));
+        return containsKey(retained(engine).structures, normalizeKey(key));
     }
 
     private static RetainedCatalog retained(Engine engine) {
@@ -90,87 +83,48 @@ public final class GenerationFindCatalog {
 
     private static RetainedCatalog loadRetained(GenerationHistory history, GenerationManifest manifest) {
         RetainedCatalog catalog = new RetainedCatalog(manifest.activeActivation().activationId());
-        Set<String> loadedPacks = new HashSet<>();
+        try {
-        Long activationId = manifest.activeActivation().parentActivationId();
+            history.forEachRecordedSemantic(semantics -> addRecorded(catalog, semantics));
-        while (activationId != null) {
+        } catch (IOException error) {
-            GenerationActivation activation = manifest.activation(activationId).orElseThrow();
+            throw new UncheckedIOException("Unable to read recorded Iris find catalog", error);
-            GenerationEpoch epoch = manifest.epoch(activation.epochId()).orElseThrow();
-            String dimensionKey = epoch.dimensionContract().dimensionKey();
-            if (loadedPacks.add(epoch.packFingerprint() + ":" + dimensionKey)) {
-                try {
-                    loadPack(catalog, history.packRoot(activationId), dimensionKey);
-                } catch (IOException error) {
-                    throw new UncheckedIOException("Unable to read retained Iris find catalog for activation "
-                            + activationId, error);
-                }
-            }
-            activationId = activation.parentActivationId();
         }
         return catalog;
     }
 
-    private static void loadPack(RetainedCatalog catalog, Path packRoot, String dimensionKey) {
+    private static void addRecorded(RetainedCatalog catalog, ChunkGenerationSemantics semantics) {
-        IrisData data = IrisData.openDatapackCompiler(packRoot.toFile());
+        if (!semantics.sealed() || semantics.activationId() == catalog.activeActivationId) {
-        try {
+            return;
-            IrisDimension dimension = data.getDimensionLoader().load(dimensionKey, false);
+        }
-            if (dimension == null) {
+        for (String key : semantics.surfaceBiomeKeys()) {
-                throw new IllegalStateException("Retained Iris dimension is absent: " + dimensionKey);
+            addBiome(catalog, key);
+        }
+        for (String key : semantics.caveBiomeKeys()) {
+            addBiome(catalog, key);
+        }
+        for (String key : semantics.regionKeys()) {
+            String normalized = normalizeKey(key);
+            if (!catalog.regions.containsKey(normalized)) {
+                IrisRegion region = new IrisRegion().setName(key);
+                region.setLoadKey(key);
+                catalog.regions.put(normalized, region);
             }
-            addStructures(catalog.structures, dimension.getStructures());
+        }
-            for (IrisBiome biome : dimension.getReachableBiomes(() -> data)) {
+        for (String key : semantics.objectKeys()) {
-                catalog.biomes.putIfAbsent(normalizeKey(biome.getLoadKey()), biome);
+            catalog.objects.add(normalizeObjectKey(key));
-                addObjects(catalog.objects, biome.getObjects());
+        }
-                addStructures(catalog.structures, biome.getStructures());
+        for (ChunkGenerationSemantics.StructureOccurrence occurrence : semantics.structures()) {
-            }
+            catalog.structures.add(normalizeKey(occurrence.key()));
-            for (IrisRegion region : dimension.getAllRegions(() -> data)) {
-                catalog.regions.putIfAbsent(normalizeKey(region.getLoadKey()), region);
-                addObjects(catalog.objects, region.getObjects());
-                addStructures(catalog.structures, region.getStructures());
-            }
-            if (dimension.hasUpperDimension() && !dimensionKey.equals(dimension.getUpperDimension())) {
-                IrisDimension upper = data.getDimensionLoader().load(dimension.getUpperDimension(), false);
-                if (upper == null) {
-                    throw new IllegalStateException("Retained Iris upper dimension is absent: "
-                            + dimension.getUpperDimension());
-                }
-                for (IrisBiome biome : upper.getReachableBiomes(() -> data)) {
-                    addObjects(catalog.objects, biome.getSurfaceObjects());
-                }
-                for (IrisRegion region : upper.getAllRegions(() -> data)) {
-                    addObjects(catalog.objects, region.getSurfaceObjects());
-                }
-            }
-        } finally {
-            data.close();
         }
     }
 
-    private static void addStructures(Set<String> structures, Iterable<IrisStructurePlacement> placements) {
+    private static void addBiome(RetainedCatalog catalog, String key) {
-        for (IrisStructurePlacement placement : placements) {
+        String normalized = normalizeKey(key);
-            if (placement == null) {
+        if (catalog.biomes.containsKey(normalized)) {
-                continue;
+            return;
-            }
-            for (String key : placement.getStructures()) {
-                String normalized = normalizeKey(key);
-                if (!normalized.isEmpty()) {
-                    structures.add(normalized);
-                }
-            }
-        }
-    }
-
-    private static void addObjects(Set<String> objects, Iterable<IrisObjectPlacement> placements) {
-        for (IrisObjectPlacement placement : placements) {
-            if (placement == null || placement.getPlace() == null) {
-                continue;
-            }
-            for (String key : placement.getPlace()) {
-                String normalized = normalizeObjectKey(key);
-                if (!normalized.isEmpty()) {
-                    objects.add(normalized);
-                }
-            }
         }
+        IrisBiome biome = new IrisBiome().setName(key);
+        biome.setLoadKey(key);
+        catalog.biomes.put(normalized, biome);
     }
 
     private static <T extends IrisRegistrant> KList<T> merge(Iterable<T> active, Map<String, T> historical) {
@@ -184,16 +138,33 @@ public final class GenerationFindCatalog {
 
     private static <T extends IrisRegistrant> T find(Iterable<T> entries, String key) {
         String normalized = normalizeKey(key);
+        T caseInsensitiveMatch = null;
         for (T entry : entries) {
-            if (normalizeKey(entry.getLoadKey()).equals(normalized)) {
+            String entryKey = normalizeKey(entry.getLoadKey());
+            if (entryKey.equals(normalized)) {
                 return entry;
             }
+            if (caseInsensitiveMatch == null && entryKey.equalsIgnoreCase(normalized)) {
+                caseInsensitiveMatch = entry;
+            }
         }
-        return null;
+        return caseInsensitiveMatch;
+    }
+
+    private static boolean containsKey(Set<String> keys, String key) {
+        if (keys.contains(key)) {
+            return true;
+        }
+        for (String candidate : keys) {
+            if (candidate.equalsIgnoreCase(key)) {
+                return true;
+            }
+        }
+        return false;
     }
 
     private static String normalizeKey(String key) {
-        return key == null ? "" : key.trim().toLowerCase(Locale.ROOT);
+        return key == null ? "" : key.trim();
     }
 
     private static String normalizeObjectKey(String key) {