Merged platform diet

- Per-chunk biome stage resolver, subterrain candidate gate, section-walk heightmaps, reused history compressors

# Conflicts:
#	core/src/main/java/art/arcane/iris/generation/runtime/Engine.java

core/src/main/java/art/arcane/iris/generation/runtime/Engine.java

@@ -347,6 +347,13 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
         return planner == null ? SubterrainCell.OUTSIDE : planner.sample(x, y + getWorld().minHeight(), z);
     }
 
+    @ChunkCoordinates
+    default boolean subterrainAbsentInChunk(int chunkX, int chunkZ) {
+        IrisComplex complex = getComplex();
+        SubterrainPlanner planner = complex == null ? null : SubterrainChunkCells.activePlanner(complex, getDimension());
+        return planner == null || !planner.hasCandidates(chunkX, chunkZ);
+    }
+
     @BlockCoordinates
     default IrisBiome getSubterrainBiome(int x, int y, int z) {
         SubterrainCell cell = getSubterrainCell(x, y, z);
@@ -406,6 +413,7 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
             return;
         }
         IrisComplex complex = getComplex();
+        boolean subterrain = !subterrainAbsentInChunk(x >> 4, z >> 4);
         int caveTop = getHeight(x, z) - 2;
         IrisRegion region = getRegion(x, 0, z);
         IrisBiome surface = null;
@@ -419,7 +427,7 @@ public interface Engine extends DataProvider, Fallible, BlockUpdater, Renderer,
             for (int index = 0; index < biomes.length; index++) {
                 int y = index * step;
                 regions[index] = region;
-                IrisBiome featureBiome = getSubterrainBiome(x, y, z);
+                IrisBiome featureBiome = subterrain ? getSubterrainBiome(x, y, z) : null;
                 if (featureBiome != null) {
                     biomes[index] = featureBiome;
                     continue;

core/src/main/java/art/arcane/iris/generation/runtime/IrisEngine.java

@@ -668,6 +668,15 @@ public class IrisEngine implements Engine {
         return gate.admitted() ? complex.getSubterrainPlanner() : null;
     }
 
+    @ChunkCoordinates
+    @Override
+    public boolean subterrainAbsentInChunk(int chunkX, int chunkZ) {
+        if (!hasGenerationRuntimeScope() && generationHistoryRuntimeRouter != null) {
+            return false;
+        }
+        return Engine.super.subterrainAbsentInChunk(chunkX, chunkZ);
+    }
+
     @BlockCoordinates
     @Override
     public IrisBiome getSubterrainBiome(int x, int y, int z) {

core/src/main/java/art/arcane/iris/generation/subterrain/SubterrainPlanner.java

@@ -107,6 +107,10 @@ public final class SubterrainPlanner {
         return List.copyOf(result);
     }
 
+    public boolean hasCandidates(int chunkX, int chunkZ) {
+        return !isEmpty() && !candidates(chunkX, chunkZ).isEmpty();
+    }
+
     public SubterrainCell sample(int x, int y, int z) {
         if (isEmpty() || y < minY || y >= maxYExclusive) {
             return SubterrainCell.OUTSIDE;

core/src/main/java/art/arcane/iris/platform/bukkit/nms/BukkitBiomePolicy.java

@@ -8,6 +8,7 @@ import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.generation.runtime.DimensionStackContext;
 import art.arcane.iris.generation.runtime.DimensionStackLayout;
 import art.arcane.iris.generation.runtime.DimensionTerrainContext;
+import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.stream.ProvisionalSampling;
@@ -27,6 +28,7 @@ import org.bukkit.block.Biome;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
@@ -46,7 +48,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
     private static final int STRONGHOLD_RING_SEARCH_RADIUS = 112;
     private static final int STRONGHOLD_RING_SEARCH_QUART_STEP = 4;
 
-    private final long seed;
+    private final RNG biomeRng;
     private final Engine engine;
     private final BukkitChunkGenerator platformGenerator;
     private final NativeBiomeRegistry<H, V> biomeCustomRegistry;
@@ -64,7 +66,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
         this.engine = engine;
         this.platformGenerator = options.platformGenerator();
         this.possibleBiomeRegistry = options.possibleBiomeRegistry();
-        this.seed = options.seed();
+        this.biomeRng = new RNG(options.seed());
         this.biomeCustomRegistry = registry;
         this.biomeRegistry = biomeCustomRegistry;
         this.fallbackBiome = resolveFallbackBiome(this.biomeRegistry, this.biomeCustomRegistry);
@@ -826,7 +828,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
             int z,
             IrisDimensionCarvingResolver.State resolverState
     ) {
-        return resolveVisibleBiomeHolder(x, y, z, resolverState, null);
+        return resolveVisibleBiomeHolder(x, y, z, resolverState, null, null);
     }
 
     private H resolveVisibleBiomeHolder(
@@ -835,32 +837,44 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
             int z,
             IrisDimensionCarvingResolver.State resolverState,
             DimensionStackLayout stackLayout
+    ) {
+        return resolveVisibleBiomeHolder(x, y, z, resolverState, stackLayout, null);
+    }
+
+    private H resolveVisibleBiomeHolder(
+            int x,
+            int y,
+            int z,
+            IrisDimensionCarvingResolver.State resolverState,
+            DimensionStackLayout stackLayout,
+            ChunkResolution chunk
     ) {
         int blockX = x << 2;
         int blockY = y << 2;
         int blockZ = z << 2;
-        Optional<String> historicalKey = engine.getComplex().historicalPhysicalBiomeKeyAt(
+        IrisComplex complex = chunk == null ? engine.getComplex() : chunk.complex;
+        Optional<String> historicalKey = complex.historicalPhysicalBiomeKeyAt(
                 blockX, blockY, blockZ);
         if (historicalKey.isPresent()) {
             return resolvePhysicalBiomeHolder(historicalKey.get());
         }
         BiomeResolution resolution = resolveBiomeResolution(
-                x, y, z, resolverState, true, stackLayout);
+                x, y, z, resolverState, true, stackLayout, chunk);
         if (resolution == null) {
             return getFallbackBiome();
         }
 
-        return resolveVisibleBiomeHolder(resolution);
+        return resolveVisibleBiomeHolder(resolution, chunk);
     }
 
-    private H resolveVisibleBiomeHolder(BiomeResolution resolution) {
+    private H resolveVisibleBiomeHolder(BiomeResolution resolution, ChunkResolution chunk) {
         if (resolution.irisBiome.isCustom()) {
-            return resolveCustomHolder(resolution);
+            return resolveCustomHolder(resolution, chunk);
         }
 
         Biome vanillaBiome = resolution.underground
-                ? resolution.irisBiome.getGroundBiome(resolution.rng, engine, resolution.blockX, resolution.blockY, resolution.blockZ)
+                ? resolution.irisBiome.getGroundBiome(biomeRng, engine, resolution.blockX, resolution.blockY, resolution.blockZ)
-                : resolution.irisBiome.getSkyBiome(resolution.rng, engine, resolution.blockX, resolution.blockY, resolution.blockZ);
+                : resolution.irisBiome.getSkyBiome(biomeRng, engine, resolution.blockX, resolution.blockY, resolution.blockZ);
         H holder = biomeRegistry.lookup(vanillaBiome);
         if (holder != null) {
             return holder;
@@ -869,11 +883,12 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
         return getFallbackBiome();
     }
 
-    private H resolveCustomHolder(BiomeResolution resolution) {
+    private H resolveCustomHolder(BiomeResolution resolution, ChunkResolution chunk) {
-        IrisBiomeCustom customBiome = resolution.irisBiome.getCustomBiome(resolution.rng, engine, resolution.blockX, resolution.blockY, resolution.blockZ);
+        IrisBiomeCustom customBiome = resolution.irisBiome.getCustomBiome(biomeRng, engine, resolution.blockX, resolution.blockY, resolution.blockZ);
         if (customBiome != null) {
-            H holder = runtimeBiomeState().customBiomes().get(customBiomeKey(
+            H holder = chunk == null
-                    resolution.dimension, customBiome.getId()));
+                    ? runtimeBiomeState().customBiomes().get(customBiomeKey(resolution.dimension, customBiome.getId()))
+                    : chunk.customHolder(resolution.dimension, customBiome);
             if (holder != null) {
                 return holder;
             }
@@ -883,7 +898,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
     }
 
     private BiomeResolution resolveStructureBiomeResolution(int x, int y, int z) {
-        return resolveBiomeResolution(x, y, z, null, false);
+        return resolveBiomeResolution(x, y, z, null, false, null, null);
     }
 
     private H resolvePhysicalBiomeHolder(String physicalKey) {
@@ -898,65 +913,50 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
         return holder;
     }
 
-    private BiomeResolution resolveBiomeResolution(
-            int x,
-            int y,
-            int z,
-            IrisDimensionCarvingResolver.State resolverState
-    ) {
-        return resolveBiomeResolution(x, y, z, resolverState, true);
-    }
-
-    private BiomeResolution resolveBiomeResolution(
-            int x,
-            int y,
-            int z,
-            IrisDimensionCarvingResolver.State resolverState,
-            boolean includeDimensionStack
-    ) {
-        return resolveBiomeResolution(
-                x, y, z, resolverState, includeDimensionStack, null);
-    }
-
     private BiomeResolution resolveBiomeResolution(
             int x,
             int y,
             int z,
             IrisDimensionCarvingResolver.State resolverState,
             boolean includeDimensionStack,
-            DimensionStackLayout stackLayout
+            DimensionStackLayout stackLayout,
+            ChunkResolution chunk
     ) {
         if (engine == null || engine.isClosed()) {
             return null;
         }
 
-        if (engine.getComplex() == null) {
+        if ((chunk == null ? engine.getComplex() : chunk.complex) == null) {
             return null;
         }
 
         int blockX = x << 2;
         int blockZ = z << 2;
         int blockY = y << 2;
-        int worldMinHeight = engine.getWorld().minHeight();
+        int worldMinHeight = chunk == null ? engine.getWorld().minHeight() : chunk.worldMinHeight;
         int internalY = blockY - worldMinHeight;
         int caveSwitchInternalY = Math.max(-8 - worldMinHeight, 40);
-        IrisBiome featureBiome = engine.getSubterrainBiome(blockX, internalY, blockZ);
+        IrisBiome featureBiome = chunk != null && !chunk.subterrain
+                ? null : engine.getSubterrainBiome(blockX, internalY, blockZ);
         if (featureBiome != null) {
-            return createBiomeResolution(featureBiome, true, engine.getDimension(), blockX, blockY, blockZ);
+            return new BiomeResolution(featureBiome, true, chunk == null ? engine.getDimension() : chunk.dimension,
+                    blockX, blockY, blockZ);
         }
         DimensionStackLayout.Layer stackLayer = includeDimensionStack
                 ? stackLayout == null
-                        ? resolveDimensionStackLayer(engine, blockX, internalY, blockZ)
+                        ? resolveDimensionStackLayer(
+                                chunk == null ? engine.getDimensionStackContext() : chunk.stackContext,
+                                blockX, internalY, blockZ)
                         : stackLayout.layerAt(internalY)
                 : null;
         IrisDimension owningDimension = stackLayer == null
-                ? engine.getDimension()
+                ? chunk == null ? engine.getDimension() : chunk.dimension
                 : stackLayer.terrainContext().getDimension();
         if (stackLayer != null && !stackLayer.terrainContext().isSelfReferencing()) {
             IrisBiome stackedBiome = stackLayer.biome();
             return stackedBiome == null
                     ? null
-                    : createBiomeResolution(
+                    : new BiomeResolution(
                             stackedBiome, false, owningDimension, blockX, blockY, blockZ);
         }
         boolean deepUnderground = internalY <= caveSwitchInternalY;
@@ -976,41 +976,31 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
                     )
                     : stackLayer.biome();
         } else if (deepUnderground) {
-            int surfaceInternalY = Engine.hostHeight(engine, blockX, blockZ, true);
+            int surfaceInternalY = chunk == null
+                    ? Engine.hostHeight(engine, blockX, blockZ, true)
+                    : chunk.hostHeight(blockX, blockZ);
             underground = internalY <= surfaceInternalY - 8;
             irisBiome = underground
                     ? engine.getCaveBiome(blockX, internalY, blockZ, resolverState)
-                    : engine.getHostSurfaceBiome(blockX, blockZ);
+                    : hostSurfaceBiome(chunk, blockX, blockZ);
         } else {
-            irisBiome = engine.getHostSurfaceBiome(blockX, blockZ);
+            irisBiome = hostSurfaceBiome(chunk, blockX, blockZ);
         }
         if (irisBiome == null && underground) {
             irisBiome = stackLayer == null
-                    ? engine.getHostSurfaceBiome(blockX, blockZ)
+                    ? hostSurfaceBiome(chunk, blockX, blockZ)
                     : stackLayer.biome();
         }
         if (irisBiome == null) {
             return null;
         }
 
-        return createBiomeResolution(
+        return new BiomeResolution(
                 irisBiome, underground, owningDimension, blockX, blockY, blockZ);
     }
 
-    private BiomeResolution createBiomeResolution(
+    private IrisBiome hostSurfaceBiome(ChunkResolution chunk, int blockX, int blockZ) {
-            IrisBiome irisBiome,
+        return chunk == null ? engine.getHostSurfaceBiome(blockX, blockZ) : chunk.hostSurfaceBiome(blockX, blockZ);
-            boolean underground,
-            IrisDimension dimension,
-            int blockX,
-            int blockY,
-            int blockZ
-    ) {
-        RNG noiseRng = new RNG(seed
-                ^ (((long) blockX) * 341873128712L)
-                ^ (((long) blockY) * 132897987541L)
-                ^ (((long) blockZ) * 42317861L));
-        return new BiomeResolution(
-                irisBiome, underground, dimension, blockX, blockY, blockZ, noiseRng);
     }
 
     private H getFallbackBiome() {
@@ -1094,12 +1084,11 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
     }
 
     private static DimensionStackLayout.Layer resolveDimensionStackLayer(
-            Engine engine,
+            DimensionStackContext stackContext,
             int blockX,
             int internalY,
             int blockZ
     ) {
-        DimensionStackContext stackContext = engine.getDimensionStackContext();
         return stackContext == null ? null : stackContext.getLayerAt(blockX, internalY, blockZ);
     }
 
@@ -1136,7 +1125,6 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
         private final int blockX;
         private final int blockY;
         private final int blockZ;
-        private final RNG rng;
 
         private BiomeResolution(
                 IrisBiome irisBiome,
@@ -1144,8 +1132,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
                 IrisDimension dimension,
                 int blockX,
                 int blockY,
-                int blockZ,
+                int blockZ
-                RNG rng
         ) {
             this.irisBiome = irisBiome;
             this.underground = underground;
@@ -1153,7 +1140,100 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
             this.blockX = blockX;
             this.blockY = blockY;
             this.blockZ = blockZ;
-            this.rng = rng;
+        }
+    }
+
+    private final class ChunkVisibleResolver implements VisibleResolver<H> {
+        private final IrisDimensionCarvingResolver.State resolverState = new IrisDimensionCarvingResolver.State();
+        private final boolean flat = platformGenerator != null && platformGenerator.usesFlatStudioTerrain();
+        private ChunkResolution chunk;
+
+        @Override
+        public H biome(int quartX, int quartY, int quartZ) {
+            if (flat) {
+                return fallbackBiome;
+            }
+            int chunkX = quartX >> 2;
+            int chunkZ = quartZ >> 2;
+            ChunkResolution current = chunk;
+            if (current == null || current.chunkX != chunkX || current.chunkZ != chunkZ) {
+                current = new ChunkResolution(chunkX, chunkZ);
+                chunk = current;
+            }
+            return resolveVisibleBiomeHolder(quartX, quartY, quartZ, resolverState, null, current);
+        }
+    }
+
+    private final class ChunkResolution {
+        private static final int COLUMNS = 16;
+
+        private final int chunkX;
+        private final int chunkZ;
+        private final IrisComplex complex;
+        private final IrisDimension dimension;
+        private final DimensionStackContext stackContext;
+        private final int worldMinHeight;
+        private final boolean subterrain;
+        private final RuntimeBiomeState<H, V> runtimeState;
+        private final int[] hostHeights = new int[COLUMNS];
+        private final boolean[] hostHeightResolved = new boolean[COLUMNS];
+        private final IrisBiome[] hostSurfaces = new IrisBiome[COLUMNS];
+        private final boolean[] hostSurfaceResolved = new boolean[COLUMNS];
+        private IrisDimension[] customDimensions = new IrisDimension[4];
+        private IrisBiomeCustom[] customBiomes = new IrisBiomeCustom[4];
+        private Object[] customHolders = new Object[4];
+        private int customCount;
+
+        private ChunkResolution(int chunkX, int chunkZ) {
+            this.chunkX = chunkX;
+            this.chunkZ = chunkZ;
+            this.complex = engine.getComplex();
+            this.dimension = engine.getDimension();
+            this.stackContext = engine.getDimensionStackContext();
+            this.worldMinHeight = engine.getWorld().minHeight();
+            this.subterrain = !engine.subterrainAbsentInChunk(chunkX, chunkZ);
+            this.runtimeState = runtimeBiomeState();
+        }
+
+        private int hostHeight(int blockX, int blockZ) {
+            int column = column(blockX, blockZ);
+            if (!hostHeightResolved[column]) {
+                hostHeights[column] = Engine.hostHeight(engine, blockX, blockZ, true);
+                hostHeightResolved[column] = true;
+            }
+            return hostHeights[column];
+        }
+
+        private IrisBiome hostSurfaceBiome(int blockX, int blockZ) {
+            int column = column(blockX, blockZ);
+            if (!hostSurfaceResolved[column]) {
+                hostSurfaces[column] = engine.getHostSurfaceBiome(blockX, blockZ);
+                hostSurfaceResolved[column] = true;
+            }
+            return hostSurfaces[column];
+        }
+
+        @SuppressWarnings("unchecked")
+        private H customHolder(IrisDimension owner, IrisBiomeCustom custom) {
+            for (int index = 0; index < customCount; index++) {
+                if (customBiomes[index] == custom && customDimensions[index] == owner) {
+                    return (H) customHolders[index];
+                }
+            }
+            H holder = runtimeState.customBiomes().get(customBiomeKey(owner, custom.getId()));
+            if (customCount == customBiomes.length) {
+                customDimensions = Arrays.copyOf(customDimensions, customCount * 2);
+                customBiomes = Arrays.copyOf(customBiomes, customCount * 2);
+                customHolders = Arrays.copyOf(customHolders, customCount * 2);
+            }
+            customDimensions[customCount] = owner;
+            customBiomes[customCount] = custom;
+            customHolders[customCount++] = holder;
+            return holder;
+        }
+
+        private static int column(int blockX, int blockZ) {
+            return ((blockX & 15) >> 2) << 2 | ((blockZ & 15) >> 2);
         }
     }
 
@@ -1181,8 +1261,7 @@ public final class BukkitBiomePolicy<H, V> implements NativeBiomeSourcePolicy<H>
     }
     @Override
     public VisibleResolver<H> visibleResolver() {
-        IrisDimensionCarvingResolver.State state = new IrisDimensionCarvingResolver.State();
+        return new ChunkVisibleResolver();
-        return (x, y, z) -> getVisibleNoiseBiomeWithActiveGenerationLease(x, y, z, state);
     }
 
 }

core/src/main/java/art/arcane/iris/structure/nativegen/NativeStructureVolumeIndex.java

@@ -13,12 +13,13 @@ import art.arcane.volmlib.util.collection.KList;
 
 import java.io.IOException;
 import java.util.Collections;
-import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 import java.util.WeakHashMap;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.function.BooleanSupplier;
 import java.util.function.IntConsumer;
 import java.util.function.Supplier;
 
@@ -38,8 +39,8 @@ public final class NativeStructureVolumeIndex {
             Collections.synchronizedMap(new WeakHashMap<>());
 
     private final OriginResolver origins;
-    private final Map<RuntimeChunkKey, KList<NativeStructureVolume>> originCache = lru(MAX_CACHED_ORIGIN_CHUNKS);
+    private final VolumeCache originCache = new VolumeCache(MAX_CACHED_ORIGIN_CHUNKS);
-    private final Map<RuntimeChunkKey, KList<NativeStructureVolume>> queryCache = lru(MAX_CACHED_QUERY_CHUNKS);
+    private final VolumeCache queryCache = new VolumeCache(MAX_CACHED_QUERY_CHUNKS);
     private final ConcurrentHashMap<RuntimeChunkKey, CompletableFuture<KList<NativeStructureVolume>>> originBuilds =
             new ConcurrentHashMap<>();
     private final ConcurrentHashMap<RuntimeChunkKey, CompletableFuture<KList<NativeStructureVolume>>> queryBuilds =
@@ -180,12 +181,10 @@ public final class NativeStructureVolumeIndex {
             Engine engine, int chunkX, int chunkZ, Integer pinnedRuntimeId
     ) {
         if (pinnedRuntimeId != null) {
-            synchronized (originCache) {
+            KList<NativeStructureVolume> cached = originCache.get(
-                KList<NativeStructureVolume> cached = originCache.get(
+                    new RuntimeChunkKey(pinnedRuntimeId, chunkKey(chunkX, chunkZ)));
-                        new RuntimeChunkKey(pinnedRuntimeId, chunkKey(chunkX, chunkZ)));
+            if (cached != null) {
-                if (cached != null) {
+                return cached;
-                    return cached;
-                }
             }
         }
         return originVolumes(engine, chunkX, chunkZ);
@@ -210,27 +209,21 @@ public final class NativeStructureVolumeIndex {
     }
 
     void evictRuntime(int runtimeId) {
-        synchronized (originCache) {
+        originBuilds.keySet().removeIf(key -> key.runtimeId() == runtimeId);
-            originBuilds.keySet().removeIf(key -> key.runtimeId() == runtimeId);
+        originCache.evictRuntime(runtimeId);
-            originCache.keySet().removeIf(key -> key.runtimeId() == runtimeId);
+        queryBuilds.keySet().removeIf(key -> key.runtimeId() == runtimeId);
-        }
+        queryCache.evictRuntime(runtimeId);
-        synchronized (queryCache) {
-            queryBuilds.keySet().removeIf(key -> key.runtimeId() == runtimeId);
-            queryCache.keySet().removeIf(key -> key.runtimeId() == runtimeId);
-        }
     }
 
     private KList<NativeStructureVolume> cached(
-            Map<RuntimeChunkKey, KList<NativeStructureVolume>> cache,
+            VolumeCache volumes,
             ConcurrentHashMap<RuntimeChunkKey, CompletableFuture<KList<NativeStructureVolume>>> builds,
             RuntimeChunkKey key,
             Supplier<KList<NativeStructureVolume>> loader
     ) {
-        synchronized (cache) {
+        KList<NativeStructureVolume> hit = volumes.get(key);
-            KList<NativeStructureVolume> hit = cache.get(key);
+        if (hit != null) {
-            if (hit != null) {
+            return hit;
-                return hit;
-            }
         }
 
         CompletableFuture<KList<NativeStructureVolume>> future = new CompletableFuture<>();
@@ -241,22 +234,16 @@ public final class NativeStructureVolumeIndex {
 
         // Close the check-then-claim window: a racer whose cache check missed before the
         // previous builder cached could claim the build slot after it retired and rebuild.
-        synchronized (cache) {
+        KList<NativeStructureVolume> published = volumes.get(key);
-            KList<NativeStructureVolume> published = cache.get(key);
+        if (published != null) {
-            if (published != null) {
+            future.complete(published);
-                future.complete(published);
+            builds.remove(key, future);
-                builds.remove(key, future);
+            return published;
-                return published;
-            }
         }
 
         try {
             KList<NativeStructureVolume> built = loader.get();
-            synchronized (cache) {
+            volumes.publish(key, built, () -> builds.get(key) == future);
-                if (builds.get(key) == future) {
-                    cache.put(key, built);
-                }
-            }
             future.complete(built);
             return built;
         } catch (RuntimeException | Error error) {
@@ -303,15 +290,45 @@ public final class NativeStructureVolumeIndex {
         }
     }
 
-    private static Map<RuntimeChunkKey, KList<NativeStructureVolume>> lru(int capacity) {
+    private static final class VolumeCache {
-        return new LinkedHashMap<>(16, 0.75F, true) {
+        private final int capacity;
-            @Override
+        private final ConcurrentHashMap<RuntimeChunkKey, KList<NativeStructureVolume>> entries = new ConcurrentHashMap<>();
-            protected boolean removeEldestEntry(
+        private final ConcurrentLinkedQueue<RuntimeChunkKey> insertionOrder = new ConcurrentLinkedQueue<>();
-                    Map.Entry<RuntimeChunkKey, KList<NativeStructureVolume>> eldest
+
-            ) {
+        private VolumeCache(int capacity) {
-                return size() > capacity;
+            this.capacity = capacity;
+        }
+
+        private KList<NativeStructureVolume> get(RuntimeChunkKey key) {
+            return entries.get(key);
+        }
+
+        private void publish(RuntimeChunkKey key, KList<NativeStructureVolume> volumes, BooleanSupplier current) {
+            boolean[] inserted = new boolean[1];
+            entries.compute(key, (ignored, previous) -> {
+                if (!current.getAsBoolean()) {
+                    return previous;
+                }
+                inserted[0] = previous == null;
+                return volumes;
+            });
+            if (!inserted[0]) {
+                return;
             }
-        };
+            insertionOrder.add(key);
+            while (entries.size() > capacity) {
+                RuntimeChunkKey eldest = insertionOrder.poll();
+                if (eldest == null) {
+                    return;
+                }
+                entries.remove(eldest);
+            }
+        }
+
+        private void evictRuntime(int runtimeId) {
+            entries.keySet().removeIf(key -> key.runtimeId() == runtimeId);
+            insertionOrder.removeIf(key -> key.runtimeId() == runtimeId);
+        }
     }
 
     static int runtimeChunkHash(int runtimeId, long chunkKey) {

core/src/main/java/art/arcane/iris/world/history/GenerationSemanticIndex.java

@@ -99,6 +99,7 @@ public final class GenerationSemanticIndex {
     private volatile IOException journalFailure;
     private long appendingRegionKey;
     private RegionShard appendingBase;
+    private boolean journalStorageReady;
 
     private GenerationSemanticIndex(
             Path dimensionRoot,
@@ -264,12 +265,13 @@ public final class GenerationSemanticIndex {
             if (updates.isEmpty()) {
                 return;
             }
-            ensureStorageDirectory();
+            ensureJournalStorage();
+            boolean existingJournal = journalEntries.containsKey(regionKey);
             appendingRegionKey = regionKey;
             appendingBase = baseRegion;
             publicationLock.unlock();
             try {
-                SemanticJournal.append(directory, regionX, regionZ, updates, unpublished, durability);
+                SemanticJournal.append(directory, regionX, regionZ, updates, unpublished, durability, existingJournal);
             } catch (JournalAppendFailure failure) {
                 journalFailure = failure;
                 throw failure;
@@ -1193,6 +1195,14 @@ public final class GenerationSemanticIndex {
         return true;
     }
 
+    private void ensureJournalStorage() throws IOException {
+        if (journalStorageReady) {
+            return;
+        }
+        ensureStorageDirectory();
+        journalStorageReady = true;
+    }
+
     private void ensureStorageDirectory() throws IOException {
         validateDimensionRoot();
         Path irisDirectory = ensureChildDirectory(dimensionRoot, "iris");
@@ -1958,18 +1968,17 @@ public final class GenerationSemanticIndex {
                 int regionZ,
                 List<ChunkGenerationSemantics> claims,
                 boolean unpublished,
-                DeferredDurability durability
+                DeferredDurability durability,
+                boolean existing
         ) throws IOException {
             Path file = directory.resolve(journalFileName(regionX, regionZ));
-            boolean created = !Files.exists(file, LinkOption.NOFOLLOW_LINKS);
+            boolean created = !existing && !Files.exists(file, LinkOption.NOFOLLOW_LINKS);
-            if (!created && !Files.isRegularFile(file, LinkOption.NOFOLLOW_LINKS)) {
+            if (!existing && !created && !Files.isRegularFile(file, LinkOption.NOFOLLOW_LINKS)) {
                 throw invalid(file, "path is not a regular file");
             }
-            FileChannel opened = FileChannel.open(
+            FileChannel opened = existing
-                    file,
+                    ? FileChannel.open(file, StandardOpenOption.WRITE)
-                    StandardOpenOption.CREATE,
+                    : FileChannel.open(file, StandardOpenOption.CREATE, StandardOpenOption.WRITE);
-                    StandardOpenOption.WRITE
-            );
             boolean uncertain = created;
             boolean restored = false;
             try (FileChannel channel = opened) {

core/src/main/java/art/arcane/iris/world/history/NativeTerrainReceipt.java

@@ -6,11 +6,16 @@ import java.io.ByteArrayOutputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.OptionalInt;
+import java.util.zip.CRC32;
+import java.util.zip.Deflater;
+import java.util.zip.DeflaterOutputStream;
 import java.util.zip.GZIPInputStream;
 import java.util.zip.GZIPOutputStream;
 
@@ -18,6 +23,8 @@ public final class NativeTerrainReceipt {
     private static final int MAGIC = 0x4952544E;
     private static final int VERSION = 1;
     private static final int MAXIMUM_BYTES = 64 * 1024 * 1024;
+    private static final ThreadLocal<Deflater> DEFLATERS =
+            ThreadLocal.withInitial(() -> new Deflater(Deflater.DEFAULT_COMPRESSION, true));
 
     private NativeTerrainReceipt() {
     }
@@ -25,7 +32,9 @@ public final class NativeTerrainReceipt {
     public static byte[] encode(SavedTerrainChunk chunk, long activationId, String epochId) throws IOException {
         ByteArrayOutputStream bytes = new ByteArrayOutputStream();
         UtfCache strings = new UtfCache();
-        try (DataOutputStream output = new DataOutputStream(new BufferedOutputStream(new GZIPOutputStream(bytes)))) {
+        Deflater deflater = DEFLATERS.get();
+        deflater.reset();
+        try (DataOutputStream output = new DataOutputStream(new BufferedOutputStream(new GzipStream(bytes, deflater)))) {
             output.writeInt(MAGIC);
             output.writeInt(VERSION);
             output.writeInt(chunk.chunkX());
@@ -196,6 +205,60 @@ public final class NativeTerrainReceipt {
     public record Decoded(SavedTerrainChunk terrain, long activationId, String epochId) {
     }
 
+    private static final class GzipStream extends DeflaterOutputStream {
+        private static final int BUFFER_BYTES = 512;
+        private static final int TRAILER_BYTES = 8;
+        private static final byte[] HEADER = gzipHeader();
+
+        private final CRC32 checksum = new CRC32();
+
+        private GzipStream(OutputStream out, Deflater deflater) throws IOException {
+            super(out, deflater, BUFFER_BYTES);
+            out.write(HEADER);
+        }
+
+        @Override
+        public void write(byte[] buffer, int offset, int length) throws IOException {
+            super.write(buffer, offset, length);
+            checksum.update(buffer, offset, length);
+        }
+
+        @Override
+        public void finish() throws IOException {
+            if (def.finished()) {
+                return;
+            }
+            def.finish();
+            while (!def.finished()) {
+                int length = def.deflate(buf, 0, buf.length);
+                if (length > 0) {
+                    out.write(buf, 0, length);
+                }
+            }
+            byte[] trailer = new byte[TRAILER_BYTES];
+            writeLittleEndian(trailer, 0, (int) checksum.getValue());
+            writeLittleEndian(trailer, 4, (int) def.getBytesRead());
+            out.write(trailer);
+        }
+
+        private static void writeLittleEndian(byte[] target, int offset, int value) {
+            target[offset] = (byte) value;
+            target[offset + 1] = (byte) (value >>> 8);
+            target[offset + 2] = (byte) (value >>> 16);
+            target[offset + 3] = (byte) (value >>> 24);
+        }
+
+        private static byte[] gzipHeader() {
+            ByteArrayOutputStream empty = new ByteArrayOutputStream();
+            try (GZIPOutputStream gzip = new GZIPOutputStream(empty)) {
+                gzip.finish();
+            } catch (IOException failure) {
+                throw new IllegalStateException("Unable to resolve the platform gzip header", failure);
+            }
+            return Arrays.copyOf(empty.toByteArray(), 10);
+        }
+    }
+
     private static final class UtfCache {
         private static final int MAXIMUM_ENTRIES = 256;
         private static final int MAXIMUM_ENCODED_BYTES = 64 * 1024;

core/src/main/java/art/arcane/iris/world/history/SavedBiomeCapture.java

@@ -36,7 +36,8 @@ public final class SavedBiomeCapture {
                 Math.addExact(startX, 15), Math.addExact(startZ, 15)).isEmpty();
         Map<Integer, List<SavedBiomeChunk.Span>> vertical = new HashMap<>(exactVolume ? 256 : 16);
         Cells cells = new Cells(activationId);
-        Column column = new Column(engine, minimumY, height, exactVolume ? 1 : 4);
+        Column column = new Column(engine, minimumY, height, exactVolume ? 1 : 4,
+                !engine.subterrainAbsentInChunk(stage.chunkX(), stage.chunkZ()));
         for (int localX = 0; localX < 16; localX++) {
             for (int localZ = 0; localZ < 16; localZ++) {
                 int blockX = startX + localX;
@@ -82,7 +83,8 @@ public final class SavedBiomeCapture {
         for (int index = 0; index < column.biomes().length; index++) {
             int worldY = minimumY + index * column.step();
             SavedBiomeChunk.Cell current = cells.cell(column.biomes()[index], column.regions()[index]);
-            if (floating != null && !column.engine().getSubterrainCell(blockX, index * column.step(), blockZ).occupied()) {
+            if (floating != null && (!column.subterrain()
+                    || !column.engine().getSubterrainCell(blockX, index * column.step(), blockZ).occupied())) {
                 current = overlay(current, floating.volumeAt(blockX & 15, worldY - minimumY, blockZ & 15));
             }
             if (transition != null) {
@@ -139,9 +141,10 @@ public final class SavedBiomeCapture {
                 Objects.requireNonNull(region, "region").getLoadKey());
     }
 
-    private record Column(Engine engine, int minimumY, int height, int step, IrisBiome[] biomes, IrisRegion[] regions) {
+    private record Column(Engine engine, int minimumY, int height, int step, boolean subterrain, IrisBiome[] biomes,
-        private Column(Engine engine, int minimumY, int height, int step) {
+                          IrisRegion[] regions) {
-            this(engine, minimumY, height, step, new IrisBiome[(height + step - 1) / step],
+        private Column(Engine engine, int minimumY, int height, int step, boolean subterrain) {
+            this(engine, minimumY, height, step, subterrain, new IrisBiome[(height + step - 1) / step],
                     new IrisRegion[(height + step - 1) / step]);
         }
     }

core/src/main/java/art/arcane/iris/world/history/SavedBiomeStore.java

@@ -49,6 +49,7 @@ public final class SavedBiomeStore {
     private static final int MAXIMUM_CACHED_CHUNKS = 128;
     private static final long MAXIMUM_CACHED_BYTES = 64L * 1024L * 1024L;
     private static final int MAXIMUM_WRITE_BATCH = 64;
+    private static final ThreadLocal<Deflater> DEFLATERS = ThreadLocal.withInitial(() -> new Deflater(Deflater.BEST_SPEED));
 
     private final Path dimensionRoot;
     private final Path directory;
@@ -464,12 +465,16 @@ public final class SavedBiomeStore {
     }
 
     private void ensureRegionFile(RegionIndex region) throws IOException {
+        if (region.fileReady) {
+            return;
+        }
         requireSafeAncestors();
         Files.createDirectories(directory);
         if (Files.exists(region.path, LinkOption.NOFOLLOW_LINKS)) {
             if (!Files.isRegularFile(region.path, LinkOption.NOFOLLOW_LINKS)) {
                 throw new IOException("Saved biome region is not a regular file: " + region.path);
             }
+            region.fileReady = true;
             return;
         }
         ByteBuffer header = ByteBuffer.allocate(HEADER_BYTES);
@@ -486,6 +491,7 @@ public final class SavedBiomeStore {
             }
             Files.move(temporary, region.path, StandardCopyOption.ATOMIC_MOVE);
             forceDirectory(directory);
+            region.fileReady = true;
         } finally {
             Files.deleteIfExists(temporary);
         }
@@ -674,11 +680,10 @@ public final class SavedBiomeStore {
         output.writeInt(chunk.chunkX());
         output.writeInt(chunk.chunkZ());
         output.writeInt(raw.size());
-        Deflater deflater = new Deflater(Deflater.BEST_SPEED);
+        Deflater deflater = DEFLATERS.get();
+        deflater.reset();
         try (DeflaterOutputStream compressed = new DeflaterOutputStream(output, deflater)) {
             raw.writeTo(compressed);
-        } finally {
-            deflater.end();
         }
         if (encoded.size() > MAXIMUM_RECORD_BYTES) {
             throw new IOException("Saved biome chunk exceeds its encoded size limit");
@@ -847,6 +852,7 @@ public final class SavedBiomeStore {
         private final int regionZ;
         private final long[] offsets = new long[1024];
         private final int[] lengths = new int[1024];
+        private boolean fileReady;
 
         private RegionIndex(Path path, int regionX, int regionZ) {
             this.path = path;

core/src/test/java/art/arcane/iris/platform/bukkit/nms/BukkitBiomeVisibleResolverTest.java

@@ -0,0 +1,111 @@
+package art.arcane.iris.platform.bukkit.nms;
+
+import art.arcane.iris.generation.biome.IrisBiome;
+import art.arcane.iris.generation.biome.IrisBiomeCustom;
+import art.arcane.iris.generation.mantle.EngineMantle;
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.GenerationSessionLease;
+import art.arcane.iris.generation.runtime.IrisComplex;
+import art.arcane.iris.generation.runtime.IrisEngine;
+import art.arcane.iris.generation.terrain.IrisDimension;
+import art.arcane.iris.generation.terrain.IrisDimensionCarvingResolver;
+import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.iris.world.IrisWorld;
+import art.arcane.volmlib.nativelib.terrain.NativeBiomeRegistry;
+import art.arcane.volmlib.nativelib.terrain.NativeBiomeSourcePolicy;
+import art.arcane.volmlib.util.collection.KList;
+import org.junit.Test;
+
+import java.lang.reflect.Field;
+import java.util.Optional;
+import java.util.concurrent.ConcurrentHashMap;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Answers.CALLS_REAL_METHODS;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class BukkitBiomeVisibleResolverTest {
+    @Test
+    public void chunkResolverMatchesThePerQuartResolution() throws Exception {
+        IrisBiome surface = customBiome("surface", "meadow");
+        IrisBiome cave = customBiome("cave", "grotto");
+        IrisBiome custom = customBiome("custom", "mirage");
+        IrisBiome feature = customBiome("feature", "bloom");
+        IrisDimension dimension = mock(IrisDimension.class);
+        when(dimension.getReachableBiomes(any())).thenReturn(new KList<>(surface, cave, custom, feature));
+        when(dimension.getCustomBiomeKey(anyString())).thenAnswer(invocation -> "pack:" + invocation.getArgument(0));
+        IrisData data = mock(IrisData.class);
+        when(data.customBiomeResourceKey(any(IrisDimension.class), anyString()))
+                .thenAnswer(invocation -> "pack:" + invocation.getArgument(1));
+        IrisComplex complex = mock(IrisComplex.class);
+        when(complex.historicalPhysicalBiomeKeyAt(anyInt(), anyInt(), anyInt())).thenReturn(Optional.empty());
+        EngineMantle mantle = mock(EngineMantle.class);
+        when(mantle.trueHeight(anyInt(), anyInt())).thenAnswer(invocation ->
+                120 + Math.floorMod(invocation.<Integer>getArgument(0) * 7 + invocation.<Integer>getArgument(1) * 3, 160));
+        IrisEngine engine = mock(IrisEngine.class);
+        when(engine.getDimension()).thenReturn(dimension);
+        when(engine.getData()).thenReturn(data);
+        when(engine.getComplex()).thenReturn(complex);
+        when(engine.getMantle()).thenReturn(mantle);
+        when(engine.getWorld()).thenReturn(IrisWorld.builder().minHeight(-64).maxHeight(320).build());
+        when(engine.getMinHeight()).thenReturn(-64);
+        when(engine.getCacheID()).thenReturn(1);
+        when(engine.acquireGenerationLease(anyString())).thenReturn(GenerationSessionLease.noop());
+        when(engine.answersFromNaturalTerrain(anyInt(), anyInt())).thenReturn(false);
+        when(engine.getHostSurfaceBiome(anyInt(), anyInt())).thenAnswer(invocation ->
+                Math.floorMod(invocation.<Integer>getArgument(0) + invocation.<Integer>getArgument(1), 8) == 0 ? custom : surface);
+        when(engine.getCaveBiome(anyInt(), anyInt(), anyInt(), any(IrisDimensionCarvingResolver.State.class)))
+                .thenAnswer(invocation -> invocation.<Integer>getArgument(1) % 3 == 0 ? custom : cave);
+        when(engine.getSubterrainBiome(anyInt(), anyInt(), anyInt())).thenAnswer(invocation ->
+                invocation.<Integer>getArgument(0) == 4 && invocation.<Integer>getArgument(1) == 40 ? feature : null);
+        when(engine.subterrainAbsentInChunk(1, 0)).thenReturn(true);
+        @SuppressWarnings("unchecked")
+        NativeBiomeRegistry<String, String> registry = mock(NativeBiomeRegistry.class);
+        when(registry.lookupCustom(anyString())).thenAnswer(invocation -> invocation.getArgument(0));
+        BukkitBiomePolicy<String, String> policy = policy(engine, registry, "fallback");
+
+        for (int chunkX = 0; chunkX <= 1; chunkX++) {
+            NativeBiomeSourcePolicy.VisibleResolver<String> resolver = policy.visibleResolver();
+            for (int quartY = -16; quartY < 80; quartY++) {
+                for (int localX = 0; localX < 4; localX++) {
+                    for (int localZ = 0; localZ < 4; localZ++) {
+                        int quartX = (chunkX << 2) + localX;
+                        String expected = policy.getVisibleNoiseBiomeWithActiveGenerationLease(
+                                quartX, quartY, localZ, new IrisDimensionCarvingResolver.State());
+                        assertEquals("quart " + quartX + "," + quartY + "," + localZ, expected,
+                                resolver.biome(quartX, quartY, localZ));
+                    }
+                }
+            }
+        }
+    }
+
+    private static IrisBiome customBiome(String key, String customId) {
+        IrisBiome biome = new IrisBiome().setCustomDerivitives(new KList<>(new IrisBiomeCustom().setId(customId)));
+        biome.setLoadKey(key);
+        return biome;
+    }
+
+    @SuppressWarnings("unchecked")
+    private static BukkitBiomePolicy<String, String> policy(Engine engine, NativeBiomeRegistry<String, String> registry,
+                                                            String fallback) throws Exception {
+        BukkitBiomePolicy<String, String> policy = mock(BukkitBiomePolicy.class, CALLS_REAL_METHODS);
+        set(policy, "engine", engine);
+        set(policy, "biomeCustomRegistry", registry);
+        set(policy, "biomeRegistry", registry);
+        set(policy, "fallbackBiome", fallback);
+        set(policy, "runtimeBiomeStates", new ConcurrentHashMap<>());
+        set(policy, "noiseBiomeCache", new ConcurrentHashMap<>());
+        return policy;
+    }
+
+    private static void set(Object target, String name, Object value) throws Exception {
+        Field field = BukkitBiomePolicy.class.getDeclaredField(name);
+        field.setAccessible(true);
+        field.set(target, value);
+    }
+}

core/src/test/java/art/arcane/iris/platform/bukkit/nms/BukkitSubterrainBiomePrecedenceTest.java

@@ -36,10 +36,12 @@ public class BukkitSubterrainBiomePrecedenceTest {
         owner.setAccessible(true);
         owner.set(policy, engine);
         DimensionStackLayout stack = mock(DimensionStackLayout.class);
+        Class<?> chunkResolution = Class.forName(BukkitBiomePolicy.class.getName() + "$ChunkResolution");
         Method resolve = BukkitBiomePolicy.class.getDeclaredMethod("resolveBiomeResolution", int.class, int.class,
-                int.class, IrisDimensionCarvingResolver.State.class, boolean.class, DimensionStackLayout.class);
+                int.class, IrisDimensionCarvingResolver.State.class, boolean.class, DimensionStackLayout.class,
+                chunkResolution);
         resolve.setAccessible(true);
-        Object resolved = resolve.invoke(policy, 3, 40, -5, null, true, stack);
+        Object resolved = resolve.invoke(policy, 3, 40, -5, null, true, stack, null);
         assertSame(feature, field(resolved, "irisBiome"));
         assertSame(host, field(resolved, "dimension"));
         assertEquals(true, field(resolved, "underground"));

core/src/test/java/art/arcane/iris/structure/nativegen/NativeStructureVolumeIndexCacheTest.java

@@ -0,0 +1,69 @@
+package art.arcane.iris.structure.nativegen;
+
+import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.volmlib.nativelib.terrain.structure.NativeStructureVolume;
+import art.arcane.volmlib.util.collection.KList;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class NativeStructureVolumeIndexCacheTest {
+    @Test
+    public void concurrentQueriesBuildEachOriginOnceAndAnswerIdentically() throws Exception {
+        Map<Long, AtomicInteger> builds = new ConcurrentHashMap<>();
+        NativeStructureVolumeIndex index = NativeStructureVolumeIndex.forTesting((engine, chunkX, chunkZ) -> {
+            builds.computeIfAbsent(((long) chunkX << 32) ^ (chunkZ & 0xffffffffL), key -> new AtomicInteger()).incrementAndGet();
+            return volumesAt(chunkX, chunkZ);
+        });
+        Engine engine = mock(Engine.class);
+        when(engine.getCacheID()).thenReturn(7);
+        KList<NativeStructureVolume> expected = NativeStructureVolumeIndex.forTesting(
+                (ignored, chunkX, chunkZ) -> volumesAt(chunkX, chunkZ)).resolve(engine, 0, 0, 47, 47);
+        ExecutorService pool = Executors.newFixedThreadPool(8);
+        try {
+            List<Future<KList<NativeStructureVolume>>> results = new ArrayList<>();
+            for (int task = 0; task < 32; task++) {
+                results.add(pool.submit(() -> index.resolve(engine, 0, 0, 47, 47)));
+            }
+            for (Future<KList<NativeStructureVolume>> result : results) {
+                assertEquals(expected, result.get(30, TimeUnit.SECONDS));
+            }
+        } finally {
+            pool.shutdown();
+            assertTrue(pool.awaitTermination(30, TimeUnit.SECONDS));
+        }
+        for (AtomicInteger count : builds.values()) {
+            assertEquals(1, count.get());
+        }
+        int distinct = builds.size();
+        index.evictRuntime(7);
+        assertEquals(expected, index.resolve(engine, 0, 0, 47, 47));
+        assertEquals(distinct, builds.size());
+        for (AtomicInteger count : builds.values()) {
+            assertEquals(2, count.get());
+        }
+    }
+
+    private static KList<NativeStructureVolume> volumesAt(int chunkX, int chunkZ) {
+        if (Math.floorMod(chunkX * 31 + chunkZ * 17, 5) != 0) {
+            return NativeStructureVolume.NONE;
+        }
+        int minX = chunkX << 4;
+        int minZ = chunkZ << 4;
+        return new KList<>(new NativeStructureVolume("test:" + chunkX + "_" + chunkZ,
+                minX - 20, -10, minZ - 20, minX + 36, 40, minZ + 36, null));
+    }
+}

core/src/test/java/art/arcane/iris/world/history/NativeTerrainReceiptTest.java

@@ -60,6 +60,15 @@ public class NativeTerrainReceiptTest {
         }
     }
 
+    @Test
+    public void repeatedEncodingOnOneThreadKeepsLegacyBytes() throws Exception {
+        for (int round = 0; round < 6; round++) {
+            SavedTerrainChunk chunk = chunk(round % 2 == 0);
+            String epoch = "epoch-" + round;
+            assertArrayEquals(legacyEncode(chunk, round, epoch), NativeTerrainReceipt.encode(chunk, round, epoch));
+        }
+    }
+
     @Test
     public void saturatedStringCachesPreserveModifiedUtfBytes() throws Exception {
         for (int padding : new int[]{0, 300}) {

core/src/test/java/art/arcane/iris/world/history/SavedBiomeStoreWriteTest.java

@@ -60,6 +60,16 @@ public class SavedBiomeStoreWriteTest {
         assertArrayEquals(expectedRegion(), Files.readAllBytes(regionPath(root)));
     }
 
+    @Test
+    public void consecutiveRecordsKeepIndependentlyCompressedBytes() throws Exception {
+        Path root = temporaryFolder.newFolder().toPath();
+        SavedBiomeStore store = SavedBiomeStore.open(root);
+        for (int x = 0; x < 4; x++) {
+            store.claimAndPersist(chunk(x, 3L));
+        }
+        assertArrayEquals(expectedRegion(4), Files.readAllBytes(regionPath(root)));
+    }
+
     @Test
     public void relaxedDurabilityPreservesRecordsWithoutForcingEachAppend() throws Exception {
         String previousMode = System.getProperty(Durability.MODE_PROPERTY);
@@ -379,6 +389,10 @@ public class SavedBiomeStoreWriteTest {
     }
 
     private static byte[] expectedRegion() throws IOException {
+        return expectedRegion(1);
+    }
+
+    private static byte[] expectedRegion(int records) throws IOException {
         ByteArrayOutputStream raw = new ByteArrayOutputStream();
         DataOutputStream data = new DataOutputStream(raw);
         data.writeLong(3L);
@@ -392,17 +406,6 @@ public class SavedBiomeStoreWriteTest {
         data.writeInt(1);
         data.write(new byte[]{0, 0, 1, (byte) 0x80, 3, 0});
         data.write(new byte[256]);
-        ByteArrayOutputStream body = new ByteArrayOutputStream();
-        DataOutputStream coordinates = new DataOutputStream(body);
-        coordinates.writeInt(0);
-        coordinates.writeInt(0);
-        coordinates.writeInt(raw.size());
-        Deflater deflater = new Deflater(Deflater.BEST_SPEED);
-        try (DeflaterOutputStream compressed = new DeflaterOutputStream(coordinates, deflater)) {
-            raw.writeTo(compressed);
-        } finally {
-            deflater.end();
-        }
         ByteArrayOutputStream region = new ByteArrayOutputStream();
         DataOutputStream output = new DataOutputStream(region);
         output.writeInt(0x4942494F);
@@ -410,9 +413,22 @@ public class SavedBiomeStoreWriteTest {
         output.writeInt(0);
         output.writeInt(0);
         output.writeInt(checksum(region.toByteArray()));
-        output.writeInt(body.size());
+        for (int x = 0; x < records; x++) {
-        output.write(body.toByteArray());
+            ByteArrayOutputStream body = new ByteArrayOutputStream();
-        output.writeInt(checksum(body.toByteArray()));
+            DataOutputStream coordinates = new DataOutputStream(body);
+            coordinates.writeInt(x);
+            coordinates.writeInt(0);
+            coordinates.writeInt(raw.size());
+            Deflater deflater = new Deflater(Deflater.BEST_SPEED);
+            try (DeflaterOutputStream compressed = new DeflaterOutputStream(coordinates, deflater)) {
+                raw.writeTo(compressed);
+            } finally {
+                deflater.end();
+            }
+            output.writeInt(body.size());
+            output.write(body.toByteArray());
+            output.writeInt(checksum(body.toByteArray()));
+        }
         return region.toByteArray();
     }