Test- 26.3

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

@@ -62,15 +62,10 @@ public final class DefaultPackBootstrapProvisioner {
         return DEFAULT_PACKS;
     }
 
-    public static ProvisionResult provision(Path dataDirectory, Consumer<String> feedback) throws IOException {
-        return provision(dataDirectory, feedback, BukkitStartupPaths.resolveCurrent());
-    }
-
-    public static ProvisionResult provision(
-            Path dataDirectory,
-            Consumer<String> feedback,
-            BukkitStartupPaths startupPaths
-    ) throws IOException {
+    public static ProvisionResult provision(BootstrapRequest request) throws IOException {
+        Path dataDirectory = request.dataDirectory();
+        Consumer<String> feedback = request.feedback();
+        BukkitStartupPaths startupPaths = request.startupPaths();
         Objects.requireNonNull(dataDirectory, "dataDirectory");
         Objects.requireNonNull(feedback, "feedback");
         BukkitStartupPaths requiredStartupPaths = Objects.requireNonNull(startupPaths, "startupPaths");
@@ -94,7 +89,8 @@ public final class DefaultPackBootstrapProvisioner {
                 3,
                 Duration.ofMillis(250),
                 MAX_ARCHIVE_BYTES,
-                levelRoot
+                levelRoot,
+                request.dataVersion()
         );
         return provision(dataDirectory, feedback, options);
     }
@@ -135,7 +131,7 @@ public final class DefaultPackBootstrapProvisioner {
             if (!Integer.toString(MARKER_SCHEMA).equals(marker.getProperty("schema"))) {
                 return false;
             }
-            IDataFixer fixer = DataVersion.getLatest().get();
+            IDataFixer fixer = DataVersion.getRuntime().get();
             if (fixer == null
                     || !IrisDatapackCompiler.compilerIdentity(fixer)
                     .equals(marker.getProperty("compilerIdentity"))) {
@@ -248,9 +244,9 @@ public final class DefaultPackBootstrapProvisioner {
             }
 
             List<File> packRoots = IrisDatapackCompiler.collectPackRoots(normalizedData, options.levelRoot());
-            IDataFixer fixer = DataVersion.getLatest().get();
+            IDataFixer fixer = options.dataVersion().get();
             if (fixer == null) {
-                throw new IOException("Latest Iris datapack fixer is unavailable during bootstrap");
+                throw new IOException("Selected Iris datapack fixer is unavailable during bootstrap");
             }
             String compilerIdentity = IrisDatapackCompiler.compilerIdentity(fixer);
             String aggregateFingerprint = packRootsFingerprint(packRoots);
@@ -915,6 +911,16 @@ public final class DefaultPackBootstrapProvisioner {
         }
     }
 
+    public record BootstrapRequest(Path dataDirectory, Consumer<String> feedback,
+                                   BukkitStartupPaths startupPaths, DataVersion dataVersion) {
+        public BootstrapRequest {
+            Objects.requireNonNull(dataDirectory);
+            Objects.requireNonNull(feedback);
+            Objects.requireNonNull(startupPaths);
+            Objects.requireNonNull(dataVersion);
+        }
+    }
+
     record ProvisionOptions(
             List<PackSpec> packs,
             List<IrisGeneratorBinding> bindings,
@@ -925,7 +931,8 @@ public final class DefaultPackBootstrapProvisioner {
             int attempts,
             Duration retryDelay,
             long maxArchiveBytes,
-            Path levelRoot
+            Path levelRoot,
+            DataVersion dataVersion
     ) {
         ProvisionOptions {
             packs = List.copyOf(Objects.requireNonNull(packs, "packs"));
@@ -936,6 +943,10 @@ public final class DefaultPackBootstrapProvisioner {
             Objects.requireNonNull(requestTimeout, "requestTimeout");
             Objects.requireNonNull(retryDelay, "retryDelay");
             Objects.requireNonNull(levelRoot, "levelRoot");
+            Objects.requireNonNull(dataVersion, "dataVersion");
+            if (dataVersion == DataVersion.UNSUPPORTED) {
+                throw new IllegalArgumentException("Unsupported bootstrap datapack version");
+            }
             if (attempts < 1 || maxArchiveBytes < 1L) {
                 throw new IllegalArgumentException("Invalid bootstrap provisioning options");
             }

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

@@ -321,7 +321,7 @@ public interface INMSBinding {
         if (!supportsIrisWorldGeneration()) {
             throw new IllegalStateException("Iris world '" + c.name() + "' cannot be created with limited NMS binding "
                     + getClass().getSimpleName()
-                    + "; set general.disableNMS=false and use a supported Minecraft server runtime (26.1.2 or 26.2)");
+                    + "; set general.disableNMS=false and use a supported Minecraft server runtime (26.1.2, 26.2 or 26.3)");
         }
         if (missingDimensionTypes(generator.getTarget().getDimension().getDimensionTypeKey())) {
             throw new IllegalStateException("Missing dimension types to create world");

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

@@ -1,7 +1,7 @@
 package art.arcane.iris.platform.bukkit.nms;
 
 final class NmsBindingSelector {
-    private static final String SUPPORTED_VERSIONS = "26.1.2 or 26.2";
+    private static final String SUPPORTED_VERSIONS = "26.1.2, 26.2 or 26.3";
     private static final String SUPPORTED_TAG = "v26_2_R1";
 
     private NmsBindingSelector() {
@@ -11,6 +11,9 @@ final class NmsBindingSelector {
         if (version == null) {
             throw new IllegalStateException("Iris requires an exact Minecraft version before selecting NMS");
         }
+        if (version.isSameRelease(26, 3, 0)) {
+            return "v26_3_R1";
+        }
         if (!version.isSameRelease(26, 2, 0) && !version.isSameRelease(26, 1, 2)) {
             throw new IllegalStateException("Iris requires Minecraft " + SUPPORTED_VERSIONS
                     + ". Detected server version: " + version.value());

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

@@ -1,6 +1,7 @@
 package art.arcane.iris.platform.bukkit.nms.datapack;
 
 import art.arcane.iris.spi.IrisLogging;
+import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.platform.bukkit.nms.INMS;
 import art.arcane.iris.platform.bukkit.nms.datapack.v1217.DataFixerV1217;
 import art.arcane.volmlib.util.collection.KMap;
@@ -8,13 +9,15 @@ import lombok.AccessLevel;
 import lombok.Getter;
 
 import java.util.function.Supplier;
+import art.arcane.iris.platform.bukkit.nms.datapack.v263.DataFixerV263;
 
 //https://minecraft.wiki/w/Pack_format
 @Getter
 public enum DataVersion {
     UNSUPPORTED("0.0.0", 0, () -> null),
     V26_1_2("26.1.2", 101, DataFixerV1217::new),
-    V26_2("26.2", 107, DataFixerV1217::new);
+    V26_2("26.2", 107, DataFixerV1217::new),
+    V26_3("26.3", 121, DataFixerV263::new);
     private static final KMap<DataVersion, IDataFixer> cache = new KMap<>();
     @Getter(AccessLevel.NONE)
     private final Supplier<IDataFixer> constructor;
@@ -49,6 +52,29 @@ public enum DataVersion {
         return fixer;
     }
 
+    public static DataVersion forMinecraftVersion(String version) {
+        if (version == null) {
+            return UNSUPPORTED;
+        }
+        return switch (version) {
+            case "26.1.2" -> V26_1_2;
+            case "26.2", "26.2.0" -> V26_2;
+            case "26.3", "26.3.0" -> V26_3;
+            default -> UNSUPPORTED;
+        };
+    }
+
+    public static DataVersion getRuntime() {
+        if (!IrisPlatforms.isBound() || IrisPlatforms.get().minecraftVersion() == null) {
+            return getLatest();
+        }
+        DataVersion version = forMinecraftVersion(IrisPlatforms.get().minecraftVersion());
+        if (version == UNSUPPORTED) {
+            throw new IllegalStateException("Unsupported Minecraft datapack version: " + IrisPlatforms.get().minecraftVersion());
+        }
+        return version;
+    }
+
     public static DataVersion getLatest() {
         return values()[values().length - 1];
     }

core/src/main/java/art/arcane/iris/platform/bukkit/nms/datapack/v263/DataFixerV263.java

@@ -0,0 +1,54 @@
+package art.arcane.iris.platform.bukkit.nms.datapack.v263;
+
+import art.arcane.iris.generation.biome.IrisBiomeCustom;
+import art.arcane.iris.platform.bukkit.nms.datapack.v1217.DataFixerV1217;
+import art.arcane.volmlib.util.json.JSONArray;
+import art.arcane.volmlib.util.json.JSONObject;
+
+import java.util.Locale;
+
+public final class DataFixerV263 extends DataFixerV1217 {
+    @Override
+    public JSONObject fixCustomBiome(IrisBiomeCustom biome, JSONObject json) {
+        JSONObject fixed = super.fixCustomBiome(biome, json);
+        JSONObject attributes = fixed.getJSONObject("attributes");
+        JSONObject effects = fixed.getJSONObject("effects");
+        for (String key : new String[]{"water_color", "foliage_color", "dry_foliage_color", "grass_color"}) {
+            color(effects, key);
+        }
+        for (String key : new String[]{"minecraft:visual/sky_color", "minecraft:visual/fog_color", "minecraft:visual/water_fog_color"}) {
+            color(attributes, key);
+        }
+        JSONObject spawners = fixed.getJSONObject("spawners");
+        for (String category : spawners.keySet()) {
+            JSONArray entries = spawners.getJSONArray(category);
+            for (int index = 0; index < entries.length(); index++) {
+                JSONObject spawn = entries.getJSONObject(index);
+                int minimum = spawn.getInt("minCount");
+                int maximum = spawn.getInt("maxCount");
+                spawn.remove("minCount");
+                spawn.remove("maxCount");
+                spawn.put("count", minimum == maximum ? minimum : new JSONObject()
+                        .put("type", "minecraft:uniform")
+                        .put("min_inclusive", minimum)
+                        .put("max_inclusive", maximum));
+            }
+        }
+        attributes.put("minecraft:gameplay/natural_mob_spawns", new JSONObject()
+                .put("spawns_by_category", spawners)
+                .put("spawn_costs", fixed.getJSONObject("spawn_costs")));
+        Object probability = fixed.remove("creature_spawn_probability");
+        if (probability != null) {
+            attributes.put("minecraft:gameplay/creature_world_gen_spawn_probability", probability);
+        }
+        fixed.remove("spawners");
+        fixed.remove("spawn_costs");
+        return fixed;
+    }
+
+    private static void color(JSONObject object, String key) {
+        if (object.opt(key) instanceof Number value) {
+            object.put(key, String.format(Locale.ROOT, "#%06x", value.intValue() & 0xFFFFFF));
+        }
+    }
+}

core/src/main/java/art/arcane/iris/platform/bukkit/nms/v1X/NMSBinding1X.java

@@ -317,6 +317,6 @@ public class NMSBinding1X implements INMSBinding {
     private IllegalStateException unsupportedStructureHook(String operation) {
         return new IllegalStateException("Iris cannot " + operation + " with limited NMS binding "
                 + getClass().getSimpleName()
-                + "; set general.disableNMS=false and use a supported Minecraft server runtime (26.1.2 or 26.2)");
+                + "; set general.disableNMS=false and use a supported Minecraft server runtime (26.1.2, 26.2 or 26.3)");
     }
 }

core/src/main/java/art/arcane/iris/structure/export/VanillaBlockState.java

@@ -1,6 +1,7 @@
 package art.arcane.iris.structure.export;
 
 import art.arcane.volmlib.util.nbt.tag.CompoundTag;
+import art.arcane.volmlib.util.nbt.mca.MCABlockStateCodecSupport;
 
 import java.util.Collections;
 import java.util.LinkedHashMap;
@@ -73,15 +74,15 @@ record VanillaBlockState(String name, Map<String, String> properties) {
         return builder.append(']').toString();
     }
 
-    CompoundTag toNbt() {
+    CompoundTag toNbt(MCABlockStateCodecSupport.Format format) {
         CompoundTag state = new CompoundTag();
-        state.putString("Name", name);
+        state.putString(format.nameKey(), name);
         if (!properties.isEmpty()) {
             CompoundTag propertyTag = new CompoundTag();
             for (Map.Entry<String, String> property : properties.entrySet()) {
                 propertyTag.putString(property.getKey(), property.getValue());
             }
-            state.put("Properties", propertyTag);
+            state.put(format.propertiesKey(), propertyTag);
         }
         return state;
     }

core/src/main/java/art/arcane/iris/structure/export/VanillaJigsawExportCompiler.java

@@ -211,7 +211,7 @@ final class VanillaJigsawExportCompiler {
             addError(diagnostics,
                     VanillaJigsawExportDiagnostic.Code.INVALID_MAX_DEPTH,
                     structureKey(structure),
-                    "Minecraft 26.2 jigsaw size must be within 0..20; Iris export requires 1..20.");
+                    "Minecraft jigsaw size must be within 0..20; Iris export requires 1..20.");
         }
         long horizontalDistance = (long) structure.getMaxSizeChunks() * 16L;
         if (horizontalDistance < 1L || horizontalDistance > MAX_HORIZONTAL_DISTANCE) {
@@ -219,7 +219,7 @@ final class VanillaJigsawExportCompiler {
                     VanillaJigsawExportDiagnostic.Code.INVALID_MAX_DISTANCE,
                     structureKey(structure),
                     "Iris maxSizeChunks maps to " + horizontalDistance
-                            + " blocks, outside Minecraft 26.2's 1..128 horizontal limit.");
+                            + " blocks, outside Minecraft's 1..128 horizontal limit.");
         }
         int terrainPadding = settings.terrainAdaptation() == VanillaJigsawExportSettings.TerrainAdaptation.NONE
                 ? 0 : 12;
@@ -315,7 +315,7 @@ final class VanillaJigsawExportCompiler {
                 addError(diagnostics,
                         VanillaJigsawExportDiagnostic.Code.INVALID_POOL_WEIGHT,
                         poolKey + "/pieces[" + index + "]",
-                        "Minecraft 26.2 template-pool weights must be within 1..150.");
+                        "Minecraft template-pool weights must be within 1..150.");
             }
             if (entry.getChance() != 1D) {
                 addError(diagnostics,
@@ -577,10 +577,12 @@ final class VanillaJigsawExportCompiler {
         JsonObject pack = new JsonObject();
         pack.addProperty("description", request.description());
         JsonArray minimum = new JsonArray();
-        minimum.add(107);
-        minimum.add(1);
+        boolean current = VanillaStructureTemplateEncoder.targets263();
+        int packFormat = current ? 121 : 107;
+        minimum.add(packFormat);
+        minimum.add(current ? 0 : 1);
         pack.add("min_format", minimum);
-        pack.addProperty("max_format", 107);
+        pack.addProperty("max_format", packFormat);
         JsonObject root = new JsonObject();
         root.add("pack", pack);
         return root;

core/src/main/java/art/arcane/iris/structure/export/VanillaJigsawExportRequest.java

@@ -65,7 +65,7 @@ public final class VanillaJigsawExportRequest {
         private final Path output;
         private String namespace = "iris";
         private String resourcePath;
-        private String description = "Iris vanilla jigsaw export for Minecraft 26.2";
+        private String description = "Iris vanilla jigsaw export";
         private VanillaJigsawExportFormat format = VanillaJigsawExportFormat.DIRECTORY;
         private VanillaJigsawExportSettings settings = VanillaJigsawExportSettings.defaults();
         private boolean replaceExisting;

core/src/main/java/art/arcane/iris/structure/export/VanillaStructureTemplateEncoder.java

@@ -1,6 +1,8 @@
 package art.arcane.iris.structure.export;
 
 import art.arcane.iris.pack.value.IrisDirection;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.volmlib.util.nbt.mca.MCABlockStateCodecSupport;
 import art.arcane.iris.structure.jigsaw.IrisJigsawConnector;
 import art.arcane.iris.structure.jigsaw.IrisJigsawPiece;
 import art.arcane.iris.structure.object.IrisObject;
@@ -51,18 +53,26 @@ final class VanillaStructureTemplateEncoder {
             }
         }
 
+        boolean lowercase = targets263();
+        MCABlockStateCodecSupport.Format format = lowercase
+                ? MCABlockStateCodecSupport.Format.LOWERCASE : MCABlockStateCodecSupport.Format.CAPITALIZED;
         CompoundTag root = new CompoundTag();
         root.put("size", intList(object.getW(), object.getH(), object.getD()));
-        root.put("palette", palette(paletteStates));
+        root.put("palette", palette(paletteStates, format));
         root.put("blocks", blocks(orderedBlocks, paletteIndexes));
         root.put("entities", new ListTag<>(CompoundTag.class));
-        root.putInt("DataVersion", DATA_VERSION_26_2);
+        root.putInt("DataVersion", lowercase ? 5023 : DATA_VERSION_26_2);
 
         ByteArrayOutputStream output = new ByteArrayOutputStream();
         NBTUtil.write(new NamedTag("", root), output, true);
         return output.toByteArray();
     }
 
+    static boolean targets263() {
+        String minecraftVersion = IrisPlatforms.get().minecraftVersion();
+        return "26.3".equals(minecraftVersion) || "26.3.0".equals(minecraftVersion);
+    }
+
     private Map<BlockPosition, BlockEntry> objectBlocks(IrisObject object) {
         Map<BlockPosition, BlockEntry> blocks = new LinkedHashMap<>();
         Vector3i center = object.getCenter();
@@ -135,10 +145,10 @@ final class VanillaStructureTemplateEncoder {
         };
     }
 
-    private ListTag<CompoundTag> palette(List<VanillaBlockState> states) {
+    private ListTag<CompoundTag> palette(List<VanillaBlockState> states, MCABlockStateCodecSupport.Format format) {
         ListTag<CompoundTag> palette = new ListTag<>(CompoundTag.class);
         for (VanillaBlockState state : states) {
-            palette.add(state.toNbt());
+            palette.add(state.toNbt(format));
         }
         return palette;
     }

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

@@ -110,7 +110,7 @@ public final class GenerationRegistryContractFactory {
                 data,
                 dimension,
                 packFingerprint,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 registries,
                 registries.generationRegistry(),
                 aliasPolicy
@@ -224,7 +224,7 @@ public final class GenerationRegistryContractFactory {
                 data,
                 dimension,
                 customBiome,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 registry
         );
     }
@@ -508,7 +508,7 @@ public final class GenerationRegistryContractFactory {
     ) throws IOException {
         return captureRequiredDefinitions(
                 requiredContracts,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 IrisPlatforms.get().registries().generationRegistry()
         );
     }
@@ -519,7 +519,7 @@ public final class GenerationRegistryContractFactory {
     ) throws IOException {
         return captureRequiredDefinitions(
                 requiredContracts,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 generationRegistry
         );
     }
@@ -603,7 +603,7 @@ public final class GenerationRegistryContractFactory {
         return requireGeneratedSource(
                 contract,
                 key,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 IrisPlatforms.get().registries().generationRegistry()
         );
     }
@@ -652,7 +652,7 @@ public final class GenerationRegistryContractFactory {
         return requireGeneratedSource(
                 contract,
                 key,
-                DataVersion.getLatest().get(),
+                DataVersion.getRuntime().get(),
                 generationRegistry
         );
     }

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

@@ -171,7 +171,7 @@ public final class SavedTerrainChunk {
             case "biomes" -> 3;
             case "noise" -> 4;
             case "surface" -> 5;
-            case "carvers" -> 6;
+            case "carvers", "terrain" -> 6;
             case "features" -> 7;
             case "initialize_light" -> 8;
             case "light" -> 9;

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

@@ -1,6 +1,9 @@
 package art.arcane.iris.world.history;
 
 import art.arcane.volmlib.util.nbt.io.NBTUtil;
+import art.arcane.iris.spi.IrisPlatforms;
+import art.arcane.iris.spi.PlatformBlockState;
+import art.arcane.volmlib.util.nbt.mca.MCABlockStateCodecSupport;
 import art.arcane.volmlib.util.nbt.tag.CompoundTag;
 import art.arcane.volmlib.util.nbt.tag.ByteArrayTag;
 import art.arcane.volmlib.util.nbt.tag.ListTag;
@@ -81,7 +84,8 @@ final class SavedTerrainChunkReader {
             if (sectionY * 16 < minimumY || sectionY * 16 >= (long) minimumY + height) {
                 continue;
             }
-            if (sections.put(sectionY, decodeSection(section)) != null) {
+            if (sections.put(sectionY, decodeSection(section, root.getInt("DataVersion") >= 5023
+                    ? MCABlockStateCodecSupport.Format.LOWERCASE : MCABlockStateCodecSupport.Format.CAPITALIZED)) != null) {
                 throw new IOException("Saved chunk contains duplicate section " + sectionY);
             }
         }
@@ -158,16 +162,29 @@ final class SavedTerrainChunkReader {
         return section;
     }
 
-    private static Section decodeSection(CompoundTag section) throws IOException {
+    private static Section decodeSection(CompoundTag section, MCABlockStateCodecSupport.Format format) throws IOException {
         CompoundTag blocks = compound(section, "block_states");
         CompoundTag biomes = compound(section, "biomes");
         ListTag<?> blockPalette = list(blocks, "palette");
         List<BoundaryColumnGeometry.Voxel> decodedBlocks = new ArrayList<>(blockPalette.size());
         for (Tag<?> entry : blockPalette) {
-            if (!(entry instanceof CompoundTag state)) {
-                throw new IOException("Saved block palette entry is not a compound");
+            Tag<?> state = entry;
+            if (format == MCABlockStateCodecSupport.Format.LOWERCASE
+                    && state instanceof CompoundTag wrapped && wrapped.size() == 1 && wrapped.containsKey("")) {
+                state = wrapped.get("");
+            }
+            if (format == MCABlockStateCodecSupport.Format.LOWERCASE && state instanceof StringTag name) {
+                PlatformBlockState resolved = IrisPlatforms.get().registries().blockOrNull(name.getValue());
+                if (resolved == null) {
+                    throw new IOException("Saved block state cannot be resolved: " + name.getValue());
+                }
+                decodedBlocks.add(decodeBlock(MCABlockStateCodecSupport.encodeBlockState(
+                        resolved.key(), name.getValue(), format), format));
+            } else if (state instanceof CompoundTag compound) {
+                decodedBlocks.add(decodeBlock(compound, format));
+            } else {
+                throw new IOException("Saved block palette entry is not a block state");
             }
-            decodedBlocks.add(decodeBlock(state));
         }
         ListTag<?> biomePalette = list(biomes, "palette");
         List<String> decodedBiomes = new ArrayList<>(biomePalette.size());
@@ -181,10 +198,10 @@ final class SavedTerrainChunkReader {
                 new Palette<>(decodedBiomes, packedData(biomes), 1, 64));
     }
 
-    private static BoundaryColumnGeometry.Voxel decodeBlock(CompoundTag state) throws IOException {
-        String name = string(state, "Name");
+    private static BoundaryColumnGeometry.Voxel decodeBlock(CompoundTag state, MCABlockStateCodecSupport.Format format) throws IOException {
+        String name = string(state, format.nameKey());
         TreeMap<String, String> properties = new TreeMap<>();
-        if (state.get("Properties") instanceof CompoundTag values) {
+        if (state.get(format.propertiesKey()) instanceof CompoundTag values) {
             for (Map.Entry<String, Tag<?>> property : values) {
                 if (!(property.getValue() instanceof StringTag value)) {
                     throw new IOException("Saved block property is not a string");
@@ -192,6 +209,13 @@ final class SavedTerrainChunkReader {
                 properties.put(property.getKey(), value.getValue());
             }
         }
+        return decodeBlock(name, properties);
+    }
+
+    private static BoundaryColumnGeometry.Voxel decodeBlock(String name, Map<String, String> properties) throws IOException {
+        if (name.isBlank()) {
+            throw new IOException("Saved block state has no resource key");
+        }
         String stateKey = stateKey(name, properties);
         if (name.equals("minecraft:air") || name.equals("minecraft:cave_air") || name.equals("minecraft:void_air")) {
             return name.equals("minecraft:air") ? AIR

core/src/main/java/art/arcane/iris/world/storage/region/NBTWorld.java

@@ -19,6 +19,8 @@
 package art.arcane.iris.world.storage.region;
 
 import art.arcane.iris.platform.bukkit.BukkitBlockResolution;
+import art.arcane.volmlib.util.nbt.mca.MCABlockStateCodecSupport;
+import art.arcane.iris.platform.bukkit.nms.datapack.DataVersion;
 
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.platform.bukkit.nms.INMS;
@@ -30,6 +32,7 @@ import art.arcane.volmlib.util.nbt.mca.NBTWorldSupport;
 import art.arcane.iris.platform.reflect.KeyedType;
 import art.arcane.volmlib.util.math.M;
 import art.arcane.volmlib.util.nbt.tag.CompoundTag;
+import art.arcane.volmlib.util.nbt.tag.Tag;
 import art.arcane.iris.generation.concurrent.HyperLock;
 import org.bukkit.NamespacedKey;
 import org.bukkit.Registry;
@@ -43,7 +46,7 @@ import java.util.Locale;
 public class NBTWorld {
     private static final class Holder {
         private static final BlockData AIR = BukkitBlockResolution.get("AIR");
-        private static final NBTWorldSupport.BlockStateCodec<BlockData> BLOCK_STATE_CODEC = NBTWorldSupport.blockStateCodec(
+        private static final NBTWorldSupport.BlockStateCodec<BlockData> BLOCK_STATE_CODEC = NBTWorldSupport.blockStateCodec(new NBTWorldSupport.BlockStateCodecOptions<>(
                 blockStateString -> BukkitBlockResolution.getOrNull(blockStateString, true),
                 BukkitBlockResolution::getAir,
                 blockData -> blockData.getAsString(true),
@@ -53,8 +56,11 @@ public class NBTWorld {
                         return "minecraft:" + blockData.getMaterial().name().toLowerCase(Locale.ROOT);
                     }
                     return key.getNamespace() + ":" + key.getKey();
-                }
-        );
+                },
+                INMS.get().getDataVersion() == DataVersion.V26_3
+                        ? MCABlockStateCodecSupport.Format.LOWERCASE
+                        : MCABlockStateCodecSupport.Format.CAPITALIZED
+        ));
         private static final Map<Biome, Integer> BIOME_IDS = computeBiomeIDs();
     }
 
@@ -127,7 +133,7 @@ public class NBTWorld {
         );
     }
 
-    public static BlockData getBlockData(CompoundTag tag) {
+    public static BlockData getBlockData(Tag<?> tag) {
         return Holder.BLOCK_STATE_CODEC.decode(tag);
     }