Modded structure state key

- Modded biome policy supplies the structure state key from the generator
- History worlds key structure state by the active epoch
- Studio worlds get a fresh transient key
- Tests cover the key binding and the structure state codec

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

@@ -105,6 +105,7 @@ import java.util.Objects;
 import java.util.OptionalLong;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.IntConsumer;
@@ -946,6 +947,14 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
                         + " requires an attached generation-history runtime router."));
     }
 
+    private String structureStateKey() {
+        Engine current = boundEngineOrNull();
+        if (current == null || allowsGenerationHistoryBypass(current)) {
+            return "transient:" + UUID.randomUUID();
+        }
+        return "epoch:" + requireHistoryRouter(current, "structure state key").history().activeEpoch().epochId();
+    }
+
     boolean allowsGenerationHistoryBypass(Engine current) {
         if (generationMode != ModdedGenerationMode.TRANSIENT_STUDIO) {
             return false;
@@ -985,7 +994,7 @@ public final class IrisModdedChunkGenerator implements NativeGeneratorOwner, Nat
         ModdedBiomePolicy<H, S> policy = new ModdedBiomePolicy<>(source);
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(this::boundEngineOrNull, this::awaitStructureEngine,
                 this::allowsGenerationHistoryBypass, this::configuredStructureBiomeKeys,
-                IrisModdedChunkGenerator::retainedBiomeKeys, this::visibleBiomeSeed));
+                IrisModdedChunkGenerator::retainedBiomeKeys, this::visibleBiomeSeed, this::structureStateKey));
         return policy;
     }
 

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

@@ -1395,6 +1395,11 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
         return requireConfiguredStructureBiomeKeys(exactStructureBiomeKeys());
     }
 
+    @Override
+    public String structureStateKey() {
+        return Objects.requireNonNull(runtime, "runtime").structureStateKey().get();
+    }
+
     @Override
     public int horizontalSearchStep(int blockY, int searchRadius) {
         return horizontalBiomeSearchQuartStep(blockY, searchRadius);
@@ -1402,6 +1407,7 @@ final class ModdedBiomePolicy<H, S> implements NativeModdedBiomePolicy<H, S> {
 
     record RuntimeCallbacks(Supplier<Engine> currentEngine, Supplier<Engine> awaitEngine,
                             Predicate<Engine> historyBypass, Supplier<Set<String>> configuredStructureKeys,
-                            Function<Engine, Set<String>> retainedBiomeKeys, LongSupplier visibleBiomeSeed) {
+                            Function<Engine, Set<String>> retainedBiomeKeys, LongSupplier visibleBiomeSeed,
+                            Supplier<String> structureStateKey) {
     }
 }

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

@@ -102,6 +102,15 @@ public class ModdedBiomePolicyTest {
         assertSame(desert, policy.orderedPossibleBiomes().getFirst());
     }
 
+    @Test
+    public void structureStateKeyComesFromTheBoundRuntime() {
+        ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(new Access(new ArrayList<>()));
+        policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> null, () -> null, engine -> false,
+                Set::of, engine -> Set.of(), () -> 0L, () -> "epoch:example"));
+
+        assertEquals("epoch:example", policy.structureStateKey());
+    }
+
     @Test
     public void missingRequiredStructureBiomesFailBeforePublishingAPartialSet() {
         AtomicReference<Set<String>> configured = new AtomicReference<>(Set.of("example:missing"));
@@ -130,7 +139,7 @@ public class ModdedBiomePolicyTest {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(
                 new Access(new ArrayList<>(List.of(forest))));
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> true,
-                () -> Set.of(forest.key()), bound -> Set.of(), () -> 0L));
+                () -> Set.of(forest.key()), bound -> Set.of(), () -> 0L, () -> "transient:test"));
 
         assertSame(forest, policy.requiredStructureBiome(6000, 0, -6000, null));
         assertSame(forest, policy.requiredStructureBiome(6000, -30, -6000, null));
@@ -212,7 +221,7 @@ public class ModdedBiomePolicyTest {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(
                 new Access(new ArrayList<>(List.of(plains, mirage))));
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> false,
-                () -> Set.of(plains.key(), mirage.key()), bound -> Set.of(), () -> 0L));
+                () -> Set.of(plains.key(), mirage.key()), bound -> Set.of(), () -> 0L, () -> "transient:test"));
         int[] columns = {0, 1024, 2048, 3072, 4096, 5120};
 
         NativeBiomeSourcePolicy.BiomeLocation<BiomeToken> found = policy.findClosestBiome3d(
@@ -241,7 +250,7 @@ public class ModdedBiomePolicyTest {
     private static ModdedBiomePolicy<BiomeToken, Object> boundTo(Engine engine) {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(new Access(new ArrayList<>()));
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> engine, () -> engine, bound -> true,
-                Set::of, bound -> Set.of(), () -> 0L));
+                Set::of, bound -> Set.of(), () -> 0L, () -> "transient:test"));
         return policy;
     }
 
@@ -249,7 +258,7 @@ public class ModdedBiomePolicyTest {
                                                                AtomicReference<Set<String>> configured) {
         ModdedBiomePolicy<BiomeToken, Object> policy = new ModdedBiomePolicy<>(new Access(entries));
         policy.bind(new ModdedBiomePolicy.RuntimeCallbacks(() -> null, () -> null, engine -> false,
-                configured::get, engine -> Set.of(), () -> 0L));
+                configured::get, engine -> Set.of(), () -> 0L, () -> "transient:test"));
         return policy;
     }
 

adapters/modded-common/src/test/java/art/arcane/volmlib/nativelib/minecraft26_2/modded/NativeModdedBiomeSourceCodecTest.java

@@ -0,0 +1,64 @@
+package art.arcane.volmlib.nativelib.minecraft26_2.modded;
+
+import art.arcane.volmlib.nativelib.terrain.NativeModdedBiomePolicy;
+import com.google.gson.JsonElement;
+import com.mojang.serialization.DataResult;
+import com.mojang.serialization.JsonOps;
+import com.mojang.serialization.MapCodec;
+import net.minecraft.SharedConstants;
+import net.minecraft.core.Holder;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.world.level.biome.Biome;
+import net.minecraft.world.level.biome.BiomeSource;
+import net.minecraft.world.level.biome.Climate;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.lang.reflect.Constructor;
+import java.util.Set;
+
+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 NativeModdedBiomeSourceCodecTest {
+    @BeforeClass
+    public static void bootstrap() {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+    }
+
+    @Test
+    public void runtimeSourceEncodeReportsErrorInsteadOfThrowing() {
+        DataResult<JsonElement> result = BiomeSource.CODEC.encodeStart(JsonOps.INSTANCE, runtimeSource("epoch:unused"));
+        assertTrue(result.isError());
+    }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    public void structureStateSourceEncodesItsGenerationKey() throws ReflectiveOperationException {
+        BiomeSource structureState = structureState(runtimeSource("epoch:example"));
+        MapCodec<BiomeSource> codec = (MapCodec<BiomeSource>) NativeModdedBiomeSource.STRUCTURE_STATE_CODEC;
+
+        JsonElement encoded = codec.codec().encodeStart(JsonOps.INSTANCE, structureState).getOrThrow();
+
+        assertEquals("epoch:example", encoded.getAsJsonObject().get("generation").getAsString());
+        assertTrue(codec.codec().parse(JsonOps.INSTANCE, encoded).isError());
+    }
+
+    private static BiomeSource structureState(NativeModdedBiomeSource<?> source) throws ReflectiveOperationException {
+        Class<?> type = Class.forName(NativeModdedBiomeSource.class.getName() + "$StructureStateBiomeSource");
+        Constructor<?> constructor = type.getDeclaredConstructor(NativeModdedBiomeSource.class, Set.class);
+        constructor.setAccessible(true);
+        return (BiomeSource) constructor.newInstance(source, Set.<Holder<Biome>>of());
+    }
+
+    @SuppressWarnings("unchecked")
+    private static NativeModdedBiomeSource<NativeModdedBiomePolicy<Holder<Biome>, Climate.Sampler>> runtimeSource(String key) {
+        NativeModdedBiomePolicy<Holder<Biome>, Climate.Sampler> policy = mock(NativeModdedBiomePolicy.class);
+        when(policy.structureStateKey()).thenReturn(key);
+        return new NativeModdedBiomeSource<>(new NativeModdedBiomeSource.Options<>(
+                mock(BiomeSource.class), () -> null, access -> policy));
+    }
+}