Limited borrowed types to modded

- Pack validation rejects borrowedDimensionType on platforms that generate their own Iris dimension type, with an error naming the supported loaders
- Dimension type keys and registry contracts honor borrowedDimensionType only when the platform generation registry supports borrowed types, so Bukkit always derives its generated iris type
- The Bukkit runtime contract always expects the generated Iris type; hotload still refuses a borrowedDimensionType change

core/src/test/java/art/arcane/iris/generation/terrain/IrisDimensionRuntimeContractTest.java

@@ -139,16 +139,15 @@ public class IrisDimensionRuntimeContractTest {
     }
 
     @Test
-    public void expectedContractUsesTheBorrowedTypeKey() {
+    public void expectedContractIsTheGeneratedIrisTypeEvenWhenThePackBorrowsOne() {
         IrisDimension dimension = borrowedDimension("aether:the_aether", 0, 256);
 
-        assertEquals("aether:the_aether", IrisDimensionRuntimeContract.expected(dimension, "iris").typeKey());
+        assertEquals("iris:skylands", IrisDimensionRuntimeContract.expected(dimension, "iris").typeKey());
     }
 
     @Test
     public void borrowedTypeAcceptsAPackRangeInsideTheBorrowedRange() {
-        IrisDimensionRuntimeContract expected = IrisDimensionRuntimeContract.expected(
-                borrowedDimension("aether:the_aether", 0, 192), "iris");
+        IrisDimensionRuntimeContract expected = borrowedContract("aether:the_aether", 0, 192);
 
         expected.requireBorrowedFit("Modded level 'aether:the_aether'",
                 new IrisDimensionRuntimeContract("aether:the_aether", 0, 256, 256));
@@ -158,8 +157,7 @@ public class IrisDimensionRuntimeContractTest {
 
     @Test
     public void borrowedTypeRejectsAPackTopAboveTheBorrowedTop() {
-        IrisDimensionRuntimeContract expected = IrisDimensionRuntimeContract.expected(
-                borrowedDimension("aether:the_aether", 0, 320), "iris");
+        IrisDimensionRuntimeContract expected = borrowedContract("aether:the_aether", 0, 320);
 
         assertBorrowedFitRejected(expected, new IrisDimensionRuntimeContract("aether:the_aether", 0, 256, 256),
                 "0..320", "0..256");
@@ -167,8 +165,7 @@ public class IrisDimensionRuntimeContractTest {
 
     @Test
     public void borrowedTypeRejectsAPackMinimumThatDiffersFromTheBorrowedMinimum() {
-        IrisDimensionRuntimeContract expected = IrisDimensionRuntimeContract.expected(
-                borrowedDimension("aether:the_aether", 16, 256), "iris");
+        IrisDimensionRuntimeContract expected = borrowedContract("aether:the_aether", 16, 256);
 
         assertBorrowedFitRejected(expected, new IrisDimensionRuntimeContract("aether:the_aether", 0, 256, 256),
                 "16..256", "0..256");
@@ -176,8 +173,7 @@ public class IrisDimensionRuntimeContractTest {
 
     @Test
     public void borrowedTypeRejectsALevelUsingAnotherType() {
-        IrisDimensionRuntimeContract expected = IrisDimensionRuntimeContract.expected(
-                borrowedDimension("aether:the_aether", 0, 256), "iris");
+        IrisDimensionRuntimeContract expected = borrowedContract("aether:the_aether", 0, 256);
 
         assertBorrowedFitRejected(expected, new IrisDimensionRuntimeContract("minecraft:overworld", 0, 256, 256),
                 "aether:the_aether", "minecraft:overworld");
@@ -192,6 +188,10 @@ public class IrisDimensionRuntimeContractTest {
         assertHotloadRejected(active, replacement, "aether:the_aether");
     }
 
+    private static IrisDimensionRuntimeContract borrowedContract(String typeKey, int minHeight, int maxHeight) {
+        return new IrisDimensionRuntimeContract(typeKey, minHeight, maxHeight - minHeight, maxHeight - minHeight);
+    }
+
     private IrisDimension borrowedDimension(String typeKey, int minHeight, int maxHeight) {
         IrisDimension dimension = new IrisDimension();
         dimension.setLoadKey("skylands");

core/src/test/java/art/arcane/iris/pack/PackValidatorBorrowedDimensionTypeTest.java

@@ -46,9 +46,23 @@ public class PackValidatorBorrowedDimensionTypeTest {
                 validate("{\"borrowedDimensionType\":42}"));
     }
 
+    @Test
+    public void rejectsBorrowedTypesOnPlatformsThatGenerateTheirOwnType() {
+        assertTrue(validate("{\"borrowedDimensionType\":\"\"}", false).isEmpty());
+        List<String> errors = validate("{\"borrowedDimensionType\":\"aether:the_aether\"}", false);
+
+        assertEquals(1, errors.size());
+        assertTrue(errors.getFirst(), errors.getFirst().contains("borrowedDimensionType"));
+        assertTrue(errors.getFirst(), errors.getFirst().contains("Fabric, Forge, and NeoForge"));
+    }
+
     private static List<String> validate(String json) {
+        return validate(json, true);
+    }
+
+    private static List<String> validate(String json, boolean borrowingSupported) {
         List<String> errors = new ArrayList<>();
-        PackDimensionValidator.validateBorrowedDimensionType("main", new JSONObject(json), errors);
+        PackDimensionValidator.validateBorrowedDimensionType("main", new JSONObject(json), borrowingSupported, errors);
         return errors;
     }
 }

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

@@ -167,7 +167,7 @@ public class GenerationRegistryContractFactoryTest {
         PlatformRegistries registries = mock(PlatformRegistries.class);
         when(registries.blockTypeKeys()).thenReturn(new KList<>());
         when(registries.entityKeys()).thenReturn(new KList<>());
-        FakeGenerationRegistry generationRegistry = new FakeGenerationRegistry("test-runtime");
+        FakeGenerationRegistry generationRegistry = new BorrowingGenerationRegistry("test-runtime");
 
         GenerationRegistryContract contract = GenerationRegistryContractFactory.create(
                 data,
@@ -187,6 +187,38 @@ public class GenerationRegistryContractFactoryTest {
         assertEquals("aether:the_aether", dimension.dimensionTypeResourceKey(generationRegistry, "borrowed-pack"));
     }
 
+    @Test
+    public void platformWithoutBorrowedTypesKeepsTheGeneratedDimensionType() throws Exception {
+        File pack = temporary.newFolder("borrowed-pack-generated");
+        IrisData data = mock(IrisData.class);
+        when(data.getDataFolder()).thenReturn(pack);
+        when(data.getContentGate()).thenReturn(mock(ContentGate.class));
+        IrisDimension dimension = spy(new IrisDimension().setBorrowedDimensionType("aether:the_aether"));
+        dimension.setLoadKey("skylands");
+        stubDimensions(data, dimension);
+        doReturn(new KList<>()).when(dimension).getReachableBiomes(any());
+        doReturn(new KList<>()).when(dimension).getAllRegions(any());
+        PlatformRegistries registries = mock(PlatformRegistries.class);
+        when(registries.blockTypeKeys()).thenReturn(new KList<>());
+        when(registries.entityKeys()).thenReturn(new KList<>());
+        FakeGenerationRegistry generationRegistry = new FakeGenerationRegistry("test-runtime");
+
+        GenerationRegistryContract contract = GenerationRegistryContractFactory.create(
+                data,
+                dimension,
+                GenerationPackFingerprint.compute(pack.toPath(), GenerationPackFingerprint.CURRENT_VERSION),
+                DataVersion.getLatest().get(),
+                registries,
+                generationRegistry
+        );
+
+        assertFalse(contract.definitions().containsKey(key(
+                GenerationRegistryContractFactory.DIMENSION_TYPE_REGISTRY, "aether:the_aether")));
+        assertTrue(contract.definitions().containsKey(key(
+                GenerationRegistryContractFactory.DIMENSION_TYPE_REGISTRY, "test:skylands_type")));
+        assertEquals("test:skylands_type", dimension.dimensionTypeResourceKey(generationRegistry, "borrowed-pack-generated"));
+    }
+
     @Test
     public void duplicateLogicalBiomeIdsKeepExactDefinitionsAndChooseStableLegacyAlias() throws Exception {
         File pack = temporary.newFolder("duplicate-biomes");
@@ -956,6 +988,17 @@ public class GenerationRegistryContractFactoryTest {
         }
     }
 
+    private static final class BorrowingGenerationRegistry extends FakeGenerationRegistry {
+        private BorrowingGenerationRegistry(String runtimeIdentity) {
+            super(runtimeIdentity);
+        }
+
+        @Override
+        public boolean supportsBorrowedDimensionTypes() {
+            return true;
+        }
+    }
+
     private static class FakeGenerationRegistry implements PlatformGenerationRegistry {
         private final String runtimeIdentity;
         private final Map<GenerationRegistryContract.PhysicalResourceKey, Definition> definitions =