Fix continent zoom compounding

- Build independent continent generators before applying zoom.
- Share continent construction across runtime contexts.
- Cover repeated construction and shared-generator isolation.

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

@@ -5,6 +5,7 @@ import art.arcane.iris.generation.stream.GenerationStreams;
 import art.arcane.iris.configuration.IrisSettings;
 import art.arcane.iris.pack.loading.IrisData;
 import art.arcane.iris.generation.image.IrisImageMapRuntime;
+import art.arcane.iris.generation.terrain.ContinentGenerator;
 import art.arcane.iris.generation.terrain.InferredType;
 import art.arcane.iris.generation.biome.IrisBiome;
 import art.arcane.iris.generation.terrain.IrisDimension;
@@ -258,9 +259,7 @@ public final class DimensionTerrainContext implements DataProvider {
         inferredStreams.put(InferredType.SHORE, shoreBiomeStream);
 
         ProceduralStream<InferredType> bridgeStream = focusBiome == null
-                ? dimension.getContinentalStyle()
-                        .create(rng.nextParallelRNG(234234565), dimensionData)
-                        .bake().scale(1D / dimension.getContinentZoom()).bake().stream()
+                ? ContinentGenerator.create(dimension, rng, dimensionData).stream()
                         .convert(value -> value >= dimension.getLandChance()
                                 ? InferredType.SEA
                                 : InferredType.LAND)

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

@@ -52,6 +52,7 @@ import art.arcane.iris.generation.decoration.IrisDecorationPart;
 import art.arcane.iris.generation.decoration.IrisDecorator;
 import art.arcane.iris.generation.noise.IrisGenerator;
 import art.arcane.iris.generation.noise.IrisGeneratorStyle;
+import art.arcane.iris.generation.terrain.ContinentGenerator;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.generation.context.IrisContext;
 import art.arcane.iris.generation.context.ChunkContext;
@@ -390,8 +391,7 @@ public class IrisComplex implements DataProvider {
                 .convertAware2D(ProceduralStream::get), "shoreBiomeStream", engine, cacheSize);
         inferredStreams.put(InferredType.SHORE, shoreBiomeStream);
         bridgeStream = focusedBiomes != null ? focusedBiomes.convert(IrisBiome::getInferredType) :
-                GenerationStreams.cache2D(engine.getDimension().getContinentalStyle().create(rng.nextParallelRNG(234234565), getData())
-                        .bake().scale(1D / engine.getDimension().getContinentZoom()).bake().stream()
+                GenerationStreams.cache2D(ContinentGenerator.create(engine.getDimension(), rng, getData()).stream()
                         .convert((v) -> v >= engine.getDimension().getLandChance() ? InferredType.SEA : InferredType.LAND), "bridgeStream", engine, cacheSize);
         ProceduralStream<IrisBiome> proceduralBaseBiomeStream = focusedBiomes != null ? focusedBiomes :
                 GenerationStreams.cache2D(bridgeStream.convertAware2D((t, x, z) -> inferredStreams.get(t).get(x, z))

core/src/main/java/art/arcane/iris/generation/terrain/ContinentGenerator.java

@@ -0,0 +1,28 @@
+package art.arcane.iris.generation.terrain;
+
+import art.arcane.iris.pack.loading.IrisData;
+import art.arcane.volmlib.util.math.RNG;
+import art.arcane.volmlib.util.noise.CNG;
+
+public final class ContinentGenerator {
+    private static final int CONTINENT_SEED_SALT = 234234565;
+
+    private ContinentGenerator() {
+    }
+
+    public static CNG create(IrisDimension dimension, RNG parentSeedSource, IrisData packData) {
+        return scaleByContinentZoom(createContinentalStyleGenerator(dimension, parentSeedSource, packData), dimension);
+    }
+
+    private static CNG createContinentalStyleGenerator(IrisDimension dimension, RNG parentSeedSource, IrisData packData) {
+        return dimension.getContinentalStyle().createNoCache(deriveContinentSeed(parentSeedSource), packData);
+    }
+
+    static RNG deriveContinentSeed(RNG parentSeedSource) {
+        return parentSeedSource.nextParallelRNG(CONTINENT_SEED_SALT);
+    }
+
+    private static CNG scaleByContinentZoom(CNG generator, IrisDimension dimension) {
+        return generator.bake().scale(1D / dimension.getContinentZoom()).bake();
+    }
+}