Preserve cave and skylands terrain with Overworld environments

src/main/java/net/dnorberg/rivencraft/book/AgeDimensionService.java

@@ -210,12 +210,19 @@ public final class AgeDimensionService {
         var biomeParameters = server.registryAccess()
                 .lookupOrThrow(Registries.MULTI_NOISE_BIOME_SOURCE_PARAMETER_LIST);
         var noiseSettings = server.registryAccess().lookupOrThrow(Registries.NOISE_SETTINGS);
-        ResourceKey<NoiseGeneratorSettings> settingsKey = profile.equals(AgeGenerationProfiles.AMPLIFIED)
-                ? NoiseGeneratorSettings.AMPLIFIED
-                : NoiseGeneratorSettings.OVERWORLD;
-        // Cave and Island/Skylands currently describe an Age's theme. Their
-        // terrain, biomes, surfaces, structures, and features use the standard
-        // Overworld pipeline until their dedicated terrain modifiers land.
+        ResourceKey<NoiseGeneratorSettings> settingsKey;
+        if (profile.equals(AgeGenerationProfiles.CAVE)) {
+            settingsKey = NoiseGeneratorSettings.NETHER;
+        } else if (profile.equals(AgeGenerationProfiles.ISLAND)) {
+            settingsKey = NoiseGeneratorSettings.END;
+        } else if (profile.equals(AgeGenerationProfiles.AMPLIFIED)) {
+            settingsKey = NoiseGeneratorSettings.AMPLIFIED;
+        } else {
+            settingsKey = NoiseGeneratorSettings.OVERWORLD;
+        }
+        // Cave retains enclosed Nether-shaped density and Island/Skylands
+        // retains floating End-shaped density. All profiles use Overworld
+        // biomes and the Overworld dimension type for sky and time behavior.
         // random_vanilla is retained as a migration alias for existing Ages.
         return new NoiseBasedChunkGenerator(
                 MultiNoiseBiomeSource.createFromPreset(