Use Overworld cave settings for Cave Ages

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

@@ -21,7 +21,7 @@ public record AgeDefinition(
     public static final ResourceLocation RANDOM_VANILLA_PROFILE = ResourceLocation.fromNamespaceAndPath(
             Rivencraft.MOD_ID, "random_vanilla"
     );
-    public static final int CURRENT_GENERATION_VERSION = 8;
+    public static final int CURRENT_GENERATION_VERSION = 9;
 
     public AgeDefinition {
         Objects.requireNonNull(id, "id");

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

@@ -254,7 +254,7 @@ public final class AgeDimensionService {
         var noiseSettings = server.registryAccess().lookupOrThrow(Registries.NOISE_SETTINGS);
         ResourceKey<NoiseGeneratorSettings> settingsKey;
         if (profile.equals(AgeGenerationProfiles.CAVE)) {
-            settingsKey = NoiseGeneratorSettings.NETHER;
+            settingsKey = NoiseGeneratorSettings.CAVES;
         } else if (profile.equals(AgeGenerationProfiles.ISLAND)) {
             settingsKey = NoiseGeneratorSettings.FLOATING_ISLANDS;
         } else if (profile.equals(AgeGenerationProfiles.AMPLIFIED)) {
@@ -262,9 +262,10 @@ public final class AgeDimensionService {
         } else {
             settingsKey = NoiseGeneratorSettings.OVERWORLD;
         }
-        // Cave retains enclosed Nether-shaped density. Island/Skylands uses
-        // uniform floating-island density without the End's central dragon
-        // island. Both use Overworld biomes and dimension environment.
+        // Cave uses Minecraft's enclosed cave density with stone, water, and
+        // Overworld-like surfaces while retaining the Age's biome source.
+        // Island/Skylands uses uniform floating-island density without the
+        // End's central dragon island. Both use the Overworld environment.
         // random_vanilla is retained as a migration alias for existing Ages.
         return new NoiseBasedChunkGenerator(
                 createBiomeSource(server, age, biomeParameters),