Add data-pack Age runtime profiles (#9)

docs/AGE_PROFILES.md

@@ -0,0 +1,50 @@
+# Age runtime profiles
+
+Rivencraft loads Age runtime profiles from server data packs at
+`data/<namespace>/rivencraft/age_profiles/<name>.json`. The resulting profile ID
+is `<namespace>:<name>`. Profiles select registered world-generation resources;
+they do not contain an Age's seed, name, spawn, or rolled traits.
+
+## Schema version 1
+
+```json
+{
+  "schema_version": 1,
+  "terrain": "noise",
+  "noise_settings": "minecraft:overworld",
+  "biome_preset": "minecraft:overworld",
+  "dimension_type": "minecraft:overworld"
+}
+```
+
+`terrain` is `noise`, `flat`, or `void`. Noise profiles require
+`noise_settings` and `biome_preset` references. Every profile requires a
+`dimension_type` reference. Omitted resource references use the Overworld
+entry. Rivencraft validates all referenced entries against the loaded dynamic
+registries during data-pack reload. An invalid profile is rejected.
+
+The built-in profile IDs are `rivencraft:standard`, `amplified`, `island`,
+`cave`, `flat`, and `void`. Their JSON files are ordinary built-in data-pack
+resources and can be overridden by a higher-priority pack. The example under
+`docs/example-age-profile-pack` can be copied into a world's `datapacks`
+directory. Valid custom profiles join the stable, sorted pool used when a new
+Age rolls its base terrain; the selected ID is then persisted with that Age.
+
+## Persistence and reload behavior
+
+An Age permanently stores its selected profile ID, generation version, seed,
+and rolled traits. `/reload` replaces the profile definitions but does not
+reroll those immutable values. An unloaded Age resolves its stored profile
+again when it loads, so intentional profile overrides affect its runtime
+resources and newly generated chunks.
+
+A profile removed after an Age was created resolves to `rivencraft:standard`.
+The legacy `rivencraft:random_vanilla` alias also resolves to `standard`.
+Rivencraft logs this fallback. Invalid built-in overrides do not replace the
+required built-in definitions; a reload fails if a required built-in profile
+is absent after resource resolution.
+
+Only schema version 1 is accepted. A future schema change must add an explicit
+migration path before incrementing the version. The saved Age generation
+version remains independent of this data-pack schema and is never silently
+rewritten.

docs/PORTING.md

@@ -47,7 +47,8 @@ Age references use UUIDs rather than dimension keys. The server-owned Age
 registry maps each stable identity to its immutable definition and runtime
 dimension, keeping saved books valid if an Age is migrated or regenerated.
 Operational lifecycle and unload behavior are documented in
-[AGES.md](AGES.md).
+[AGES.md](AGES.md). The server data-pack schema for runtime generation is
+documented in [AGE_PROFILES.md](AGE_PROFILES.md).
 
 The core mod must remain usable without Create, Ponder, or Immersive Portals.
 The built-in legacy animation is the dependency-free destination preview.

docs/example-age-profile-pack/data/example/rivencraft/age_profiles/highlands.json

@@ -0,0 +1,7 @@
+{
+  "schema_version": 1,
+  "terrain": "noise",
+  "noise_settings": "minecraft:amplified",
+  "biome_preset": "minecraft:overworld",
+  "dimension_type": "minecraft:overworld"
+}

docs/example-age-profile-pack/pack.mcmeta

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+{
+  "pack": {
+    "pack_format": 48,
+    "description": "Example Rivencraft Age runtime profile"
+  }
+}