rivencraft/docs/AGE_PROFILES.md

# 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.

Each built-in profile now has a matching `terrain/<name>` Symbol Page. Put one
of those pages after the Link Panel in a Book Binder to select that terrain
instead of the seed-selected random profile. Standard, Amplified, and Cave use
their corresponding registered noise settings; Island uses Minecraft's
floating-islands noise settings; Flat and Void use flat-source generators.
The Cave and Island pages are Rivencraft terrain choices based on existing
profiles, not claims that Legacy had identically named terrain symbols.
Every family retains a safe cobblestone arrival platform. An omitted terrain
page still uses the deterministic seed-selected profile.

## Written biome selection (generation version 16)

Biome pages follow the terrain page and precede the distribution-control page
in the Binder. Bundled controls are Native, Single, Tiled, Grid, and Tiny through
Huge regions. Single needs one distinct biome; Tiled/Grid and Tiny–Huge need
two. An authored book receives seeded filler only when it falls below that
minimum, while extra authored pages are retained as weighted entries. A book
with no biome pages selects a seeded count from two up to the number of
eligible biomes for Tiled/Grid and Tiny–Huge. The eligible pool comes from the
terrain's biome preset, or `#rivencraft:cave_biomes` for Cave terrain, so future
biome integrations can expand it without changing the count rule. Single uses
one; Native uses its preset biome pool. This random-age maximum does not truncate
authored pages: the Binder's 27 symbol-page positions bound an authored book.
Native cannot be paired with explicit biome pages. Legacy filled Tiny–Huge to
three; Rivencraft deliberately uses two so a pair of written biome pages stays
exactly as written.
The Pages creative tab offers pages for every registered vanilla biome.
Hand-authored symbol definitions take precedence; the remaining vanilla pages
are generated from the biome registry, so they do not each need a JSON file.
Custom/modded biomes still require a data-pack symbol definition.

Standard, Amplified, and Sky Island terrain fill from the vanilla Overworld
biome preset, including its underground Lush Caves, Dripstone Caves, and Deep
Dark biomes. Standard terrain therefore keeps Overworld-style cave generation,
and cave biome pages can also be written explicitly. Sky islands can use an
explicitly authored End biome page.
Cave terrain fills only from `#rivencraft:cave_biomes` (Lush Caves, Dripstone
Caves, and Deep Dark by default); explicitly authored Nether biome pages are
also accepted. Other cave/biome pairings are diagnosed and blocked for now.
Milestone 6 instability should allow such illegal combinations as unstable
Ages, without silently treating them as ordinary cave generation. Flat terrain
uses Overworld choices when a distribution is authored; its Native default
remains Plains. Void terrain defaults to The Void and needs additional authored
biomes for a multi-biome distribution.

The resolved list of biome IDs, their order/repetitions, and distribution are
frozen into the Age plan. A removed biome ID emits a warning and uses an
eligible fallback for that load; restoring the biome recovers the original
selection. Generation-version-15 Ages keep their prior registry-wide biome
selection algorithm instead of being silently regenerated.

## Written environment

Lighting pages select Normal, Dark, or Bright lighting for the new Age. A Sky
page selects Minecraft's Overworld, Nether, or End sky effects; the chosen
effects also determine the destination preview backdrop. Overworld sky tint
continues to come from the destination biome. A written sky changes only that
Age's dimension type, not the source world or other Ages.

Normal, Fast, Slow, Off, Always, and Storm weather pages use the existing Age
weather controller. Zero, Half, Full, and Double Length pages set the day-cycle
period, and Nadir, Rising, Zenith, and Setting pages set its initial phase.
Repeated numeric modifiers combine in written order. A Zero Length Age keeps
the nonzero minimum clock rate that avoids client skybox bounce. Pages for
Cloudy, forced Rain, and Snow are not offered: vanilla precipitation rendering
cannot reproduce those Legacy distinctions yet, and Snow remains planned for
the optional season integrations. A data pack that supplies these unsupported
weather choices receives a binding error rather than a false success.

The Pages creative tab and optional JEI page ingredients use the same generated
index of bundled environment symbols. Existing Age definitions and page-free
random Ages retain their saved or seeded environment unchanged.

## Persistence and reload behavior

An Age permanently stores its selected profile ID, generation version, seed,
and rolled traits. For an **authored** Age, the generation plan also stores a
copy of the resolved runtime profile: terrain shape, noise settings, biome
preset, and dimension type. `/reload` cannot reinterpret that plan; an unloaded
authored Age uses the saved profile snapshot when it loads, even if the defining
symbol or profile JSON has since changed. An older, page-free Age has no plan
and continues to resolve its saved profile ID at load time.

Registered noise, biome-preset, and dimension-type IDs are validated when
profiles load. Before loading an authored Age, the saved references are checked
again. If a data pack supplying one has been removed, the dimension stays
unloaded and the log identifies the missing resource; the Age's plan is not
silently replaced. Restore the pack to load that Age. A custom dimension type
retains its own skylight capability: normal lighting cannot make a Nether-style
type skylit.

A profile removed after a page-free 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.