The world has generations

A world is read with one Generation (src/overworld/world.ts), set when it is built and carried to its cave layer.

• First is the live world. Every map a player has seen is its output, so its output never changes. test/overworld/generation-fingerprint.test.ts pins it, and a change that moves that fingerprint moves every player's towns, gym seats and catch origins.
• Second reads hashed simplex fields (src/core/simplex.ts) and keyed rolls. Its fields never repeat, and a roll added to it moves nothing already rolled. It is pinned too, so changing it is a decision rather than an accident.

VITE_WORLD_GENERATION=2 builds the shared world on the second.

Rows tied to the ground carry their generation

Positions, towns, gym seats and challenges, raids, stops, snapshots, encounters, fled keys and every claim table have a generation column with no default. A build reads and writes only WORLD_GENERATION (src/overworld/current.ts), so switching generations hides the other world's rows instead of deleting them.

• Every query on those tables filters on generation, and every insert writes it. A forgotten insert fails on the missing column; a forgotten filter does not, so check reads by hand.
• The generation is part of each key, since ids built from chunk seeds read the same in both worlds. Raids are the exception: their id stays the key, and a later generation's raid id starts with #<generation>.
• A new table holding anything placed by the world gets the column and the key the same way.

Placing something: name the roll

Anything that decides where a thing stands takes its rolls from world.draws(key), never from a fresh AleaRNG:

const draws = world.draws(`${chunk.seed}landmarks`);
const count = MIN + Math.floor(draws.random('count') * SPREAD);
const order = shuffled(sourceOf(draws, 'order'), cells);

• The first generation ignores the name and reads the stream in call order, so never reorder the calls in an existing roll: that alone changes the live world.
• The second keys each roll on its name and how many of that name came before. A new decision gets a new name rather than an extra call under an old one.
• A helper that wants a plain source (a shuffle, pickFreeCell) takes sourceOf(draws, name).

Content that turns over with the clock (spawns, raids, NPCs, caches, nests) keeps its own AleaRNG seeds, because the server re-derives and stores them. So does the battle engine.

Fields

A field is a Noise2D. On the second generation it is new SimplexNoise(hashString(seed), salt, octaves), with a salt of its own in FieldSalt. Its values are mapped onto the first generation's Perlin spread, so every threshold in src/overworld/fields.ts cuts the world in the same proportions on both. A new octave count needs its own measured knot table in simplex.ts; the noise test checks the proportions.

A cell's climate is read through world.getCellBiome, getCellClimate or getCellElevation, which remember each chunk's values; never sample the climate or warp fields directly, and never put a second memo in front of those calls. Second-generation fields read at one shared point go through a SimplexStack, which pays for the lattice once.