Hash-seeded generative series

A series is one sketch that yields a unique piece per hash, and the same hash always yields the same piece. Everything random must flow from a single seeded RNG derived from the hash.

1. Deterministic RNG from the hash

Never call Math.random(). Seed a small PRNG from the token hash.

fxhash provides $fx.rand() (uniform 0..1, deterministic from the token). Wrap it:

// fxhash: $fx.rand() is already deterministic per token
const R = () => $fx.rand()