Two small file-private helpers move into dedicated modules under
src/store/:
- `waveformRefreshGen.ts` — the per-track generation counter that
guards against applying a stale waveform read after the cache was
invalidated. Exposes `bumpWaveformRefreshGen` (existing) +
`getWaveformRefreshGen` (new accessor that replaces the two direct
reads at `refreshWaveformForTrack`).
- `hotCacheTouch.ts` — `touchHotCacheOnPlayback` with its empty-id
guards, called from every `audio_play` entry point.
Both file-private; no caller-side changes outside playerStore's own
imports. 8 focused tests pin the generation-increment + isolation
contract and the touch helper's empty-id guards.
playerStore 3302 → 3291 LOC.
Frank Stellmacher