The two parallel maps that bound the per-track loudness backfill
retries (`analysisBackfillInFlightByTrackId`,
`analysisBackfillAttemptsByTrackId`) plus the `MAX_BACKFILL_ATTEMPTS_PER_TRACK`
constant and the `resetLoudnessBackfillStateForTrackId` reseed helper
move into `src/store/loudnessBackfillState.ts`. The new module exposes
a thin API:
- `isBackfillInFlight` / `getBackfillAttempts` (reads)
- `markBackfillInFlight(trackId, nextAttempt)` (atomic flag + counter)
- `clearBackfillInFlight` (after promise settles)
- `resetBackfillAttempts` (after refresh-hit)
- `resetLoudnessBackfillStateForTrackId` (full reset across both id forms)
playerStore's five direct-access sites inside `refreshLoudnessForTrack`
become API calls; the mutables are no longer reachable from outside the
module. 13 focused tests pin atomicity, independence between tracks,
the partial-clear shapes (flag-only / counter-only), and the two-form
reseed expansion.
playerStore 3263 → 3261 LOC (small line delta because the inflight
flag + counter setup collapses to one call but the reset helper is no
longer inline).
Frank Stellmacher