Smoke test failed: "A Timer is still pending even after the widget
tree was disposed." Both workers fired their initial-delay Timer
via `Timer(duration, _sweep)` and stored only the periodic ticker
in the cancellable field — the one-shot Timer leaked past dispose
and tripped the test framework's invariant check.
Track both as _initialTimer + _intervalTimer; cancel both in
dispose(). Behavior is unchanged in production (ref.onDispose only
fires on process death normally); this is purely a test-harness
fix.
Periodic worker that walks cached_artists for missing album lists
and cached_albums for missing track lists, then fills them via
/api/artists/:id + /api/albums/:id. Newly-discovered album covers
are pre-warmed into flutter_cache_manager's disk cache too.
Solves the "tap an artist → empty album area → pop in" experience:
artistAlbumsProvider was drift-first but the cache only got
populated when the user navigated TO an artist. SyncController's
/api/library/sync delta doesn't carry per-artist album lists (those
are query-time derived). Now the filler pre-populates them in the
background so the drift hit is real on first tap.
Pacing (intentionally conservative):
* 10-second initial delay so SyncController has time to land its
first sync — the WHERE NOT EXISTS query has nothing to do until
cached_artists is populated.
* 5-minute interval thereafter. Once steady state is reached the
sweep is a cheap drift query + early exit.
* 200ms throttle between per-entity REST requests — never competes
with active playback.
* 200 entities per sweep cap so a fresh install with thousands of
artists doesn't tie up the network for one continuous run. Next
sweep picks up where this one left off (NOT EXISTS naturally
skips already-filled rows).
Wall time estimate for a 1000-artist library: ~3-4 minutes spread
over multiple sweeps. Single round-trip per artist (new
getArtistDetail API method returns artist + albums in one shot).
Activated from app.dart's postFrameCallback alongside the existing
SyncController / Prefetcher / MetadataPrefetcher / LiveEvents
hooks. Disposed via ref.onDispose when the provider scope tears
down (effectively process death in practice).
bvandeusen