tracks.mbid was 100% NULL: the scanner only extracted album + artist
MBIDs, never the recording MBID. The ListenBrainz similarity worker is
gated on tracks.mbid IS NOT NULL, so track_similarity could never
populate — starving For-You/radio's strongest candidate source
(lb_similar) on every library.
- mbids.go: add extractRecordingMBID (mbz.Recording / Picard
musicbrainz_recordingid). Separate fn so extractMBIDs' signature +
unit tests stay untouched.
- scanner.go: persist recording MBID via UpsertTrack (heals on the
file_path conflict, so re-scans backfill for free).
- BackfillTrackMBIDs: one-shot pass mirroring BackfillMBIDs, wired as
scan Stage 2b (idempotent via SetTrackMbidIfNull, gated by
BackfillCap, log-only progress).
- migration 0029: tracks_mbid_unique (0002, written when the column
was always NULL) wrongly assumes one MBID == one track. A recording
appears on multiple releases, so rows legitimately share a recording
MBID. Replace with a non-unique partial index. Zero-risk: column is
100% NULL at migration time.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
