bvandeusenandClaude Opus 5
4f9b083eec
Migration 0050 adds candidate_artist_tags + candidate_artist_tag_state: folksonomy tags for artists NOT in the library, which track_tags cannot hold because it's FK'd to tracks(id) and a Discover candidate has no local row. Slice 6 ranks against these; this slice only fills the cache. The reuse the task claimed is real and verified: MusicBrainz's fetchEntityTags(ctx, "artist", mbid, scale) already existed for the #1519 recording→artist fallback, so FetchArtistTags is a thin wrapper. Two subtleties it does NOT inherit: - Weight scale is 1.0, not artistTagWeightFactor (0.6). That discount exists because FetchTrackTags uses artist tags as a *proxy* for a track's; here the artist IS the subject. Applying it would make these weights incomparable with track_tags — exactly the comparison slice 6 depends on. Pinned by a test. - fetchEntityTags reports existing-but-untagged as (empty, nil) so the track path can fall through. There's no next level here, so empty becomes the terminal ErrNotFound; otherwise the enricher would settle a candidate as "enriched" with zero tags. ArtistTagProvider is the split TrackTagProvider's own doc comment anticipated ("e.g. artist-level tags"). Last.fm gains artist.getTopTags, which returns the same toptags envelope, so the response type and normalizer are reused unchanged. Rather than write the merge-and-classify loop twice, extracted it from EnrichTrack into runChain(). The ErrNotFound-vs-transient split is the load-bearing part — those lead to opposite persistence decisions — so it now has direct unit tests it never had while inlined. Bookkeeping is a separate table, not columns, because the "providers had nothing" outcome must be recordable for a candidate with zero tag rows, and there is no per-candidate row to hang columns off ( artist_similarity_unmatched holds many rows per candidate). Absence of a state row means "never processed", so a transient failure writes nothing and stays eligible. Two capacity realities are designed for, not papered over: - The pool is O(library artists x neighbours) and MusicBrainz allows ~1 req/s, so it can never drain in one pass. The eligibility query returns candidates in descending summed-similarity order, so the ones that can actually reach a deck are enriched first. - candidateBatch (50) is smaller than the track batch (200): tracks are finite and drain to completion, candidates are effectively unbounded and would otherwise starve the track arm forever. GC sweeps both tables — the similarity feed churns, and a candidate that joins the library has its tags in track_tags now. Tags swept before state so a mid-sweep crash leaves a valid state, not a re-fetch loop. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>