Discord report (Skowl): downloaded a compilation album ("High Tea
Music: Vol 1") where every track has a different artist (Eclypse,
Andromedik, T & Sugah, Gourski, etc.) and the AcoustID scanner
flagged every single track as Wrong Song. The file tags had the
correct per-track artist (e.g. "Eclypse" for "City Lights"), but
the scanner compared against the album-level artist ("Andromedik",
the curator). Raw similarity 12% → Wrong Song flag.
# Why the prior multi-value fix didn't help
Foxxify's case (just-merged PR): AcoustID returned multi-value
credit "Okayracer, aldrch & poptropicaslutz!" — primary IS in the
credit. Splitting found it.
Skowl's case: both sides single-value but DIFFERENT artists.
Splitter has nothing to find — Eclypse simply isn't in "Andromedik".
Different bug.
# Cause
Scanner SQL at `core/repair_jobs/acoustid_scanner.py:281` joined
the `artists` table via `tracks.artist_id` which points at the
ALBUM artist (the curator/label-name applied to every row in a
compilation). The `tracks.track_artist` column already holds the
correct per-track artist for compilations — populated by every
server-scan path (Plex `originalTitle`, Jellyfin `ArtistItems`,
Navidrome per-track `artist`) AND the auto-import / direct-download
post-process flow (`record_soulsync_library_entry` writes it when
different from album artist). Scanner just wasn't reading it.
# Fix
```sql
SELECT t.id, t.title,
COALESCE(NULLIF(t.track_artist, ''), ar.name) AS artist,
...
```
Prefers per-track artist when populated, falls back to album artist
for legacy rows / single-artist albums where `track_artist` is NULL.
`NULLIF(t.track_artist, '')` handles the empty-string-instead-of-null
case some legacy rows might have.
# Composes with Foxxify's multi-value fix
For the rare compilation track where AcoustID ALSO returns a
multi-value credit (e.g. compilation track has multiple credited
performers), both paths work together — `track_artist` gives the
correct expected primary, then the helper splits the credit and
finds it.
# Tests added (2)
- `test_load_db_tracks_prefers_track_artist_for_compilation` —
reporter's exact case: track with `track_artist='Eclypse'` AND
`artist_id` pointing at album artist 'Andromedik' resolves to
'Eclypse'. Second track with NULL `track_artist` falls back to
album artist 'Andromedik' (single-artist + legacy compat).
- `test_load_db_tracks_falls_back_when_track_artist_empty_string`
— empty string in `track_artist` (some legacy rows) → NULLIF
returns NULL → COALESCE falls back to album artist.
Both use a real SQLite DB so the COALESCE/NULLIF logic + JOIN
runs against actual schema (SimpleNamespace fakes can't simulate
JOINs).
# Verification
- 6/6 scanner tests pass (2 new + 4 existing)
- 2586 full suite passes (+2 from prior commit)
- Ruff clean
812db1fbbf