Third round of the multi-artist report. The earlier fixes (Deezer contributors
upgrade, _artists_list, feat_in_title/artist_separator) were all in place and
correct — but gated on source == 'deezer', and on the real Search → Download
Now path NOTHING carried the source: core/search/sources.py serialized tracks
with no source field, search.js's enrichedTrack didn't add one, so
get_import_source() resolved '' and the whole Deezer-specific block silently
skipped. Files were tagged with only the primary artist until a Retag (which
rebuilds context with the source set — exactly why retagging always fixed it).
The earlier tests passed because they set context['source'] directly — the one
field the real flow never had (same mock-drift as the #823 append tests).
Reproduced with Netti93's exact track (deezer 3966840171) through the real
extract_source_metadata: before — source '', artists ['August Burns Red'];
after — source 'deezer', contributors fetched, artists ['August Burns Red',
'Polaris'], title 'Sonic Salvation (feat. Polaris)' per feat_in_title.
Fix, three layers:
- core/search/sources.py: serialized tracks/albums/artists carry "source"
(the canonical name the orchestrator already passes; '' when unnamed).
- core/imports/context.py get_import_source: also reads '_source' from the
nested dicts (track_info/original_search/album/artist) — additionally fixes
the discography/wishlist flows, which always passed '_source' that nothing
read.
- search.js: enrichedTrack + the album-download path carry source through to
the download task.
Tests: real-payload staging-shaped contexts (source in track_info, '_source'
shape, and the pre-fix sourceless shape staying safe — mocked Deezer client),
serializer source-field tests, resolver fallback tests; exact-shape serializer
tests updated for the new key. 1977 import/metadata/search tests pass (the
only 2 failures are the known soundcloud ones).
bcd69c8baa