Discord-reported scenario: a single "Super Single" by Artist1 feat.
Artist2 is also on Artist1's "Super Album". When the album is fully
owned, Artist1's discography correctly shows the single as complete,
but Artist2's discography (where the same track also appears as a
single) shows it as missing.
Two layers needed for the fix:
Scanner: the Jellyfin/Emby path was keeping only ArtistItems[0],
which is almost always equal to the album artist — so the
distinguishing per-track credit was silently suppressed. Now joins
every ArtistItems entry with "; " and stores the value when there
are multiple credits OR when the single credit differs from the
album artist. Plex's originalTitle already carries the full multi-
artist tag, so Plex users benefit without needing the scanner change.
Scorer: _calculate_track_confidence now splits track_artist on the
common multi-artist delimiters real-world tags use (",", ";", "&",
"feat.", "ft.", "featuring", "vs.", "x") and scores each piece
independently against the search artist, taking the max along with
the whole-string similarity as the floor. Never reduces a score —
purely additive matching for previously-missed featured-artist
credits.
Adds 12 regression tests covering the reported scenario, primary-
artist back-compat, every delimiter variant (parametrized), no-
regression on exact match, and the scanner storing every ArtistItem.
Existing Jellyfin-scanned rows persist their old single-artist value
until the next library scan rewrites them; Plex rows benefit
immediately on next match without needing a rescan.
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