fix: a second copy of a track counts once, joining words don't part two titles, and a newer matcher retries an older one's refusals (M502 #5569)

The second run's refusals were mostly albums holding a track twice (a
two-track single with three files), which no edition can pair, and
release names that differ only in "+" against "/". Tracks are now read
once per disc, number and title, and "and", "&" and "+" count for nothing
when titles are compared; an edition's own title also counts as the
album's name.

library_album_matches records which matcher version decided each album.
Refusals by an older version are matched again, even after the listing is
done, so an improvement reaches them without a migration.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/wanted/match.go

@@ -85,8 +85,13 @@ type albumMatch struct {
 	Detail string
 }
 
+// tracksToMatch reads an album's tracks, each once: a second copy of a
+// track (the same disc, number and title, as a duplicate file in another
+// format is) would otherwise count against the match as a track no edition
+// has.
 func tracksToMatch(rows []dbq.ListAlbumTracksToMatchRow) []libraryTrack {
 	out := make([]libraryTrack, 0, len(rows))
+	seen := make(map[string]bool, len(rows))
 	for _, r := range rows {
 		t := libraryTrack{Title: r.Title, LengthMs: int(r.DurationMs), Recording: deref(r.Mbid)}
 		if r.DiscNumber != nil {
@@ -95,6 +100,11 @@ func tracksToMatch(rows []dbq.ListAlbumTracksToMatchRow) []libraryTrack {
 		if r.TrackNumber != nil {
 			t.Number = int(*r.TrackNumber)
 		}
+		key := fmt.Sprintf("%d/%d/%s", max(t.Disc, 1), t.Number, strings.Join(release.Tokens(t.Title), " "))
+		if seen[key] {
+			continue
+		}
+		seen[key] = true
 		out = append(out, t)
 	}
 	return out
@@ -165,9 +175,15 @@ func agrees(n, tracks int) bool {
 	return tracks > 0 && n*10 >= tracks*matchAgreement
 }
 
-// sameTitle: the same words, not merely one holding the other.
+// sameTitle: the same words, not merely one holding the other. "And",
+// "&" and "+" join two titles however a release spells it ("Brain Stew +
+// Jaded", "Brain Stew / Jaded"), so they count for nothing.
 func sameTitle(a, b string) bool {
-	return slices.Equal(release.Tokens(a), release.Tokens(b))
+	words := func(s string) []string {
+		return slices.DeleteFunc(release.Tokens(s), func(w string) bool { return w == "and" })
+	}
+	wa, wb := words(a), words(b)
+	return len(wa) > 0 && slices.Equal(wa, wb)
 }
 
 // matchAlbum finds the release group a library album is. A MusicBrainz
@@ -204,7 +220,9 @@ func (s *Service) matchAlbum(ctx context.Context, a dbq.ListAlbumsToMatchRow, tr
 				continue
 			}
 			tried[c.Group] = true
-			n, size, miss, err := s.agreementWith(ctx, c.Group, tracks, sameTitle(c.Title, a.Title))
+			n, size, miss, err := s.agreementWith(ctx, c.Group, tracks, func(edition string) bool {
+				return sameTitle(c.Title, a.Title) || sameTitle(edition, a.Title)
+			})
 			if err != nil {
 				return err
 			}
@@ -328,7 +346,9 @@ func (s *Service) searchCandidates(ctx context.Context, a dbq.ListAlbumsToMatchR
 // agreementWith is how many of the album's tracks the group's best edition
 // agrees with, that edition's length, and how it differs. A group
 // MusicBrainz no longer has, or lists no edition of, agrees with none (-1).
-func (s *Service) agreementWith(ctx context.Context, group string, tracks []libraryTrack, titlesEnough bool) (n, size int, miss string, err error) {
+// ownName says whether an edition, by its title, is called what the album
+// is, so that its track titles are enough.
+func (s *Service) agreementWith(ctx context.Context, group string, tracks []libraryTrack, ownName func(edition string) bool) (n, size int, miss string, err error) {
 	eds, err := s.cat.Releases(ctx, group)
 	switch {
 	case errors.Is(err, catalogue.ErrNotFound):
@@ -343,7 +363,7 @@ func (s *Service) agreementWith(ctx context.Context, group string, tracks []libr
 			edition = append(edition, editionTrack{Medium: int(t.MediumPosition), Position: int(t.Position),
 				Title: t.Title, LengthMs: int(t.LengthMs), Recording: t.RecordingMbid})
 		}
-		if got, m := trackAgreement(tracks, edition, titlesEnough); got > n || (got == n && abs(len(edition)-len(tracks)) < abs(size-len(tracks))) {
+		if got, m := trackAgreement(tracks, edition, ownName(e.Release.Title)); got > n || (got == n && abs(len(edition)-len(tracks)) < abs(size-len(tracks))) {
 			n, size, miss = got, len(edition), m
 		}
 	}