feat: the same song on several releases counts as one song (M498 #5438)

A single and the album it is on stay two files, since each fulfils its own
release in Lidarr, but they are one song to the listener.

- tracks.song_id links copies; the generated song_key (song_id, else the
  track's own id) is what they share (migration 0076).
- The resolver links each cross-release group every pass (idempotent; only
  with auto-resolve on) and, when a link is new, shares existing likes across
  the song and logs them for sync.
- A like or unlike (web and Subsonic) reaches every copy; each change is
  logged and published so clients update every heart.
- The Liked list and its count show the song once; Shuffle and the mix writer
  take one copy per song.
- A merge keeps the removed copy's song link; "Not the same song" on the
  Across releases tab dismisses the group and undoes the link.

Shared plays ("heard via another copy") are left for a later step.

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

internal/api/admin_duplicates.go

@@ -331,15 +331,17 @@ func (h *handlers) handleRunDuplicateSweep(w http.ResponseWriter, _ *http.Reques
 
 // handleDismissDuplicateGroup implements POST
 // /api/admin/library/duplicates/{id}/dismiss: "these are not duplicates". The
-// sweep keeps the dismissal and will not propose that set of tracks again. 404
-// duplicate_group_not_pending when the group was already resolved or is gone.
+// sweep keeps the dismissal and will not propose that set of tracks again. On a
+// cross-release group it also undoes the song link (M498 #5438): the copies
+// stop sharing likes from here on. 404 duplicate_group_not_pending when the
+// group was already resolved or is gone.
 func (h *handlers) handleDismissDuplicateGroup(w http.ResponseWriter, r *http.Request) {
 	id, ok := parseUUID(chi.URLParam(r, "id"))
 	if !ok {
 		writeAdminJSONErr(w, http.StatusBadRequest, "invalid_id")
 		return
 	}
-	n, err := dbq.New(h.pool).DismissDuplicateGroup(r.Context(), id)
+	n, err := h.dismissDuplicateGroup(r.Context(), id)
 	if err != nil {
 		h.logger.Error("admin: dismiss duplicate group", "err", err)
 		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
@@ -352,6 +354,25 @@ func (h *handlers) handleDismissDuplicateGroup(w http.ResponseWriter, r *http.Re
 	writeJSON(w, http.StatusOK, map[string]string{"status": "dismissed"})
 }
 
+// dismissDuplicateGroup dismisses the group and unlinks its copies as one song,
+// together.
+func (h *handlers) dismissDuplicateGroup(ctx context.Context, id pgtype.UUID) (int64, error) {
+	tx, err := h.pool.Begin(ctx)
+	if err != nil {
+		return 0, err
+	}
+	defer func() { _ = tx.Rollback(ctx) }()
+	tq := dbq.New(tx)
+	n, err := tq.DismissDuplicateGroup(ctx, id)
+	if err != nil || n == 0 {
+		return n, err
+	}
+	if err := tq.UnlinkDuplicateGroupSongs(ctx, id); err != nil {
+		return 0, err
+	}
+	return n, tx.Commit(ctx)
+}
+
 // mergeDuplicateRequest chooses the copy to keep. An empty survivor_track_id
 // keeps the report's proposal.
 type mergeDuplicateRequest struct {

internal/api/likes.go

@@ -3,6 +3,7 @@ package api
 import (
 	"errors"
 	"net/http"
+	"slices"
 
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgtype"
@@ -50,20 +51,36 @@ func (h *handlers) handleLikeTrack(w http.ResponseWriter, r *http.Request) {
 		writeErr(w, apierror.InternalMsg("lookup failed", err))
 		return
 	}
-	rows, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: id})
+	liked, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: id})
 	if err != nil {
 		h.logger.Error("api: like track insert", "err", err)
 		writeErr(w, apierror.InternalMsg("insert failed", err))
 		return
 	}
-	if rows == 1 {
+	if slices.Contains(liked, id) {
 		_ = playevents.CaptureContextualLikeIfPlaying(r.Context(), q, user.ID, id, h.logger)
 	}
-	h.logLikeChange(r, syncpkg.EntityLikeTrack, user.ID, id, syncpkg.OpUpsert)
-	h.publishLikeEvent(user.ID, id, "track", true)
+	// The like is on the song (M498 #5438): every copy it reached changes on
+	// the client too.
+	for _, t := range withTrack(id, liked) {
+		h.logLikeChange(r, syncpkg.EntityLikeTrack, user.ID, t, syncpkg.OpUpsert)
+		h.publishLikeEvent(user.ID, t, "track", true)
+	}
 	w.WriteHeader(http.StatusNoContent)
 }
 
+// withTrack is the tracks a like or unlike changed, led by the one asked for,
+// which is reported even when it was already in that state.
+func withTrack(id pgtype.UUID, changed []pgtype.UUID) []pgtype.UUID {
+	out := []pgtype.UUID{id}
+	for _, t := range changed {
+		if t != id {
+			out = append(out, t)
+		}
+	}
+	return out
+}
+
 func (h *handlers) handleUnlikeTrack(w http.ResponseWriter, r *http.Request) {
 	user, ok := requireUser(w, r)
 	if !ok {
@@ -74,7 +91,8 @@ func (h *handlers) handleUnlikeTrack(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	q := dbq.New(h.pool)
-	if err := q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: id}); err != nil {
+	unliked, err := q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: id})
+	if err != nil {
 		h.logger.Error("api: unlike track", "err", err)
 		writeErr(w, apierror.InternalMsg("delete failed", err))
 		return
@@ -83,8 +101,10 @@ func (h *handlers) handleUnlikeTrack(w http.ResponseWriter, r *http.Request) {
 		h.logger.Error("api: soft-delete contextual_likes", "err", err)
 		// Don't fail the response — soft-delete is best-effort.
 	}
-	h.logLikeChange(r, syncpkg.EntityLikeTrack, user.ID, id, syncpkg.OpDelete)
-	h.publishLikeEvent(user.ID, id, "track", false)
+	for _, t := range withTrack(id, unliked) {
+		h.logLikeChange(r, syncpkg.EntityLikeTrack, user.ID, t, syncpkg.OpDelete)
+		h.publishLikeEvent(user.ID, t, "track", false)
+	}
 	w.WriteHeader(http.StatusNoContent)
 }
 

internal/db/dbq/events.sql.go

@@ -261,7 +261,7 @@ func (q *Queries) InsertSkipEvent(ctx context.Context, arg InsertSkipEventParams
 }
 
 const listRecentSessionTracks = `-- name: ListRecentSessionTracks :many
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source FROM tracks t
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key FROM tracks t
 JOIN play_events pe ON pe.track_id = t.id
 WHERE pe.session_id = $1
   AND pe.started_at < $2
@@ -308,6 +308,8 @@ func (q *Queries) ListRecentSessionTracks(ctx context.Context, arg ListRecentSes
 			&i.TagReadVersion,
 			&i.MissingSince,
 			&i.MbidSource,
+			&i.SongID,
+			&i.SongKey,
 		); err != nil {
 			return nil, err
 		}

internal/db/dbq/history.sql.go

@@ -14,7 +14,7 @@ import (
 const listUserHistory = `-- name: ListUserHistory :many
 SELECT pe.id           AS event_id,
        pe.started_at,
-       t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+       t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
        albums.title    AS album_title,
        artists.name    AS artist_name
   FROM play_events pe
@@ -82,6 +82,8 @@ func (q *Queries) ListUserHistory(ctx context.Context, arg ListUserHistoryParams
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.AlbumTitle,
 			&i.ArtistName,
 		); err != nil {

internal/db/dbq/likes.sql.go

@@ -34,9 +34,12 @@ func (q *Queries) CountLikedArtists(ctx context.Context, userID pgtype.UUID) (in
 }
 
 const countLikedTracks = `-- name: CountLikedTracks :one
-SELECT count(*) FROM general_likes WHERE user_id = $1
+SELECT count(DISTINCT t.song_key) FROM general_likes l
+  JOIN tracks t ON t.id = l.track_id
+ WHERE l.user_id = $1
 `
 
+// Liked songs, each counted once however many releases hold it.
 func (q *Queries) CountLikedTracks(ctx context.Context, userID pgtype.UUID) (int64, error) {
 	row := q.db.QueryRow(ctx, countLikedTracks, userID)
 	var count int64
@@ -76,10 +79,13 @@ func (q *Queries) LikeArtist(ctx context.Context, arg LikeArtistParams) error {
 	return err
 }
 
-const likeTrack = `-- name: LikeTrack :execrows
+const likeTrack = `-- name: LikeTrack :many
 INSERT INTO general_likes (user_id, track_id)
-VALUES ($1, $2)
+SELECT $1::uuid, t.id
+  FROM tracks t
+ WHERE t.song_key = (SELECT s.song_key FROM tracks s WHERE s.id = $2::uuid)
 ON CONFLICT (user_id, track_id) DO NOTHING
+RETURNING track_id
 `
 
 type LikeTrackParams struct {
@@ -87,12 +93,27 @@ type LikeTrackParams struct {
 	TrackID pgtype.UUID
 }
 
-func (q *Queries) LikeTrack(ctx context.Context, arg LikeTrackParams) (int64, error) {
-	result, err := q.db.Exec(ctx, likeTrack, arg.UserID, arg.TrackID)
+// A like is on the song (M498 #5438): every copy of it sharing the track's
+// song_key is liked. Returns the tracks newly liked, for the sync log; empty
+// when the song was already liked.
+func (q *Queries) LikeTrack(ctx context.Context, arg LikeTrackParams) ([]pgtype.UUID, error) {
+	rows, err := q.db.Query(ctx, likeTrack, arg.UserID, arg.TrackID)
 	if err != nil {
-		return 0, err
+		return nil, err
 	}
-	return result.RowsAffected(), nil
+	defer rows.Close()
+	var items []pgtype.UUID
+	for rows.Next() {
+		var track_id pgtype.UUID
+		if err := rows.Scan(&track_id); err != nil {
+			return nil, err
+		}
+		items = append(items, track_id)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
 }
 
 const listLikedAlbumIDs = `-- name: ListLikedAlbumIDs :many
@@ -260,10 +281,14 @@ func (q *Queries) ListLikedTrackIDs(ctx context.Context, userID pgtype.UUID) ([]
 }
 
 const listLikedTrackRows = `-- name: ListLikedTrackRows :many
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source FROM tracks t
-JOIN general_likes l ON l.track_id = t.id
-WHERE l.user_id = $1
-ORDER BY l.liked_at DESC
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key FROM tracks t
+JOIN (SELECT DISTINCT ON (lt.song_key) l.track_id, l.liked_at
+        FROM general_likes l
+        JOIN tracks lt ON lt.id = l.track_id
+       WHERE l.user_id = $1
+       ORDER BY lt.song_key, (lt.missing_since IS NOT NULL), l.liked_at, lt.id) l
+  ON l.track_id = t.id
+ORDER BY l.liked_at DESC, t.id
 LIMIT $2 OFFSET $3
 `
 
@@ -273,6 +298,8 @@ type ListLikedTrackRowsParams struct {
 	Offset int32
 }
 
+// One row per liked song: of its copies, the one present on disk, then the
+// one liked first.
 func (q *Queries) ListLikedTrackRows(ctx context.Context, arg ListLikedTrackRowsParams) ([]Track, error) {
 	rows, err := q.db.Query(ctx, listLikedTrackRows, arg.UserID, arg.Limit, arg.Offset)
 	if err != nil {
@@ -303,6 +330,8 @@ func (q *Queries) ListLikedTrackRows(ctx context.Context, arg ListLikedTrackRows
 			&i.TagReadVersion,
 			&i.MissingSince,
 			&i.MbidSource,
+			&i.SongID,
+			&i.SongKey,
 		); err != nil {
 			return nil, err
 		}
@@ -342,8 +371,13 @@ func (q *Queries) UnlikeArtist(ctx context.Context, arg UnlikeArtistParams) erro
 	return err
 }
 
-const unlikeTrack = `-- name: UnlikeTrack :exec
-DELETE FROM general_likes WHERE user_id = $1 AND track_id = $2
+const unlikeTrack = `-- name: UnlikeTrack :many
+DELETE FROM general_likes
+ WHERE user_id = $1::uuid
+   AND (track_id = $2::uuid
+        OR track_id IN (SELECT t.id FROM tracks t
+                         WHERE t.song_key = (SELECT s.song_key FROM tracks s WHERE s.id = $2::uuid)))
+RETURNING track_id
 `
 
 type UnlikeTrackParams struct {
@@ -351,7 +385,24 @@ type UnlikeTrackParams struct {
 	TrackID pgtype.UUID
 }
 
-func (q *Queries) UnlikeTrack(ctx context.Context, arg UnlikeTrackParams) error {
-	_, err := q.db.Exec(ctx, unlikeTrack, arg.UserID, arg.TrackID)
-	return err
+// Unlikes the song: every copy sharing the track's song_key. Returns the
+// tracks unliked, for the sync log.
+func (q *Queries) UnlikeTrack(ctx context.Context, arg UnlikeTrackParams) ([]pgtype.UUID, error) {
+	rows, err := q.db.Query(ctx, unlikeTrack, arg.UserID, arg.TrackID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []pgtype.UUID
+	for rows.Next() {
+		var track_id pgtype.UUID
+		if err := rows.Scan(&track_id); err != nil {
+			return nil, err
+		}
+		items = append(items, track_id)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
 }

internal/db/dbq/models.go

@@ -754,6 +754,8 @@ type Track struct {
 	TagReadVersion    int16
 	MissingSince      pgtype.Timestamptz
 	MbidSource        *string
+	SongID            pgtype.UUID
+	SongKey           pgtype.UUID
 }
 
 type TrackAcoustidLookup struct {

internal/db/dbq/recommendation.sql.go

@@ -208,7 +208,7 @@ WITH plays AS (
     WHERE user_id = $2 AND was_skipped = false
     GROUP BY track_id
 )
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
        albums.title AS album_title,
        artists.name AS artist_name
 FROM plays p
@@ -271,6 +271,8 @@ func (q *Queries) ListMostPlayedTracksForArtist(ctx context.Context, arg ListMos
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.AlbumTitle,
 			&i.ArtistName,
 		); err != nil {
@@ -291,7 +293,7 @@ WITH plays AS (
     WHERE user_id = $1 AND was_skipped = false
     GROUP BY track_id
 )
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
        albums.title AS album_title,
        artists.name AS artist_name
 FROM plays p
@@ -356,6 +358,8 @@ func (q *Queries) ListMostPlayedTracksForUser(ctx context.Context, arg ListMostP
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.AlbumTitle,
 			&i.ArtistName,
 		); err != nil {
@@ -695,7 +699,7 @@ func (q *Queries) ListRediscoverArtistsForUser(ctx context.Context, arg ListRedi
 
 const loadRadioCandidates = `-- name: LoadRadioCandidates :many
 SELECT
-    t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+    t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
     (l.user_id IS NOT NULL)::bool AS is_liked,
     pe.last_played_at::timestamptz AS last_played_at,
     pe.play_count,
@@ -777,6 +781,8 @@ func (q *Queries) LoadRadioCandidates(ctx context.Context, arg LoadRadioCandidat
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.IsLiked,
 			&i.LastPlayedAt,
 			&i.PlayCount,
@@ -925,7 +931,7 @@ random_fill AS (
     LIMIT $9
 )
 SELECT
-    t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+    t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
     (l.user_id IS NOT NULL)::bool AS is_liked,
     pe.last_played_at::timestamptz AS last_played_at,
     pe.play_count,
@@ -1053,6 +1059,8 @@ func (q *Queries) LoadRadioCandidatesV2(ctx context.Context, arg LoadRadioCandid
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.IsLiked,
 			&i.LastPlayedAt,
 			&i.PlayCount,

internal/db/dbq/songs.sql.go

@@ -0,0 +1,150 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: songs.sql
+
+package dbq
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const linkTracksAsSong = `-- name: LinkTracksAsSong :one
+
+WITH keys AS (
+    SELECT DISTINCT song_key FROM tracks WHERE id = ANY($1::uuid[])
+), target AS (
+    SELECT song_key FROM keys ORDER BY song_key LIMIT 1
+), moved AS (
+    UPDATE tracks t
+       SET song_id = (SELECT song_key FROM target)
+     WHERE t.song_key IN (SELECT song_key FROM keys)
+       AND t.song_key <> (SELECT song_key FROM target)
+    RETURNING t.id
+)
+SELECT (SELECT song_key FROM target)::uuid AS song_key,
+       (SELECT count(*) FROM moved)::bigint AS moved
+`
+
+type LinkTracksAsSongRow struct {
+	SongKey pgtype.UUID
+	Moved   int64
+}
+
+// Song links (M498 #5438): copies of one song on different releases share a
+// song_key (migration 0076).
+// Links the tracks into one song, joining any songs they already belong to.
+// The song keeps the lowest key among them, so linking the same set again
+// changes nothing. Returns that key and how many tracks moved to it.
+func (q *Queries) LinkTracksAsSong(ctx context.Context, trackIds []pgtype.UUID) (LinkTracksAsSongRow, error) {
+	row := q.db.QueryRow(ctx, linkTracksAsSong, trackIds)
+	var i LinkTracksAsSongRow
+	err := row.Scan(&i.SongKey, &i.Moved)
+	return i, err
+}
+
+const listTrackSongKeys = `-- name: ListTrackSongKeys :many
+SELECT id, song_key FROM tracks WHERE id = ANY($1::uuid[])
+`
+
+type ListTrackSongKeysRow struct {
+	ID      pgtype.UUID
+	SongKey pgtype.UUID
+}
+
+func (q *Queries) ListTrackSongKeys(ctx context.Context, ids []pgtype.UUID) ([]ListTrackSongKeysRow, error) {
+	rows, err := q.db.Query(ctx, listTrackSongKeys, ids)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListTrackSongKeysRow
+	for rows.Next() {
+		var i ListTrackSongKeysRow
+		if err := rows.Scan(&i.ID, &i.SongKey); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const mergeInheritSongLink = `-- name: MergeInheritSongLink :exec
+UPDATE tracks s
+   SET song_id = l.song_key
+  FROM tracks l
+ WHERE s.id = $1::uuid
+   AND l.id = $2::uuid
+   AND s.song_id IS NULL
+   AND l.song_key <> l.id
+`
+
+type MergeInheritSongLinkParams struct {
+	SurvivorID pgtype.UUID
+	LoserID    pgtype.UUID
+}
+
+// A merge keeps the removed copy's song link: when the copy being removed was
+// linked to copies on other releases and the survivor was not, the survivor
+// joins that song.
+func (q *Queries) MergeInheritSongLink(ctx context.Context, arg MergeInheritSongLinkParams) error {
+	_, err := q.db.Exec(ctx, mergeInheritSongLink, arg.SurvivorID, arg.LoserID)
+	return err
+}
+
+const shareSongLikes = `-- name: ShareSongLikes :many
+INSERT INTO general_likes (user_id, track_id, liked_at)
+SELECT l.user_id, t.id, min(l.liked_at)
+  FROM general_likes l
+  JOIN tracks lt ON lt.id = l.track_id
+  JOIN tracks t  ON t.song_key = lt.song_key
+ WHERE lt.song_key = $1::uuid
+ GROUP BY l.user_id, t.id
+ON CONFLICT (user_id, track_id) DO NOTHING
+RETURNING user_id, track_id
+`
+
+type ShareSongLikesRow struct {
+	UserID  pgtype.UUID
+	TrackID pgtype.UUID
+}
+
+// A like on any copy of the song becomes a like on every copy, dated the
+// earliest. Returns the likes added, for the sync log.
+func (q *Queries) ShareSongLikes(ctx context.Context, songKey pgtype.UUID) ([]ShareSongLikesRow, error) {
+	rows, err := q.db.Query(ctx, shareSongLikes, songKey)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ShareSongLikesRow
+	for rows.Next() {
+		var i ShareSongLikesRow
+		if err := rows.Scan(&i.UserID, &i.TrackID); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const unlinkDuplicateGroupSongs = `-- name: UnlinkDuplicateGroupSongs :exec
+UPDATE tracks SET song_id = NULL
+ WHERE song_id IS NOT NULL
+   AND id IN (SELECT track_id FROM duplicate_group_members WHERE group_id = $1)
+`
+
+// "Not the same song": the group's copies stop sharing a song. Likes already
+// shared stay where they are.
+func (q *Queries) UnlinkDuplicateGroupSongs(ctx context.Context, groupID pgtype.UUID) error {
+	_, err := q.db.Exec(ctx, unlinkDuplicateGroupSongs, groupID)
+	return err
+}

internal/db/dbq/tracks.sql.go

@@ -247,7 +247,7 @@ func (q *Queries) FindMissingTrackByMbid(ctx context.Context, mbid string) ([]Fi
 }
 
 const getTrackByID = `-- name: GetTrackByID :one
-SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source FROM tracks WHERE id = $1
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key FROM tracks WHERE id = $1
 `
 
 func (q *Queries) GetTrackByID(ctx context.Context, id pgtype.UUID) (Track, error) {
@@ -274,12 +274,14 @@ func (q *Queries) GetTrackByID(ctx context.Context, id pgtype.UUID) (Track, erro
 		&i.TagReadVersion,
 		&i.MissingSince,
 		&i.MbidSource,
+		&i.SongID,
+		&i.SongKey,
 	)
 	return i, err
 }
 
 const getTrackByPath = `-- name: GetTrackByPath :one
-SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source FROM tracks WHERE file_path = $1
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key FROM tracks WHERE file_path = $1
 `
 
 func (q *Queries) GetTrackByPath(ctx context.Context, filePath string) (Track, error) {
@@ -306,12 +308,14 @@ func (q *Queries) GetTrackByPath(ctx context.Context, filePath string) (Track, e
 		&i.TagReadVersion,
 		&i.MissingSince,
 		&i.MbidSource,
+		&i.SongID,
+		&i.SongKey,
 	)
 	return i, err
 }
 
 const getTracksByIDs = `-- name: GetTracksByIDs :many
-SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source FROM tracks WHERE id = ANY($1::uuid[])
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key FROM tracks WHERE id = ANY($1::uuid[])
 `
 
 // Batched lookup used by /api/library/sync to hydrate upsert payloads
@@ -346,6 +350,8 @@ func (q *Queries) GetTracksByIDs(ctx context.Context, dollar_1 []pgtype.UUID) ([
 			&i.TagReadVersion,
 			&i.MissingSince,
 			&i.MbidSource,
+			&i.SongID,
+			&i.SongKey,
 		); err != nil {
 			return nil, err
 		}
@@ -358,7 +364,7 @@ func (q *Queries) GetTracksByIDs(ctx context.Context, dollar_1 []pgtype.UUID) ([
 }
 
 const listArtistTracksForUser = `-- name: ListArtistTracksForUser :many
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
        albums.title AS album_title,
        artists.name AS artist_name
 FROM tracks t
@@ -419,6 +425,8 @@ func (q *Queries) ListArtistTracksForUser(ctx context.Context, arg ListArtistTra
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.AlbumTitle,
 			&i.ArtistName,
 		); err != nil {
@@ -519,7 +527,7 @@ func (q *Queries) ListMissingTracks(ctx context.Context, arg ListMissingTracksPa
 }
 
 const listRandomTracksForUser = `-- name: ListRandomTracksForUser :many
-SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source,
+SELECT t.id, t.title, t.album_id, t.artist_id, t.track_number, t.disc_number, t.duration_ms, t.file_path, t.file_size, t.file_format, t.bitrate, t.mbid, t.genre, t.added_at, t.updated_at, t.tag_source, t.tag_sources_version, t.tag_read_version, t.missing_since, t.mbid_source, t.song_id, t.song_key,
        albums.title AS album_title,
        artists.name AS artist_name
 FROM tracks t
@@ -577,6 +585,8 @@ func (q *Queries) ListRandomTracksForUser(ctx context.Context, arg ListRandomTra
 			&i.Track.TagReadVersion,
 			&i.Track.MissingSince,
 			&i.Track.MbidSource,
+			&i.Track.SongID,
+			&i.Track.SongKey,
 			&i.AlbumTitle,
 			&i.ArtistName,
 		); err != nil {
@@ -709,7 +719,7 @@ func (q *Queries) ListTrackPathsForReconcile(ctx context.Context) ([]ListTrackPa
 }
 
 const listTracksByAlbum = `-- name: ListTracksByAlbum :many
-SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source FROM tracks
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key FROM tracks
 WHERE album_id = $1
   AND NOT EXISTS (
     SELECT 1 FROM lidarr_quarantine q
@@ -756,6 +766,8 @@ func (q *Queries) ListTracksByAlbum(ctx context.Context, arg ListTracksByAlbumPa
 			&i.TagReadVersion,
 			&i.MissingSince,
 			&i.MbidSource,
+			&i.SongID,
+			&i.SongKey,
 		); err != nil {
 			return nil, err
 		}
@@ -829,7 +841,7 @@ func (q *Queries) MarkTracksMissing(ctx context.Context, ids []pgtype.UUID) (int
 }
 
 const searchTracks = `-- name: SearchTracks :many
-SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source FROM tracks
+SELECT id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key FROM tracks
 WHERE title ILIKE '%' || $1::text || '%'
   AND NOT EXISTS (
     SELECT 1 FROM lidarr_quarantine q
@@ -883,6 +895,8 @@ func (q *Queries) SearchTracks(ctx context.Context, arg SearchTracksParams) ([]T
 			&i.TagReadVersion,
 			&i.MissingSince,
 			&i.MbidSource,
+			&i.SongID,
+			&i.SongKey,
 		); err != nil {
 			return nil, err
 		}
@@ -939,7 +953,7 @@ ON CONFLICT (file_path) DO UPDATE SET
     -- next scan can short-circuit them again (#2499).
     tag_read_version = EXCLUDED.tag_read_version,
     updated_at = now()
-RETURNING id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source
+RETURNING id, title, album_id, artist_id, track_number, disc_number, duration_ms, file_path, file_size, file_format, bitrate, mbid, genre, added_at, updated_at, tag_source, tag_sources_version, tag_read_version, missing_since, mbid_source, song_id, song_key
 `
 
 type UpsertTrackParams struct {
@@ -999,6 +1013,8 @@ func (q *Queries) UpsertTrack(ctx context.Context, arg UpsertTrackParams) (Track
 		&i.TagReadVersion,
 		&i.MissingSince,
 		&i.MbidSource,
+		&i.SongID,
+		&i.SongKey,
 	)
 	return i, err
 }

internal/db/migrations/0076_track_song_link.down.sql

@@ -0,0 +1,3 @@
+DROP INDEX IF EXISTS tracks_song_key_idx;
+ALTER TABLE tracks DROP COLUMN IF EXISTS song_key;
+ALTER TABLE tracks DROP COLUMN IF EXISTS song_id;

internal/db/migrations/0076_track_song_link.up.sql

@@ -0,0 +1,15 @@
+-- 0076_track_song_link.up.sql — the same song on several releases counts as
+-- one song (Scribe milestone #498, #5438; operator decision D-b).
+--
+-- A single and the album it came from each hold the song, and Lidarr keeps
+-- both: each fulfils its own release. Minstrel keeps both files and links
+-- them, so a like on one is a like on the song, and a mix or radio picks the
+-- song once rather than once per release.
+--
+-- song_id is set only on a linked track, to the song_key the link chose.
+-- song_key is what everything reads: the track's own id until it is linked.
+-- No foreign key: the track whose id names a song may itself be merged away
+-- later, and the key still groups the copies left.
+ALTER TABLE tracks ADD COLUMN song_id uuid;
+ALTER TABLE tracks ADD COLUMN song_key uuid GENERATED ALWAYS AS (COALESCE(song_id, id)) STORED;
+CREATE INDEX tracks_song_key_idx ON tracks (song_key);

internal/db/queries/likes.sql

@@ -1,20 +1,42 @@
--- name: LikeTrack :execrows
+-- name: LikeTrack :many
+-- A like is on the song (M498 #5438): every copy of it sharing the track's
+-- song_key is liked. Returns the tracks newly liked, for the sync log; empty
+-- when the song was already liked.
 INSERT INTO general_likes (user_id, track_id)
-VALUES ($1, $2)
-ON CONFLICT (user_id, track_id) DO NOTHING;
+SELECT sqlc.arg(user_id)::uuid, t.id
+  FROM tracks t
+ WHERE t.song_key = (SELECT s.song_key FROM tracks s WHERE s.id = sqlc.arg(track_id)::uuid)
+ON CONFLICT (user_id, track_id) DO NOTHING
+RETURNING track_id;
 
--- name: UnlikeTrack :exec
-DELETE FROM general_likes WHERE user_id = $1 AND track_id = $2;
+-- name: UnlikeTrack :many
+-- Unlikes the song: every copy sharing the track's song_key. Returns the
+-- tracks unliked, for the sync log.
+DELETE FROM general_likes
+ WHERE user_id = sqlc.arg(user_id)::uuid
+   AND (track_id = sqlc.arg(track_id)::uuid
+        OR track_id IN (SELECT t.id FROM tracks t
+                         WHERE t.song_key = (SELECT s.song_key FROM tracks s WHERE s.id = sqlc.arg(track_id)::uuid)))
+RETURNING track_id;
 
 -- name: ListLikedTrackRows :many
+-- One row per liked song: of its copies, the one present on disk, then the
+-- one liked first.
 SELECT t.* FROM tracks t
-JOIN general_likes l ON l.track_id = t.id
-WHERE l.user_id = $1
-ORDER BY l.liked_at DESC
+JOIN (SELECT DISTINCT ON (lt.song_key) l.track_id, l.liked_at
+        FROM general_likes l
+        JOIN tracks lt ON lt.id = l.track_id
+       WHERE l.user_id = $1
+       ORDER BY lt.song_key, (lt.missing_since IS NOT NULL), l.liked_at, lt.id) l
+  ON l.track_id = t.id
+ORDER BY l.liked_at DESC, t.id
 LIMIT $2 OFFSET $3;
 
 -- name: CountLikedTracks :one
-SELECT count(*) FROM general_likes WHERE user_id = $1;
+-- Liked songs, each counted once however many releases hold it.
+SELECT count(DISTINCT t.song_key) FROM general_likes l
+  JOIN tracks t ON t.id = l.track_id
+ WHERE l.user_id = $1;
 
 -- name: ListLikedTrackIDs :many
 SELECT track_id FROM general_likes WHERE user_id = $1 ORDER BY liked_at DESC;

internal/db/queries/songs.sql

@@ -0,0 +1,55 @@
+-- Song links (M498 #5438): copies of one song on different releases share a
+-- song_key (migration 0076).
+
+-- name: LinkTracksAsSong :one
+-- Links the tracks into one song, joining any songs they already belong to.
+-- The song keeps the lowest key among them, so linking the same set again
+-- changes nothing. Returns that key and how many tracks moved to it.
+WITH keys AS (
+    SELECT DISTINCT song_key FROM tracks WHERE id = ANY(sqlc.arg(track_ids)::uuid[])
+), target AS (
+    SELECT song_key FROM keys ORDER BY song_key LIMIT 1
+), moved AS (
+    UPDATE tracks t
+       SET song_id = (SELECT song_key FROM target)
+     WHERE t.song_key IN (SELECT song_key FROM keys)
+       AND t.song_key <> (SELECT song_key FROM target)
+    RETURNING t.id
+)
+SELECT (SELECT song_key FROM target)::uuid AS song_key,
+       (SELECT count(*) FROM moved)::bigint AS moved;
+
+-- name: ShareSongLikes :many
+-- A like on any copy of the song becomes a like on every copy, dated the
+-- earliest. Returns the likes added, for the sync log.
+INSERT INTO general_likes (user_id, track_id, liked_at)
+SELECT l.user_id, t.id, min(l.liked_at)
+  FROM general_likes l
+  JOIN tracks lt ON lt.id = l.track_id
+  JOIN tracks t  ON t.song_key = lt.song_key
+ WHERE lt.song_key = sqlc.arg(song_key)::uuid
+ GROUP BY l.user_id, t.id
+ON CONFLICT (user_id, track_id) DO NOTHING
+RETURNING user_id, track_id;
+
+-- name: UnlinkDuplicateGroupSongs :exec
+-- "Not the same song": the group's copies stop sharing a song. Likes already
+-- shared stay where they are.
+UPDATE tracks SET song_id = NULL
+ WHERE song_id IS NOT NULL
+   AND id IN (SELECT track_id FROM duplicate_group_members WHERE group_id = sqlc.arg(group_id));
+
+-- name: ListTrackSongKeys :many
+SELECT id, song_key FROM tracks WHERE id = ANY(sqlc.arg(ids)::uuid[]);
+
+-- name: MergeInheritSongLink :exec
+-- A merge keeps the removed copy's song link: when the copy being removed was
+-- linked to copies on other releases and the survivor was not, the survivor
+-- joins that song.
+UPDATE tracks s
+   SET song_id = l.song_key
+  FROM tracks l
+ WHERE s.id = sqlc.arg(survivor_id)::uuid
+   AND l.id = sqlc.arg(loser_id)::uuid
+   AND s.song_id IS NULL
+   AND l.song_key <> l.id;

internal/library/duplicate_merge.go

@@ -269,6 +269,9 @@ func foldTrackInto(
 	if err := tq.MergeInheritTrackMbid(ctx, dbq.MergeInheritTrackMbidParams{SurvivorID: survivorID, LoserID: loserID}); err != nil {
 		return f, fmt.Errorf("inherit recording mbid: %w", err)
 	}
+	if err := tq.MergeInheritSongLink(ctx, dbq.MergeInheritSongLinkParams{SurvivorID: survivorID, LoserID: loserID}); err != nil {
+		return f, fmt.Errorf("inherit song link: %w", err)
+	}
 
 	// Everything the loser carried now sits on the survivor, so the CASCADE
 	// this delete sets off has nothing left to destroy.

internal/library/duplicate_resolve.go

@@ -89,6 +89,8 @@ type DuplicateResolveResult struct {
 	Merged          int
 	MergeFailed     int
 	ReleaseChanges  []ReleaseChange
+	// SongsLinked counts cross-release groups newly linked as one song.
+	SongsLinked int
 }
 
 // LidarrPathKey is the part of a path Minstrel and Lidarr agree on: the last
@@ -177,7 +179,18 @@ func ResolveDuplicates(
 		return res, err
 	}
 
-	if !act || !res.LidarrConsulted {
+	if !act {
+		return res, nil
+	}
+
+	// Linking removes nothing and needs nothing from Lidarr.
+	linked, err := linkCrossRelease(ctx, pool, logger, groups)
+	res.SongsLinked = linked
+	if err != nil {
+		return res, err
+	}
+
+	if !res.LidarrConsulted {
 		return res, nil
 	}
 
@@ -222,6 +235,66 @@ func ResolveDuplicates(
 	return res, nil
 }
 
+// linkCrossRelease links each cross-release group's copies as one song
+// (#5438): a like on one is a like on all, and the Liked list, shuffle and the
+// mixes count the song once. Linking an already-linked group changes nothing,
+// so this runs every pass; likes are shared only when a link is new, since a
+// like made after it reaches every copy as it is made.
+func linkCrossRelease(ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger, groups []*resolveGroup) (int, error) {
+	linked := 0
+	for _, g := range groups {
+		if g.class != ClassCrossRelease {
+			continue
+		}
+		if ctx.Err() != nil {
+			return linked, ctx.Err()
+		}
+		ids := make([]pgtype.UUID, len(g.members))
+		for i, m := range g.members {
+			ids[i] = m.TrackID
+		}
+		moved, err := linkSong(ctx, pool, ids)
+		if err != nil {
+			logger.Warn("duplicate resolve: song link failed", "group_id", syncpkg.FormatUUID(g.id), "err", err)
+			continue
+		}
+		if moved {
+			linked++
+		}
+	}
+	return linked, nil
+}
+
+// linkSong links the tracks as one song and, when that changed anything,
+// shares their likes across the song and logs each added like for sync.
+func linkSong(ctx context.Context, pool *pgxpool.Pool, ids []pgtype.UUID) (bool, error) {
+	tx, err := pool.Begin(ctx)
+	if err != nil {
+		return false, err
+	}
+	defer func() { _ = tx.Rollback(ctx) }()
+	tq := dbq.New(tx)
+	link, err := tq.LinkTracksAsSong(ctx, ids)
+	if err != nil {
+		return false, fmt.Errorf("link: %w", err)
+	}
+	if link.Moved == 0 {
+		return false, nil
+	}
+	added, err := tq.ShareSongLikes(ctx, link.SongKey)
+	if err != nil {
+		return false, fmt.Errorf("share likes: %w", err)
+	}
+	likeIDs := make([]string, len(added))
+	for i, a := range added {
+		likeIDs[i] = syncpkg.EncodeLikeID(syncpkg.FormatUUID(a.UserID), syncpkg.FormatUUID(a.TrackID))
+	}
+	if err := syncpkg.LogChanges(ctx, tx, syncpkg.EntityLikeTrack, likeIDs, syncpkg.OpUpsert); err != nil {
+		return false, fmt.Errorf("log shared likes: %w", err)
+	}
+	return true, tx.Commit(ctx)
+}
+
 func foldResolveGroups(rows []dbq.ListDuplicateGroupsForResolveRow) []*resolveGroup {
 	var groups []*resolveGroup
 	for _, r := range rows {
@@ -250,7 +323,7 @@ func resolveNote(g *resolveGroup) string {
 			return "Lidarr tracks every copy as its own track, so removing one would make Lidarr download it again."
 		}
 	case ClassCrossRelease:
-		return "Each copy belongs to its own release, and Lidarr keeps each one. Nothing is removed."
+		return "Each copy belongs to its own release, and Lidarr keeps each one. Nothing is removed; they count as one song."
 	case ClassMismatch:
 		return "Identical audio filed under different titles: one file carries another song's tags."
 	}
@@ -674,5 +747,5 @@ func (w *DuplicateResolveWorker) tickOnce(ctx context.Context) {
 	}
 	w.logger.Info("duplicate resolve complete",
 		"groups", res.Groups, "lidarr", res.LidarrConsulted, "merged", res.Merged,
-		"merge_failed", res.MergeFailed, "release_changes", len(res.ReleaseChanges))
+		"merge_failed", res.MergeFailed, "release_changes", len(res.ReleaseChanges), "songs_linked", res.SongsLinked)
 }

internal/library/song_link_test.go

@@ -0,0 +1,208 @@
+package library
+
+import (
+	"context"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgtype"
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/dbtest"
+)
+
+// songLinkFixture is the single and the album it came from: one song on two
+// releases, in one pending acoustic group, and a user who liked the single.
+type songLinkFixture struct {
+	single, albumCut dbq.Track
+	groupID          pgtype.UUID
+	user             dbq.User
+}
+
+func newSongLinkFixture(t *testing.T, pool *pgxpool.Pool) songLinkFixture {
+	t.Helper()
+	ctx := context.Background()
+	q := dbq.New(pool)
+	exec := func(sql string, args ...any) {
+		t.Helper()
+		if _, err := pool.Exec(ctx, sql, args...); err != nil {
+			t.Fatalf("exec %q: %v", sql, err)
+		}
+	}
+	artist, err := q.UpsertArtist(ctx, dbq.UpsertArtistParams{Name: "Link Artist", SortName: "Link Artist"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	track := func(album, path string) dbq.Track {
+		t.Helper()
+		a, err := q.UpsertAlbum(ctx, dbq.UpsertAlbumParams{Title: album, SortTitle: album, ArtistID: artist.ID})
+		if err != nil {
+			t.Fatal(err)
+		}
+		tr, err := q.UpsertTrack(ctx, dbq.UpsertTrackParams{
+			Title: "Feel Good Inc.", AlbumID: a.ID, ArtistID: artist.ID,
+			DurationMs: 1000, FilePath: path, FileSize: 100, FileFormat: "mp3",
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return tr
+	}
+	f := songLinkFixture{
+		single:   track("Feel Good Inc. (single)", "/music/Link Artist/Feel Good Inc/01 Feel Good Inc.mp3"),
+		albumCut: track("Demon Days", "/music/Link Artist/Demon Days/06 Feel Good Inc.mp3"),
+	}
+	f.user, err = q.CreateUser(ctx, dbq.CreateUserParams{
+		Username: dbtest.TestUserPrefix + "song-link", PasswordHash: "x", ApiTokenHash: "song-link-token",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := pool.QueryRow(ctx,
+		`INSERT INTO duplicate_groups (member_key, tier) VALUES ('song-link', 'acoustic') RETURNING id`,
+	).Scan(&f.groupID); err != nil {
+		t.Fatal(err)
+	}
+	exec(`INSERT INTO duplicate_group_members (group_id, track_id) VALUES ($1, $2), ($1, $3)`, f.groupID, f.single.ID, f.albumCut.ID)
+	exec(`INSERT INTO general_likes (user_id, track_id) VALUES ($1, $2)`, f.user.ID, f.single.ID)
+	return f
+}
+
+// A cross-release group becomes one song: its copies share a song key, the
+// like on the single reaches the album cut (and is logged for sync), the Liked
+// list shows the song once, a like or unlike on either copy reaches both, and
+// "not the same song" undoes the link.
+func TestCrossReleaseCopiesCountAsOneSong_Integration(t *testing.T) {
+	pool := newPool(t)
+	ctx := context.Background()
+	q := dbq.New(pool)
+	f := newSongLinkFixture(t, pool)
+
+	res, err := ResolveDuplicates(ctx, pool, nil, "", nil, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Classes[ClassCrossRelease] != 1 || res.SongsLinked != 1 {
+		t.Fatalf("classes %v, linked %d; want one cross-release group linked", res.Classes, res.SongsLinked)
+	}
+	keys := songKeys(t, q, f.single.ID, f.albumCut.ID)
+	if keys[0] != keys[1] {
+		t.Fatalf("song keys differ after linking: %v", keys)
+	}
+
+	liked, err := q.ListLikedTrackIDs(ctx, f.user.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(liked) != 2 {
+		t.Errorf("liked track ids = %d, want both copies", len(liked))
+	}
+	var logged int
+	if err := pool.QueryRow(ctx,
+		`SELECT count(*) FROM library_changes WHERE entity_type = 'like_track' AND op = 'upsert'`,
+	).Scan(&logged); err != nil {
+		t.Fatal(err)
+	}
+	if logged != 1 {
+		t.Errorf("logged %d shared likes, want 1 (the album cut)", logged)
+	}
+	if n, err := q.CountLikedTracks(ctx, f.user.ID); err != nil || n != 1 {
+		t.Errorf("CountLikedTracks = %d (%v), want 1 song", n, err)
+	}
+	rows, err := q.ListLikedTrackRows(ctx, dbq.ListLikedTrackRowsParams{UserID: f.user.ID, Limit: 10})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 {
+		t.Errorf("Liked list has %d rows, want the song once", len(rows))
+	}
+
+	// A second pass changes nothing.
+	if res, err := ResolveDuplicates(ctx, pool, nil, "", nil, true); err != nil || res.SongsLinked != 0 {
+		t.Errorf("second pass linked %d (%v), want 0", res.SongsLinked, err)
+	}
+
+	unliked, err := q.UnlikeTrack(ctx, dbq.UnlikeTrackParams{UserID: f.user.ID, TrackID: f.albumCut.ID})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(unliked) != 2 {
+		t.Errorf("unlike removed %d likes, want both copies", len(unliked))
+	}
+	added, err := q.LikeTrack(ctx, dbq.LikeTrackParams{UserID: f.user.ID, TrackID: f.single.ID})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(added) != 2 {
+		t.Errorf("like added %d, want both copies", len(added))
+	}
+	if again, err := q.LikeTrack(ctx, dbq.LikeTrackParams{UserID: f.user.ID, TrackID: f.single.ID}); err != nil || len(again) != 0 {
+		t.Errorf("repeat like added %d (%v), want 0", len(again), err)
+	}
+
+	if err := q.UnlinkDuplicateGroupSongs(ctx, f.groupID); err != nil {
+		t.Fatal(err)
+	}
+	keys = songKeys(t, q, f.single.ID, f.albumCut.ID)
+	if keys[0] == keys[1] {
+		t.Error("song keys still shared after unlinking")
+	}
+}
+
+// Without the operator's permission the resolver links nothing.
+func TestCrossReleaseLinkNeedsAutoResolve_Integration(t *testing.T) {
+	pool := newPool(t)
+	ctx := context.Background()
+	q := dbq.New(pool)
+	f := newSongLinkFixture(t, pool)
+	if _, err := ResolveDuplicates(ctx, pool, nil, "", nil, false); err != nil {
+		t.Fatal(err)
+	}
+	keys := songKeys(t, q, f.single.ID, f.albumCut.ID)
+	if keys[0] == keys[1] {
+		t.Error("linked with auto-resolve off")
+	}
+}
+
+// A merge keeps the removed copy's link to the song on another release.
+func TestMergeInheritsSongLink_Integration(t *testing.T) {
+	pool := newPool(t)
+	ctx := context.Background()
+	q := dbq.New(pool)
+	f := newSongLinkFixture(t, pool)
+	if _, err := q.LinkTracksAsSong(ctx, []pgtype.UUID{f.single.ID, f.albumCut.ID}); err != nil {
+		t.Fatal(err)
+	}
+	// A third, unlinked copy of the album cut stands in for a survivor.
+	other, err := q.UpsertTrack(ctx, dbq.UpsertTrackParams{
+		Title: "Feel Good Inc.", AlbumID: f.albumCut.AlbumID, ArtistID: f.albumCut.ArtistID,
+		DurationMs: 1000, FilePath: "/music/Link Artist/Demon Days/06 Feel Good Inc (1).mp3", FileSize: 90, FileFormat: "mp3",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := q.MergeInheritSongLink(ctx, dbq.MergeInheritSongLinkParams{SurvivorID: other.ID, LoserID: f.albumCut.ID}); err != nil {
+		t.Fatal(err)
+	}
+	keys := songKeys(t, q, other.ID, f.single.ID)
+	if keys[0] != keys[1] {
+		t.Error("survivor did not join the song")
+	}
+}
+
+func songKeys(t *testing.T, q *dbq.Queries, ids ...pgtype.UUID) []pgtype.UUID {
+	t.Helper()
+	rows, err := q.ListTrackSongKeys(context.Background(), ids)
+	if err != nil {
+		t.Fatal(err)
+	}
+	byID := map[pgtype.UUID]pgtype.UUID{}
+	for _, r := range rows {
+		byID[r.ID] = r.SongKey
+	}
+	out := make([]pgtype.UUID, len(ids))
+	for i, id := range ids {
+		out[i] = byID[id]
+	}
+	return out
+}

internal/playlists/system.go

@@ -1070,6 +1070,10 @@ func insertSystemPlaylist(ctx context.Context, qtx *dbq.Queries, userID pgtype.U
 		return pgtype.UUID{}, fmt.Errorf("insert playlist row: %w", err)
 	}
 
+	tracks, err = oneCopyPerSong(ctx, qtx, tracks)
+	if err != nil {
+		return pgtype.UUID{}, err
+	}
 	for _, t := range tracks {
 		var pickKind *string
 		if t.PickKind != "" {
@@ -1096,6 +1100,34 @@ func insertSystemPlaylist(ctx context.Context, qtx *dbq.Queries, userID pgtype.U
 	return p.ID, nil
 }
 
+// oneCopyPerSong keeps the first of a song's copies on different releases
+// (M498 #5438): a mix holds the song once, in its best-ranked place.
+func oneCopyPerSong(ctx context.Context, qtx *dbq.Queries, tracks []rankedCandidate) ([]rankedCandidate, error) {
+	ids := make([]pgtype.UUID, len(tracks))
+	for i, t := range tracks {
+		ids[i] = t.TrackID
+	}
+	rows, err := qtx.ListTrackSongKeys(ctx, ids)
+	if err != nil {
+		return nil, fmt.Errorf("song keys: %w", err)
+	}
+	songOf := make(map[pgtype.UUID]pgtype.UUID, len(rows))
+	for _, r := range rows {
+		songOf[r.ID] = r.SongKey
+	}
+	seen := make(map[pgtype.UUID]bool, len(tracks))
+	out := tracks[:0:0]
+	for _, t := range tracks {
+		song, ok := songOf[t.TrackID]
+		if ok && seen[song] {
+			continue
+		}
+		seen[song] = true
+		out = append(out, t)
+	}
+	return out, nil
+}
+
 // uuidStringPL renders a pgtype.UUID as the canonical 8-4-4-4-12 form.
 // (pgtype.UUID's String method exists on some pgx versions but not others;
 // also the playlists package needs this independent of test helpers.)

internal/recommendation/shuffle.go

@@ -104,11 +104,24 @@ func Shuffle(
 	deferred := make([]Candidate, 0, len(scored)-limit)
 	artistCount := map[pgtype.UUID]int{}
 	albumCount := map[pgtype.UUID]int{}
+	// One song on several releases is played once (M498 #5438): after its
+	// best-scoring copy, the others are dropped, not held back.
+	songs := map[pgtype.UUID]bool{}
+	repeat := func(c Candidate) bool { return c.Track.SongKey.Valid && songs[c.Track.SongKey] }
+	take := func(c Candidate) {
+		if c.Track.SongKey.Valid {
+			songs[c.Track.SongKey] = true
+		}
+		out = append(out, c)
+	}
 
 	for _, s := range scored {
 		if len(out) == limit {
 			break
 		}
+		if repeat(s.c) {
+			continue
+		}
 		overArtist := caps.MaxPerArtist > 0 && artistCount[s.c.Track.ArtistID] >= caps.MaxPerArtist
 		overAlbum := caps.MaxPerAlbum > 0 && albumCount[s.c.Track.AlbumID] >= caps.MaxPerAlbum
 		if overArtist || overAlbum {
@@ -118,7 +131,7 @@ func Shuffle(
 		}
 		artistCount[s.c.Track.ArtistID]++
 		albumCount[s.c.Track.AlbumID]++
-		out = append(out, s.c)
+		take(s.c)
 	}
 
 	// Pass two: the caps could not fill the request, so relax them rather
@@ -128,7 +141,10 @@ func Shuffle(
 		if len(out) == limit {
 			break
 		}
-		out = append(out, c)
+		if repeat(c) {
+			continue
+		}
+		take(c)
 	}
 	return out
 }

internal/recommendation/shuffle_test.go

@@ -84,3 +84,30 @@ func titles(cs []Candidate) []string {
 // pure tests; the Track.Title field is the human-readable handle. Track ID
 // is left as zero pgtype.UUID and never compared.
 var _ pgtype.UUID
+
+// One song on two releases is played once, in its better-scoring copy's place,
+// and a capped copy held back for pass two does not slip back in either.
+func TestShuffle_OneCopyPerSong(t *testing.T) {
+	song := func(c Candidate, key string) Candidate {
+		_ = c.Track.SongKey.Scan("00000000-0000-0000-0000-" + key)
+		return c
+	}
+	album := pgtype.UUID{Bytes: [16]byte{9}, Valid: true}
+	single := song(cand("000000000001", ScoringInputs{IsGeneralLiked: true}), "00000000000a")
+	albumCut := song(cand("000000000002", ScoringInputs{}), "00000000000a")
+	other := cand("000000000003", ScoringInputs{})
+	single.Track.AlbumID, albumCut.Track.AlbumID = album, pgtype.UUID{Bytes: [16]byte{8}, Valid: true}
+
+	out := Shuffle([]Candidate{albumCut, single, other}, defaultWeights(), time.Now(), fixedRNG(0.5), 10, DiversityCaps{})
+	if got := titles(out); len(got) != 2 || got[0] != "000000000001" {
+		t.Errorf("got %v, want the liked single once and the other song", got)
+	}
+
+	// The single is capped out of pass one; pass two takes one copy, not both.
+	capped := cand("000000000004", ScoringInputs{IsGeneralLiked: true})
+	capped.Track.AlbumID = album
+	out = Shuffle([]Candidate{capped, single, albumCut}, defaultWeights(), time.Now(), fixedRNG(0.5), 3, DiversityCaps{MaxPerAlbum: 1})
+	if len(out) != 2 {
+		t.Errorf("got %v, want two tracks: one copy of the song", titles(out))
+	}
+}

internal/subsonic/star.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net/http"
+	"slices"
 
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgtype"
@@ -39,12 +40,13 @@ func (m *mediaHandlers) handleStar(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if trackID.Valid {
-		rows, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: trackID})
+		// Stars the song: every copy of it (M498 #5438).
+		liked, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: trackID})
 		if err != nil {
 			WriteFail(w, r, ErrGeneric, "Could not star track")
 			return
 		}
-		if rows == 1 {
+		if slices.Contains(liked, trackID) {
 			_ = playevents.CaptureContextualLikeIfPlaying(r.Context(), q, user.ID, trackID, m.logger)
 		}
 	}
@@ -75,7 +77,7 @@ func (m *mediaHandlers) handleUnstar(w http.ResponseWriter, r *http.Request) {
 	params := r.URL.Query()
 	q := dbq.New(m.pool)
 	if t, ok := parseUUID(params.Get("id")); ok {
-		_ = q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: t})
+		_, _ = q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: t})
 		_ = playevents.SoftDeleteContextualLikes(r.Context(), q, user.ID, t)
 	}
 	if a, ok := parseUUID(params.Get("albumId")); ok {

web/src/routes/admin/duplicates/+page.svelte

@@ -30,7 +30,8 @@
   // purpose. A third tab lists what the resolver did.
   //
   // Dismissing a group says "these are not duplicates", and the sweep will not
-  // propose that set again. Merging (#3911) keeps one copy, moves the others'
+  // propose that set again. On the cross-release tab it reads "Not the same
+  // song" and also undoes the link that made the copies one song (#5438). Merging (#3911) keeps one copy, moves the others'
   // likes, plays and playlist entries onto it, and deletes their files, so it
   // asks twice. The server refuses to remove a copy Lidarr uses.
 
@@ -337,7 +338,8 @@
         <p class="mt-3 text-text-primary">No songs repeated across releases.</p>
         <p class="mt-1 text-sm text-text-secondary">
           A single and the album it's on, or two editions of one album, show here. Each copy
-          belongs to its own release, so none is removed.
+          belongs to its own release, so none is removed. They count as one song: a like on one
+          is a like on all, and a mix plays it once.
         </p>
       {:else}
         <p class="mt-3 text-text-primary">Nothing needs review.</p>
@@ -366,7 +368,7 @@
                 disabled={dismissing === group.id || merging === group.id}
                 class="rounded-md border border-border px-3 py-1.5 text-sm text-text-secondary hover:bg-surface-hover hover:text-text-primary disabled:opacity-50"
               >
-                Not duplicates
+                {tab === 'cross_release' ? 'Not the same song' : 'Not duplicates'}
               </button>
               <button
                 type="button"

web/src/routes/admin/duplicates/duplicates.test.ts

@@ -323,6 +323,15 @@ describe('admin duplicates', () => {
       expect(createDuplicatesQuery).toHaveBeenLastCalledWith('cross_release');
     });
 
+    // Copies across releases are linked as one song; dismissing one says they
+    // are not, which is what the button names.
+    test('Across releases dismisses as Not the same song', async () => {
+      renderWith(response());
+      await fireEvent.click(screen.getByRole('tab', { name: /across releases/i }));
+      await fireEvent.click(screen.getByRole('button', { name: 'Not the same song' }));
+      expect(dismissDuplicateGroup).toHaveBeenCalledWith('g-1');
+    });
+
     test('Resolved automatically lists merges and release changes', async () => {
       renderWith(response(), [
         {