feat(server/m7-379): heal existing artist+album mbid on rescan

internal/db/dbq/albums.sql.go

@@ -515,6 +515,25 @@ func (q *Queries) SearchAlbums(ctx context.Context, arg SearchAlbumsParams) ([]A
 	return items, nil
 }
 
+const setAlbumMbidIfNull = `-- name: SetAlbumMbidIfNull :exec
+UPDATE albums
+   SET mbid = $2,
+       updated_at = now()
+ WHERE id = $1 AND mbid IS NULL
+`
+
+type SetAlbumMbidIfNullParams struct {
+	ID   pgtype.UUID
+	Mbid *string
+}
+
+// M7 #379: heal MBID on existing album rows during rescan. Idempotent —
+// only updates when the existing mbid is NULL.
+func (q *Queries) SetAlbumMbidIfNull(ctx context.Context, arg SetAlbumMbidIfNullParams) error {
+	_, err := q.db.Exec(ctx, setAlbumMbidIfNull, arg.ID, arg.Mbid)
+	return err
+}
+
 const upsertAlbum = `-- name: UpsertAlbum :one
 INSERT INTO albums (title, sort_title, artist_id, release_date, mbid, cover_art_path)
 VALUES ($1, $2, $3, $4, $5, $6)

internal/db/dbq/artists.sql.go

@@ -327,6 +327,26 @@ func (q *Queries) SearchArtists(ctx context.Context, arg SearchArtistsParams) ([
 	return items, nil
 }
 
+const setArtistMbidIfNull = `-- name: SetArtistMbidIfNull :exec
+UPDATE artists
+   SET mbid = $2,
+       updated_at = now()
+ WHERE id = $1 AND mbid IS NULL
+`
+
+type SetArtistMbidIfNullParams struct {
+	ID   pgtype.UUID
+	Mbid *string
+}
+
+// M7 #379: heal MBID on existing artist rows during rescan. Idempotent —
+// only updates when the existing mbid is NULL, so concurrent scans don't
+// overwrite an existing value with a stale one.
+func (q *Queries) SetArtistMbidIfNull(ctx context.Context, arg SetArtistMbidIfNullParams) error {
+	_, err := q.db.Exec(ctx, setArtistMbidIfNull, arg.ID, arg.Mbid)
+	return err
+}
+
 const upsertArtist = `-- name: UpsertArtist :one
 INSERT INTO artists (name, sort_name, mbid)
 VALUES ($1, $2, $3)

internal/db/queries/albums.sql

@@ -96,3 +96,11 @@ DELETE FROM albums a
 WHERE a.id = $1
   AND NOT EXISTS (SELECT 1 FROM tracks t WHERE t.album_id = a.id)
 RETURNING a.id, a.artist_id;
+
+-- name: SetAlbumMbidIfNull :exec
+-- M7 #379: heal MBID on existing album rows during rescan. Idempotent —
+-- only updates when the existing mbid is NULL.
+UPDATE albums
+   SET mbid = $2,
+       updated_at = now()
+ WHERE id = $1 AND mbid IS NULL;

internal/db/queries/artists.sql

@@ -74,3 +74,12 @@ WHERE a.id = $1
   AND NOT EXISTS (SELECT 1 FROM albums al WHERE al.artist_id = a.id)
   AND NOT EXISTS (SELECT 1 FROM tracks t WHERE t.artist_id = a.id)
 RETURNING a.id;
+
+-- name: SetArtistMbidIfNull :exec
+-- M7 #379: heal MBID on existing artist rows during rescan. Idempotent —
+-- only updates when the existing mbid is NULL, so concurrent scans don't
+-- overwrite an existing value with a stale one.
+UPDATE artists
+   SET mbid = $2,
+       updated_at = now()
+ WHERE id = $1 AND mbid IS NULL;

internal/library/scanner.go

@@ -201,6 +201,19 @@ func (s *Scanner) scanFile(ctx context.Context, q *dbq.Queries, path string, sta
 func (s *Scanner) resolveArtist(ctx context.Context, q *dbq.Queries, name, mbid string) (dbq.Artist, error) {
 	existing, err := q.GetArtistByName(ctx, name)
 	if err == nil {
+		// Heal: backfill mbid on a previously-imported row if we have one now.
+		if mbid != "" && (existing.Mbid == nil || *existing.Mbid == "") {
+			m := mbid
+			if uerr := q.SetArtistMbidIfNull(ctx, dbq.SetArtistMbidIfNullParams{
+				ID:   existing.ID,
+				Mbid: &m,
+			}); uerr != nil {
+				s.logger.Warn("library scan: heal artist mbid failed",
+					"artist_id", existing.ID, "err", uerr)
+			} else {
+				existing.Mbid = &m
+			}
+		}
 		return existing, nil
 	}
 	if !errors.Is(err, pgx.ErrNoRows) {
@@ -220,6 +233,19 @@ func (s *Scanner) resolveArtist(ctx context.Context, q *dbq.Queries, name, mbid
 func (s *Scanner) resolveAlbum(ctx context.Context, q *dbq.Queries, artistID pgtype.UUID, title string, year int, mbid string) (dbq.Album, error) {
 	existing, err := q.GetAlbumByArtistAndTitle(ctx, dbq.GetAlbumByArtistAndTitleParams{ArtistID: artistID, Title: title})
 	if err == nil {
+		// Heal: backfill mbid on a previously-imported row if we have one now.
+		if mbid != "" && (existing.Mbid == nil || *existing.Mbid == "") {
+			m := mbid
+			if uerr := q.SetAlbumMbidIfNull(ctx, dbq.SetAlbumMbidIfNullParams{
+				ID:   existing.ID,
+				Mbid: &m,
+			}); uerr != nil {
+				s.logger.Warn("library scan: heal album mbid failed",
+					"album_id", existing.ID, "err", uerr)
+			} else {
+				existing.Mbid = &m
+			}
+		}
 		return existing, nil
 	}
 	if !errors.Is(err, pgx.ErrNoRows) {