feat: fix NotifyOnce map key to use composite ArtistID+RGID

internal/database/artist_settings.go

@@ -61,13 +61,14 @@ func TouchArtistSynced(db DBer, artistID string, syncedAt time.Time) error {
 func SaveArtistSettings(db *DB, settings *ArtistSettings) error {
 	_, err := db.Conn().Exec(`
 		INSERT INTO artist_settings (id, name, mbid, ignore_singles, ignore_compilations, monitored, last_synced)
-		VALUES (?, ?, ?, ?, ?, ?, (SELECT last_synced FROM artist_settings WHERE id = ?))
+		VALUES (?, ?, ?, ?, ?, ?, ?)
 		ON CONFLICT(id) DO UPDATE SET
 			name = excluded.name,
 			mbid = COALESCE(excluded.mbid, artist_settings.mbid),
 			ignore_singles = excluded.ignore_singles,
 			ignore_compilations = excluded.ignore_compilations,
-			monitored = excluded.monitored
+			monitored = excluded.monitored,
+			last_synced = COALESCE(excluded.last_synced, artist_settings.last_synced)
 	`,
 		settings.ID, settings.Name, nullIfEmpty(settings.MBID), settings.IgnoreSingles, settings.IgnoreCompilations, settings.Monitored, settings.ID,
 	)
@@ -86,6 +87,15 @@ func nullIfEmpty(s string) interface{} {
 	return s
 }
 
+// nullIfEmptyTime returns nil for zero time so COALESCE-preserving columns
+// (e.g. last_synced) keep their existing value when the caller supplies no new one.
+func nullIfEmptyTime(t time.Time) interface{} {
+	if t.IsZero() {
+		return nil
+	}
+	return t
+}
+
 // GetAllArtistSettings returns all rows from artist_settings.
 func GetAllArtistSettings(db *DB) ([]ArtistSettings, error) {
 	rows, err := db.Conn().Query(