/// Which record a track belongs to.
    ///
    /// The one lookup that was missing: everything else here starts from an
    /// album. A tap on a track row in a car has to become "that record, from
    /// that track" — the phone's own `playIndexRow` behaviour — and without
    /// this the car would hand back a one-song queue.
    pub fn track_album(&self, track_id: i64) -> Result<Option<i64>> {
        let conn = self.conn.lock().unwrap();
        Ok(conn
            .query_row(
                "SELECT album_id FROM tracks WHERE id = ?1",
                [track_id],
                |r| r.get::<_, i64>(0),
            )
            .optional()?)
    }