/// Open an EXISTING database without writing a byte to it.
    ///
    /// [`Library::open`] cannot be used from a process that does not own the
    /// library: it runs `PRAGMA journal_mode = WAL` and a batch of
    /// `CREATE TABLE IF NOT EXISTS`, both writes, and on Android it may be
    /// racing the real app. Android Auto browses and plays from a
    /// service-started process with no Activity in it, and this is the door
    /// it uses.
    ///
    /// A read-only open of a WAL database is legal from SQLite 3.22 (this
    /// tree bundles 3.46) as long as the `-shm` and `-wal` files exist and
    /// are readable, OR there is write permission on the DIRECTORY holding
    /// the database. The second always holds for us — the reader is the
    /// app's own uid and owns `…/Library/.soulstream/` — which is why this
    /// works even though `journal_mode=WAL` is persistent and every
    /// SoulStream database is in it.
    ///
    /// `NO_MUTEX` because the connection is behind this struct's own
    /// `Mutex`; `URI` because the default flags carry it and dropping it
    /// would quietly change how a path with a `?` in it is read.
    pub fn open_read_only(db_path: &Path) -> Result<Library> {
        let conn = Connection::open_with_flags(
            db_path,
            rusqlite::OpenFlags::SQLITE_OPEN_READ_ONLY
                | rusqlite::OpenFlags::SQLITE_OPEN_NO_MUTEX
                | rusqlite::OpenFlags::SQLITE_OPEN_URI,
        )?;
        Ok(Library {
            conn: Mutex::new(conn),
        })
    }