In the previous version of Mosaic, you could start playback of a disc on the Rossini Player with Mosaic, but the track buttons were not functional. To jump tracks from a device, you had to download and run the old “dCS Rossini” app.
Now as of version 1.2 of Mosaic, the track buttons work as expected, either jumping to the beginning of the current track or to the next track.
I can now finally delete the old “dCS Rossini” app!
Update: Not so fast; there is still no way to jump to a specific track or program tracks on a disc in the Mosaic app, so I have to keep the dCS Rossini app around after all.