Make a separate d-bus server
The d-bus server should not try to bind to eu.planete_kraus.Tarot. This name is that of the GUI. If you close the GUI, it should close the app. The dbus daemon should not be closed.
The problem is with the Flatpak. It will not be able to listen to eu.planete_kraus.TarotServer. Is that a problem? We could use an anonymous service.