Issue EVIOCGRAB on all input devices on non-default seats
The following discussion from !494 (merged) should be addressed:
Btw. do not try this without an actual normal desktop running. If you are in VT text mode, then the udev seat assignment will not stop the insecure keyboard typing going to the console!
In that thread, @whot suggest to issue
EVIOCGRAB on the input devices to avoid leaking them to the console. There are corner case issues with doing that (things like rfkill stop getting the events), but those can be ignored on non-default seats.
This would need to be implemented in all three lauchers.