It is more than event routing, you do not really want for any client to be able to claim any combination, without any further insight by either compositor or user.
Ideally, what you want, is for the client expose a set of (described) actions, with suggested key bindings. Users can then enable / disable / change the bindings in some central place, which would also take care about collisions, reserved global keybinding or reserved local keybinding (key shortcuts, that are always supposed to be available to the focused app).
Ideally, what you want, is for the client expose a set of (described) actions, with suggested key bindings. Users can then enable / disable / change the bindings in some central place, which would also take care about collisions, reserved global keybinding or reserved local keybinding (key shortcuts, that are always supposed to be available to the focused app).