Clients can connect to unity-system-compositor but are never visible

[Daniel van Vugt]

Clients can connect to unity-system-compositor but are never visible. The screen just stays black...

Even tried with:
$ sudo unity-system-compositor --vt 1 --debug-without-dm --enable-hardware-cursor=1
and remembering to set the client to the correct output ID:
$ sudo mir_demo_client_egltriangle -f -o 34 # is my primary monitor

If this is a security feature (which I guess it should be to stop arbitrary clients coming to the front) then it's still broken:
  (a) Even the first client that connects is never visible; and
  (b) I don't know of any way to bring a certain client (nested shell) to the front in USC. If we don't have a key combo for that, we probably need one.