Code review comment for lp:~alan-griffiths/mir/msh_SystemCompositorWindowManager

> We have always assumed one surface per system-compositor client, so it's not
> clear what's the correct behavior if such a client creates and posts to
> multiple surfaces. I guess the proposed approach of always focusing the
> "default" surface is OK for now, but perhaps in the future on_session_ready
> method should be extended to also provide the surface that became ready.

What we actually have (c.f. the nested code and spinner) is one surface for each output for each system-compositor client.