exception SurfaceNotFound

The surface id is not one this compositor handed out, or its client has already let it go.

Distinct from ArenaNotFound because they are different mistakes: a bad arena id means "you named memory I cannot map", a bad surface id means "you named a window that is not yours or is not there any more". Only the second one can arrive because of a race the caller did not lose on purpose — a window the user closed while a call was in flight.