There are different sockets. Bug #1236912 was about the sockets apps in the user's session are supposed to be able to access, ie $XDG_RUNTIME_DIR/mir_socket. /run/mir_socket is AIUI different and not supposed to be accessed by apps.
There are different sockets. Bug #1236912 was about the sockets apps in the user's session are supposed to be able to access, ie $XDG_RUNTIME_ DIR/mir_ socket. /run/mir_socket is AIUI different and not supposed to be accessed by apps.