3.3: DRM/KMS capture is not session-scoped -- the worker grabs a CRTC's physical
scanout regardless of which session owns the display -- but the peer was
authorized only once at accept. Capture the peer uid and re-check it at the top of
the forward loop: root is always allowed, any other peer must still be the
active-session uid, fail closed otherwise. A session change now tears the stream
down within one frame (~33ms) instead of leaking the incoming user's screen to the
outgoing user's --server.
4.1: connect_drm accepted any producer. Reject a non-root peer (peer_uid != 0) so a
process that won the socket-path race cannot feed the consumer a display list,
frames and dma-buf fds while the DRM path suppresses the portal consent prompt.