One liveness primitive instead of two. The PID argument was a vestige
(format-checked, never probed, since the kill -0 removal); dropping it
means a roster with a garbage SERVER_PID can no longer mask a live
socket in host/moderation/role resolution.
tmux-party: share a tmux session with people on the same UNIX host.
Single-file POSIX shell (party) with a filesystem + tmux server-access
trust model. See README.md.
