cmux-tui SSH terminals have no CLI relay for cmux commands

In cmux SSH workspaces routed through cmux-tui (the default when no relay port is set), the remote shell's PATH has only the cmux-tui shims dir, and the env has CMUX_TUI_SOCKET/CMUX_TUI_TERMINAL_ID but no CMUX_SOCKET_PATH. So a cmux CLI on the host (e.g. cmux open) has no socket path back to the Mac, and deploying a newer cmuxd-remote doesn't help, because that legacy relay path is never started for cmux-tui workspaces. A working ingress is the daemon's notification ledger: notification create --terminal $CMUX_TUI_TERMINAL_ID with a marked body that the Mac provider intercepts, checks against a staleness window and the owning pane, then acks. Check /proc/<pid>/environ of a live shell to confirm which env and PATH it actually got.