live_server_holds_one_pty_master_fd_per_pane counted only /proc/<pid>/fd links
resolving to exactly /dev/ptmx. On devpts setups such as WSL2 and many
containers, a PTY master fd resolves to /dev/pts/ptmx instead, so the test found
zero masters and failed with "had 0 ptmx master fds; expected 1" even though the
server held the pane's master fd. Match both ptmx node paths; pty slaves still
resolve to /dev/pts/<N> and stay uncounted, so the one-master-per-pane invariant
is unchanged.
Andrew Krasnoff