Guard HOME for set -u in the rescue paths, surface a failed rescue mv
instead of silently dropping the transcript, and never delete the
party dir after a failed save in either close or clean (close now
refuses to delete and exits nonzero on a failed rescue too, matching
clean, since a message promising the transcript survived followed by
rm -rf was a false assurance). Also stop log --stop from announcing a
stop that never started, and sync README's knock/log/write(1) wording
with the actual behavior.
tmux pipe-pane on every pane of the party session, appending into
<party dir>/log (0640, party group) so any attendee can grab a copy.
Start and stop are announced to everyone attached; close rescues a
non-empty transcript to the host's home before removing the dir.
Panes opened later are picked up by re-running party log (a
pane_pipe check keeps already-piped panes single-piped, since tmux's
pipe-pane -o toggles an existing pipe closed rather than skipping it).
Raw output, escapes included. Close polls the transcript for size
stability before rescuing it, since a cross-filesystem mv is
copy+unlink and could otherwise drop bytes still draining from the
pipe-pane writers.
