feat: party log records a group-readable transcript

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.

party.1

@@ -16,6 +16,10 @@
 .Nm
 .Cm clean
 .Nm
+.Cm log
+.Op Fl -stop
+.Op Fl -party Ar name
+.Nm
 .Cm join
 .Op Ar name
 .Op Fl -passive
@@ -142,6 +146,23 @@ Host-only.
 Remove the caller's own dead party directories: crash leftovers whose
 tmux server no longer answers.
 Never touches live parties, other users' directories, or symlinks.
+.It Cm log Op Fl -stop Op Fl -party Ar name
+Record the party into
+.Pa log
+inside the per-party directory (host only), via
+.Xr tmux 1
+.Ic pipe-pane .
+The file is group-readable so any attendee can grab a copy.
+Starting and stopping is announced to everyone attached.
+Panes opened after logging starts are not captured until
+.Cm log
+is re-run; output is raw (ANSI escapes included, read with
+.Ql less -R ) .
+.Fl -stop
+ends recording.
+.Cm close
+rescues a non-empty transcript to the host's home directory before
+removing the party directory.
 .It Cm join Op Ar name Op Fl -passive
 Join a party.
 With no
@@ -314,6 +335,11 @@ every read, not trusted from the file.
 Auto-generated helper that fans
 .Cm display-message
 out to every attached client on join/leave.
+.It Pa ${PARTY_SOCKET_DIR}/party-${USER}:${NAME}.d/log
+Transcript written by
+.Cm log ;
+removed with the party directory unless rescued by
+.Cm close .
 .El
 .Sh EXIT STATUS
 .Bl -tag -width Ds
@@ -493,6 +519,11 @@ has no equivalent of
 The watcher boundary is set at
 .Cm join Fl -passive
 time and is fixed for the life of that client.
+.Pp
+Every member of the party's group can read a
+.Cm log
+transcript, since the per-party directory is the perimeter, including
+group members who were never invited.
 .Sh SEE ALSO
 .Xr tmux 1 ,
 .Xr screen 1 ,