Two problems made the auto-attach loop:
$TMUX was the only nesting guard, and it is trivially lost - sudo -i,
env -i, ssh, and dropbear all hand back an interactive tty shell with it
unset, so a shell below tmux would start another tmux. The guard also
never checked for a login shell, so anything spawning `$SHELL -i`
(fzf-tmux, file-manager shell escapes, editor :sh) dragged in a whole
tmux client and a fresh grouped session. Now guarded on a login shell
with stdin and stdout both a terminal, a $TERM that can host tmux, and
an exported $TMUX_AUTOSTART that survives into panes and into nested
shells that strip $TMUX.
detach-on-destroy was off while the per-client sessions set
destroy-unattached on. Those fight: detaching destroys the session, and
off means the client is then switched to the most recently active
remaining session instead of being allowed to leave - so detach put you
back into "main". Restored to on, which is also the default.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
