switch tmux to individual sessions

mksh/mkshrc

@@ -216,10 +216,12 @@ PS4='[$EPOCHREALTIME] '; PS1='#'; (( USER_ID )) && PS1='→'; PS1=$'\001\r''${|
 	\\builtin return $e
 } '"${hostcol}${bld}$PS1 ${rst}"
 
-# tmux auto-attach: one shared session per host. No -exec, so if tmux is
-# missing or exits/crashes for any reason, this shell just continues normally.
+# tmux auto-attach: bare invocation so tmux.conf's default-client-command
+# grants each connection its own session grouped with "main" (shared panes,
+# independent window navigation). No -exec, so if tmux is missing or
+# exits/crashes for any reason, this shell just continues normally.
 tmuxbin=$(\\builtin whence -p tmux 2>/dev/null)
 if [[ $- = *i* ]] && [[ -t 0 ]] && [[ -z $TMUX ]] && [[ -n $tmuxbin ]]; then
-  "$tmuxbin" new-session -A -s "${HOSTNAME:-main}"
+  "$tmuxbin"
 fi
 unset tmuxbin

tmux/tmux.conf

@@ -4,6 +4,12 @@ set-option -g focus-events on
 set -s escape-time 0
 set -g detach-on-destroy off
 set -g destroy-unattached off
+
+# bare `tmux` (no subcommand, e.g. from mkshrc's auto-attach) gets its own
+# session grouped with "main" - shared panes/windows, independent per-client
+# current-window navigation. Self-cleans on detach via destroy-unattached.
+new-session -d -s main
+set -g default-client-command "new-session -t main ; set-option destroy-unattached on"
 # set -g default-terminal "screen-256color"
 set -g default-terminal "tmux-256color"
 set -g history-limit 50000