Detect concurrent tmux servers via sockets, not ps argv

The previous heuristic in `all_tmux_processes` grepped `ps` output for
lines starting with the literal string "tmux". This had two failure
modes that both broke auto-save in practice:

  - False negative: tmux invoked via absolute path
    (e.g. `/opt/homebrew/bin/tmux ...` on macOS Homebrew installs)
    never matched `^tmux` and was invisible to the count.

  - False positive: every client process whose argv[0] started with
    "tmux" was counted as a server. Any single tmux server with two
    or more clients attached would trip the "another server running"
    gate, causing continuum to silently skip injecting its save
    interpolation into status-right and disable auto-save until the
    extra clients went away.

The post-startup branch of `another_tmux_server_running` tried to
compensate by subtracting `tmux list-clients` from the ps count, but
that only listed clients of the current server and inherited the same
ps-matching weaknesses.

Replace with socket-based counting. Each tmux server owns exactly one
Unix domain socket in its socket directory; a live server responds to
`tmux -S <socket> list-sessions`. Stale socket files left over from
crashed servers do not respond and are correctly excluded.

This collapses the dual-mode wrapper in continuum.tmux: the same check
is correct on startup and afterward, so the post-startup branch goes
away.

Removes: all_tmux_processes, number_tmux_processes_except_current_server,
number_current_server_client_processes.
Adds: current_tmux_socket_path, number_other_live_tmux_servers.
Public function names (another_tmux_server_running,
another_tmux_server_running_on_startup, current_tmux_server_pid) are
preserved so external callers like continuum_restore.sh keep working.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

continuum.tmux

@@ -19,12 +19,7 @@ handle_tmux_automatic_start() {
 }
 
 another_tmux_server_running() {
-	if just_started_tmux_server; then
-		another_tmux_server_running_on_startup
-	else
-		# script loaded after tmux server start can have multiple clients attached
-		[ "$(number_tmux_processes_except_current_server)" -gt "$(number_current_server_client_processes)" ]
-	fi
+	another_tmux_server_running_on_startup
 }
 
 delay_saving_environment_on_first_plugin_load() {

scripts/helpers.sh

@@ -22,28 +22,50 @@ current_tmux_server_pid() {
 		cut -f2 -d","
 }
 
-all_tmux_processes() {
-	# ignores `tmux source-file .tmux.conf` command used to reload tmux.conf
-	local user_id=$(id -u)
-	ps -u $user_id -o "command pid" |
-		\grep "^tmux" |
-		\grep -v "^tmux source"
+current_tmux_socket_path() {
+	echo "$TMUX" |
+		cut -f1 -d","
 }
 
-number_tmux_processes_except_current_server() {
-	all_tmux_processes |
-		\grep -v " $(current_tmux_server_pid)$" |
-		wc -l |
-		sed "s/ //g"
-}
+# Counts other live tmux servers running for this user.
+#
+# A tmux server holds its socket FD with the socket's filesystem path
+# in lsof's NAME column; a client only holds a peer-pointer connection
+# (no path). Unique path-shaped NAMEs across `tmux` processes equal
+# the set of servers. Each candidate is probed with `list-sessions` to
+# exclude stale socket files from crashed servers.
+#
+# Falls back to scanning the current socket's directory if lsof is
+# unavailable (covers default-dir cases, misses `-S /elsewhere/path`).
+number_other_live_tmux_servers() {
+	local current_socket socket_dir count sock candidates
+	current_socket="$(current_tmux_socket_path)"
+	count=0
 
-number_current_server_client_processes() {
-	tmux list-clients |
-		wc -l |
-		sed "s/ //g"
+	if command -v lsof >/dev/null 2>&1; then
+		# Pull every absolute-path NAME column from `lsof -U` rows where
+		# the command is `tmux` and the user is the current user. Dedupe.
+		candidates="$(lsof -U -a -c tmux -u "$(id -u)" 2>/dev/null \
+			| awk 'NR>1 && $NF ~ /^\// { print $NF }' \
+			| sort -u)"
+	elif [ -n "$current_socket" ]; then
+		# Fallback: scan the current socket's directory only.
+		socket_dir="$(dirname "$current_socket")"
+		candidates="$(find "$socket_dir" -maxdepth 1 -type s 2>/dev/null)"
+	else
+		echo 0
+		return
+	fi
+
+	for sock in $candidates; do
+		[ "$sock" = "$current_socket" ] && continue
+		if tmux -S "$sock" list-sessions >/dev/null 2>&1; then
+			count=$((count + 1))
+		fi
+	done
+	echo "$count"
 }
 
 another_tmux_server_running_on_startup() {
-	# there are 2 tmux processes (current tmux server + 1) on tmux startup
-	[ "$(number_tmux_processes_except_current_server)" -gt 1 ]
+	[ "$(number_other_live_tmux_servers)" -gt 0 ]
 }