fix(stop): an unconfirmed /exit no longer claims a kill-chain fallback (Issue #60, Linux item 2)

An agent that exits on /exit never turns `working`, so send_keys_safe
returns 4 although the stop then ends cleanly. The line now says the
delivery is unconfirmed and that the stop waits for the session to exit;
the kill steps keep their own lines, printed only when they run. Exit
judgement and the kill chain are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.agents/skills/multi-agent-mux-stop/scripts/stop_session.sh

@@ -239,7 +239,7 @@ graceful_stop() {
   if [ "$exitkey" = "Ctrl+C" ] || [ "$exitkey" = "C-c" ]; then
     herdr send-keys -t "$SESSION_NAME" C-c 2>/dev/null || true
   else
-    send_keys_safe "$SESSION_NAME" "$exitkey" "stop$$" || echo "graceful: safe delivery failed (rc=$?) — falling back to kill chain"
+    send_keys_safe "$SESSION_NAME" "$exitkey" "stop$$" || echo "graceful: delivery of '$exitkey' unconfirmed (rc=$?) — waiting for the session to exit"
   fi
   _wait_session_gone "$SESSION_NAME" 5 || true
   if ! herdr has-session -t "$SESSION_NAME" 2>/dev/null; then