fix: harden sentinel guard for /stop during setup and shutdown

- /stop during sentinel returns helpful message instead of queuing
- Shutdown loop skips sentinel entries instead of catching AttributeError
- _handle_stop_command guards against sentinel (defensive)
- Added tests for both edge cases (7 total race guard tests)

gateway/run.py

@@ -1056,6 +1056,8 @@ class GatewayRunner:
         self._running = False
 
         for session_key, agent in list(self._running_agents.items()):
+            if agent is _AGENT_PENDING_SENTINEL:
+                continue
             try:
                 agent.interrupt("Gateway shutting down")
                 logger.debug("Interrupted running agent for session %s during shutdown", session_key[:20])
@@ -1354,8 +1356,12 @@ class GatewayRunner:
 
             running_agent = self._running_agents.get(_quick_key)
             if running_agent is _AGENT_PENDING_SENTINEL:
-                # Agent is being set up but not ready yet — queue the message
-                # so it will be picked up after the agent starts.
+                # Agent is being set up but not ready yet.
+                if event.get_command() == "stop":
+                    # Nothing to interrupt — agent hasn't started yet.
+                    return "⏳ The agent is still starting up — nothing to stop yet."
+                # Queue the message so it will be picked up after the
+                # agent starts.
                 adapter = self.adapters.get(source.platform)
                 if adapter:
                     adapter._pending_messages[_quick_key] = event
@@ -2326,8 +2332,10 @@ class GatewayRunner:
         session_entry = self.session_store.get_or_create_session(source)
         session_key = session_entry.session_key
         
-        if session_key in self._running_agents:
-            agent = self._running_agents[session_key]
+        agent = self._running_agents.get(session_key)
+        if agent is _AGENT_PENDING_SENTINEL:
+            return "⏳ The agent is still starting up — nothing to stop yet."
+        if agent:
             agent.interrupt()
             return "⚡ Stopping the current task... The agent will finish its current step and respond."
         else:

tests/gateway/test_session_race_guard.py

@@ -195,3 +195,73 @@ async def test_command_messages_do_not_leave_sentinel():
     assert session_key not in runner._running_agents, (
         "Command handlers must not leave sentinel in _running_agents"
     )
+
+
+# ------------------------------------------------------------------
+# Test 6: /stop during sentinel returns helpful message
+# ------------------------------------------------------------------
+@pytest.mark.asyncio
+async def test_stop_during_sentinel_returns_message():
+    """If /stop arrives while the sentinel is set (agent still starting),
+    it should return a helpful message instead of crashing or queuing."""
+    runner = _make_runner()
+    event1 = _make_event(text="hello")
+    session_key = build_session_key(event1.source)
+
+    barrier = asyncio.Event()
+
+    async def slow_inner(self_inner, ev, src, qk):
+        await barrier.wait()
+        return "ok"
+
+    with patch.object(GatewayRunner, "_handle_message_with_agent", slow_inner):
+        task1 = asyncio.create_task(runner._handle_message(event1))
+        await asyncio.sleep(0)
+
+        # Sentinel should be set
+        assert runner._running_agents.get(session_key) is _AGENT_PENDING_SENTINEL
+
+        # Send /stop — should get a message, not crash
+        stop_event = _make_event(text="/stop")
+        result = await runner._handle_message(stop_event)
+        assert result is not None, "/stop during sentinel should return a message"
+        assert "starting up" in result.lower()
+
+        # Should NOT be queued as pending
+        adapter = runner.adapters[Platform.TELEGRAM]
+        assert session_key not in adapter._pending_messages
+
+        barrier.set()
+        await task1
+
+
+# ------------------------------------------------------------------
+# Test 7: Shutdown skips sentinel entries
+# ------------------------------------------------------------------
+@pytest.mark.asyncio
+async def test_shutdown_skips_sentinel():
+    """During gateway shutdown, sentinel entries in _running_agents
+    should be skipped without raising AttributeError."""
+    runner = _make_runner()
+    session_key = "telegram:dm:99999"
+
+    # Simulate a sentinel in _running_agents
+    runner._running_agents[session_key] = _AGENT_PENDING_SENTINEL
+
+    # Also add a real agent mock to verify it still gets interrupted
+    real_agent = MagicMock()
+    runner._running_agents["telegram:dm:88888"] = real_agent
+
+    runner.adapters = {}  # No adapters to disconnect
+    runner._running = True
+    runner._shutdown_event = asyncio.Event()
+    runner._exit_reason = None
+    runner._shutdown_all_gateway_honcho = lambda: None
+
+    with patch("gateway.status.remove_pid_file"), \
+         patch("gateway.status.write_runtime_status"):
+        await runner.stop()
+
+    # Real agent should have been interrupted
+    real_agent.interrupt.assert_called_once()
+    # Should not have raised on the sentinel