fix(gateway): cancel active runs during shutdown

Track adapter background message-processing tasks, cancel them during gateway shutdown, and interrupt running agents before disconnecting adapters. This prevents old gateway instances from continuing in-flight work after stop/replace, which was contributing to the restart-time task continuation/flicker behavior reported in #1414. Adds regression coverage for adapter task cancellation and shutdown interrupts.

gateway/platforms/base.py

@@ -356,6 +356,10 @@ class BasePlatformAdapter(ABC):
         # Key: session_key (e.g., chat_id), Value: (event, asyncio.Event for interrupt)
         self._active_sessions: Dict[str, asyncio.Event] = {}
         self._pending_messages: Dict[str, MessageEvent] = {}
+        # Background message-processing tasks spawned by handle_message().
+        # Gateway shutdown cancels these so an old gateway instance doesn't keep
+        # working on a task after --replace or manual restarts.
+        self._background_tasks: set[asyncio.Task] = set()
         # Chats where auto-TTS on voice input is disabled (set by /voice off)
         self._auto_tts_disabled_chats: set = set()
 
@@ -778,7 +782,15 @@ class BasePlatformAdapter(ABC):
             return  # Don't process now - will be handled after current task finishes
         
         # Spawn background task to process this message
-        asyncio.create_task(self._process_message_background(event, session_key))
+        task = asyncio.create_task(self._process_message_background(event, session_key))
+        try:
+            self._background_tasks.add(task)
+        except TypeError:
+            # Some tests stub create_task() with lightweight sentinels that are not
+            # hashable and do not support lifecycle callbacks.
+            return
+        if hasattr(task, "add_done_callback"):
+            task.add_done_callback(self._background_tasks.discard)
     
     @staticmethod
     def _get_human_delay() -> float:
@@ -988,6 +1000,21 @@ class BasePlatformAdapter(ABC):
             if session_key in self._active_sessions:
                 del self._active_sessions[session_key]
     
+    async def cancel_background_tasks(self) -> None:
+        """Cancel any in-flight background message-processing tasks.
+
+        Used during gateway shutdown/replacement so active sessions from the old
+        process do not keep running after adapters are being torn down.
+        """
+        tasks = [task for task in self._background_tasks if not task.done()]
+        for task in tasks:
+            task.cancel()
+        if tasks:
+            await asyncio.gather(*tasks, return_exceptions=True)
+        self._background_tasks.clear()
+        self._pending_messages.clear()
+        self._active_sessions.clear()
+
     def has_pending_interrupt(self, session_key: str) -> bool:
         """Check if there's a pending interrupt for a session."""
         return session_key in self._active_sessions and self._active_sessions[session_key].is_set()

gateway/run.py

@@ -900,8 +900,19 @@ class GatewayRunner:
         """Stop the gateway and disconnect all adapters."""
         logger.info("Stopping gateway...")
         self._running = False
-        
+
+        for session_key, agent in list(self._running_agents.items()):
+            try:
+                agent.interrupt("Gateway shutting down")
+                logger.debug("Interrupted running agent for session %s during shutdown", session_key[:20])
+            except Exception as e:
+                logger.debug("Failed interrupting agent during shutdown: %s", e)
+
         for platform, adapter in list(self.adapters.items()):
+            try:
+                await adapter.cancel_background_tasks()
+            except Exception as e:
+                logger.debug("✗ %s background-task cancel error: %s", platform.value, e)
             try:
                 await adapter.disconnect()
                 logger.info("✓ %s disconnected", platform.value)
@@ -909,6 +920,9 @@ class GatewayRunner:
                 logger.error("✗ %s disconnect error: %s", platform.value, e)
 
         self.adapters.clear()
+        self._running_agents.clear()
+        self._pending_messages.clear()
+        self._pending_approvals.clear()
         self._shutdown_all_gateway_honcho()
         self._shutdown_event.set()
         

tests/gateway/test_gateway_shutdown.py

@@ -0,0 +1,106 @@
+import asyncio
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from gateway.config import GatewayConfig, Platform, PlatformConfig
+from gateway.platforms.base import BasePlatformAdapter, MessageEvent, SendResult
+from gateway.run import GatewayRunner
+from gateway.session import SessionSource, build_session_key
+
+
+class StubAdapter(BasePlatformAdapter):
+    def __init__(self):
+        super().__init__(PlatformConfig(enabled=True, token="***"), Platform.TELEGRAM)
+
+    async def connect(self):
+        return True
+
+    async def disconnect(self):
+        return None
+
+    async def send(self, chat_id, content, reply_to=None, metadata=None):
+        return SendResult(success=True, message_id="1")
+
+    async def send_typing(self, chat_id, metadata=None):
+        return None
+
+    async def get_chat_info(self, chat_id):
+        return {"id": chat_id}
+
+
+def _source(chat_id="123456", chat_type="dm"):
+    return SessionSource(
+        platform=Platform.TELEGRAM,
+        chat_id=chat_id,
+        chat_type=chat_type,
+    )
+
+
+@pytest.mark.asyncio
+async def test_cancel_background_tasks_cancels_inflight_message_processing():
+    adapter = StubAdapter()
+    release = asyncio.Event()
+
+    async def block_forever(_event):
+        await release.wait()
+        return None
+
+    adapter.set_message_handler(block_forever)
+    event = MessageEvent(text="work", source=_source(), message_id="1")
+
+    await adapter.handle_message(event)
+    await asyncio.sleep(0)
+
+    session_key = build_session_key(event.source)
+    assert session_key in adapter._active_sessions
+    assert adapter._background_tasks
+
+    await adapter.cancel_background_tasks()
+
+    assert adapter._background_tasks == set()
+    assert adapter._active_sessions == {}
+    assert adapter._pending_messages == {}
+
+
+@pytest.mark.asyncio
+async def test_gateway_stop_interrupts_running_agents_and_cancels_adapter_tasks():
+    runner = object.__new__(GatewayRunner)
+    runner.config = GatewayConfig(platforms={Platform.TELEGRAM: PlatformConfig(enabled=True, token="***")})
+    runner._running = True
+    runner._shutdown_event = asyncio.Event()
+    runner._exit_reason = None
+    runner._pending_messages = {"session": "pending text"}
+    runner._pending_approvals = {"session": {"command": "rm -rf /tmp/x"}}
+    runner._shutdown_all_gateway_honcho = lambda: None
+
+    adapter = StubAdapter()
+    release = asyncio.Event()
+
+    async def block_forever(_event):
+        await release.wait()
+        return None
+
+    adapter.set_message_handler(block_forever)
+    event = MessageEvent(text="work", source=_source(), message_id="1")
+    await adapter.handle_message(event)
+    await asyncio.sleep(0)
+
+    disconnect_mock = AsyncMock()
+    adapter.disconnect = disconnect_mock
+
+    session_key = build_session_key(event.source)
+    running_agent = MagicMock()
+    runner._running_agents = {session_key: running_agent}
+    runner.adapters = {Platform.TELEGRAM: adapter}
+
+    with patch("gateway.status.remove_pid_file"), patch("gateway.status.write_runtime_status"):
+        await runner.stop()
+
+    running_agent.interrupt.assert_called_once_with("Gateway shutting down")
+    disconnect_mock.assert_awaited_once()
+    assert runner.adapters == {}
+    assert runner._running_agents == {}
+    assert runner._pending_messages == {}
+    assert runner._pending_approvals == {}
+    assert runner._shutdown_event.is_set() is True