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.

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