fix(mcp): reset AsyncExitStack after cleanup for reconnect (#618)

src/agents/mcp/server.py

@@ -1010,6 +1010,10 @@ async def cleanup(self):
             finally:
                 self.session = None
                 self._get_session_id = None
+                # AsyncExitStack cannot be reused after aclose(); reconnect() and second connect()
+                # need a fresh stack or enter_async_context will fail / leak resources (#618).
+                self.exit_stack = AsyncExitStack()
+                self.server_initialize_result = None
 
 
 class MCPServerStdioParams(TypedDict):

tests/mcp/test_connect_disconnect.py

@@ -67,3 +67,35 @@ async def test_manual_connect_disconnect_works(
 
     await server.cleanup()
     assert server.session is None, "Server should be disconnected"
+
+
+@pytest.mark.asyncio
+@patch("mcp.client.stdio.stdio_client", return_value=DummyStreamsContextManager())
+@patch("mcp.client.session.ClientSession.initialize", new_callable=AsyncMock, return_value=None)
+@patch("mcp.client.session.ClientSession.list_tools")
+async def test_connect_after_cleanup_uses_fresh_exit_stack(
+    mock_list_tools: AsyncMock, mock_initialize: AsyncMock, mock_stdio_client
+):
+    """Reconnect must work: cleanup() closes AsyncExitStack, so connect() needs a new stack."""
+    server = MCPServerStdio(
+        params={
+            "command": tee,
+        },
+        cache_tools_list=True,
+    )
+
+    tools = [
+        MCPTool(name="tool1", inputSchema={}),
+        MCPTool(name="tool2", inputSchema={}),
+    ]
+    mock_list_tools.return_value = ListToolsResult(tools=tools)
+
+    await server.connect()
+    assert server.session is not None
+    await server.cleanup()
+    assert server.session is None
+
+    await server.connect()
+    assert server.session is not None
+    await server.cleanup()
+    assert server.session is None