fix: Fix error handling when MCP server is unreachable

Currently ADK web hangs and logs "AGSI callable returned without completing response" when the server is unreachable. To fix, set timeouts for connecting to server.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 828648928

tests/unittests/tools/mcp_tool/test_mcp_session_manager.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import asyncio
+from datetime import timedelta
 import hashlib
 from io import StringIO
 import json
@@ -279,6 +281,47 @@ class TestMCPSessionManager:
     # Should not create new session
     existing_session.initialize.assert_not_called()
 
+  @pytest.mark.asyncio
+  @patch("google.adk.tools.mcp_tool.mcp_session_manager.stdio_client")
+  @patch("google.adk.tools.mcp_tool.mcp_session_manager.AsyncExitStack")
+  @patch("google.adk.tools.mcp_tool.mcp_session_manager.ClientSession")
+  async def test_create_session_timeout(
+      self, mock_session_class, mock_exit_stack_class, mock_stdio
+  ):
+    """Test session creation timeout."""
+    manager = MCPSessionManager(self.mock_stdio_connection_params)
+
+    mock_session = MockClientSession()
+    mock_exit_stack = MockAsyncExitStack()
+
+    mock_exit_stack_class.return_value = mock_exit_stack
+    mock_stdio.return_value = AsyncMock()
+    mock_exit_stack.enter_async_context.side_effect = [
+        ("read", "write"),  # First call returns transports
+        mock_session,  # Second call returns session
+    ]
+    mock_session_class.return_value = mock_session
+
+    # Simulate timeout during session initialization
+    mock_session.initialize.side_effect = asyncio.TimeoutError("Test timeout")
+
+    # Expect ConnectionError due to timeout
+    with pytest.raises(ConnectionError, match="Failed to create MCP session"):
+      await manager.create_session()
+
+    # Verify ClientSession called with timeout
+    mock_session_class.assert_called_with(
+        "read",
+        "write",
+        read_timeout_seconds=timedelta(
+            seconds=manager._connection_params.timeout
+        ),
+    )
+    # Verify session was not added to pool
+    assert not manager._sessions
+    # Verify cleanup was called
+    mock_exit_stack.aclose.assert_called_once()
+
   @pytest.mark.asyncio
   async def test_close_success(self):
     """Test successful cleanup of all sessions."""