RuntimeError: “Attempted to exit cancel scope” when using MCPToolset with ADK on Vertex AI Agent Engine

[priyayarrabolu-boop]

Hi everyone,

I’m running a custom ADK agent on Vertex AI Agent Engine using an LlmAgent configured with a LocalMCPToolsetWrapper(MCPToolset) and a stdio MCP connection. As soon as the first tool call occurs, the agent crashes with the following error:

This appears to happen during the MCP client setup/teardown. Due to this crash:

• The agent process terminates immediately
• The expected OAuth consent flow never executes
• Logic that should return an empty list (to trigger OAuth) is never reached

I’m trying to understand whether:

1. This is a known issue with the ADK + MCP integration
2. There is a stable combination of versions for google-adk, mcp, and anyio that avoids this error
3. Anyone has found a workaround or fix for this behavior

Any guidance or suggestions would be greatly appreciated. Thank you!