Workers runtime error in examples/mcp-worker-authenticated when restarting cursor

[jldec]

When restarting Cursor after configuring and authenticating the MCP in examples/mcp-worker-authenticated, I see the following error message.

The error is not fatal - subsequent requests will succeed, and the MCP tools keep working.

Steps to reproduce

• npm run dev in examples/mcp-worker-authenticated
• add MCP url to Cursor "Tools and MCP" settings:

  {
    "mcpServers": {
      "mcp-auth": {
        "url": "http://localhost:8787/mcp"
      }
    }
  }

• Click on the "Connect" button in the new MCP to authenticate in browser
• The 2 tools (hello and whoami) should become available - you can try calling them from the AI agent.
• Quit and restart Cursor - notice the errors in the console where the MCP is running. Usually I see 2 of these Errors, but sometimes as many as 5.
  ✘ [ERROR] Uncaught Error: The Workers runtime canceled this request because it detected that your Worker's code had hung and would never generate a response. Refer to: https://developers.cloudflare.com/workers/observability/errors/

Notes

• I have only been able to reproduce this with examples/mcp-worker-authenticated running in dev, and configured from Cursor.
• The issue does not occur e.g. when calling with MCP inspector, or Claude.
• I can reproduce reliably, but I believe this is timing sensitive. I'm running the latest main branch of this repo.
• When I tried to use a remote KV binding, the issue becomes harder to reproduce, but still happens intermittently.
• When I added logging to the example worker by parsing the request body early, and passing it to the handler, the issue stopped happening.
• I also cannot reproduce this when the worker is deployed to Cloudflare.

[jldec]

One theory may be that this is related to how Cursor does auth. I noticed that the scopes are none in the authentication dialog.

[jldec]

never mind, The MCP inspector also requests none for Scopes.

[mattzcarey]

Hey, I am probs not cleaning up a broken connection correctly. I'll look into this thanks.