MCPClient hangs when connecting to GitHub MCP server with streamable_http transport

[sicoyle]

Dapr Agents MCPClient.connect_streamable_http() hangs indefinitely when connecting to GitHub's MCP server (https://api.githubcopilot.com/mcp/) and calling list_tools() or other operations that return SSE responses.

The issue only occurs outside of debuggers - when running with a debugger attached, the timing overhead prevents the race condition and it works correctly.

Root Cause:
GitHub's MCP server only supports POST requests, not GET. The MCP SDK's streamablehttp_client transport has bug:

1. Background GET stream starts: streamablehttp_client launches a background task for server-initiated SSE messages via GET
2. GitHub returns 405: GitHub doesn't support GET, returns "405 Method Not Allowed"
3. The GET stream retries twice (1 second each), then the background task exits
4. When subsequent POST requests return text/event-stream content (like tools/list), the transport's SSE response handling expects the GET stream task to be alive for coordination
5. Since the GET stream task is dead, the POST SSE response waits forever

You can repro consistently with https://github.com/sicoyle/release-note-agent

Relevant logs:

INFO:httpx:HTTP Request: POST https://api.githubcopilot.com/mcp/ "HTTP/1.1 202 Accepted"
INFO:httpx:HTTP Request: GET https://api.githubcopilot.com/mcp/ "HTTP/1.1 405 Method Not Allowed"
INFO:mcp.client.streamable_http:GET stream disconnected, reconnecting in 1000ms...
INFO:httpx:HTTP Request: POST https://api.githubcopilot.com/mcp/ "HTTP/1.1 200 OK"
DEBUG:mcp.client.streamable_http:Sending client message: root=JSONRPCRequest(method='tools/list'...)
# Hangs here

There are currently many hanging related issues on the MCP python sdk repo:
https://github.com/modelcontextprotocol/python-sdk/issues?q=is%3Aissue%20state%3Aopen%20hang

So, Dapr Agent users will likely also experience issues relating to the MCP Client and streamable_http transport, any POST_only MCP server, and Github's MCP server.

[sicoyle]

made the mcp pkg issue modelcontextprotocol/python-sdk#1941

[sicoyle]

update: I am waiting on feedback on my upstream PR for this. This will not occur for every MCP server, and is a silent bug I've propagated the error on in the MCP SDK repo so users in Dapr Agents land can get feedback if this occurs.

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 60 days. It will be closed in the next 7 days unless it is tagged (pinned, good first issue, help wanted or triaged/resolved) or other activity occurs. Thank you for your contributions.

[github-actions]

This issue has been automatically closed because it has not had activity in the last 67 days. If this issue is still valid, please ping a maintainer and ask them to label it as pinned, good first issue, help wanted or triaged/resolved. Thank you for your contributions.