[Bug] Failed to connect to remote mcp server

[qingfei1994]

Search before asking

• I searched in the issues and found nothing similar.

Description

I customized a ReactAgent with a remote mcp server something like this.

class ReActAgentWithMCP(ReActAgent):
    """ReAct Agent with MCP integration."""
    @mcp_server
    @staticmethod
    def my_mcp_server() -> MCPServer:
        """Define MCP server connection."""
        return MCPServer(endpoint="https://xxxx/mcp/")

But fail to use MCP server.

2026-01-06 14:31:37,332 - INFO - Using Any for unsupported type: typing.Sequence[~T]
2026-01-06 14:31:37,400 - INFO - No module named google.cloud.bigquery_storage_v1. As a result, the ReadFromBigQuery transform *CANNOT* be used with `method=DIRECT_READ`.
2026-01-06 14:31:37,619 - INFO - HTTP Request: POST https://test.work/mcp/ "HTTP/1.1 200 OK"
2026-01-06 14:31:37,619 - INFO - Negotiated protocol version: 2025-03-26
2026-01-06 14:31:37,661 - INFO - HTTP Request: POST https://test.work/mcp/ "HTTP/1.1 202 Accepted"
2026-01-06 14:31:37,841 - INFO - HTTP Request: POST https://test.work/mcp/ "HTTP/1.1 200 OK"
  + Exception Group Traceback (most recent call last):
  |   File "/flink-agents/python/flink_agents/examples/react_agent_diagnose.py", line 140, in <module>
  |     main()
  |   File "/flink-agents/python/flink_agents/examples/react_agent_diagnose.py", line 128, in main
  |     .apply(log_analysis_react_agent)
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/runtime/remote_execution_environment.py", line 97, in apply
  |     self.__agent_plan = AgentPlan.from_agent(agent, self.__config)
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/plan/agent_plan.py", line 137, in from_agent
  |     for provider in _get_resource_providers(agent):
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/plan/agent_plan.py", line 330, in _get_resource_providers
  |     _add_mcp_server(name, resource_providers, mcp_server)
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/plan/agent_plan.py", line 380, in _add_mcp_server
  |     for prompt in mcp_server.list_prompts()
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 259, in list_prompts
  |     return asyncio.run(self._list_prompts_async())
  |   File "/opt/homebrew/Cellar/python@3.10/3.10.19_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/runners.py", line 44, in run
  |     return loop.run_until_complete(main)
  |   File "/opt/homebrew/Cellar/python@3.10/3.10.19_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/base_events.py", line 649, in run_until_complete
  |     return future.result()
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 263, in _list_prompts_async
  |     async with self._get_session() as session:
  |   File "/opt/homebrew/Cellar/python@3.10/3.10.19_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/contextlib.py", line 217, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 175, in _get_session
  |     async with streamablehttp_client(
  |   File "/opt/homebrew/Cellar/python@3.10/3.10.19_1/Frameworks/Python.framework/Versions/3.10/lib/python3.10/contextlib.py", line 217, in __aexit__
  |     await self.gen.athrow(typ, value, traceback)
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/mcp/client/streamable_http.py", line 480, in streamablehttp_client
  |     async with anyio.create_task_group() as tg:
  |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 781, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/mcp/client/streamable_http.py", line 504, in streamablehttp_client
    |     yield (
    |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 175, in _get_session
    |     async with streamablehttp_client(
    |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 781, in __aexit__
    |     raise BaseExceptionGroup(
    | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Traceback (most recent call last):
      |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 186, in _get_session
      |     yield session
      |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/flink_agents/api/tools/mcp.py", line 264, in _list_prompts_async
      |     prompts_response = await session.list_prompts()
      |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/mcp/client/session.py", line 423, in list_prompts
      |     return await self.send_request(
      |   File "/flink-1.20.3/bin/test_venv/lib/python3.10/site-packages/mcp/shared/session.py", line 288, in send_request
      |     raise McpError(response_or_error.error)
      | mcp.shared.exceptions.McpError: prompts not supported

I guess the reason is that the mcp server I used doesn't provide list_prompts interface.
is it possible for Users to manually defining them in the MCPServer constructor instead of fetching it thru the mcp server?

How to reproduce

defining an agent with a defined MCP server without list_prompts interface

Version and environment

master, flink version 1.20.6

Are you willing to submit a PR?

• I'm willing to submit a PR!

[wenjin272]

Hi, @qingfei1994, thanks for your reporting this bug.

I think the reason is indeed what you said, the custom mcp server doesn't provide list_prompts interface. In current implementation, flink-agents will always try to call the list_prompts of mcp server when compile the agent plan.

I think we should support the mcp server without any prompts to provide. But I don't quite understand what "defining them in the MCPServer constructor" means. I see you are willing to submit a PR, so if possible, we can discuss this in the PR.

[qingfei1994]

@wenjin272 What I mean by "defining them in MCPServer constructor" is something like this.

class ReActAgentWithMCP(ReActAgent):
    """ReAct Agent with MCP integration."""
    @mcp_server
    @staticmethod
    def my_mcp_server() -> MCPServer:
        """Define MCP server connection."""
        return MCPServer(endpoint="https://xxxx/mcp/",prompts=[prompt])

when declaring a MCPServer within an agent, passing the prompt to the constructor so that agents could use. Let me submit a PR to well explain my idea.