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fix(mcp): skip session pooling for HTTP/SSE transports to avoid anyioRuntimeError (#3203) (#3224)

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* fix(mcp): skip session pooling for HTTP/SSE transports to avoid anyio RuntimeError (#3203)

  HTTP/SSE transports use anyio.TaskGroup internally for streamable
  connections. These task groups have cancel scopes bound to the async task
  that created them, so closing a pooled session from a different task
  raises RuntimeError. Restrict session pooling to stdio transports only.

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* docs: clarify MCP pooling applies only to stdio tools

Agent-Logs-Url: https://github.com/bytedance/deer-flow/sessions/2dd9881d-54c6-45fd-90bc-154a09e29841

Co-authored-by: WillemJiang <219644+WillemJiang@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
This commit is contained in:
Willem Jiang
2026-05-27 08:32:57 +08:00
committed by GitHub
parent 92905e9e3e
commit 162fb2143e
2 changed files with 90 additions and 4 deletions
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backend/packages/harness/deerflow/mcp/tools.py
+13 -4
View File
@@ -1,4 +1,4 @@
"""Load MCP tools using langchain-mcp-adapters with persistent sessions."""
"""Load MCP tools using langchain-mcp-adapters with stdio session pooling."""
from __future__ import annotations
@@ -173,8 +173,10 @@ def _make_session_pool_tool(
async def get_mcp_tools() -> list[BaseTool]:
"""Get all tools from enabled MCP servers.
Tools are wrapped with persistent-session logic so that consecutive
calls within the same thread reuse the same MCP session.
Tools using stdio transport are wrapped with persistent-session logic so
consecutive calls within the same thread reuse the same MCP session.
HTTP/SSE tools are returned unwrapped to avoid cross-task TaskGroup
cleanup errors.
Returns:
List of LangChain tools from all enabled MCP servers.
@@ -251,6 +253,9 @@ async def get_mcp_tools() -> list[BaseTool]:
logger.info(f"Successfully loaded {len(tools)} tool(s) from MCP servers")
# Wrap each tool with persistent-session logic.
# Only pool stdio sessions. HTTP/SSE transports use anyio TaskGroups
# internally which cannot be closed from a different async task, so
# pooling them causes RuntimeError on cleanup (see #3203).
wrapped_tools: list[BaseTool] = []
for tool in tools:
tool_server: str | None = None
@@ -260,7 +265,11 @@ async def get_mcp_tools() -> list[BaseTool]:
break
if tool_server is not None:
wrapped_tools.append(_make_session_pool_tool(tool, tool_server, servers_config[tool_server], tool_interceptors))
transport = servers_config[tool_server].get("transport", "stdio")
if transport == "stdio":
wrapped_tools.append(_make_session_pool_tool(tool, tool_server, servers_config[tool_server], tool_interceptors))
else:
wrapped_tools.append(tool)
else:
wrapped_tools.append(tool)