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

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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.
This commit is contained in:
Willem Jiang
2026-05-26 09:15:21 +08:00
parent f9b7071304
commit 2d84ddb1ae
2 changed files with 81 additions and 1 deletions
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backend/packages/harness/deerflow/mcp/tools.py
+8 -1
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@@ -251,6 +251,9 @@ 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 +263,11 @@ 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)