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fix: serialize streamable-http MCP requests per session#2682

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seratch merged 2 commits intomainfrom
dev/elainegan/mcp-streamable-http-request-isolation
Mar 16, 2026
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fix: serialize streamable-http MCP requests per session#2682
seratch merged 2 commits intomainfrom
dev/elainegan/mcp-streamable-http-request-isolation

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@elainegan-openai elainegan-openai commented Mar 16, 2026

Summary

Serialize request RPCs per MCPServerStreamableHttp session so one failed request cannot cancel sibling in-flight requests that share the same underlying streamable-HTTP transport task group.

This is a narrow SDK-side workaround for the shared transport behavior in the mcp client dependency. It keeps the public API unchanged and only affects how MCPServerStreamableHttp schedules requests on a single connected session.

Test plan

  • make sync
  • make format
  • make lint
  • make typecheck
  • make tests
  • uv run python -m pytest tests/mcp/test_client_session_retries.py -k 'serialized_session_requests_prevent_sibling_cancellation or test_call_tool_retries_until_success' -q

Issue number

N/A

Checks

  • I've added new tests (if relevant)
  • I've added/updated the relevant documentation
  • I've run make lint and make format
  • I've made sure tests pass

@github-actions github-actions bot added bug Something isn't working feature:mcp labels Mar 16, 2026
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elainegan-openai commented Mar 16, 2026

@codex please review

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💡 Codex Review

openai-agents-python/src/agents/mcp/server.py

Lines 685 to 694 in 26d2fd0

return await self.session.list_prompts()
async def get_prompt(
self, name: str, arguments: dict[str, Any] | None = None
) -> GetPromptResult:
"""Get a specific prompt from the server."""
if not self.session:
raise UserError("Server not initialized. Make sure you call `connect()` first.")
return await self.session.get_prompt(name, arguments)

P2 Badge Serialize prompt RPCs with the session lock

MCPServerStreamableHttp enables _serialize_session_requests, but list_prompts/get_prompt bypass _maybe_serialize_request and call ClientSession directly. That leaves prompt RPCs able to run concurrently with tool RPCs, so one failed request can still cancel an in-flight sibling on the shared streamable-HTTP transport.

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@elainegan-openai
Serialize prompt RPCs with session lock
89106c1 
Route prompt RPCs through the existing request lock and add regression coverage for list_prompts/get_prompt so prompt calls cannot cancel in-flight tool calls on streamable HTTP.\n\nCo-authored-by: Codex <[email protected]>
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elainegan-openai commented Mar 16, 2026

@codex please review

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chatgpt-codex-connector bot commented Mar 16, 2026

Codex Review: Didn't find any major issues. 🎉

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  • Comment "@codex review".

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@seratch seratch changed the title Serialize streamable-http MCP requests per session fix: serialize streamable-http MCP requests per session Mar 16, 2026
@seratch seratch merged commit a5cd815 into main Mar 16, 2026
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@seratch seratch deleted the dev/elainegan/mcp-streamable-http-request-isolation branch March 16, 2026 02:54
@seratch seratch added this to the 0.12.x milestone Mar 16, 2026
@seratch seratch mentioned this pull request Mar 21, 2026
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