Python: Isolate MCP lifecycle task context

[Jose Alvarez (jpalvarezl)]

Motivation & Context

The MCP lifecycle owner may be created while request-scoped ContextVar values are active. Because asyncio.create_task() copies the current context, transient call-specific header state can otherwise become part of the long-lived connection task's context. Lifecycle-owned connection work must not retain that call-specific override, while unrelated request context must remain available during connection setup.

Description & Review Guide

• What are the major changes? Temporarily masks _mcp_call_headers while creating the lifecycle-owner task, then immediately restores the caller's value. A regression test verifies that the owner does not inherit call-scoped headers while preserving unrelated ContextVar state.
• What is the impact of these changes? Connection-lifetime work no longer retains transient call-header overrides, while legitimate request context remains available. There is no public API change, and the implementation remains compatible with the Python 3.10 support floor.
• What do you want reviewers to focus on? The narrow context boundary around task creation and whether the regression test captures both header isolation and preservation of unrelated context.

Related Issue

N/A - trivial change. Using the right context for run.

AI Assistance

• No material AI assistance was used.
• This is an AI-assisted contribution. I reviewed, understood, and verified all submitted content and accept responsibility for it.

AI assistance details: Implementation, regression testing, and PR description.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR links to an agreed issue with no competing open PR, or the Related Issue section documents a trivial-change or repository-automation exception.
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" in the title prefix, before or after a language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

🟡 Changes recommended

Initial authentication breaks for documented ContextVar-backed header providers unless credentials are resolved before entering the isolated context.

1 open finding

• Owner isolation loses caller ContextVar credentials during handshake · New

What changed in this PR

Isolates Python MCP lifecycle tasks from transient caller context without changing the public API.

Changes:

• Creates the lifecycle-owner task inside an empty Context.
• Adds a regression test for call-header context isolation.

File	Description
python/​packages/​core/​tests/​core/​test_mcp.py	Tests that lifecycle work does not inherit call headers.
python/​packages/​core/​agent_framework/​_mcp.py	Isolates lifecycle task context at creation.

🧠 Review effort: Balanced

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[github-actions]

MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): 55f8deeeb88b
Model: gpt-5.6-sol

Overview

The PR creates the MCP lifecycle-owner task in a fresh context, and its focused regression test demonstrates that framework call-header state is not retained by the owner. Existing lifecycle locks, cancellation cleanup, and Python 3.10-compatible task creation are strong guardrails. However, clearing the entire context also removes the documented user ContextVar credential source for streamable HTTP header providers, which can break or mis-authenticate the initialization handshake.

Reviewed the supplied pull-request change set across correctness, security/reliability, architecture, and failure behavior.
1 verified finding remained after source verification (1 high) across 1 file. Details are attached to the affected lines below.

Affected areas: python/packages/core/agent_framework/_mcp.py

[github-code-quality]

Code coverage overview

Languages: Python

Python / code-coverage/python

main 8a365f4	jpalvarezl-mcp-heade... 080bc11	+/-
92%	92%	0%

ℹ️ Calculations represent line coverage. Results may change as calculations are updated.