Python: Scope MCP headers to transport requests

[SergeyMenshykh]

Motivation & Context

When multiple MCP tools reuse the same HTTP client, provider output should remain associated with the transport request that initiated it. This keeps shared-client behavior deterministic while retaining the existing construction and connection model.

Description & Review Guide

• What are the major changes?
  • Add a private HTTP client proxy that associates MCP transport requests with their originating tool.
  • Scope header_provider request-hook processing to matching transport requests.
  • Remove tool-specific request hooks on close and restore them on reconnect.
  • Preserve provider-header handling across same-origin requests and redirects.
  • Add regression coverage for shared clients, tools without providers, hook lifecycle, delegation, and redirects.
• What is the impact of these changes?
  • Tools can continue sharing an httpx.AsyncClient with consistent per-tool provider behavior. There are no public API changes.
• What do you want reviewers to focus on?
  • The private proxy delegation and the request-hook lifecycle during connection, redirects, close, and reconnect.

Related Issue

N/A — no public issue. Related PR #7892 adds static connect-time headers; this PR instead scopes existing header_provider processing when an HTTP client is reused.

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 is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after any language prefix) — a workflow keeps the label and the title prefix in sync automatically.

[Copilot]

🟡 Changes recommended

Redirect chains can retain and expose previously injected headers when the provider’s key set changes.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Scopes MCP provider headers per tool when sharing an HTTP client.

Changes:

• Adds a transport proxy and tool-specific request ownership.
• Manages hooks across close, reconnect, and redirects.
• Adds regression tests and guidance.

File summaries

File	Description
python/packages/core/agent_framework/_mcp.py	Implements scoped header injection and cleanup.
python/packages/core/tests/core/test_mcp.py	Tests sharing, delegation, lifecycle, and redirects.
python/packages/core/AGENTS.md	Documents header-provider request scoping.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced

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[github-actions]

MAF Automated Review — Iteration 1

Result: Findings reported
Scope: full PR (1 commit(s)): 9e90a73c3951
Model: gpt-5.6-sol-fast

Overview

The PR scopes shared-client header providers by tagging transport requests with a per-tool owner, delegates the underlying HTTP client surface, and removes and restores request hooks across normal close and reconnect. Owner checks, cross-origin stripping, and shared-client lifecycle tests provide strong coverage for ordinary request and redirect flows. A cancellation race remains: the caller can detach the authentication hook while the lifecycle owner is still performing transport teardown.

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

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