[methatp0]

Fixes gh-159964.

Capture a copy of the submitting thread's context for each submitted task and execute the callable within that context. This prevents a task from inheriting stale context from whichever worker happened to start first and keeps context-variable rebinding in one task isolated from subsequent tasks.

The change includes a regression test for context propagation across reused workers, documentation, and a NEWS entry.

Validation: lint and the C API documentation check pass. The full CI matrix is running; the local CPython test suite could not be run in this environment.

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[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #35288083 | 📁 Comparing 526dfe8 against main (b577a54)

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2 files changed

± library/concurrent.futures.html
± whatsnew/changelog.html

[ngoldbaum]

Thanks for the patch. I was planning to work on this issue, and I’ll take it from here. The proposed change fixes the reproducer, but unconditional context propagation also changes downstream behavior. I want to think about compatibility questions and performance before settling on an implementation. I’m closing this PR to avoid parallel work; I’ll follow up on the issue.