GeezerVison

Summary

Split the portable descriptor/termination fixes out of #8954 for the current Python 3.14 main branch.

• Close raw CRT descriptor numbers in os.closerange, ignoring close errors as required. A range can contain already-closed descriptors and cannot safely be represented by OwnedFd values.
• Use the host CRT _exit for Python os._exit, failed child exec, the fatal-signal fallback, and faulthandler's exit=True watchdog. Ordinary interpreter shutdown and the non-host fallback are unchanged.

The diff is four Rust files, with no canonical test, workflow, dependency, or profile changes.

Validation

Independently tested on the main-based commit, rather than reusing the mega-PR results:

• Normal commit hooks and strict workspace/C-API Clippy passed.
• Workspace tests: 1,352 passed, 18 ignored; separate C-API tests: 116 passed, 4 ignored.
• C-API-enabled dev and CI production-feature release builds passed, with the Python 3.14 runtime and this checkout's test-source paths verified.
• Both existing test_os closerange cases, full FileTests, test_atexit, and three canonical child-failure cases passed. Existing platform/implementation skips are unchanged.
• A child-scoped native C fixture verified that normal exit runs C atexit handlers and flushes buffered C stdio, while os._exit(0/37) and watchdog exit=True do neither. Failed child exec avoids inherited C exit handlers while the parent still cleans up normally. This passed in dev and release builds.

Full local test_os was not run because the sandbox denies its asyncio AF_UNIX socketpair. The unchanged hosted tests remain enabled. Local execution was Linux only; cross-platform CI is pending.

AI assistance

Codex assisted with implementation, extraction, source review, and validation. Both commits retain their Assisted-by disclosure trailers.