fix(windows): preserve worker recovery errors

[knewstimek]

Fix Windows worker recovery after retained logs exhaust _wmktemp's small name space.

cbm_mkstemp now draws a random six-digit suffix and opens the file exclusively. If recovery setup fails, the original worker outcome remains the reported error. Artifact creation also logs its errno.

The Windows regression test retains 64 files from one template. It fails before this change, when _wmktemp runs out of names, and passes with the fix.

Split from #2268. No encoding or compile database changes.

[github-actions]

Thanks for opening this — it has been seen, and it is queued.

This note is automated, but it is not a brush-off: it exists so you know where your PR stands instead of having to guess from silence.

Current review status: working through a backlog. 0.9.1-rc.1 is out, so the release freeze that held reviews is over — but it left a large queue of open pull requests behind it, and we are reading through them oldest-first. The background is in discussion #1144.

What that means for this PR, concretely:

• It will not be closed for inactivity. No stale bot touches pull requests here.
• It may still sit a while before a human reads it. That is on us, not on you.
• Older PRs are read first, so a recent one is not being skipped — it is behind a queue.

Things that will genuinely speed it up whenever review does happen:

• Keep it rebased on main — the tree is moving quickly right now, and a conflicting branch cannot be reviewed as the diff you intended.
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If this fixes a bug, a reproduction we can run is worth more than a description of the symptom.

Thanks for contributing, and sorry in advance for the wait.

[DeusData]

Merged — thank you, @knewstimek. Running out of mkstemp names once a worker keeps more than a few dozen temp files is exactly the kind of Windows-only failure that shows up only under real load, and your deterministic test pins it well.

We confirmed it in both directions on our Windows ARM64 VM before merging:

• main + your test only: platform_mkstemp_retained_files_exceed_crt_namespace fails at test_platform.c:488 (descriptor >= 0), with everything else passing;
• your PR merged onto today's main: the platform suite passes, 25/25, including that test.

Two small follow-ups, neither a blocker:

1. In cbm_mkstemp, save errno right after _wopen fails. The retry loop's later calls can overwrite it before it is reported.
2. The two clang-format reflow hunks in tests/test_platform.c (the segment[] literal and the unreadable[] list) are unrelated to the fix. Leaving such hunks out of future PRs keeps git blame pointing at the real change.

Thank you again for the careful Windows work.