readClaudeUsage() and readHostSnapshot() validated the stored receivedAt
with new Date(), which accepts "1" or a bare date. Both now go through
isIsoTimestamp(), exported by claude-usage.js and built on the sanitizer's
own check, so no regex is duplicated.
The existing 500 tests failed at mkdir, before the temp file existed, so
removing the unlinkSync() cleanup of either writer left the suite green. Two
new cases make the rename fail after the temp write (the target is a
non-empty directory) and require that no temp file is left.
Refs #54
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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