[AnthonyRonning]

The stale-draft sweep test failed during 0.0.8 preparation at its final deletion assertion. Its fixture closed one File handle and assumed the lease was gone, although duplicated or inherited descriptors can retain that OS lock.

Explicitly unlock the fixture's lease before checking abandoned-copy cleanup, and derive the synthetic age from the directory's recorded modification time. Add a Unix regression proving that a duplicated descriptor still protects the payload after the original handle closes, and that cleanup succeeds after explicit unlock. Production staging, cleanup and lock checks are unchanged.

Validation:

• All nine focused staging tests passed.
• The same nine tests passed in 40 independent processes at eight test threads: 360 passes, no failures.
• Full pinned Agent just ci passed: all four strict Clippy configurations, warning-denied build/tests, 759 runtime tests, 1,010 desktop tests, 307 headless tests and 65 updater tests.
• All required commit hooks passed. Hosted Agent CI, Dev packages and downloaded Linux verification, and store performance passed at f4762293: 21 successful checks and 18 intentional skips.

The original failure log did not record which sweep guard or removal step prevented deletion, so this does not attribute that particular run to a fork or establish a production cleanup defect. Agent 0.0.8 remains on hold for review; this PR changes no app versions or runtime behavior.

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}