DMG failures lose their useful state when dmgbuild performs forced
cleanup. Capture open handles immediately after a failed native detach,
before the supplier retries or cleans up the staging image.
Use the resolved dmgbuild toolset and its paired Python interpreter.
Report scoped lsof results, including process IDs, descriptors and paths.
Keep detach results, arguments, signing and retry policy unchanged.
Verification: three JS tests and two portable Python tests pass.
The macOS held-file test is added but skipped on this Windows host.
Real builder download/interception and Node-to-Python wiring pass.
ESLint, Ruff, syntax and new-file formatting checks pass.
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