Merge upstream b1f003e186 while preserving PM runtime ownership and
Python 3.14 worker startup, Windows signing, and macOS wait recovery.
Keep retired runtime modules deleted. Port upstream updater preflight
checks into the checkout strategy and preserve live build logging.
Carry checkpoint filename handling and process recovery into the current
module layout. Regenerate locks and adapt incoming platform test markers.
Focused Python and JavaScript tests, desktop and root-test typechecks,
conflict-path lint checks, lock validation, and retired-import checks pass.
The full test suite and packaged release builds were not run.
Use mktemp -d before launching the optional UI; skip UI if allocation fails. Native Chrome collision and allocation-failure probes preserve preexisting directories.
Track the path actually launched, preserving the no-UI case and unrelated profiles. Adapted the ownership approach from #104362.
Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>
