Same shape as the POSIX hand-off: windows.ps1 heartbeats line 2 from its
own process, so `taskkill /F` (no finally runs) left line 1 naming a dead
pid while the resumed `hermes update` (the line-4 delegate) or a completion
survivor still held the checkout, and an old packaged Desktop - which judges
lines 1 and 2 alone - deleted the marker and booted its backend.
After its claim the hand-off starts a hidden watcher (-MarkerOp custody
-CustodyOf <pid>, Start-MarkerCustodian). Once the hand-off exits with its
claim still published and the delegate running or the checkout lock held,
the watcher names itself on line 1 under the marker lock, heartbeats line 2
and releases the marker when both end (bounded like the R6 wait).
Invoke-MarkerRelease stops the watcher once the hand-off's own release is
decided. The Windows kill-cell test now also runs the reader be3fd671d7
shipped; that reader runner moves to a helper shared with the POSIX test.
d899d5a74b