Review follow-ups on the #96187 cherry-pick: skip on win32 like the
sibling tests that shell out; reuse the file's `exec` helper; one temp
root so a failing second mkdtemp cannot leak the shim dir; quote the
shim's redirect target; guard the payload-prefix sentinel so a renamed
loop marker can never make the test execute the real spawn payload;
drop the lockMetadata fields the assertions never read. Move the
mutexPath contract into withRemoteUpdateMutex's doc comment instead of
a third inline restatement.
kshitijk4poor
06402ecb7c