Documents the deliberate narrowings vs main that kshitijk4poor asked to be
stated, each verified at this head: a launch that waits more than 10 s for
another launch's interrupted-pull repair exits 1 (main warned and
continued); the Windows git->ZIP fallback runs only from an untouched
checkout; a Desktop build refuses when the checkout's .git (where the
shared checkout lock lives) is not writable. Also states the S2 rule: an
unwritable host restart record falls back to the profile's marker only on
an install with no other profile, else the update refuses before moving.
9199fc8c30