diffLiveConfig walked `after` alone, so it had no branch for a path that
existed before the run and does not after. A test run that DELETES a file from
the developer's real config dir passed the guard silently -- the least
recoverable case in the threat model this guard exists to cover.
The review named the missing `pre.exists && !post.exists` branch. That branch is
necessary and not sufficient: deletion arrives in two shapes and it reaches only
one of them.
- A FIXED owned entry (GSD_OWNED_ENTRIES x roots, plus every extra target) is
recorded at both ends whether it exists or not, so a deletion reads
{exists:true} -> {exists:false}. This is the shape the named branch fixes.
- A gsd-prefixed child is DISCOVERED by readdirSync, so a deleted one is
absent from `after` entirely and never enters an after-keyed loop at all.
The named branch is unreachable for it.
So the walk is now over the UNION of both key sets, with the explicit branch for
the first shape and an `!post` branch for the second. Both are covered by a
test, and reverting the fix fails both -- the prefixed-child test is the one
that would still fail with only the prescribed branch in place.
Addresses review finding: Blocker 2.
6a1fbf96fd