gates.snapshot.json listed ~800 file paths under their config, so every
new or deleted frontend file regenerated it (31% of commits, E34 S2) and
the regen diff buried the gate changes it exists to show. Now a scope is
named by path (scopeOf: src, src tests, ui, lib tests, …), the snapshot
holds one effective config per scope (2345 → 1456 lines), and a new test
fails when a file's config is not its scope's.
Not narrowed: a new file in a known place changes nothing (it gets its
scope's config, checked), a glob that moves one file into another config
fails (seen: an override on Feed.tsx → "src: src/components/Feed.tsx"), a
scope whose rules change is a snapshot diff, and a file no config lints
is still a register miss.