Self-review follow-ups on the salvage of #33177 + #33188 + #33209:
W3 (real, lock_path.write_text was non-atomic AND the read path silently
resets data to an empty installed dict on JSONDecodeError — a crash mid-
write could nuke ALL hub provenance, not just official-optional). Switch
to the same mkstemp + fsync + atomic_replace pattern that _write_manifest
already uses in this module.
W5 (dead code) — _validate_category_name had one caller on origin/main
(install_from_quarantine), swapped to _validate_install_parent_path by
#33177. Remove the now-unused definition to avoid the attractive-nuisance
of contributors picking the wrong validator.
Behavior preserved on the happy path; verified all 200 skills/hub tests
plus the three E2E scenarios (destructive restore, backfill idempotency,
adversarial nonexistent skill) still pass after both fixes.
0537e2600d