Changes to EXPLICIT, authenticated, audited rollback of a plugin to a PRIOR version (1.5.0). Validates the target artifact (structure + trust) with the anti-downgrade floor lowered to EXACTLY the target's own version; a lower or untrusted artifact still fails (a rollback authenticates the OPERATOR, never the bytes). Persists the version pin to the overlay (survives restart) and hot-swaps via the same rebuild-and-swap path as plugins/reload