Brummel
6966cce702
Eight tasks addressing the architect's two [high] drift items (lambda-captures-of-mut-var diagnostic + codegen comment cleanup), two [medium] items (stale mut.1-stub history comments in DESIGN.md and codegen), plus the bench compile_check.py check_ms regression (~30-50% relative; closed by short-circuiting the empty mut_scope_stack walk in synth's Term::Var arm). Architect's [low] item (prose render of MutVar drops type annotation) deliberately deferred per architect recommendation — prose surface design is itself pending. Plan unblocks the follow-on Stateful-islands milestone (effect- handler infrastructure + !Mut + refs) per architect gate.