Add assess_already_landed_handoff_report verifier to block Pinned reviewed
head, Scratch worktree used, legacy Mutations/Workspace mutations None when
git fetch or other mutations occurred, and narrative/handoff drift after the
already-landed gate fires. Wire into build_final_report and review_proofs.
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
