/pre-land-refuters — unbiased dual-model validation before landing

Loop position: move 6 (prove acceptance) of the operating loop — the shared-trunk pawl: fresh-context refuters attack the completion claim before landing.

Proven in the ag-s43tg prune landing (2026-06-12): the refuter panel caught 9 real misses self-review passed over — a silently-failed edit, a CI-breaking test, stale image manifests, gate-weakening test retirements, and an upstream delete/modify conflict. Self-review is biased toward "looks good"; refuters are prompted to win by finding what's wrong.