A document rendered after the LEGS table broke is accepted as current by the pre-fix parser with no gate column at all, so mutant-doc-drifts alone would pass a tree that never had the column. The new leg reads that same mutant's fresh render and requires rc 0 with a '-' cell, pinning the failure mode the repair removes. Measured: q132_verify.py 9 legs, 0 fault, rc 0.