nx_frameab_gate.nx

nx_frameab_gate.nx -- THE REFEREE FOR THE FRAMETRACE A/B WIRING (nx_frameab). nx_abstat_gate already proves the STATISTICS. This gate proves the three things nx_frameab adds on top of them, each of which can be wrong while the arithmetic stays perfect: 1. the CONFOUND GUARD, in BOTH directions -- a guard that refuses everything passes every deny test, so the positive control (an identical-budget pair it must ALLOW) is the load-bearing tooth here; 2. the two per-frame INDICATOR DERIVATIONS at their boundaries, where an off-by-one hides; 3. the end-to-end push, so a real window really does produce the axis verdicts claimed. license_tier: ORIGINAL No hw writes (Rule 26).