nx_contentdiff_gate.nx

nx_contentdiff_gate.nx -- THE REFEREE FOR THE PROMOTE CAPABILITY RULER. WHY IT EXISTS: nx_contentdiff_lib is the arithmetic behind BOTH the hand-run oracle (nx_contentdiff) AND the staging guard inside md_promote_staged, i.e. it decides whether a promote is allowed to destroy printable content. On 2026-09-03 a census found it had NO GATE ANYWHERE -- the ruler that judges every promote in the estate was itself unjudged, so every property it claims rested on the fact that nobody had seen it misbehave. ★A GREEN THAT NEVER HAD A CORRESPONDING RED IS UNVERIFIED, and here there was not even a green: there was no test. It proves the properties the promote decision actually rests on: * the loss measure is CORRECT on constructed subset / superset / identical / disjoint inputs; * it is FAIL-CLOSED -- an empty or unreadable candidate is TOTAL loss, never clean (the direction that matters, because the flattering failure here silently blesses a broken artifact); * the SYMMETRY class names all four outcomes, so a rename cannot read as a removal; * the SOURCE-PATH partition is narrow enough that it cannot swallow real content, and it RECONCILES. license_tier: ORIGINAL Read-only. No hw writes (Rule 26). expect_exit: 0