nx_artifactdrift_gate.nx

nx_artifactdrift_gate.nx -- THE BITE PROOF FOR THE FORK-ROOT AXIS (2026-08-31). WHY THIS GATE EXISTS. On 2026-08-31 a compare regen returned `published=201 fails=0 verdict=GREEN` and published NOTHING: every one of the 201 lines reported prev= EQUAL to its new byte count. The cause was a THIRD TWIN nobody was censusing -- nx_compare_regen chdirs into buildroot and forks the BARE path `_offc/nx_swcompare_*.elf`, so buildroot/_offc is the copy the publisher actually executes, and /api/promote never writes it. FOUR INDEPENDENT AGENTS each verified their promote against the serving root and/or nishihost/_offc and all four missed it, because nx_catalog enumerates SOURCE/BUILT/STAGED/PROMOTED/_offc and NOT buildroot/_offc -- so every row read BUILT==PROMOTED. nx_artifactdrift grew a FORK-ROOT axis for exactly this. That axis had never been proven to go SILENT. A detector that has only ever fired on real data is HALF verified: firing proves it can speak, never that its silence means anything. A GREEN THAT NEVER HAD A CORRESPONDING RED IS UNVERIFIED -- AND SO IS A RED THAT NEVER HAD A CORRESPONDING GREEN. THIS GATE NEVER TOUCHES buildroot/_offc. The subject fork root is argv[7], overridable precisely so a gate can point the axis at a FIXTURE tree. A gate that must perturb the directory the compare publisher forks in order to report on it is a gate that can take the estate down to test itself. Every fixture lives under /tmp/nx_artifactdrift_gate/ and the subject trend log is redirected there too, so this can never append to knowledge/status/artifactdrift.log -- a gate must not share its fixture with a production beat. THREE LEGS, because the axis has three honest answers and all three must be proven: RED a planted twin that differs -> FIRES and NAMES it, carrying BOTH byte counts GREEN a byte-identical twin -> SILENT (FORK-STALE=0 and no offender line at all) ABSTAIN a fork root it cannot open -> UNPROVEN, and must NOT report agreement The GREEN leg additionally asserts the twin was EXAMINED (FORK-IDENTICAL=1): a zero from an EMPTY directory is the gate-passes-on-the-empty-set defect, and would look exactly like a real green. Exit carries the verdict via gv_verdict (0 GREEN / 1 RED / 3 SKIP). license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0