nx_gk_fixture_gate.nx

nx_gk_fixture_gate.nx -- THE REFEREE FOR gk_fixture_dir, the per-RUN gate fixture directory (2026-09-03). THE DEFECT IT GUARDS, measured the day it shipped. Two runs of nx_bck_elide_gate launched in the same second against two DIFFERENT compilers BOTH returned verdict=SKIP with "the named compiler built none of the fixtures". Neither run was faulty; the pass under test was working (its own log showed BCK-ELIDE sites=4 elided=2 throughout). They had overwritten each other's fixtures in the single directory both had hardcoded. Run sequentially, the same gate on the same box is 13/13 GREEN. The estate already enforced the PER-GATE half of this law (gate scratch in /tmp/<gate>/, never shared with a production beat). The PER-RUN half did not exist, and its absence fails in the ABSTAINING direction -- a false SKIP acquits nothing and alarms nobody, it just deletes the evidence. THE ANTI-VACUITY PROBLEM THIS GATE HAD TO SOLVE. A tooth saying "gk_fixture_dir returned a path" passes for a function that returns a CONSTANT, which is precisely the broken shape. So the load-bearing tooth is that TWO calls differ, and it is paired with a NEGATIVE CONTROL that builds the OLD constant-path shape by hand and asserts it COLLIDES. Without that control a reader cannot tell a working discriminator from a test that could never fail. exit: 0 GREEN . 1 RED license_tier: ORIGINAL No hw writes.