nx_buildmode_gate.nx

nx_buildmode_gate.nx -- THE REFEREE for nx_buildmode_lib (LN44, 2026-09-03). The subject decides which flags the build lane hands the compiler, so its failure modes are expensive in both directions: too eager and it silently changes every artifact in the estate on adoption day; too quiet and the estate keeps shipping its slowest mode. The load-bearing tooth here is therefore the SAFETY property, not the feature: with NO conf present the reader must return ZERO flags and an EMPTY cache-key token, so adopting the lib cannot change one byte of one artifact until somebody writes a row. THE CACHE-KEY TOOTH IS NOT DECORATION. nx_sov_build_run caches artifacts under a key that today encodes the compiler sha, the assembler sha and the debug flag. A mode that changes emitted code without entering that key would serve an artifact compiled under the OTHER mode and present it as a cache hit -- silently correct-looking and wrong. So the gate asserts two different modes yield two different tokens, and that no mode yields an empty one. Fixture is PER-RUN via gk_fixture_dir, so two concurrent runs cannot clobber each other into a false SKIP -- the defect measured on nx_bck_elide_gate the same day this shipped. exit: 0 GREEN . 1 RED license_tier: ORIGINAL No hw writes.