nx_neverbrick_gate.nx

nx_neverbrick_gate.nx -- proves the Rule-26 reversibility classifier actually discriminates, and that it fails CLOSED. Rule 26 says never-brick must be proven mechanically, never asserted; this is the proof, and it calls the SHIPPING functions in nx_mcu_brick.nx so it cannot drift from what a real write chokepoint runs. NON-VACUITY IS THE POINT. Two failure modes would make this gate a liar, so both have controls: - a classifier that returns RED for EVERYTHING passes every safety test and blocks the product. T4 and T8 are the positive controls: the real esp32-ai flash workload MUST come back GREEN. - a classifier that returns GREEN for everything would sail through the positive tests. T1/T2 are the negative controls: undeclared and null namespaces MUST come back RED. - T7 is the neg-control on T6's READER: if nb_efuse_kills_recovery returned 1 unconditionally, T6 would pass while measuring nothing. A check and its own neg-control failing together means the instrument is broken. T5 is the keystone assertion: the same flash write that is GREEN with the ROM download path intact MUST be RED once DIS_DOWNLOAD_MODE is burned. Flash reversibility is conditional, not intrinsic. license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0