nx_mcu_q4_gate.nx

nx_mcu_q4_gate.nx -- pins the int4 x int8 MCU kernel to EXACT integer answers. Every expectation below is hand-computable, so this gate asserts EQUALITY, not closeness. That matters: the two classic ways to get this kernel wrong -- swapping the low/high nibble order, and reading int8 activations as unsigned -- both still produce plausible, well-scaled numbers. A tolerance-based check would wave them through. So each control is chosen so that the WRONG implementation yields a DIFFERENT NUMBER, and the gate names that number: T2 a swapped packer would emit 0x0F where we require 0xF0. T5b an unsigned read of byte 255 yields 255, not -1. T7b an unsigned-activation dot yields -2011, not 37 -- and the gate asserts it is NOT -2011. T12 is the composition property real inference depends on: summing per-group dots must equal the whole row dot, or every grouped matvec silently drifts from the reference. license_tier: ORIGINAL No hw writes (Rule 26). expect_exit: 0