Function w4a16_v3_kernel 

pub fn w4a16_v3_kernel(gpu: &dyn GpuBackend) -> KernelHandle

2026-09-25: The w4a16_gemm_t_m128_v3 handle. KernelHandle(0), with no lookup and so no boot-audit row, unless METRALE_W4A16_VARIANT=v3; then it panics when the target lacks the kernel. Its user (qwen3_attention/prefill_weights.rs) launches it only for v == 3 and a nonzero handle.