Function write_gpu_hex 

pub fn write_gpu_hex(
    eng: &SimtEngine,
    vectors: &[(Vec<Vec<i64>>, Vec<bool>)],
) -> (String, String)

Build the golden input/output hex, computing the outputs with eval_gpu_simt — the reference the silicon lock separately certifies bit-identical to the VM (so these goldens ARE the VM oracle). The input hex is one word per load slot per vector (uniforms, mask, then per-lane varyings — the load_slots order); the output hex is each lane output then the reduced scalar. vectors[t] provides (lane_inputs, mask) for vector t. Returns (in_hex, out_hex).