Test loads real model weights, runs attention forward for layers 0-4, compares production B1 mixed FP8 FMHA output vs PyTorch SDPA reference. This will reveal the FMHA cosine degradation (was 0.679 at L1) with real data patterns, not just synthetic random data. Production values: HD=512, NOPE=448, ROPE=64, H=128, 8 GPUs.