Record Qwen arithmetic audit

PARITY.md

@@ -73,6 +73,48 @@ Comfy input dtype, full-precision weight construction, SDPA backend selection,
 and residual/BF16 rounding boundaries. Do not run another full inference merely
 to rediscover this projection result.
 
+## Qwen Layer-0 Arithmetic Audit After `4050afe`
+
+The follow-up statement audit covered every remaining active layer-0 arithmetic
+boundary outside the already-fixed SDPA wrapper: full-precision NVFP4 dispatch,
+weight/scales, `pre_quant_scale`, BF16 GEMM, activation layout, Q/K RMSNorm,
+O projection/residual, post-attention norm, SiLU/gate/up product, down
+projection, and final residual.
+
+**Result: no further source-proven active mismatch was found.** For the actual
+checkpoint, Comfy and direct both use BF16 input, BF16 NVFP4 dequantization,
+BF16 `F.linear`, no projection biases, identical pre-scale ordering, identical
+MLP evaluation order, and ordinary BF16 residual additions. Explicit flattening
+and `.contiguous()` in direct are not a demonstrated numerical difference for
+the captured contiguous batch-one input.
+
+Do not modify `nvfp4.py` or Qwen MLP/residual code to chase the remaining
+layer-0 delta. The next justified work is a bounded component experiment that
+identifies the actual selected SDPA kernel/GQA fallback and verifies capture
+consistency; it is not another full denoising or video run.
+
+### Bounded SDPA/Layer-0 Result
+
+The bounded replay was completed with the fresh projection-capture tensors.
+For the reference's 17-token layer-0 attention, both paths have native cuDNN
+GQA available (`flash=False`, `cudnn=True`, `efficient=False`). Therefore the
+direct SDPA wrapper takes the same native-GQA branch Comfy takes.
+
+| Boundary | Mean absolute error | Maximum absolute error |
+| --- | ---: | ---: |
+| O-projected attention | `0.000244372` | `0.0161562` |
+| First residual | `0.00026845` | `0.0213833` |
+| Post-attention RMSNorm | `3.87714e-05` | `0.000426032` |
+| MLP output | `0.000674194` | `0.0500984` |
+| Layer-0 output | `0.000808998` | `0.0526199` |
+
+This confirms the residual error is already present in the captured projection
+outputs and is amplified by the MLP. The NVFP4 and MLP code audits found no
+remaining active source-level branch difference. Further edits to flattening,
+contiguity, dequantization dtype, `pre_quant_scale`, SiLU ordering, or residual
+adds would be speculative and are prohibited until a new code-path difference
+is demonstrated.
+
 ## Current Runtime Scope
 
 | Component | Implemented | Known limitation |