[Diffusion] Add FLUX.2-klein BF16 HWR contract (#6651)

Signed-off-by: hsliuustc0106 <hsliuustc0106@users.noreply.github.com>
Signed-off-by: hsliuustc0106 <liuhongsheng4@huawei.com>
Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>
Co-authored-by: hsliuustc0106 <hsliuustc0106@users.noreply.github.com>

docs/user_guide/diffusion/offloader/distributed_layerwise_offload.md

@@ -112,6 +112,12 @@ perform a collective and uses the same rank-local transfer behavior.
 HWR is an opt-in startup optimization for models that declare the final-layout
 BF16 restore contract. Use it only with no-AllGather DLO:
 
+The validated BF16 model contracts currently cover MiniMax H3 and
+`black-forest-labs/FLUX.2-klein-4B`. FLUX.2-klein-9B shares the same model
+class but has not been validated against this contract. FLUX.2-dev, online
+FP8, HSDP, LoRA/adapted weights, and non-default load formats remain outside
+the validated scope.
+
 ```bash
 vllm serve /path/to/model --omni \
   --enable-distributed-layerwise-offload \