[Diffusion] Add FLUX.2-klein BF16 HWR contract

Signed-off-by: hsliuustc0106 <hsliuustc0106@users.noreply.github.com>

docs/design/feature/offloader/distributed_layerwise_offload.md

@@ -220,9 +220,12 @@ model revision and parallel layout with `required`. TP coordinates have distinct
 identities, while equivalent DP replicas share them.
 
 The current producer/consumer boundary is the model-declared final-layout BF16
-contract (MiniMax H3 today). It supports ordinary-loader final layouts for TP1
-and TP2 rank identities plus SP layout identities; online quantization, HSDP,
-LoRA/adapted weights, and non-default load formats remain ineligible. HWR mode
+contract (MiniMax H3 and `black-forest-labs/FLUX.2-klein-4B`). The FLUX.2-klein
+contract covers both transformer block stacks, constructor-stable packed QKV
+mapping state, BF16 parameters, and any persistent loader-owned `beta`/`eps`
+buffers. It supports ordinary-loader final layouts for TP1 and TP2 rank
+identities plus SP layout identities; online quantization, HSDP, LoRA/adapted
+weights, and non-default load formats remain ineligible. HWR mode
 `disabled`, DLO-disabled, and DLO AllGather configurations stop before source
 identity or store construction and retain the existing checkpoint-mmap or
 ordinary-loader path.