[Bugfix][Diffusion] Restore the TRTLLM attention default for the MiniMax-H3 modular alias (#7162)

Signed-off-by: princepride <wangzhipeng628@gmail.com>

vllm_omni/diffusion/model_metadata.py

@@ -48,12 +48,16 @@ _DIFFUSION_MODEL_METADATA: dict[str, DiffusionModelMetadata] = {
         attention_mask_free=True,
     ),
     # The modular alias is served by MiniMaxH3Pipeline and has the same
-    # Ref2VA request contract. Keep admission limits in sync with it.
+    # Ref2VA request contract and packed-sequence layout. Every field must stay
+    # in sync with it: the repository root ``model_index.json`` declares this
+    # alias, so serving the checkpoint by repo id resolves here rather than to
+    # ``MiniMaxH3Pipeline``.
     "MiniMaxH3ModularPipeline": DiffusionModelMetadata(
         supports_multimodal_inputs=True,
         max_multimodal_image_inputs=9,
         supports_mixed_reference_inputs=True,
         final_output_type="video",
+        attention_mask_free=True,
     ),
     "Magi2Pipeline": DiffusionModelMetadata(
         supports_multimodal_inputs=True,