[diffusion][bugfix] Separate Diffusers hooks from model metadata (#6749)

Signed-off-by: david6666666 <530634352@qq.com>
Signed-off-by: Gao Han <hgaoaf@connect.ust.hk>
Co-authored-by: Gao Han <hgaoaf@connect.ust.hk>

tests/diffusion/test_diffusion_plugin_hooks.py

@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: Apache-2.0
-# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
 
 """
 Unit tests for diffusion engine plugin extensibility hooks.
@@ -20,6 +20,8 @@ from vllm_omni.diffusion.registry import (
     _DIFFUSION_MODELS,
     _DIFFUSION_POST_PROCESS_FUNCS,
     _DIFFUSION_PRE_PROCESS_FUNCS,
+    get_diffusion_post_process_func,
+    get_diffusion_pre_process_func,
     register_diffusion_model,
 )
 from vllm_omni.platforms.interface import OmniPlatform, OmniPlatformEnum
@@ -112,6 +114,49 @@ class TestRegisterDiffusionModel:
         assert _DIFFUSION_POST_PROCESS_FUNCS["LegacyActionPipeline"] == "test_post_process"
 
 
+@pytest.mark.parametrize(
+    ("model_class_name", "get_process_func"),
+    [
+        ("QwenImagePipeline", get_diffusion_post_process_func),
+        ("WanImageToVideoPipeline", get_diffusion_post_process_func),
+        ("WanImageToVideoPipeline", get_diffusion_pre_process_func),
+    ],
+)
+def test_diffusers_backend_skips_native_process_hooks(model_class_name, get_process_func):
+    od_config = SimpleNamespace(
+        model_class_name=model_class_name,
+        custom_pipeline_args=None,
+        diffusion_load_format="diffusers",
+    )
+
+    with patch("vllm_omni.diffusion.registry._load_process_func") as load_process_func:
+        assert get_process_func(od_config) is None
+
+    load_process_func.assert_not_called()
+
+
+@pytest.mark.parametrize(
+    ("model_class_name", "get_process_func"),
+    [
+        ("QwenImagePipeline", get_diffusion_post_process_func),
+        ("WanImageToVideoPipeline", get_diffusion_post_process_func),
+        ("WanImageToVideoPipeline", get_diffusion_pre_process_func),
+    ],
+)
+def test_custom_pipeline_preserves_native_process_hooks(model_class_name, get_process_func):
+    process_func = Mock()
+    od_config = SimpleNamespace(
+        model_class_name=model_class_name,
+        custom_pipeline_args={"pipeline_class": "custom.Pipeline"},
+        diffusion_load_format="diffusers",
+    )
+
+    with patch("vllm_omni.diffusion.registry._load_process_func", return_value=process_func) as load_process_func:
+        assert get_process_func(od_config) is process_func
+
+    load_process_func.assert_called_once()
+
+
 class TestWorkerUsesHook:
     """Test that DiffusionWorker resolves model runner via platform hook."""