[Refactor][Diffusion] Read the resolved offload policy outside the config layer (#7327)

Signed-off-by: specture724 <specture724@gmail.com>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
Co-authored-by: Hongsheng Liu <liuhongsheng4@huawei.com>

tests/diffusion/offloader/test_legacy_flag_readers.py

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+"""Runtime code reads the resolved offload policy, not the legacy booleans."""
+
+import re
+from pathlib import Path
+
+import pytest
+
+import vllm_omni
+
+pytestmark = [pytest.mark.diffusion, pytest.mark.cpu, pytest.mark.core_model]
+
+# `enable_cpu_offload`, `enable_layerwise_offload` and
+# `enable_distributed_layerwise_offload` are compatibility aliases that
+# `resolve_offload` materializes from the resolved policy. Only the layer that
+# declares and resolves them may read them; everything else asks
+# `vllm_omni.diffusion.offloader.config` for the strategy or the selected
+# components, so the aliases can be removed without sweeping the runtime again.
+COMPATIBILITY_LAYER = {
+    "config/omni_config.py",
+    "config/stage_config.py",
+    "engine/arg_utils.py",
+    "diffusion/data.py",
+    "diffusion/offloader/base.py",
+    "diffusion/offloader/config.py",
+    "quantization/tools/compare_diffusion_trajectory_similarity.py",
+}
+
+READER = re.compile(
+    r"""\.enable_(?:cpu|layerwise|distributed_layerwise)_offload\b"""
+    r"""|getattr\(\s*[^,]+,\s*["']enable_(?:cpu|layerwise|distributed_layerwise)_offload["']"""
+)
+
+
+def test_no_runtime_module_reads_the_legacy_offload_flags():
+    root = Path(vllm_omni.__file__).parent
+    offenders = [
+        f"{path.relative_to(root)}:{number}"
+        for path in sorted(root.rglob("*.py"))
+        if str(path.relative_to(root)) not in COMPATIBILITY_LAYER
+        for number, line in enumerate(path.read_text().splitlines(), start=1)
+        if READER.search(line)
+    ]
+
+    assert offenders == [], (
+        "Read the resolved policy instead: resolve_offload_strategy(od_config), "
+        "offload_enabled(od_config), offload_streams_blocks(od_config), or "
+        f"should_offload_component(od_config, component). Offending reads: {offenders}"
+    )