test(writer/qa): 覆盖 engine=None 委托工厂的真实门禁路径

tests/test_phase5_writer_orchestrator.py

@@ -69,3 +69,17 @@ def test_generate_with_async_engine_produces_filled_docx(tmp_path):
     loaded = Document(str(out))
     joined = "\n".join(p.text for p in loaded.paragraphs)
     assert "异步引擎内容" in joined
+
+
+def test_generate_delegates_to_factory_when_engine_none(monkeypatch, tmp_path):
+    # 门禁真实路径：engine=None 时应委托 build_inference_engine() 构造真实引擎
+    monkeypatch.setattr("genesis.writer.orchestrator.build_inference_engine", lambda: FakeEngine())
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    contents = WriteOrchestrator().generate(
+        _ss(str(tpl)), str(out), samples_dir="nonexistent_dir_xyz", engine=None
+    )
+    assert len(contents) == 1
+    loaded = Document(str(out))
+    assert "自动生成的内容" in "\n".join(p.text for p in loaded.paragraphs)