diff --git a/_AI_USAGE_LOG.md b/_AI_USAGE_LOG.md
index f500b45..d2bad83 100644
--- a/_AI_USAGE_LOG.md
+++ b/_AI_USAGE_LOG.md
@@ -104,4 +104,5 @@
 | 2026-08-13 | 测试验证 | Phase5 T15 端到端 e2e + DocxInjector 真实接口对齐（inject/sections） | tests/test_phase5_e2e.py; src/genesis/writer/docx_injector.py | gstack-subagent |
 | 2026-08-13 | 文档规范 | Phase5 T16 design.md 追加 Phase 5 Writer/QA 子系统章节 + 日志补齐 | docs/design.md; _AI_USAGE_LOG.md | gstack-subagent |
 
-| 2026-08-13 23:11 | Agent 实现 | 接通真实 LLM 引擎工厂（P5-T10 门禁接线）：新增 inference/factory.py，orchestrator/qa_loop 接入，脚本校验适配，补工厂测试 | src/genesis/inference/factory.py; src/genesis/writer/orchestrator.py; src/genesis/qa/qa_loop.py; scripts/run_phase5_slice.py; tests/test_inference_factory.py | hy3-free |
\ No newline at end of file
+| 2026-08-13 23:11 | Agent 实现 | 接通真实 LLM 引擎工厂（P5-T10 门禁接线）：新增 inference/factory.py，orchestrator/qa_loop 接入，脚本校验适配，补工厂测试 | src/genesis/inference/factory.py; src/genesis/writer/orchestrator.py; src/genesis/qa/qa_loop.py; scripts/run_phase5_slice.py; tests/test_inference_factory.py | hy3-free |
+| 2026-08-13 23:20 | 测试验证 | P5-T10 引擎工厂接线：补 engine=None 委托工厂测试（orchestrator/qa_loop），全量 296 passed / 99.04% | tests/test_phase5_writer_orchestrator.py; tests/test_phase5_qa_loop.py | hy3-free |
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diff --git a/tests/test_phase5_qa_loop.py b/tests/test_phase5_qa_loop.py
index 3b0a5ed..fb34fad 100644
--- a/tests/test_phase5_qa_loop.py
+++ b/tests/test_phase5_qa_loop.py
@@ -54,3 +54,14 @@ def test_qa_loop_regenerates_only_failed(tmp_path):
     assert report.passed is True
     assert engine.calls["A"] == 1   # A 首次即通过，未被重生成
     assert engine.calls["B"] == 2   # B 失败后被重生成一次
+
+
+def test_run_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.qa.qa_loop.build_inference_engine", lambda: ImprovingEngine())
+    tpl = tmp_path / "tpl.docx"
+    out = tmp_path / "out.docx"
+    _make_template(str(tpl))
+    loop = QALoop(max_rounds=3)
+    report = loop.run(_ss(str(tpl)), str(out), samples_dir="nonexistent_dir_xyz", engine=None)
+    assert report.passed is True
diff --git a/tests/test_phase5_writer_orchestrator.py b/tests/test_phase5_writer_orchestrator.py
index a3bb4ab..498598e 100644
--- a/tests/test_phase5_writer_orchestrator.py
+++ b/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)