fix(writer): 透传底层 LLM 错误详情（401 等）便于门禁定位

_AI_USAGE_LOG.md

@@ -105,4 +105,5 @@
 | 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 |
-| 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 |
+| 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 |
+| 2026-08-13 23:35 | 测试验证 | P5-T10 门禁诊断：修复 WriterGenerationError 吞掉底层 LLM 错误（如 401 详情），补透传测试 | src/genesis/writer/writer_agent.py; tests/test_phase5_writer_agent.py | hy3-free |

src/genesis/writer/writer_agent.py

@@ -98,7 +98,15 @@ class WriterAgent:
         if asyncio.iscoroutine(result):
             result = asyncio.run(result)
         if result.status not in ("ok", "fallback"):
-            raise WriterGenerationError(f"引擎返回异常状态: {result.status}")
+            # 透传底层错误详情（如 401 鉴权失败原因），便于人工门禁定位
+            err = getattr(result, "error", None)
+            code = getattr(result, "error_code", None)
+            suffix = ""
+            if err:
+                suffix += f"; {err}"
+            if code:
+                suffix += f" (code={code})"
+            raise WriterGenerationError(f"引擎返回异常状态: {result.status}{suffix}")
         return result.data
 
     def generate_chapter(self, context: GenerationContext) -> ChapterContent:

tests/test_phase5_writer_agent.py

@@ -88,3 +88,26 @@ def test_generate_chapter_with_async_engine():
     content = agent.generate_chapter(_ctx("db_design", "DB 設計"))
     assert content.chapter_id == "db_design"
     assert content.blocks and content.blocks[0].type == "paragraph"
+
+
+def test_generate_chapter_propagates_engine_error_detail():
+    class FailingEngine:
+        def chat_structured(self, *, session_id, prompt, variables, schema, retry_count=2):
+            return SimpleNamespace(
+                data={},
+                status="failed",
+                error="LLM HTTP 401: invalid key",
+                error_code="LLM_NETWORK_ERROR",
+            )
+
+    agent = WriterAgent(
+        session_id="s",
+        engine=FailingEngine(),
+        prompt_registry=FakePromptRegistry(),
+        state=WriterState(["db_design"]),
+        max_retries=1,
+    )
+    with pytest.raises(WriterGenerationError) as exc:
+        agent.generate_chapter(_ctx("db_design", "DB 設計"))
+    assert "LLM HTTP 401" in str(exc.value)
+    assert "LLM_NETWORK_ERROR" in str(exc.value)