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

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: