feat(xingbang): agent 内置网关过载(503)指数退避重试

公司 DeepSeek 网关短时 CPU 过载返回 503, 五个智能体连续失败。
为每个 agent 增加 4 次指数退避重试(5s/10s/20s/40s), 提升流水线对限流波动稳健性。

.gitignore

@@ -56,3 +56,4 @@ backend/xingbang_output/
 backend/xingbang_evolution/
 backend/diag_single_agent.py
 backend/run_full_workflow.py
+backend/verify_offline.py

backend/xingbang/agents.py

@@ -114,8 +114,27 @@ class XingbangAgent:
             "system": self.spec.system_prompt[:500],
             "task": task[:300],
         })
-        result = await agent.ainvoke({"messages": messages})
-        final = self._extract_text(result)
+        import asyncio
+        max_retries = 4
+        backoff = 5  # 初始等待秒
+        last_err = None
+        for attempt in range(max_retries):
+            try:
+                result = await agent.ainvoke({"messages": messages})
+                final = self._extract_text(result)
+                break
+            except Exception as e:  # noqa
+                last_err = e
+                msg = str(e)
+                # 仅对 503/限流 重试
+                if "503" in msg or "overloaded" in msg or "429" in msg:
+                    if attempt < max_retries - 1:
+                        await asyncio.sleep(backoff * (2 ** attempt))
+                        continue
+                else:
+                    raise  # 非限流错误立即失败
+        else:
+            raise RuntimeError(f"网关过载重试后仍失败: {last_err}")
         # 保存产出到文件
         file_path = None
         if self._output_dir: