fix(rate-limit): _is_rate_limited 识别 RetryError 的 429 形态，登录 429 真正触发自动退避

生产实测：登录时 garth 把 429 折进 RetryError（'too many 429 error responses'），无 status_code、无 'rate limit' 字样，旧检测漏判 → 走 else 分支存原始报错、不调 _note_rate_limit，冷却永远不落库，用户可反复撞 Garmin。\n\n- garmin.py: _is_rate_limited 沿 __cause__ 链找 429 响应，并接受文本中的 '429' 标记。\n- garmin_auth.py: 退避文案 6h 改为 24h。\n- 生产：已补挂 24h 冷却（2026-08-30 10:00 北京），RetryError 形状验证识别为 429。

backend/services/garmin.py

@@ -204,8 +204,22 @@ def _is_rate_limited(e):
     if response is not None and getattr(response, "status_code", None) == 429:
         return True
 
-    haystacks = [str(e), str(getattr(e, "doc", "") or "")]
-    return any("rate limit" in h.lower() for h in haystacks)
+    # The 429 can be buried several layers down: garth/urllib3 fold the final
+    # 429 into a RetryError whose message is 'too many 429 error responses' —
+    # no status code survives and the words "rate limit" never appear. Walk the
+    # cause chain and also accept the "429" marker itself.
+    seen = set()
+    cur = e
+    while cur is not None and id(cur) not in seen:
+        seen.add(id(cur))
+        response = getattr(cur, "response", None)
+        if response is not None and getattr(response, "status_code", None) == 429:
+            return True
+        text = f"{cur} {getattr(cur, 'doc', '') or ''}"
+        if "429" in text or "rate limit" in text.lower():
+            return True
+        cur = getattr(cur, "__cause__", None) or getattr(cur, "__context__", None)
+    return False
 
 
 class MFARequired(RuntimeError):

backend/services/garmin_auth.py

@@ -121,7 +121,7 @@ def _run_login(session_id, user_id, garmin_email, password, is_cn, import_garmin
         if garmin_svc._is_rate_limited(e):
             garmin_svc._note_rate_limit(user_id)
             error = (
-                "Garmin 返回 429 限流（登录接口）。已自动退避 6 小时，"
+                "Garmin 返回 429 限流（登录接口）。已自动退避 24 小时，"
                 "请等待冷却窗口结束后再试——反复尝试会越撞越久。"
             )
         else: