fix: 翻译主流程失败时 raise(不再返回占位符); add_usage TTL 用 replace(day=1) 防 0 TTL

backend/app/services/translation/service.py

@@ -59,17 +59,16 @@ class TranslationService:
 
     async def add_usage(self, chars: int) -> None:
         r = get_redis()
-        # 用 INCRBY + EXPIRE 月初;简单做法:每次 set + 设 TTL
         key = _month_key()
+        now = datetime.now(timezone.utc)
+        # 下个月第一天
+        if now.month == 12:
+            next_month = now.replace(year=now.year + 1, month=1, day=1)
+        else:
+            next_month = now.replace(month=now.month + 1, day=1, hour=0, minute=0, second=0, microsecond=0)
+        ttl = max(60, int((next_month - now).total_seconds()) + 86400)  # +1 天 buffer
         async with r.pipeline(transaction=False) as pipe:
             pipe.incrby(key, chars)
-            # 月底过期(下下月 1 日)
-            now = datetime.now(timezone.utc)
-            if now.month == 12:
-                next_month = now.replace(year=now.year + 1, month=1, day=1)
-            else:
-                next_month = now.replace(month=now.month + 1, day=1)
-            ttl = int((next_month - now).total_seconds()) + 86400
             pipe.expire(key, ttl)
             await pipe.execute()
 
@@ -106,6 +105,7 @@ class TranslationService:
 
         # 3) 调用
         async with self._sem:
+            res = None
             try:
                 res = await engine.translate(text, source=source, target=target)
             except Exception as e:
@@ -113,13 +113,14 @@ class TranslationService:
                 logger.exception("translate failed with %s: %s", engine.name, e)
                 fb = self._fallback()
                 if fb is not None and engine is not fb:
-                    res = await fb.translate(text, source=source, target=target)
-                else:
-                    res = TranslationResult(
-                        text=text + f"\n\n[翻译失败: {e}]",
-                        engine="skip",
-                        chars=chars,
-                    )
+                    try:
+                        res = await fb.translate(text, source=source, target=target)
+                    except Exception as e2:
+                        logger.exception("fallback %s also failed: %s", fb.name, e2)
+                        res = None
+            if res is None:
+                # 主 + fallback 都失败:抛异常,让上层标记 status=failed
+                raise RuntimeError(f"translation failed for {chars} chars (engine={engine.name})")
 
         # 4) 写缓存(无论引擎)
         try: