fix: get_pending_detector_serial 不再删除记录，避免 B2 消费后 B4 拿不到序列号

src/models.py

@@ -866,7 +866,7 @@ async def get_vehicle_base_test_by_type(type_num: int) -> dict | None:
 # ─── tb_pending_detector ───────────────────────────────────────────
 
 async def get_pending_detector_serial(dnt_id: int) -> str:
-    """获取并清除待插入的车检器序列号（一次性消费）"""
+    """获取待插入的车检器序列号"""
     pool = await get_pool()
     async with pool.acquire() as conn:
         async with conn.cursor(aiomysql.DictCursor) as cur:
@@ -876,10 +876,5 @@ async def get_pending_detector_serial(dnt_id: int) -> str:
             )
             row = await cur.fetchone()
             if row:
-                # 清除已消费的记录
-                await cur.execute(
-                    "DELETE FROM tb_pending_detector WHERE dnt_id=%s",
-                    (dnt_id,),
-                )
                 return row["detector_serial"] or ""
             return ""