diff --git a/inventory-backend/app/services/trans_service.py b/inventory-backend/app/services/trans_service.py
index 6fddfc3..df20fa9 100644
--- a/inventory-backend/app/services/trans_service.py
+++ b/inventory-backend/app/services/trans_service.py
@@ -95,8 +95,11 @@ class TransService:
 
                 # ==============================================
                 # ★ 防线3：并发超卖与负库存 - 锁行后再查可用库存
+                #   ⚠️ 不要在此加 joinedload(ModelClass.base)！PG 禁止 FOR UPDATE
+                #      应用到 outer join 的 nullable 侧，会报 FeatureNotSupported
+                #      并有死锁风险。stock.base 走单条 lazy 加载是已知取舍。
                 # ==============================================
-                stock = ModelClass.query.options(joinedload(ModelClass.base)).with_for_update().get(stock_id)
+                stock = ModelClass.query.with_for_update().get(stock_id)
                 if not stock: raise ValueError(f"库存不存在 ID:{stock_id}")
 
                 # ==============================================