feat: add one-to-one box mode with duplicate bind check

Add box_mode field to BoxSaveRequest and DuplicateZongpaiBindError
exception. In one-to-one mode, prevent the same zongpai from being
packed into multiple boxes, returning 409 with existing box info.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/services/box_service.py

@@ -23,6 +23,13 @@ class DuplicateBoxItemError(Exception):
         self.box_no = box_no
 
 
+class DuplicateZongpaiBindError(Exception):
+    def __init__(self, paichan_no: str, box_no: int, zongpai_no: str):
+        self.paichan_no = paichan_no
+        self.box_no = box_no
+        self.zongpai_no = zongpai_no
+
+
 def query_erp_info(db: Session, zongpai_no: str) -> dict:
     """从 ERP 视图查询总排号对应的排产号和数量。"""
     sql = text(_erp_info_sql(db))
@@ -101,6 +108,19 @@ def save_box_record(db: Session, req: BoxSaveRequest) -> dict:
     erp = query_erp_info(db, req.zongpai_no)
     paichan_no = erp["paichan_no"]
 
+    if req.box_mode == "one-to-one":
+        existing_box_no = (
+            db.query(FinishedGoodsBox.box_no)
+            .join(FinishedGoodsBoxItem, FinishedGoodsBox.id == FinishedGoodsBoxItem.box_id)
+            .filter(
+                FinishedGoodsBox.paichan_no == paichan_no,
+                FinishedGoodsBoxItem.zongpai_no == req.zongpai_no,
+            )
+            .scalar()
+        )
+        if existing_box_no is not None:
+            raise DuplicateZongpaiBindError(paichan_no, existing_box_no, req.zongpai_no)
+
     box = (
         db.query(FinishedGoodsBox)
         .filter(