fix(inbound/buy): 批号自增改为按物料精准取最近一条

- 新增 get_latest_batch_record_by_base_id：SQL 直接 filter(base_id)+order by in_date/id desc first()，O(1) 不分页
- 新增 GET /inbound/buy/latest-record
- 修复原“拉全表前1000条再前端过滤”导致的历史被截断→批号退回000001/重复入库被拦（如 CCAB0029）

inventory-backend/app/api/v1/inbound/buy.py

@@ -353,3 +353,18 @@ def get_last_location():
 
     location = BuyInboundService.get_last_location_by_base_id(base_id)
     return jsonify({"code": 200, "msg": "success", "data": {"location": location}})
+
+
+@inbound_buy_bp.route('/latest-record', methods=['GET'])
+@permission_required('inbound_buy')
+def get_latest_batch_record():
+    """
+    按物料精准取最近一次采购入库记录（批号自增用）。
+    返回 data: {'has_history': bool, 'mode': 'serial'|'batch', 'latest_batch': str}
+    """
+    base_id = request.args.get('base_id', type=int)
+    if not base_id:
+        return jsonify({"code": 400, "msg": "base_id required"}), 400
+
+    data = BuyInboundService.get_latest_batch_record_by_base_id(base_id)
+    return jsonify({"code": 200, "msg": "success", "data": data})

inventory-backend/app/services/inbound/buy_service.py

@@ -601,6 +601,28 @@ class BuyInboundService:
         return [r[0] for r in
                 db.session.query(StockBuy.warehouse_location).filter(StockBuy.base_id == base_id).distinct().all()]
 
+    @staticmethod
+    def get_latest_batch_record_by_base_id(base_id):
+        """
+        按物料精准取“最近一次采购入库记录”（SQL 直接 filter base_id + limit，O(1)、不分页）。
+        用于采购入库表单的批号自增：避免以前端拉 getBuyList 前 1000 条再过滤造成的
+        “历史被截断 → 误判无历史 → 批号退回 000001/重复入库被拦”问题。
+        返回: {'has_history': bool, 'mode': 'serial'|'batch', 'latest_batch': str}
+        """
+        if not base_id:
+            return {'has_history': False, 'mode': 'batch', 'latest_batch': ''}
+        latest = StockBuy.query.filter(
+            StockBuy.base_id == base_id
+        ).order_by(
+            StockBuy.in_date.desc().nullslast(),
+            StockBuy.id.desc()
+        ).first()
+        if latest is None:
+            return {'has_history': False, 'mode': 'batch', 'latest_batch': ''}
+        if latest.serial_number:
+            return {'has_history': True, 'mode': 'serial', 'latest_batch': latest.batch_number or ''}
+        return {'has_history': True, 'mode': 'batch', 'latest_batch': latest.batch_number or ''}
+
     @staticmethod
     def get_last_location_by_base_id(base_id):
         """