AmazonOA #4
MERN E-commerce: Admin Add/Delete Product
估计简单非算法题评测数据准备中，可先阅读题面
考点（AI 标注）模拟/实现
POST /api/products 缺 tag 数量校验 (≥3), DELETE /api/products/:id 删除不持久化 (缺 filter {_id: ObjectId(id)}).
考点: mongoose validation, ObjectId 转换, 401/400 error code 区分.