Request to add an item to the cart.
{ "$schema": "https://json-schema.org/draft/2020-12/schema", "title": "CartItemInput", "description": "Request to add an item to the cart.", "type": "object", "required": [ "productId", "quantity" ], "properties": { "productId": { "type": "string", "description": "Product SKU to add.", "example": "SKU-123456" }, "quantity": { "type": "integer", "description": "Quantity to add.", "example": 2 } } }