add_to_cart
ChatGPTAdd a product to the shopping cart. IMPORTANT: productId must be the
id field from product-search results (a variant GID, e.g. gid://shopify/ProductVariant/...) — never pass a product page URL or metadata.product_gid. If cartId is omitted, a new cart is created — its ID is returned in the response. Pass this cartId to all subsequent cart operations.





