Query BigCommerce product catalog and cart data via the GraphQL Storefront API including complex variant selection and pricing

Steps

1. Generate a Storefront API token via POST /v3/storefront/api-token (customer-specific token) or use the channel token from the control panel for anonymous requests
2. Send GraphQL queries to the channel's storefront GraphQL endpoint with Authorization: Bearer <token> and the appropriate Origin header matching the storefront domain
3. Query products with variant pricing using site { products { edges { node { variants { edges { node { prices { price { value currencyCode } } } } } } } } }
4. For cart operations, use the addCartLineItems and updateCartLineItem mutations; the cart is identified by entityId which maps to BigCommerce's cart ID
5. Handle the prices object carefully: price is the base price, salePrice is the promotional price, and priceWithTax or priceWithoutTax reflect the store's tax display setting