Since the recent developer changelog from Shopify (https://shopify.dev/changelog/storefront-api-changes-when-cart-id-is-missing-the-key-param), cart mutations require the cart key in addition to the cart ID. However, I cannot find where to get the key. It is not visible from other queries (e.g. GetCartFromId) and it is not in the payload the webhook CARTS_UPDATE sends. Can someone tell me where to get the key when I have the cartID?
