How to get cart token from StoreFront GraphQL API

I am building a custom Frontend for my store on top on StoreFront GraphQL API. For some purpose, I need the cart token whenever the cart is updated (i.e. lineitems are updated).

When adding line items, I get back a checkout response which has an ID - a base64 string which is something like gid://shopify/Checkout/?key=.

Is the cart token in that URL? Otherwise how can the cart token be obtained?

Couldn’t you listen for and handle the checkout creation webhook? That would pass along the cart token and everything else, right?