The checkout link for one cart

IT BUYS NOTHING. This route reads the cart and returns two URLs; it posts to no order, payment or checkout-processing route, and no /v1/ route does. A key cannot start charging an account (ADR-010 §1): for the account's own offsets the API builds a cart and returns a checkout link, and the purchase happens in the browser, where a person sees the price and pays. offset settles through PayPal and removal through Stripe; the type on the URL picks which. The cart comes back beside the links so a caller can show what is about to be bought.