Identify the buyer on the Musée d'Orsay ticket shop

Give the buyer's email to the official Musée d'Orsay ticket shop, for the basket filled with add_to_cart, and report what the shop needs before payment. Every order needs a Musée d'Orsay customer account, and the shop only keeps a new account once its first order is paid. A browser already identified returns already_identified and changes nothing. Otherwise the email decides: an existing account returns sign_in_required (sign in with its password in this browser), an unknown email returns new_customer_details_required with the sign-up fields the shop asks for (name, email, password, country). The script never types a password, never creates an account and stops before payment: run complete_booking next.