American did rebook us, and we're sitting in a flight to L.A. There we board an Air China flight, thankfully in Business Class, and are scheduled to land with about three hours to spare before the Xi'an flight departs.
There was clearly some confusion between us and the agent, leading us to walk all the way over to the United C gates to catch a United flight that didn't exist. We were lucky to catch a shuttle bus back.
It will help if we can sleep on the Air China flight. We're ready for a nap.