A customer bought a gift card at my Marina branch. Can they spend it at my Downtown branch?

No. Each branch is its own restaurant here, and a gift card is a balance held by the restaurant that issued it, so the code is only known at the branch that sold it. The same is true of store credit and house accounts. If you want a present that works at both, the honest answer today is to sell the card at the branch the customer will eat at, and to say so on the card. The Outstanding figure on Marketing → Gift cards is per branch for the same reason: it is money that one branch holds and owes.