A customer put my last two portions in their cart and then never ordered. Is my stock stuck?

No. A cart holds nothing. The count only comes down when an order is placed, and the order is checked against the live count at that moment. So those two portions stayed on sale for everyone else the whole time. If somebody else takes them first, the first customer is told the dish has just sold out when they try to check out, and nothing is charged. Inventory tracking for restaurants here counts orders, not intentions, which is what keeps a dish from being sold out by people who were only looking.