Since the pandemic upended dining habits, full-service restaurants have struggled to bring people back to their tables. Last year, about 4,500 more independent restaurants closed than opened, suffering from rising costs, shrinking margins, and an increasing preference from consumers for fast-food or delivery. Ben Leventhal, the co-founder of Eater and Resy, is currently building a platform with the goal of reversing this trend: a loyalty app called Blackbird, which he hopes will make restaurants more connected to each other and to their customers.