Every change cascaded through the social graph, redrawing the map and obliging Mainway to update ceaselessly. Mainway’s purpose, in other words, was neither storage nor preparation of a simple list.

Take Vine, for example. Founded in 2012 by the tech entrepreneurs Dom Hofmann, Rus Yusupov, and Colin Kroll—and acquired that same year by Twitter—the app skyrocketed to success as the first ...