Last fall, walking down Mission Street, in San Francisco, I noticed a new addition to an otherwise unremarkable parking lot at the base of Bernal Heights Hill: a large, white trailer, about the size of three parking spaces, plastered with a banner that read “food pick up here.” On one side was a list of restaurant brands with names and logos that seemed algorithmically generated: WokTalk, Burger Bytes, Fork and Ladle, Umami, American Eclectic Burger, Wings & Things.

The trailer was hooked up to a generator, which was positioned behind two portable toilets; it occupied parking spots once reserved for Maven, an hourly-car-rental startup, funded by General Motors and marketed to gig-economy workers. (G.M. shut down Maven in April.) Through a small window cut into the side, I could see two men moving around what appeared to be a kitchen. The generator hummed; the air carried the comforting smell of fryer oil; the toilets were padlocked. One of the men came to the window and apologized: I couldn’t order food directly, he told me—I would have to order through the apps...