On a metallic door in San Francisco’s Mission District, a single character—“π”—offers a cryptic clue as to the virtuous circle of labor taking place beyond.The door opens to reveal furious activity involving both humans and machines. A woman uses two joysticks to operate a pair of tabletop robotic arms that carefully lift and fold T-shirts into a neat pile. Several larger robots move pantry items from one cluttered box to another. In one corner of the room a man operates a plastic pincer that fi...