In The Truman Show, Laura Linney is Truman’s upbeat wife—Meryl—and a sales channel at the very same time. In one moment, she is comforting him; the next, she is swivelling back toward the camera with a fresh box of Mococoa with “all-natural cocoa beans from the upper slopes of Mount Nicaragua.” She’s performing marital intimacy while chasing a product-placement bonus. It’s as gross as it is captivating. That character was an arresting caricature in the 1998 film. Today, she is an obvious ancestor to two-faced AI agents. When you deputize an AI agent to shop for you, you basically tell...