Sabi is building a baseball cap that turns thoughts into prompts for AI agents. An early wired helmet version hit up to 77% accuracy in the lab, the company says. That error rate would sink a keyboard. An AI agent might live with it. Brain-computer interfaces were built for a harder job. Neuralink, valued at $42 billion, implants chips so people with paralysis can control a computer by thinking. Precision like that has mostly meant hardware inside the skull. Khosla, who led the round, put the…