Introducing Headlong, an open source agent microharness featuring persistent agency. Your agent keeps thinking between external interactions in a self-guided loop inspired by human inner monologue. Headlong is a complete agent harness with a core of less than 10K lines of Bash, available on GitHub. Most agent harnesses are reactive: you give your agent a task, it works until the task is done, and then it sits frozen until the next request. Some harnesses add cron jobs or heartbeats that wake the agent on a schedule to run a fixed checklist and then put it back to sleep. In Headlong the agent i