Coding agent
An agent whose tools can read and edit files and run commands, so it can write code, run it, see what broke and try again. Claude Code, Codex and Cursor's agent are coding agents.
Running what it wrote is the difference. Chat hands you code you have to test yourself. A coding agent can run it, which means a check you set up can reach the agent while you are somewhere else. Everything in chapter 9 depends on this.
Say it to your agent
“Start the server with bun run dev, curl localhost:3000/api/health, and paste the response. Don't tell me it works until you have run it.”