Chapter 12. Agentic Coding: Claude Code, Codex and OpenCode
In this section
- Chapter 12. Agentic Coding: Claude Code, Codex and OpenCodeHow to direct a coding agent on a real job, wherever it runs, and check its result against work you have already done.
- 12.1 From a chat to a coding agentHow a coding agent differs from the chat app you already use, why the folder you give it is its world, and why its passing tests are its own evidence while your check, written first, decides.
- 12.2 The workspace: folder, session and where it runsThe three choices before any coding task: which folder the agent works in, which session it uses and which machine it runs on.
- 12.3 Permissions, and plan before you actHow to set a coding agent's permissions by how hard a mistake would be to undo, and why its plan is the review you can do before any code exists.
- 12.4 Rules the agent readsHow to write the AGENTS.md every session reads, what adding a CLAUDE.md changes, how to back the rules that must never break with a setting, and how to keep instructions lean.
- 12.5 Context, sessions and choosing the effortHow a long session loses track, the four moves that manage context, and how to choose the model and effort for a task.
- 12.6 Many sessions at once: a coordinator, threads and side chatsHow to split a coding job across a coordinator, worker threads, subagents and side chats without the parts colliding, and review each part.
- 12.7 The same agent outside the appHow the same coding agent runs from a terminal, an editor, a script and a pipeline, and why the fewer people watch a seat, the tighter its permissions.
- 12.8 How today's tools realize itHow Claude Code, Codex and OpenCode each apply this chapter's ideas, a short practice for each lesson in tabs, and the differences that change a decision.
- Lab 12: the first repository, on three agentsChapter 12's lab: make Brightline's script folder safe for a coding agent, have it build the due-by-Friday script, check its result against Ana's note, and give the same brief to a second agent.
- Check yourselfRecall and practice for the whole chapter: the flashcards, and a final quiz round from all eight concepts.