New tools.
Emerging patterns.

The codebase has a new audience.

We spent decades developing best practices for software engineers: how to structure code, document decisions, review changes, and share knowledge across a team. Those practices grew around human collaborators, with human ways of reading code and building an understanding of a system.

Now agents are collaborators too. The code we produce, and the tools and documentation around it, must be readable and usable by them. They need to find their way around, understand constraints, run the system, and check their work. That puts the old playbook up for revision. Some practices still earn their place. Others need to be rewritten or thrown out.

The challenge gets sharper when many agents work alongside developers in a large codebase. Context has to be discoverable, changes need clear boundaries, and feedback must be easy to obtain. This book collects the patterns emerging from that shift: practical ways to help people and agents work on the same system without losing track of how it fits together.