If you let an AI agent loose on a non-trivial codebase, two things happen. First, it gets a lot done. Second, it gets a lot done in the style of whatever it last read. Drop it into a file with anemic models and inline authorization checks, and the next thing it writes will be an anemic model with an inline authorization check. Agents are mirrors with momentum.

This post is about how we stopped fighting that and started using it. It covers two iterations of a system we call the harness — the set of files, rules, and workflows that constrain what an agent produces in our Laravel + React monorepo. The first iteration was a scattering of CLAUDE.md files in subdirectories. The second is a .claude/ folder with rules, agents, commands, and skills. The second is dramatically better, and the reasons are worth writing down.

The audience here is engineers who are picking up agentic coding and want a concrete pattern they can copy.