4 incidents, 4 rules: how my CLAUDE.md wrote itself

If you have 30 seconds. An effective CLAUDE.md doesn't document, it constrains — each rule answers a time the agent got it wrong. This article gives the four-layer structure I use for a 91,000-line ERP (root CLAUDE.md, AGENTS.md, per-module .claude/rules/, auto-loaded skill), four operational rules