How I made every AI coding agent on my machine follow the same rules with one markdown file

I use Claude Code, GitHub Copilot, OpenAI Codex CLI, and Cursor - sometimes in the same day. Each one drifts the same way: skips planning, forgets tests, picks stale library versions, and asks twelve questions in the middle of a build. So I wrote one markdown template and a small installer that drops the same rules into every agent on my machine. Here is the design.