Single-source AI agent rules still drift without machine-wide detection

A developer built a tool called agent-fanout to generate AI coding agent instruction files (CLAUDE.md, Cursor rules, GitHub Copilot instructions) from a single AGENTS.md source, aiming to prevent configuration drift across tools. While the approach keeps files consistent within one repository and CI catches unauthorized direct edits, it leaves several gaps unaddressed. Global config files stored outside repositories, other repos copy-pasted from each other, and machines with multiple checkouts all fall outside CI's reach. To address this, the developer also created agent-drift, a companion script that scans entire directory trees and groups instruction files by content similarity to surface divergence across repository boundaries. The author warns that relying solely on generation creates a false sense of coverage, and that detection across the whole machine is equally necessary.