Comment by mpoteat

The AGENTS.md support was implemented via our new extensibility system for CC, called Mods, which is launching soon-ish. A mod is a plugin with a new type of hook, which we call a function hook.

If folks play around with it, I would love feedback on the relevant issue: https://github.com/anthropics/claude-code/issues/91870

Mods allow quite a bit more customizability and control. I really believe in the idea.