Thanks, Adam. By default, from v2.1.277, Claude Code reads AGENTS.md only when no CLAUDE.md, .claude/CLAUDE.md or CLAUDE.local.md sits in the working directory or above it, so with one of them present there's nothing to rank. With @AGENTS.md at the top of CLAUDE.md, the shared lines load first, but the docs say Claude Code can follow either line when two contradict. Codex has a fixed order: at most one file per directory, AGENTS.md ahead of any name in project_doc_fallback_filenames, and the file closest to the working directory overrides the ones above it. So keep every shared rule in AGENTS.md and give CLAUDE.md only lines that don't contradict them.