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Codex reads AGENTS.md, not CLAUDE.md. So on that small task it never saw your rules at all.
You don't have to write them twice. Move the rules into AGENTS.md and turn CLAUDE.md into a one-liner that points at it:
Read AGENTS.md for the project rules.
Claude Code follows the pointer, Codex reads AGENTS.md directly, and there's one file to keep up to date. A symlink (ln -s AGENTS.md CLAUDE.md) works too, but a pointer is easier to understand for the next person who opens the repo.
A few other tools read AGENTS.md these days as well, so check the docs of whatever you use before writing a third file.
Did the pointer file. Codex picked up the rules on the first task and asked before touching the bookings table, which is rule number one in there. 
sam_builds
sam_builds Cursor picked up the AGENTS.md in my repo too. One file for everything, finally. katie_on_cursor