Just this morning I have run across an even narrower case of how AGENTS.md (in this case with GPT-5.3 Codex) can be completely ignored even if filled with explicit instructions.

I have a line there that says Codex should never use Node APIs where Bun APIs exist for the same thing. Routinely, Claude Code and now Codex would ignore this.

I just replaced that rule with a TypeScript-compiler-powered AST based deterministic rule. Now the agent can attempt to commit code with banned Node API usage and the pre-commit script will fail, so it is forced to get it right.

I've found myself migrating more and more of my AGENTS.md instructions to compiler-based checks like these - where possible. I feel as though this shouldn't be needed if the models were good, but it seems to be and I guess the deterministic nature of these checks is better than relying on the LLM's questionable respect of the rules.