Unless I specifically say "use git", it won't bother using git, apparently saying "configure AGENTS.md to us best practices" isn't enough for it to (at least in this case) use git. If this was isolated I might put that down to bad luck, given the nature of LLMs, but I have been finding Codex uses the wrong approaches all over the place, also stops in the middle of tasks, skips some tasks entirely (sometimes while marking them as done, other times it just doesn't get around to it).
I'd rank the output of Claude as similar to a junior with 1-3 years experience. It's not great, but it's certainly serviceable, a bit of tweaking even shippable. Codex… what I see is more like a student project. Or perhaps someone in the first month of their first job. Even the absolute worst human developers I've worked with after university weren't as bad as Codex, but several of them I'd rank worse than Claude.