> Takes a little effort upfront to ensure your configuration is wired correctly for both harnesses, but it is pretty easy to get them 90% identical

You don't need to put in any effort, just get Claude (Codex CLI if Claude is down) to generate the multi-harness config for you.

You sound like you might be a beginner so let me help you out with some advice -- You can get your multi-harness configurations completely identical by simply telling Claude to research the Codex spec and eliminate all feature drift between your configs. Hope this helps.

I more meant feature-level differences. For instance, Claude Code has agent teams, and Codex CLI does not. Or for a while, Codex had "/goal" and Claude Code did not (though now Claude Code has it too). To your point, it is usually possible to polyfill these gaps either with custom code/skills/hooks or with third party plugins.