Just use a fallback, like Codex CLI. 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 (there will almost always be some experimental / edge case features that differ across harnesses, but in my experience those are negligible in practice).
> 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.