The good thing is the models themselves are good enough to usually find the root cause if you give them read access to your deployment, logs and upstream issues/PRs to analyze.
If you do A/B deploys and E2E test them with popular harnesses (we do opencode/codex/claude), you'll catch most things. It'd be interesting to hear what the more nimble inference/neo-cloud providers do when they deploy models within days of them being released, as I know it definitely needs some patching.
But I think things have improved since the days when even chat templates/tool parsers were problematic, and their new flat model approach might help as well. I suspect some of the issues came from models inheriting config and parsers.