The more you can afford to build up your understanding of the problem space and define what inputs & outputs look like, the more flexible you can be with evals. Unfortunately, this is a lot of work and requires thinking and discussion with your team and those involved.
https://poyo.co/note/20260217T130137/
I wrote about general ideas I take towards simple single prompt features, but most of it is applicable to more involved agentic approaches too.