You have an agent that works. Now someone asks how you know, and the honest answer is that you tried it about thirty times and it seemed fine.
That answer is fine for a prototype. It stops being fine the moment the thing is in front of people who did not build it.
An evaluation harness for AI agents is what replaces "it seemed fine". It is not a framework you install. It is four decisions, and you can make all four this week.
Decision one: where the cases come from
Not from your imagination. This is the one that quietly ruins most attempts.
