As awesome as this is, because as much as I want to create an agent for my customer that is predictable and "deterministic", I can't help but think of how wasteful, expensive and not-fun this is.

Good for the author that it's fun for them, but for me it seems like I am in that "monkey ladder banana" experimemt: doing something because others are and the customer is giving me bana... sorry, money for it, convinced it will help him (the money would 100% stop if I started looping prompt optimizations like this).

If I have so many tools and MCPs as I do currently, and with each the behavior regresses and changes wildly, it seems I should either merge tools and do more automations and come back to the prompt. (The alternative being training my own model?)

RLHF might help, you don't have to train a model from scratch.