One of the most important thing I couldn't have justified before: trust your instinct on prompt and agent design.
You'll feel something is wrong in a prompt or a trajectory long before you can explain why. That feeling is real signal. It's built from reading hundreds of runs, and it fires before the analysis catches up.
Don't dismiss it because you can't name it yet. Note it, watch for it again, and the explanation will come. The instinct comes first. The words come after.