How do you evaluate a RAG system’s performance when the answer is not present in the retrieved documents? (Does it correctly say "I don't know"?)

You’ve updated your system prompt to fix a specific bug. How do you ensure this "fix" didn't break 10 other things the model was previously doing correctly?

How do you calculate the ROI of a prompt change? If a new prompt is 5% more accurate but 50% more expensive in tokens, how do you decide if it’s worth it?

Define Exact Match (EM) vs. F1 Score in the context of an extraction task (e.g., extracting dates from a PDF). When should you use EM?