Log the model that answered, and catch an alias move

LoggedClient wraps any client with a system_one method and writes one JSON line per call: requested model, answered model, request ID if the client exposes one, tokens, cost, and a compact answer per question with a confidence. Noul confidence is $|2p - 1|$, so all three question types can be compared on one scale. drift_report groups the rows by answering model and raises three warnings. The decision that matters most is logging confidence, not just the answer: an alias move can leave every top choice unchanged and still shift every confidence-based route, and the demo is built to show exactly that.