Kai T.

Here is a legacy module: {CODE} Refactor it without changing behavior. Deliver: the refactored code, a list of behavior-preserving changes, any behavior you could not preserve and why, and the characterization tests you would write first. Prefer small named functions over comments.

Stack trace: {TRACE} Context: {STACK / FRAMEWORK}. Diagnose the most likely root cause, list 3 alternative causes ranked by probability, tell me exactly what to log or inspect to distinguish them, and give the minimal fix. No speculation presented as fact.