Debugging

Use this skill when something is broken and the cause is unknown — a failing test, a crash, an error message, wrong output, a regression, a hang, or behaviour that differs between environments — and it has to be found and fixed at the root. Also use it to build the failing proof for a suspected defect before fixing it, as in a proof-driven bug hunt. Triggers: user says "debug", "broken", "doesn't work", "failing", "error", "exception", "stack trace", "crash", "regression", "it used to work", "hangs", "why does", "root cause", "works on my machine", "reproduce", "prove it".