debug

Investigation-first debugging — gather evidence, form confirmed root-cause hypothesis, hand off to fix mode with diagnosis file. TRIGGER when: user reports a symptom or failing test with Python traceback, or asks to investigate a runtime/CI failure with reproducible evidence; phrases: \"debug this failure\", \"why is X broken\", \"find the root cause of <error>\", \"investigate this CI failure\". SKIP when: pure config quality issues (use /foundry:audit); broad system-wide diagnosis without traceback (use /foundry:investigate); user already knows the fix (use /develop:fix); non-Python project.