root-cause

Use when diagnosing a bug, test failure, or unexpected behavior before permanent remediation, and especially after a fix attempt has already failed, or when guessing has started ("maybe it's X, let me try changing it"). Triggers: 'debug this failure', 'why did this test fail', 'the fix did not work'. Active response uses incident-investigation; a dispatched causal helper can use this method within its assignment. A bounded evidence lookup does not require a full diagnosis.