systematic-debugging

Use when encountering ANY bug, test failure, error message, performance issue, or unexpected behavior, BEFORE proposing fixes. Forces root-cause investigation before any code change. Iron law - no fixes without evidence. TRIGGER on "this is broken", "test is failing", "why is X doing Y", "it crashed", "production issue", or any unexpected output. Cross-refs test-driven-development for writing the regression test, bug-hunt chain for the canonical fix pipeline.