diagnoselisted

## Activation Triggers - IMMEDIATELY when investigating incidents, recurring issues, systemic failures, or bugs with long call chains. - CONTRAST with fpf and refine: diagnose investigates why something is broken (past, causal, unknown type); fpf evaluates competing options to decide a path forward (future); refine improves known artifacts (present, corrective). Prefer diagnose when "problem" or "issue" appears without alternatives. ## What This Skill Changes **Default behavior:** Claude assumes symptoms are the problem — it fixes where errors appear and follows the happy path forward through code, missing the actual trigger. **With this skill:** Claude traces backward from symptoms to root causes. Each investigation method (A3, Five Whys, Fishbone, Stack Trace) targets a different problem structure. AUTO mode removes method-selection overhead when the problem type is already clear. **Why this matters:** Fixing symptoms is the most expensive kind of fix. Every "I fixed it" that recurs with a different input is a symptom-level fix. Systematic root cause tracing produces solutions that don't come back. --- ## Decision Router IF investigating a specific incident, recurring issue, or major problem needing structured documentation → use **A3** mode — ALWAYS spawn a tp-explorer subagent to investigate before analysis. You MUST read `references/a3-methodology.md` BEFORE executing A3 mode. IF problem has a clear single causal chain from symptom to root → use **FIVE-WHYS** mod