---
description: "Run 4-phase root cause analysis — reproduce, isolate, hypothesize, verify. Use when a bug is confirmed but root cause is unclear, after investigate-bug, or when user mentions root cause analysis."
alwaysApply: false
---

# Diagnose Root

**Boundary**: Canonical, reusable 4-phase RCA engine. Invoked by `investigate-bug` (as step 2 of the end-to-end flow) and by `fix-bug` (when no bug file exists). Does not write the bug file — that is `investigate-bug`'s responsibility.

Four phases — do not skip. Update the active `specs/bugs/BUG-*.md` file at each phase.

## Phases

1. **Reproduce** — minimal steps; record environment; capture logs.
2. **Isolate** — narrow to module/function; binary-search commits or config.
3. **Hypothesize** — list ranked hypotheses with falsification test each.
4. **Verify** — run falsification; confirm single root cause; link to fix plan.

> **HARD GATE** — Do not propose a fix until phase 4 confirms one root cause with evidence.

## Verify

→ verify: `[ "$(grep -lE 'Reproduce' specs/bugs/BUG-*.md 2>/dev/null | grep -cv "\.okf\.md$")" -ge 1 ]`