Cursor rule

1---
2description: "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."
3alwaysApply: false
4---
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6# Diagnose Root
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8**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.
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10Four phases — do not skip. Update the active `specs/bugs/BUG-*.md` file at each phase.
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12## Phases
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141. **Reproduce** — minimal steps; record environment; capture logs.
152. **Isolate** — narrow to module/function; binary-search commits or config.
163. **Hypothesize** — list ranked hypotheses with falsification test each.
174. **Verify** — run falsification; confirm single root cause; link to fix plan.
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19> **HARD GATE** — Do not propose a fix until phase 4 confirms one root cause with evidence.
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21## Verify
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23→ verify: `[ "$(grep -lE 'Reproduce' specs/bugs/BUG-*.md 2>/dev/null | grep -cv "\.okf\.md$")" -ge 1 ]`
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