Diagnose A six-phase loop for systematic bug investigation. The key insight: invest disproportionate effort in Phase 1 . With a reliable feedback loop, phases 2–6 become mechanical. When to use this skill - Hard bugs that resist quick fixes - Performance regressions with unclear root cause - Flaky failures that need repeated-run evidence - Any failure where previous fix attempts failed When not to use this skill - Quick targeted fixes with obvious root cause → use - Symptom-first log triage → use - Broad test-policy design → use The Six Phases Phase 1 — Build a feedback loop (invest here firs…