systematic-debugging

# Systematic Debugging <!-- routing-eval reads this line; it lives in the BODY so the always-on skill LISTING stays inside Claude Code's budget (1% of the context window) — an overflowing listing gets descriptions truncated or dropped, which strips the very keywords a match depends on. --> Trigger phrases: "debug", "root cause", "why is this failing", "intermittent bug", "can't reproduce", "is broken", "crashes" One rule holds the whole skill together: **no fix without a confirmed root cause.** A patch that makes the symptom disappear without a proven cause is not a fix — it's a coin flip that hides the bug until it returns somewhere worse. This skill is the discipline that turns "try things until it works" into "understand, then change one thing." > **Kit adaptation (local, .claude/):** Distinct from `iterate` (a self-correction loop over a *task*) and `reflect` > (meta-review of an approach) — this skill is for a *defect*. §4 Prohibitions apply; a fix still goes through the > project's review/test gates. Don't disable a test or a gate to make a symptom pass (that is masking, not fixing). ## The loop (do them in order — skipping a step is why bugs come back) 1. **Reproduce** — a reliable, minimal repro. Can't reproduce → that IS the first problem; see `references/techniques.md` (intermittent/heisenbug). 2. **Isolate** — shrink the surface until the failure is in the smallest possible slice (bisect commits, halve the input, disable half the system). 3. **Hypothe...