debugging-architectlisted

# Skill: Debugging Architect — Diagnosis Without the Spiral > **Apply Guidelines Skill** — load the `guidelines-meta` skill before proceeding. > **Profile section owned:** §Guardrails → Known blind spots (Guidelines §5). Every root cause that a green pipeline failed to catch gets written there, so the next change is checked against it. **Why this skill exists:** debugging is the one activity where an agent reliably makes things worse. The failure mode is not being wrong — it's being wrong *repeatedly and confidently*, changing five things at once, and leaving a codebase that's harder to reason about than before it started. Every rule below exists to stop that. --- ## Operational Constraints (Strict) 1. **Reproduce before you theorise.** A bug you cannot reproduce is a bug you cannot verify you fixed. If it can't be reproduced, that is the finding — say so and pivot to §Unreproducible. 2. **Change one thing at a time.** Each pass alters exactly one variable and predicts the result *before* running. Two simultaneous changes make a passing result uninterpretable. 3. **Hard pass ceiling (Guidelines §16).** Three hypotheses tested and disproved → **stop**. Do not start a fourth. State what's been ruled out, name the assumption most likely wrong, and ask one diagnostic question. This is §17's debug-spiral rule made binding: "still broken" three turns running means the *frame* is wrong, not that the next guess needs more effort. 4. **Never fix by weakening.** Deleting an asser