assistant-debugging

name	assistant-debugging
description	Diagnose unknown failures by reproducing and isolating before fixing. Use for debugging, root causes, flaky tests, or unexplained breakage.
effort	high
triggers	[{"pattern":"debug|root cause|investigate (failure|bug|issue)|why .* broken|reproduce (bug|issue)|flaky test|production issue|failing test|test failure","priority":88,"reminder":"This request matches assistant-debugging. Load and follow this SKILL.md and its contracts before patching code. Reproduce and isolate root cause before fixing."}]

Evidence-First Debugging

Goal

Find and fix the real cause of a failure with the smallest durable change and evidence that explains the symptom, cause, fix, and verification.

Success Criteria

• The symptom and expected behavior are explicit.
• Reproduction evidence exists, or an exact blocker explains why it cannot.
• Competing hypotheses are tested and disconfirming evidence is retained.
• Root cause is supported by code, config, or runtime evidence.
• Verification covers the original failure path and a relevant regression check.

Constraints

• Use local, company-safe diagnostics by default; redact secrets and private data.
• Ask before destructive, production-affecting, network, migration, or sensitive-data diagnostics.
• Do not patch from a guess or claim root cause when evidence supports only mitigation.
• Ask for missing context only when it materially blocks safe reproduction or isolation.

Progressive Contract Loading

Canonical tier files are contracts/input.yaml, contracts/output.yaml, contracts/phase-gates.yaml, and contracts/handoffs.yaml.

Read contracts/index.yaml first. Canonical contracts remain authoritative, but load only the boundary currently being enforced:

• entry for symptom, scope, reproduction target, safety, and edit permission;
• current_phase for SCOPE, REPRODUCE, HYPOTHESIZE, ISOLATE, FIX, or VERIFY;
• selected_handoff only when investigation or fix delegation is selected; and
• completion only for the artifact being returned.

If a selector is missing or invalid, load the full named canonical contract. Do not load every contract at entry.

Ownership

assistant-debugging owns diagnosis until the failure mechanism is reproducible or bounded strongly enough for a fix. Generic workflow may coordinate planning, delegation, and review, but specialist gates are authoritative.

Method

1. SCOPE — capture symptom, expected behavior, affected path, recent changes, constraints, and severity.
2. REPRODUCE — run the smallest safe failing test/command or record the exact blocker with available log/code/config evidence.
3. HYPOTHESIZE — keep at least three plausible causes unless evidence justifies fewer. Rank by likelihood, diagnostic cost, and blast radius.
4. ISOLATE — run the cheapest high-signal check first. Track supporting and disconfirming evidence until one cause predicts the symptom and fix.
5. FIX — add a regression test when feasible, then make the smallest change that addresses the cause. Label uncertain emergency changes as mitigations.
6. VERIFY — rerun the reproduction, focused test, relevant regressions, and normal project checks. Skipped checks remain residual risk.

Use assistant-debugging before assistant-tdd when a meaningful RED test cannot yet be written. Once the mechanism is understood, hand the regression test and evidence into the TDD cycle. Use assistant-review after non-trivial or risky fixes.

Output

Return status, symptom, reproduction or blocker, ranked hypotheses, root cause and confidence, fix summary, verification results, and residual risks.

Stop Rules

• Stop before speculative edits when the failure is neither reproduced nor bounded.
• Stop and ask before unsafe diagnostics.
• If every hypothesis is refuted, gather new evidence instead of cycling guesses.
• Use mitigated or inconclusive when proof is insufficient for root cause.