phase-gated-debugging

# Phase-Gated Debugging ## Overview AI coding agents see an error and immediately edit code. They guess at fixes, get it wrong, and spiral. This skill enforces a strict 5-phase protocol where you CANNOT edit source code until the root cause is identified and confirmed. Based on [claude-debug](https://github.com/krabat-l/claude-debug) (full plugin with PreToolUse hook enforcement). ## When to Use Use this skill when: - a bug keeps getting "fixed" without resolving the underlying issue - you need to slow an agent down and force disciplined debugging before code edits - the failure is intermittent, a regression, performance-related, or otherwise hard to isolate - you want an explicit user confirmation checkpoint before any fix is applied ## The Protocol ### Phase 1: REPRODUCE Run the failing command/test. Capture the exact error. Run 2-3 times for consistency. - Do NOT read source code - Do NOT hypothesize - Do NOT edit any files ### Phase 2: ISOLATE Read code. Add diagnostic logging marked `// DEBUG`. Re-run with diagnostics. Binary search to narrow down. - Only `// DEBUG` marked logging is allowed - Do NOT fix the bug even if you see it ### Phase 3: ROOT CAUSE Analyze WHY at the isolated location. Use "5 Whys" technique. Remove debug logging. State: "This is my root cause analysis: [explanation]. Do you agree, or should I investigate further?" **WAIT for user confirmation. Do NOT proceed without it.** ### Phase 4: FIX Remove all `// DEBUG` lines. Apply minimal change addressing confirmed root cause. - Only edit files related to root cause - Do NOT refactor unrelated code ### Phase 5: VERIFY Run original failing test — must pass. Run related tests. For intermittent bugs, run 5+ times. If verification fails: root cause was wrong, go back to Phase 2. ## Bug-Type Strategies | Type | Technique | |------|-----------| | Crash/Panic | Stack trace backward — trace the bad value to its source | | Wrong Output | Binary search — log midpoint, halve search space each iteration | | Intermittent | Compare passing vs failing run logs — find ordering divergence | | Regression | `git bisect` — find the offending commit | | Performance | Timing at stage boundaries — find the bottleneck | ## Key Rules 1. NEVER edit source code in phases 1-3 (except `// DEBUG` in phase 2) 2. NEVER proceed past phase 3 without user confirmation 3. ALWAYS reproduce before investigating 4. ALWAYS verify after fixing ## Limitations - Use this skill only when the task clearly matches the scope described above. - Do not treat the output as a substitute for environment-specific validation, testing, or expert review. - Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.