phase-gated-debugging

name	phase-gated-debugging
description	ALWAYS use this when the user mentions Phase Gated Debugging, asks to build, debug, review, document, automate, test, configure, migrate, or make decisions in this domain, or the task clearly depends on Phase Gated Debugging; scope: Use when debugging any bug. Apply the bundled workflow, references, scripts, Senior Master standard, and Codex strict review gate before final output.

Phase-Gated Debugging

Selective Reading Rule

Start with:

• references/senior-master-standard.md
• references/usage-routing.md
• references/quality-checklist.md

Then load only the inherited docs, scripts, assets, or examples that match the user's actual task.

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 (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.