systematic-debugging（系统调试）

Systematic Debugging

Core principle: Find root cause before attempting fixes. Symptom fixes are failure.

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

Phase 1: Root Cause Investigation

BEFORE attempting ANY fix:

1. Read Error Messages Carefully

- Read stack traces completely - Note line numbers, file paths, error codes - Don't skip warnings

1. Reproduce Consistently

- What are the exact steps? - If not reproducible → gather more data, don't guess

1. Check Recent Changes

- Git diff, recent commits - New dependencies, config changes - Environmental differences

1. Gather Evidence in Multi-Component Systems WHEN system has multiple components (CI → build → signing, API → service → database): Add diagnostic instrumentation before proposing fixes: For EACH component boundary: - Log what data enters/exits component - Verify environment/config propagation - Check state at each layer Run once to gather evidence → analyze → identify failing component Example: # Layer 1: Workflow echo "=== Secrets available: ===" echo "IDENTITY: ${IDENTITY:+SET}${IDENTITY:-UNSET}" # Layer 2: Build script env | grep IDENTITY || echo "IDENTITY not in environment" # Layer 3: Signing security find-identity -v
2. Trace Data Flow See references/root-cause-tracing.md for backward tracing technique. Quick version: Where does bad value originate? Trace up call chain until you find the source. Fix at source.

Phase 2: Pattern Analysis

1. Find Working Examples - Similar working code in codebase
2. Compare Against References - Read reference implementations COMPLETELY, don't skim
3. Identify Differences - List every difference, don't assume "that can't matter"
4. Understand Dependencies - Components, config, environment, assumptions

Phase 3: Hypothesis and Testing

1. Form Single Hypothesis - "I think X is root cause because Y" - be specific
2. Test Minimally - SMALLEST possible change, one variable at a time
3. Verify - Worked → Phase 4. Didn't work → form NEW hypothesis, don't stack fixes
4. When You Don't Know - Say so. Don't pretend.

Phase 4: Implementation

1. Create Failing Test Case

- Use the test-driven-development skill - MUST have before fixing

1. Implement Single Fix

- ONE change at a time - No "while I'm here" improvements

1. Verify Fix

- Test passes? Other tests still pass? Issue resolved?

1. If Fix Doesn't Work

- Count attempts - If < 3: Return to Phase 1 with new information - If ≥ 3: Escalate (below)

Escalation: 3+ Failed Fixes

Pattern indicating architectural problem:

• Each fix reveals new problems elsewhere
• Fixes require massive refactoring
• Shared state/coupling keeps surfacing

Action: STOP. Question fundamentals:

• Is this pattern fundamentally sound?
• Are we continuing through inertia?
• Refactor architecture vs. continue fixing symptoms?

Discuss with human partner before more fix attempts. This is wrong architecture, not failed hypothesis.

Red Flags → STOP and Return to Phase 1

If you catch yourself thinking:

• "Quick fix for now, investigate later"
• "Just try changing X"
• "I'll skip the test"
• "It's probably X"
• "Pattern says X but I'll adapt it differently"
• Proposing solutions before tracing data flow
• "One more fix" after 2+ failures

Human Signals You're Off Track

• "Is that not happening?" → You assumed without verifying
• "Will it show us...?" → You should have added evidence gathering
• "Stop guessing" → You're proposing fixes without understanding
• "Ultrathink this" → Question fundamentals
• Frustrated "We're stuck?" → Your approach isn't working

Response: Return to Phase 1.

Supporting Techniques

Reference files in references/:

• root-cause-tracing.md - Trace bugs backward through call stack
• defense-in-depth.md - Add validation at multiple layers after finding root cause
• condition-based-waiting.md - Replace arbitrary timeouts with condition polling

Related skills:

• test-driven-development - Creating failing test case (Phase 4)
• verification-before-completion - Verify fix before claiming success