Debugging & System Investigation

> Output style: Follow process/development-protocols/communication-standards.md — answer-first, plain language, no unexplained jargon, TL;DR on long responses.

Comprehensive framework combining systematic debugging, root cause tracing, defense-in-depth validation, verification protocols, and system-level investigation (logs, CI/CD, databases, performance).

Core Principle

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

Random fixes waste time and create new bugs. Find root cause, fix at source, validate at every layer, verify before claiming success.

When to Use

Code-level: Test failures, bugs, unexpected behavior, build failures, integration problems System-level: Server errors, CI/CD pipeline failures, performance degradation, database issues, log analysis Always: Before claiming work complete

Techniques

1. Systematic Debugging (references/systematic-debugging.md)

Four-phase framework: Root Cause Investigation → Pattern Analysis → Hypothesis Testing → Implementation. Complete each phase before proceeding. No fixes without Phase 1.

Load when: Any bug/issue requiring investigation and fix

2. Root Cause Tracing (references/root-cause-tracing.md)

Trace bugs backward through call stack to find original trigger. Fix at source, not symptom. Includes scripts/find-polluter.sh for bisecting test pollution.

Load when: Error deep in call stack, unclear where invalid data originated

3. Defense-in-Depth (references/defense-in-depth.md)

Validate at every layer: Entry validation → Business logic → Environment guards → Debug instrumentation

Load when: After finding root cause, need comprehensive validation

4. Verification (references/verification.md)

Iron law: NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE. Run command. Read output. Then claim result.

Load when: About to claim work complete, fixed, or passing

5. Investigation Methodology (references/investigation-methodology.md)

Five-step structured investigation for system-level issues: Initial Assessment → Data Collection → Analysis → Root Cause ID → Solution Development

Load when: Server incidents, system behavior analysis, multi-component failures

6. Log & CI/CD Analysis (references/log-and-ci-analysis.md)

Collect and analyze logs from servers, CI/CD pipelines (GitHub Actions), application layers. Tools: gh CLI, structured log queries, correlation across sources.

Load when: CI/CD pipeline failures, server errors, deployment issues

7. Performance Diagnostics (references/performance-diagnostics.md)

Identify bottlenecks, analyze query performance, develop optimization strategies. Covers database queries, API response times, resource utilization.

Load when: Performance degradation, slow queries, high latency, resource exhaustion

8. Reporting Standards (references/reporting-standards.md)

Structured diagnostic reports: Executive Summary → Technical Analysis → Recommendations → Evidence

Load when: Need to produce investigation report or diagnostic summary

9. Task Management (references/task-management-debugging.md)

Track investigation pipelines via Claude Native Tasks (TaskCreate, TaskUpdate, TaskList). Hydration pattern for multi-step investigations with dependency chains and parallel evidence collection. Fallback: Task tools are CLI-only — if unavailable (VSCode extension), use TodoWrite for tracking. Debug workflow remains fully functional.

Load when: Multi-component investigation (3+ steps), parallel log collection, coordinating debugger subagents

10. Frontend Verification (references/frontend-verification.md)

Visual verification of frontend implementations via Chrome MCP (Claude Chrome Extension) or vc-agent-browser skill fallback. Detect if frontend-related → check Chrome MCP availability → screenshot + console error check → report. Skip if not frontend.

Load when: Implementation touches frontend files (tsx/jsx/vue/svelte/html/css), UI bugs, visual regressions

Quick Reference

Code bug       → systematic-debugging.md (Phase 1-4)
  Deep in stack  → root-cause-tracing.md (trace backward)
  Found cause    → defense-in-depth.md (add layers)
  Claiming done  → verification.md (verify first)

System issue   → investigation-methodology.md (5 steps)
  CI/CD failure  → log-and-ci-analysis.md
  Slow system    → performance-diagnostics.md
  Need report    → reporting-standards.md

Frontend fix   → frontend-verification.md (Chrome/devtools)

Tools Integration

• Database: sqlite3 CLI and drizzle-kit studio for SQLite/libSQL diagnostics
• CI/CD: gh CLI for GitHub Actions logs and pipeline debugging
• Codebase: vc-docs-seeker skill for package/plugin docs; vc-scout skill for codebase exploration
• Scouting: /vc-scout or /vc-scout ext for finding relevant files
• Frontend: Chrome browser or vc-agent-browser skill for visual verification (screenshots, console, network)
• Skills: Activate vc-problem-solving skill when stuck on complex issues

Red Flags

Stop and follow process if thinking:

• "Quick fix for now, investigate later"
• "Just try changing X and see if it works"
• "It's probably X, let me fix that"
• "Should work now" / "Seems fixed"
• "Tests pass, we're done"

All mean: Return to systematic process.