debug

Debugging & System Investigation

Comprehensive debugging framework combining systematic investigation, root cause tracing, defense-in-depth validation, verification protocols, and system-level diagnostics.

Core Principle

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

Random fixes waste time and create new bugs. Find the 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, before claiming work complete

System-level: CI/CD pipeline failures, log analysis, database diagnostics, performance bottlenecks, infrastructure issues

Especially when: Under time pressure, "quick fix" seems obvious, tried multiple fixes, don't fully understand issue, about to claim success

Techniques

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

Four-phase framework:

• Phase 1: Root Cause Investigation (read errors, reproduce, check changes, gather evidence)
• Phase 2: Pattern Analysis (find working examples, compare, identify differences)
• Phase 3: Hypothesis and Testing (form theory, test minimally, verify)
• Phase 4: Implementation (create test, fix once, verify)

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 at 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 data passes through. Four layers: Entry validation → Business logic → Environment guards → Debug instrumentation

Load when: After finding root cause, need to add comprehensive validation

4. Verification (references/verification.md)

Run verification commands and confirm output before claiming success.

Iron law: NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION EVIDENCE

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

5. Investigation Methodology

For system-level issues (CI/CD, infrastructure, data pipeline):

1. Scope - Define what is broken and what is working
2. Gather - Collect logs, metrics, error outputs before touching anything
3. Isolate - Narrow to smallest reproducible case
4. Hypothesize - Form one theory, test it, reject or confirm
5. Fix & Validate - Fix at root, verify at every affected layer

Load when: Issue is not code-local — spans services, environments, or pipelines

6. Log & CI/CD Analysis

Use gh CLI and structured queries to diagnose pipeline failures:

# View failed CI run logs
gh run view <run-id> --log-failed

# List recent runs for a workflow
gh run list --workflow=<name> --limit 10

# Watch a running workflow
gh run watch <run-id>

For structured logs: filter by severity, timestamp range, and correlation ID before reading raw output.

Load when: CI/CD failure, deployment issue, or log-driven investigation

7. Performance Diagnostics

Identify bottlenecks before optimizing:

• Profile first — measure before guessing
• Check slow queries with EXPLAIN ANALYZE (PostgreSQL) or equivalent
• Identify N+1 query patterns in ORM usage
• Check memory allocation patterns for leaks
• Use psql for live database diagnostics

Load when: Slowness reported, timeout errors, resource exhaustion

8. Reporting Standards

For multi-component investigations, write a structured diagnostic report:

## Diagnostic Report
- **Issue:** [one-line description]
- **Root Cause:** [where and why it fails]
- **Evidence:** [logs, output, reproduction steps]
- **Fix Applied:** [what was changed]
- **Verification:** [command run + result]
- **Remaining Risk:** [any open questions]

Save to plans/reports/debugger-{date}-{slug}.md.

Load when: Investigation spans multiple components or will be shared with others

9. Task Management

For multi-component investigations, track progress with a checklist rather than holding state mentally:

- [ ] Reproduce the issue
- [ ] Identify root cause
- [ ] Fix applied
- [ ] Tests passing
- [ ] Verification complete

Add this checklist to the active plan or investigation report. Check items off as each step completes.

Load when: Investigation touches 3+ components or files

10. Frontend Verification

For visual bugs or UI regressions, use browser developer tools (or the agent-browser skill) to inspect rendering, network, and console errors directly in the browser.

Use /ck-scout ext to search for frontend-specific patterns before diving into devtools.

Load when: Visual regression, layout bug, client-side network error, or UI behavior that differs from expected

Quick Reference

Code bug → systematic-debugging.md (Phase 1-4)
  Error deep in stack? → root-cause-tracing.md (trace backward)
  Found root cause? → defense-in-depth.md (add layers)
  About to claim success? → verification.md (verify first)

System issue → Investigation Methodology (5 steps)
  CI/CD failure? → Log & CI/CD Analysis (gh CLI)
  Slow/timeout? → Performance Diagnostics
  Multi-component? → Task Management checklist + Reporting Standards
  Visual/UI bug? → Frontend Verification (agent-browser / browser devtools)

Tools Integration

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.