Debugging

Systematic debugging framework. Find root cause BEFORE fixing.

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Core Principle

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

Random fixes waste time and create new bugs.

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When to Use

• Test failures
• Bugs and errors
• Unexpected behavior
• Performance issues
• Build failures
• Before claiming "fixed"

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Four-Phase Process

Phase 1: Investigate

1. Read the error - Full message, stack trace
2. Reproduce - Confirm the bug exists
3. Check recent changes - git diff, git log
4. Gather evidence - Logs, console output

Phase 2: Analyze

1. Find working example - Similar code that works
2. Compare - What's different?
3. Identify pattern - Where does it diverge?

Phase 3: Hypothesize

1. Form theory - "It breaks because..."
2. Test minimally - Smallest change to verify
3. Confirm - Does fix work?

Phase 4: Fix

1. Write test first - Reproduces bug
2. Apply fix - Single focused change
3. Verify - Test passes, no regressions

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Root Cause Tracing

When error is deep in call stack:

1. Start at error location
2. Trace backward: where did bad data come from?
3. Continue tracing until source found
4. Fix at SOURCE, not symptom

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Verification Protocol

Iron Law: NO COMPLETION CLAIMS WITHOUT FRESH VERIFICATION

# Run verification
npm test  # or yarn test, pytest, etc.

# Check output
# THEN claim result

Wrong: "Should work now" Right: "Tests pass: [paste output]"

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Red Flags (Stop & Follow Process)

• "Quick fix for now"
• "Just try changing X"
• "It's probably X"
• "Should work now"
• "Seems fixed"

All mean: Return to Phase 1.

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Quick Reference

Bug found
  → Phase 1: Read error, reproduce, check changes
  → Phase 2: Find working example, compare
  → Phase 3: Form hypothesis, test minimally
  → Phase 4: Write test, fix, verify

Deep stack error?
  → Trace backward to source
  → Fix at source, not symptom

About to claim fixed?
  → Run verification command
  → Read output
  → THEN claim result

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References

For detailed techniques, see:

• references/systematic-debugging.md - Full four-phase details
• references/root-cause-tracing.md - Call stack tracing
• references/verification.md - Verification protocols

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