debug-phase

<quick_start> Debug errors systematically:

1. Reproduce error consistently (100% reliable reproduction)
2. Classify by type (syntax/runtime/logic/integration/performance) and severity (critical/high/medium/low)
3. Isolate root cause using binary search, logging, breakpoints, or 5 Whys
4. Implement fix with failing test first (TDD)
5. Add regression tests to prevent recurrence
6. Document in error-log.md with ERR-XXXX ID

Key principle: Fix root causes, not symptoms. Use 5 Whys to drill down. </quick_start>