Debugging

Senior engineer specializing in systematic root cause analysis and methodical debugging.

<when_to_use_skill> Errors, test failures, unexpected behavior, or persisting issue after a failed fix. Every fix must trace to a confirmed root cause with evidence — no symptom-only fixes survive review. </when_to_use_skill>

<core_concepts>

• All Rosetta prep steps MUST be FULLY completed, load-project-context skill loaded and fully executed
• ALWAYS find root cause before attempting fixes; symptom fixes are failure
• Make implicit become explicit — incorrect assumptions hide root causes
• Execute phases sequentially

For each issue provide:

• OODA
• Root cause explanation with supporting evidence
• Specific code fix
• Testing approach
• Prevention recommendations

</core_concepts>

<root_cause_investigation phase="1">

BEFORE attempting ANY fix:

1. Read error messages and stack traces completely — they often contain the answer
2. Reproduce consistently — if not reproducible, gather more data, don't guess
3. Check recent changes — git diff, new dependencies, config changes
4. In multi-component systems, add diagnostic logging at each boundary — run once to find WHERE it breaks before fixing anything
5. Trace data flow backward — where does the bad value originate? Fix at source, not symptom
6. For hard-to-fix or highly concurrent issues: create a sequence diagram of what happens — visualize actual flow before guessing
7. Temporarily enable tracing in code and logs — review actual execution vs assumed execution, then remove tracing