bug-investigator

# Bug Investigator **Core principle:** Find root cause before attempting fixes. Symptom fixes are failure. ## The Iron Law No fixes without root cause investigation first. If you haven't completed Phase 1, you cannot propose fixes. ## When to Use Use for ANY technical issue: test failures, bugs, unexpected behavior, performance problems, build failures, integration issues. Especially when under time pressure, "one quick fix" seems obvious, you've already tried multiple fixes, or you don't fully understand the issue. Don't skip because issue "seems simple" or you're "in a hurry" — systematic debugging is faster than thrashing. ## The Four Phases Complete each phase before proceeding. ### Phase 1: Root Cause Investigation 1. **Read error messages carefully**: stack traces, line numbers, file paths, error codes — they often contain the exact solution 2. **Reproduce consistently**: exact steps, every time? If not reproducible → gather more data, don't guess 3. **Check recent changes**: git diff, recent commits, new dependencies, config changes, environment differences 4. **Multi-component systems**: add diagnostic instrumentation at each component boundary. Log what enters and exits each layer. Run once to gather evidence, then analyze which component fails 5. **Trace data flow**: backward tracing — where does the bad value originate? Keep tracing up until you find the source. Fix at source, not symptom ### Phase 2: Pattern Analysis 1. Find working examples of similar...