## Systematic Debugging: Root Cause Analysis

A previous attempt at this stage FAILED. Do NOT blindly retry the same approach. Follow this 4-phase investigation:

### Phase 1: Evidence Collection
- Read the error output from the previous attempt carefully
- Identify the EXACT line/file where the failure occurred
- Check if the error is a symptom or the root cause
- Look for patterns: is this a known error type?

### Phase 2: Hypothesis Formation
- List 3 possible root causes for this failure
- For each hypothesis, identify what evidence would confirm or deny it
- Rank hypotheses by likelihood

### Phase 3: Root Cause Verification
- Test the most likely hypothesis first
- Read the relevant source code — don't guess
- Check if previous artifacts (plan.md, design.md) are correct or flawed
- If the plan was correct but execution failed, focus on execution
- If the plan was flawed, document what was wrong

### Phase 4: Targeted Fix
- Fix the ROOT CAUSE, not the symptom
- If the previous approach was fundamentally wrong, choose a different approach
- If it was a minor error, make the minimal fix
- Document what went wrong and why the new approach is better

IMPORTANT: If you find existing artifacts from a successful previous stage, USE them — don't regenerate from scratch.

### Required Output (Mandatory)

Your output MUST include these sections when this skill is active:

1. **Root Cause Hypothesis**: List 3 possible root causes ranked by likelihood with specific evidence that would confirm/deny each
2. **Evidence Gathered**: Exact file:line location of failure, error messages, logs, code examination results, artifact validation (plan.md, design.md correctness)
3. **Fix Strategy**: Description of the ROOT CAUSE fix (not the symptom), with rationale for why this approach differs from the previous failed attempt
4. **Verification Plan**: How to verify the fix works (test cases, specific checks, expected behavior confirmation)

If any section is not applicable, explicitly state why it's skipped.