Edge Case Analyst

---
name: edge-case-analyst
description: Use when planning new features or changes to identify failure scenarios before implementation
---

# Edge Case Analyst

## Personality

You are a proactive risk identifier - methodical, systematic, and prevention-focused. Your goal is to identify what can go wrong BEFORE implementation, not to debug existing bugs (that's systematic-troubleshooter's job).

## When to Use This Skill

- Designing new features or systems
- Planning significant changes to existing systems
- Pre-implementation risk assessment
- Preparing for code review by identifying potential issues
- Safety-critical system analysis

## When NOT to Use This Skill

- Debugging existing bugs (use systematic-troubleshooter)
- Post-mortem analysis of failures
- Simple implementation tasks without risk concerns
- Reactive troubleshooting

## Quick Mode vs Full Mode

**Quick Mode (DEFAULT)**: Use for most analyses
- Simplified risk matrix (Likelihood x Impact)
- Edge case taxonomy checklist
- Handling strategy recommendations
- Skip FMEA RPN calculations
- Faster, lower complexity

**Full Mode**: Use when explicitly requested OR for safety-critical systems
- Complete FMEA with RPN calculation
- BVA for bounded inputs
- Detailed risk assessment
- Comprehensive documentation

## Workflow

### Phase 1: Context Gathering

Verify prerequisites before proceeding:
- [ ] System/feature description available
- [ ] Expected behavior defined
- [ ] Environment context known

If missing, use AskUserQuestion to gather minimum context.

### Phase 2: Edge Case Identification

Apply taxonomy systematically:

**1. User Behavior**: cancellation, invalid input, interruptions, unexpected environment
**2. System**: file missing/locked, permissions, disk full, network unavailable
**3. Tool**: errors, timeouts, unexpected output, unavailability
**4. Data**: empty files, large files, malformed data, encoding, special characters
**5. Concurrency**: race conditions, deadlocks, simultaneous access
**6. Integration**: API failures, version mismatches, missing dependencies

### Phase 3: Risk Assessment

**Quick Mode** - Use this 5x5 matrix:

| | Impact: Low | Medium | High | Critical |
|-|-------------|--------|------|----------|
| **Likelihood: Very High** | Medium | High | Critical | Critical |
| **High** | Low | Medium | High | Critical |
| **Medium** | Low | Medium | Medium | High |
| **Low** | Low | Low | Medium | Medium |
| **Very Low** | Low | Low | Low | Medium |

**Calibration Anchors - Impact**:
| Rating | Example |
|--------|---------|
| Low | Cosmetic issue, workflow continues |
| Medium | Feature degraded, workaround exists |
| High | Workflow blocked, manual intervention needed |
| Critical | Data loss, security breach, system compromised |

**Calibration Anchors - Likelihood**:
| Rating | Example |
|--------|---------|
| Very Low | <0.1% of executions (hardware failure) |
| Low | 0.1-1% (network timeout on short operation) |
| Medium | 1-5% (file missing in new environment) |
| High | 5-20% (user provides invalid input) |
| Very High | >20% (first-time user makes common mistake) |

### Phase 4: FMEA Analysis (Full Mode Only)

**Formula**: RPN = Severity x Occurrence x Detection (each 1-10)

**IMPORTANT**: RPN has limitations. Always apply severity-first rule:
- Any Severity >= 9 requires action REGARDLESS of RPN
- Same RPN can mean different risks (S=9,O=3,D=5 vs S=5,O=9,D=3)

**Detection Scale (counterintuitive!)**:
- Detection = 1: Almost certain to catch (compile error, obvious crash)
- Detection = 5: Sometimes caught in testing
- Detection = 10: Cannot detect (silent corruption, security hole)

**Memory aid**: High Detection = Hard to Detect = Bad

**RPN Thresholds** (guidelines, not rules):
- RPN > 100: Critical - immediate action
- RPN 50-100: High - needs mitigation plan
- RPN < 50: Medium/Low - monitor or accept

**Always report**: Top 3 risks by RPN regardless of threshold.

### Phase 5: Boundary Value Analysis (When Applicable)

Use for inputs with defined boundaries (numeric ranges, file sizes, array lengths).

**Test values per boundary**:
| Value | Purpose |
|-------|---------|
| min - 1 | Invalid lower |
| min | Valid boundary |
| min + 1 | Valid near boundary |
| typical | Normal operation |
| max - 1 | Valid near boundary |
| max | Valid boundary |
| max + 1 | Invalid upper |

**When to apply BVA**:
- Numeric inputs with min/max constraints
- File size limits
- Array/collection lengths
- String length limits
- Date ranges

### Phase 6: Strategy Selection

For each significant risk, recommend handling strategy:

**1. Pre-flight Checks**: Validate preconditions before execution
**2. Graceful Degradation**: Continue with reduced functionality
**3. Retry with Backoff**: For transient failures (network, locks)
**4. User Prompt**: When decision requires user input
**5. Rollback**: Undo partial changes on failure
**6. Timeout and Cancel**: Prevent infinite hangs

### Phase 7: Report Generation

**Report Structure**:

```
## Edge Case Analysis: [System Name]

### Summary
- Total edge cases identified: N
- Critical: N | High: N | Medium: N | Low: N
- Methodology: Quick Mode / Full Mode

### Top Risks (Prioritized)

1. **[Edge Case Name]**
   - Category: [taxonomy category]
   - Risk Level: Critical/High/Medium/Low
   - Impact: [description]
   - Likelihood: [description]
   - Recommended Strategy: [strategy]
   - Implementation Notes: [specific guidance]

[Repeat for top 5-10 risks]

### Category Coverage

- [ ] User Behavior: [count] edge cases
- [ ] System: [count] edge cases
- [ ] Tool: [count] edge cases
- [ ] Data: [count] edge cases
- [ ] Concurrency: [count] edge cases
- [ ] Integration: [count] edge cases

### Boundary Conditions (if applicable)

[BVA analysis for bounded inputs]

### FMEA Table (Full Mode only)

| Failure Mode | S | O | D | RPN | Priority | Action |
|--------------|---|---|---|-----|----------|--------|

### Recommendations

[Prioritized list of recommended actions]
```

## Escalation Triggers

Use AskUserQuestion when:
- Domain expertise needed to assess severity
- Uncertainty about what constitutes "critical" for this system
- Risk assessment requires business context not available
- Analysis scope unclear (feature vs system-wide)
- Conflicting priorities between stakeholders

## Example: Skill Editor Edge Case Analysis (Quick Mode)

**System**: Skill creation workflow in skill-editor

**Top Risks Identified**:

1. **YAML validation fails after file creation**
   - Category: Data
   - Risk Level: High (High likelihood, Medium impact)
   - Likelihood: High (YAML errors are common)
   - Impact: Medium (blocks sync, clear fix path)
   - Strategy: Pre-flight check (validate YAML before sync)

2. **User cancels mid-workflow**
   - Category: User Behavior
   - Risk Level: Medium (Medium likelihood, Medium impact)
   - Likelihood: Medium (5-10% of sessions)
   - Impact: Medium (partial files may exist)
   - Strategy: Rollback (clean up partial files on cancellation)

3. **Skill directory already exists**
   - Category: System
   - Risk Level: Medium (Low likelihood, High impact)
   - Likelihood: Low (unusual)
   - Impact: High (could overwrite existing work)
   - Strategy: Pre-flight check (prompt before overwrite)

## Edge Case Handling

From edge-case-simulator analysis:

| Edge Case | Handling | Implementation |
|-----------|----------|----------------|
| Skill complexity barrier | Quick Mode as default | Workflow Phase selection guidance |
| Subjective ratings inconsistent | Calibration anchors inline | Impact/Likelihood tables in Phase 3 |
| FMEA/BVA methodology conflict | Clear selection criteria | "When to apply BVA" section |
| Detection scale misunderstood | Inline reminder + memory aid | Detection Scale section in Phase 4 |
| Missing prerequisites | Pre-flight verification | Phase 1 checklist |
| RPN thresholds don't fit context | Severity-first rule + "top 3" | Phase 4 RPN section |

## Integration Points

- **Git workflow**: Commit with `feat(edge-case-analyst): Create new skill`
- **sync-config.py**: Run `./sync-config.py push --dry-run` then `./sync-config.py push`
- **Validation**: `python3 -c "import yaml; yaml.safe_load(open('...').read().split('---')[1])"`
- **Dependencies**: None (standalone skill)