# issue-04-performance-documentation: Create PERFORMANCE.md with benchmark analysis

## Description
Create comprehensive performance documentation that proves Phase 1 success. PERFORMANCE.md must document benchmark methodology, raw results from all benchmarks, performance breakdown by pipeline stage, CPython comparison analysis, and statistical confidence reporting.

## Architecture Reference
Read architecture.md Section "Performance Budget Breakdown" and "Testing Strategy" for:
- Target performance metrics (< 100μs cold start, ≥50x CPython speedup)
- Benchmark categories (cold start, warm execution, CPython baseline)
- Statistical requirements (CV < 10%)
- Performance breakdown by stage (lexing ~5μs, parsing ~10μs, compilation ~15μs, VM ~5μs)

## Interface Contracts
- Creates: `PERFORMANCE.md` with sections:
  - **Methodology**: How benchmarks run, hardware specs, statistical methods
  - **Results**: Raw data from criterion benchmarks (cold_start_simple, warm_execution, cpython_subprocess_baseline)
  - **Breakdown**: Performance by pipeline stage (lexing, parsing, compilation, VM execution, formatting)
  - **Comparison**: CPython speedup analysis with confidence intervals
  - **Variance**: Statistical confidence reporting (CV < 10%)
  - **Reproduction**: Instructions for running benchmarks
- Implements: Documentation validation for AC1.2 (< 100μs), AC1.3 (≥50x), AC1.5 (< 10% CV)
- Exports: Complete Phase 1 deliverable proving microsecond performance
- Consumes: Criterion JSON outputs from benchmark-infrastructure-setup, startup-execution-benchmarks, cpython-comparison-benchmark

## Files
- **Create**: `PERFORMANCE.md` (root directory)

## Dependencies
- issue-02-startup-execution-benchmarks (provides: Cold/warm benchmark results)
- issue-03-cpython-comparison-benchmark (provides: CPython baseline data)

## Provides
- AC1.4 validation: PERFORMANCE.md exists with required sections
- Complete Phase 1 deliverable
- Reproducible benchmark instructions
- Performance analysis proving < 100μs target and ≥50x speedup

## Acceptance Criteria
- [ ] PERFORMANCE.md exists with all required sections
- [ ] Methodology section documents benchmark setup and hardware
- [ ] Results section includes actual numbers from criterion benchmarks
- [ ] Breakdown section shows timing for each pipeline stage
- [ ] Comparison section proves ≥50x speedup vs CPython
- [ ] Variance section documents CV < 10% for all benchmarks
- [ ] Reproduction instructions enable others to verify results

## Testing Strategy

### Test Files
- `PERFORMANCE.md`: Manual verification of content

### Test Categories
- **Manual verification**: `cat PERFORMANCE.md | grep -E '(Methodology|Results|Breakdown|Comparison)'` - verifies all sections exist
- **Content validation**: Document includes actual benchmark numbers from criterion output
- **Speedup verification**: Speedup ratio ≥50x is documented with evidence
- **Reproduction check**: Instructions for running `cargo bench` are present

### Run Command
```bash
# Verify file exists and has required sections
test -f PERFORMANCE.md && grep -q 'Cold Start' PERFORMANCE.md
# Verify all section headers present
grep -E '(Methodology|Results|Breakdown|Comparison|Variance|Reproduction)' PERFORMANCE.md
```
