# Baseline Comparison Study — Audit

## Security & Privacy

| Check | Status | Notes |
|-------|--------|-------|
| No PII in experiment data | PASS | Only user_id (opaque u64) used for assignment and aggregation |
| No external network calls | PASS | All computation is local, read-only over in-memory indexes |
| No new storage writes | PASS | Experiment module is purely read-only; no WAL entries, no fjall writes |
| Config validation | PASS | All three TidalDb methods validate config before processing |
| No secrets or credentials | PASS | No API keys, tokens, or auth material involved |

## Correctness & Safety

| Check | Status | Notes |
|-------|--------|-------|
| No panics on edge cases | PASS | Zero views yields 0.0 rates; zero control yields defined lift values |
| No integer overflow | PASS | Signal counts are u64; views/clicks/completions summed as u64 |
| No floating-point NaN | PASS | All division guarded by zero-check; `relative_lift` handles all zero-denominator cases |
| Deterministic assignment | PASS | FNV-1a hash is platform-independent (fixed constants, explicit byte ordering) |
| No unsafe code | PASS | No `unsafe` blocks in any experiment code |
| No unwrap in library code | PASS | All `unwrap()` confined to `#[cfg(test)]` blocks and integration tests |

## Performance

| Check | Status | Notes |
|-------|--------|-------|
| No hot-path impact | PASS | Experiment code is invoked on-demand, not in signal write or retrieve paths |
| Signal type resolution | PASS | Type IDs resolved once per report, not per user |
| Allocation profile | PASS | Two Vec allocations (treatment/control user lists) per report; no per-user allocations |
| O(n*m) scan acknowledged | INFO | `user_signal_count` scans full DashMap per user; acceptable for PG1 pilot scale (<1000 users) |

## API Surface

| Check | Status | Notes |
|-------|--------|-------|
| Public types re-exported | PASS | ExperimentConfig, ExperimentGroup, ExperimentReport, GroupMetrics, MetricLift all accessible from `tidaldb::` |
| No breaking changes | PASS | All additions are new types/methods; no existing API modified |
| Doc comments complete | PASS | All public types, methods, and error conditions documented |
| Error types consistent | PASS | Uses existing TidalError::InvalidInput and TidalError::Internal |

## Test Coverage

| Area | Unit Tests | Integration Tests |
|------|-----------|------------------|
| Assignment determinism | 1 | 1 |
| Balanced split | 2 (50/50, 10/90) | 1 (50/50) |
| Config validation | 6 | 0 |
| Lift math | 4 | 1 |
| Profile routing | 0 | 1 |
| Report aggregation | 0 | 2 |
| Chronological profile | 1 | 2 |
| **Total** | **16** | **7** |

## Verdict

**APPROVED.** No security, correctness, or performance concerns. The implementation is read-only, adds no overhead to existing hot paths, and has thorough test coverage across both unit and integration tests. The O(n*m) scan in `user_signal_count` is documented and acceptable for pilot scale.