# Domain Coverage

> Where each core principle applies across the domains. The complement to `principles-matrix.md`: the matrix maps domain → core; this maps core → domains.

## Core Principle Coverage

| Core Principle | Domains that derive from it | Count |
|----------------|---------------------------|-------|
| C1 Correctness | All 11 (security, data, api, testing, performance, observability, errors, uiux, documentation, concurrency, devops) | Universal |
| C2 Clarity | uiux, api, data, testing, observability, errors, documentation, devops | 8 |
| C3 Simplicity | security, data, testing, performance, documentation, concurrency, devops | 7 |
| C4 Locality | testing, concurrency | 2 |
| C5 Reversibility | api, data, uiux, concurrency, devops | 5 |
| C6 Composability | api, security, observability, errors, documentation, concurrency | 6 |
| C7 Observability | api, data, testing, performance, observability, errors, devops | 7 |
| C8 Economy | security, testing, performance, observability, concurrency | 5 |

## Interpretation

- **C1 Correctness** is universal — every domain derives from it. This confirms C1 as the floor.
- **C4 Locality** is the narrowest (2 domains: testing independence, concurrency boundaries). Locality is inherently domain-specific; not a gap.
- **C2 Clarity** and **C7 Observability** are the next-most-derived, confirming they are cross-cutting concerns.
- **C6 Composability** appears in 6 domains — it is most relevant where parts combine (api, errors, observability, documentation, concurrency) and least relevant where the unit is monolithic.

## Per-Domain Coverage

| Domain | C-rules derived from | Notes |
|--------|---------------------|-------|
| UI/UX | C1, C2, C3, C5, C7 | User-facing; clarity + reversibility |
| API | C1, C2, C3, C5, C6, C7 | Contracts; composability + stability |
| Security | C1, C3, C6, C7, C8 | 8/10 non-tradeable (promoted to C1) |
| Data | C1, C2, C3, C5, C7 | Truth + migration safety |
| Testing | C1, C2, C3, C4, C7, C8 | Independence (C4) is unique |
| Performance | C1, C3, C6, C7, C8 | Economy + measurement |
| Observability | C1, C2, C6, C7, C8 | Self-referential (P7 derives from C7) |
| Errors | C1, C2, C5, C6, C7 | Errors as data + reversibility |
| Documentation | C1, C2, C3, C5, C6 | Docs-as-code + living docs |
| Concurrency | C1, C3, C4, C5, C6, C7, C8 | Broadest derivation; locality (C4) unique |
| DevOps | C1, C2, C3, C5, C7 | Reproducibility + rollback |

## Gaps and Notes

- No domain derives from only one C-rule. The minimum is 4 (UI/UX: C1, C2, C3, C5, C7 — actually 5). Every domain is multi-rooted.
- **Concurrency** has the broadest derivation (7 C-rules) — it touches the most core concerns.
- **UI/UX** and **API** are the most user-facing; they emphasize C2 (Clarity) heavily.
- **Security** is the only domain with explicit non-tradeable declarations; this promotes 8 of its rules to C1-equivalent per `core/conflict-resolution.md` §6.