Swift Data

This enforces the clinic modular MVVM-C architecture for SwiftData on iOS 26 and Swift 6.2, keeping all SwiftData types locked inside the Data layer while feature modules work with domain structs and repository protocols. It covers the full workflow from @Model entity design through stale-while-revalidate reads, optimistic queued writes, sync coordinators with retry policies, and routing persistence errors through centralized AppError infrastructure. Use it when you need architectural guardrails that prevent SwiftData from leaking into ViewModels or when you're wiring up background sync with conflict resolution. The troubleshooting section alone is worth having open during any data layer refactor.