Example: Banking App

A reference architecture for a security-first banking app. Demonstrates how the toolkit's agents, skills, and standards combine on a high-sensitivity product.

What it demonstrates

• Clean Architecture + MVVM across Accounts, Transfers, and Auth features.
• OAuth2 + PKCE auth with Keychain storage and biometric app-lock.
• TLS public-key pinning for the banking API.
• REST integration with idempotent transfers and typed error mapping.
• High unit-test coverage of money-handling logic.

Module Map

Clean Architecture (Transfers slice)

• Domain: Money, Account, TransferUseCase (validates funds, currency), TransferRepository.
• Data: TransferDTO, mapper, RemoteTransferRepository with an idempotency key per transfer.
• Presentation: TransferViewModel (state enum), TransferView.

struct TransferUseCase {
    let repository: TransferRepository
    func execute(amount: Money, from: Account, to accountID: String) async throws -> Receipt {
        guard amount.cents > 0 else { throw TransferError.invalidAmount }
        guard from.balance >= amount else { throw TransferError.insufficientFunds }
        return try await repository.transfer(amount: amount, from: from.id,
                                             to: accountID, idempotencyKey: UUID().uuidString)
    }
}

Authentication

• Authorization Code + PKCE via ASWebAuthenticationSession (skills/security/ios/oauth2.md).
• Tokens in Keychain (...ThisDeviceOnly), refresh via a single-flight TokenManager actor.
• Biometric app-lock gates the dashboard (skills/security/ios/biometric_auth.md).

Security

• Public-key pinning on the banking host with a backup pin (skills/security/ios/ssl_pinning.md).
• No secrets/PII in logs; sensitive fields excluded from screenshots/backups.
• Audited against checklists/security_review.md.

Dependency Injection

• BankingAppContainer composition root wires clients → repositories → use cases → ViewModels.
• Features expose make…View(client:tokenManager:) factories.

Error Handling

• NetworkError → TransferError/DomainError; the UI shows actionable messages ("Insufficient funds", "Try again").
• Transfers are idempotent so a retried request never double-charges.

Testing Strategy

• Unit: money math, TransferUseCase (funds/limits/currency), refresh races.
• Integration: DTO decode + error mapping via URLProtocol stubs and fixtures.
• UI: login → dashboard → transfer happy path only.

Scalability Considerations

• Feature modules build/test independently; new products (Cards, Loans) added as modules.
• Pagination for transaction history (skills/networking/ios/pagination.md).
• Caching of account summaries with short TTL; invalidation after transfers.

Build it with the toolkit

workflows/implement_authentication.md → workflows/integrate_rest_api.md → workflows/perform_security_audit.md.