A React Native (Expo) app for the library services in this set: search the catalog and borrow a copy, or ask the AI assistant — and confirm every change on the same card, whether you asked for it or the assistant proposed it.
Live mode on iOS against the Python library API and the assistant API. Right: a book title
carrying “ignore all previous instructions…” made the assistant propose a loan for m_attacker —
it arrives as a warned card and runs only if the person confirms.
It exists to show three things a mobile client in a multi-service system needs, and how to make each one fail loudly:
| How | Fails when | |
|---|---|---|
| Types from contracts | src/api/*.gen.ts are generated from the services' committed OpenAPI documents; calls go through typed openapi-fetch clients |
a service changes its contract and the app has not followed (npm run contracts:check) · the app calls a path or field that does not exist (tsc) |
| Mock-first, but honest mocks | Without a service URL the app runs on in-memory mocks; every mock response satisfies the generated schema type |
a mock drifts from the real API (tsc) |
| The same client against real services | npm run test:live drives the generated clients against running services; CI starts them from their own repositories |
the wiring works on mocks but not on the wire |
| Human approval in the UI | One ConfirmCard for all changes; an assistant proposal the user never asked for arrives suspicious and shows the service's reasons |
a change could run without a tap (screen tests) |
The live test earned its place on day one: Expo SDK 57's global fetch
rejects the Request objects openapi-fetch sends ("Unsupported BodyInit
type"). The mock-backed screen tests could not see it — the mocks read the
Request themselves. The app now bridges it (expoFetch in
src/api/clients.ts).
| Tab | Talks to | Contract |
|---|---|---|
| Catalog | the library API — Python or .NET; one spec, one contract | contracts/openapi.json in either |
| Assistant | the tool-calling assistant's HTTP API | contracts/openapi.json there |
Borrowing from the catalog needs a copy id; the library API gained
GET /catalog/books/{isbn}/copies for this app — spec first
(feature 003, rule CAT-R3),
then both implementations, then the regenerated types here.
npm install
npm start # mock mode: no services needed
# live mode
EXPO_PUBLIC_LIBRARY_URL=http://localhost:8000 \
EXPO_PUBLIC_ASSISTANT_URL=http://localhost:8001 npm start
npm run check # lint, strict tsc, screen tests, contract gate
npm run test:live # generated clients against running services (env as above)| Path | |
|---|---|
src/api/ |
Generated types, typed clients, contract-checked mocks |
src/ui/ConfirmCard.tsx |
The one approval surface |
src/features/catalog/ |
Search → copies → borrow |
src/features/assistant/ |
Conversation with proposals as cards |
src/__tests__/ |
Screen flows on mocks; live.test.ts against real services |
scripts/contracts.sh |
Generate / check types from both published contracts |
Part of a set: llm-tool-calling-assistant · spec-driven-ddd-python · spec-driven-ddd-dotnet · gitops-reference · ai-native-engineering. By Hasan Özkan · LinkedIn