A full-stack AI application has several boundaries. The browser collects input and presents state. The backend authenticates the user, validates the request, retrieves data, and calls the model. Storage holds durable records. The browser should not contain private service credentials.
Trace one request end to end before adding features. Identify request IDs, timeout behavior, and which layer owns each error. A browser error message may originate from an unavailable backend, rejected authentication, failed retrieval, or invalid generated output.
Keep the model behind an application contract so the UI does not depend on one provider’s raw response shape. That allows testing with a fake model and replacing an adapter without rewriting the whole product.
Exercise: draw a request from a text box to a grounded answer. Annotate the identity and data crossing every boundary and show an error path.
Check: you can locate where input validation, authorization, model credentials, and response validation belong.