Extending CityScout to Web: Multi-Surface Product Design

A web surface makes sense when the product needs a larger planning canvas. People often research travel across tabs, share plans with other people, or revisit details from a desktop before they leave. Web is a better fit for that kind of work than a phone-only interface.

That does not make the web the primary experience. It makes it the planning and sharing layer. The trip itself still belongs on iOS, where the app can stay close to maps, quick decisions, and the on-the-ground rhythm of moving through a city.

A shared API contract is the right anchor for multiple surfaces. The iOS app and the future web app should both speak to the same itinerary and guide shapes, so the product does not fork into two subtly different versions of the same trip.

If the web layer lands, I would want the schema, validation rules, and endpoint behavior to stay aligned across clients. Whether that lives in a monorepo or another shared workspace shape is a future decision, but the architectural direction is clear: keep the contract central and avoid duplication.

Browser clients raise the security bar. They make shared secrets harder to protect, increase the surface area for abuse, and demand more care around auth, rate limiting, and response shaping. That is another reason the AI boundary should stay on the server.

• Never expose model credentials to the browser.
• Treat client requests as untrusted until validated on the server.
• Prefer explicit auth and rate limits over optimistic assumptions.
• Keep the itinerary contract stable enough that clients do not need special logic for every endpoint.

Once a product has multiple surfaces, tests stop being optional polish. They become the easiest way to keep the contract honest while the UI evolves. The web layer should not move the system faster than the tests can describe it.

The direction I want to keep tightening is straightforward: test the contract, test the failure modes, and make sure the product stays production-ready before expanding the surface area again. That is how the web layer can add value without adding confusion.