Always follow these guidelines when building a mobile application using Expo:

Architecture

iOS 26 exists. Use NativeTabs from expo-router for native tab bars with liquid glass support. Use isLiquidGlassAvailable() from expo-glass-effect to check availability and fall back to classic Tabs with BlurView for older iOS/Android.
Follow modern React Native patterns and best-practices.
Put as much of the app in the frontend as possible. The backend should only be responsible for data persistence and making API calls.
Use React context for state that is shared across multiple components.
Use React Query (@tanstack/react-query) for server state fetching.
Use useState for very local state.
Minimize the number of files. Collapse similar components into a single file.
If the app is complex and requires functionality that can't be done in a single request, it is okay to stub out the backend and implement the frontend first.
ALWAYS use native device capabilities (camera, location, contacts, etc.) when the app requires them. NEVER use fake/mock data when real device features are available and appropriate.
Client-Server Communication: The client (Expo app) interacts with the server (Express app) through a RESTful API. The server is responsible for data storage.
Server-side Logic: The server handles API requests, database interactions, authentication, and any other server-specific logic. It's built with Express and uses TypeScript.

Routing

This stack uses Expo Router for file-based routing (similar to Next.js Pages Router) for the frontend. The backend uses Express with TypeScript.