ADR-001: Tech stack

Status: Accepted

Context

A two-person (extensible) household needs a mobile app to track shared spending with real-time sync across phones and a future web client.

Decision

• Expo + React Native + TypeScript for one codebase across Android/iOS and a future web target.
• Expo Router for file-based navigation.
• NativeWind for styling (Tailwind semantics in RN).
• TanStack Query for server state, Zustand for local UI state.
• React Hook Form + Zod for forms and validation.
• expo-sqlite for the offline cache.
• Supabase (Postgres + Auth + RLS + Realtime) as the backend from day one.

Alternatives considered

• Flutter: native feel but a separate stack from the team's React experience.
• Local-only storage: rejected because real-time multi-device sharing is a hard requirement and a web client cannot read on-device storage.
• Firebase: viable, but Postgres + RLS gives stronger relational modeling and a cleaner web reuse path.

Consequences

Android-only SMS parsing requires a native module behind a platform check. NativeWind pulls a web react-dom peer that requires legacy-peer-deps. Jest is pinned to v29 to match the Expo SDK 56 preset.