Implement persistent Spark state with Zustand `useSparkStore` in `src/store/appStore.ts`, including safe load/save patterns that avoid hydration overwrite bugs. Use when building or updating any Spark that reads or writes user data across app sessions, especially when adding `getSparkData`/`setSparkData` logic, migrating from local storage patterns, or debugging data-loss after app restart.
2026-02-28