Design an Offline-First Sync Engine

Problem

Design a local-first sync engine that keeps the client instant while syncing to the server.

Requirements

• Apply mutations locally immediately (optimistic)
• Queue and sync to server
• Reconcile server updates and conflicts
• Work offline and catch up on reconnect

What evaluators look for

• Clear model: local store, mutation queue, sync layer
• Conflict resolution strategy
• Idempotency and ordering

Extension

Discuss how you keep the UI consistent during a failed/retried sync.