Design a Real-Time Collaborative Design Editor

Problem

Design the backend for a real-time collaborative editor (multiple users editing a CAD/design doc together — Autodesk's domain).

Requirements

Functional:

• Multiple users edit the same document live
• See others' cursors/changes in real time
• Conflict resolution on concurrent edits
• Version history

Non-functional:

• Thousands of concurrent docs
• Low-latency sync
• No lost edits

Discussion points

1. CRDT vs OT for conflict resolution
2. WebSocket session/presence management
3. Persistence and version history
4. Large-document partial loading
5. Offline edits and reconciliation