Design a Collaborative Document Editor

Design a collaborative document editor where several users can edit the same document and see each other's changes. ### Constraints & Assumptions The source names collaborative-document design without specifying an algorithm or scale. Define a concrete initial document model, such as plain text, and discuss rich text or offline editing as explicit extensions. Separate durable edits from ephemeral cursor presence. ### Clarifying Questions Must offline edits merge? What ordering and conflict behavior should users see? Are documents plain text or structured rich text? Who can edit, view, or share? What history and recovery guarantees are required? ### What a Strong Answer Covers A document/operation model, convergence strategy, synchronization and reconnection, snapshots/history, access control, presence, and operational failure handling. ### Follow-up Questions Why is last-write-wins replacement of the whole document inadequate? How do concurrent insertions at the same position converge? What changes when a client reconnects with old edits or loses permission?