Collaborative editor (Google Docs)

Let dozens of people edit the same document concurrently in real time, offline or online, and converge to the exact same state. The core design combines Operational Transformation (OT) or sequence CRDTs with an append-only operation log, background snapshot compaction, and ephemeral cursor/presence fan-out.

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Duration 45:00

Requirements checklist

Multiple users edit the same rich-text document simultaneously and see each other's changes and cursors in real time.Strong eventual convergence: any two collaborators who have received the same set of operations display the exact same document.Offline editing and reconnect without losing or duplicating operations; version history and point-in-time restore.Local typing is zero-latency (optimistic local apply); remote collaborators see edits within ~100–200 ms.Zero data loss once an operation is acknowledged; idempotent operation replay across reconnects.Cap active editors per document (~100 concurrent writers) while supporting thousands of read-only viewers.

Clarifying questions

How many concurrent editors vs read-only viewers must a single document support?
Do we need long-lived offline editing with automatic merge, or primarily online collaboration?
Is the document plain text, rich text (spans), or block-structured (Notion/Figma)?
What granularity of version history must be retained?

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requirements

Suggested time: about 6 minutes. Distinguishes persistent op log from ephemeral presence and read-only viewer fan-out.

Notes for requirements