Capacity Planning

Design a collaborative document editor: many people open the same document and type into it at once, every keystroke shows up for the others within a moment, and everyone's screen converges to the identical text with no edit ever silently lost.

In scope: concurrent text editing, real-time propagation of edits, presence (cursors and selections), and reconnecting after being offline. Rich formatting beyond plain text, sharing permissions, and peer-to-peer editing without a server are variants, covered briefly at the end.