Design a browser-based graphics editor

Design a graphics editor that runs in the browser for documents made of layers. A user opens a document, selects, moves, resizes and restyles layers, and imports images, and every edit must feel instant while being saved durably in the background. Multiplayer editing and plugins are out of scope.

Cover the split between client and server, how the document is represented in memory and in storage, rendering, keeping large image assets out of the document data, autosave with safe retries, and recovering unsaved edits after a refresh or a network drop.