From a flow sketch to an importable backup
Preset 1: Flow sketch (flow-sketch). Open /app/?lang=en&tool=whiteboard and choose "Flow sketch": the scene has three rectangles (start → refine → review), two bound arrows and the Chinese title. All coordinates are fixed (e.g. the first rectangle is x=80,y=120,w=160,h=72) with fixed seeds for reproducibility.
Steps: (1) use the whiteboard inspect action to view validation and positions; (2) use export with format=excalidraw to download draw-export-<timestamp>.excalidraw; (3) re-import that file and check positions again — rectangle x/y/width/height, arrow points and Chinese text match item by item (the Node test roundTripScene asserts positionsEqual / chinesePreserved / arrowPointsPreserved are all true); (4) format=svg produces download content only; SVG is never injected into the DOM.
If the current canvas has changes, export a backup first; New/preset/import return a confirmation token and only replace after confirmation. Drafts are off by default and write al:draw:v1:* only when enabled; use "Clear this site only" on shared devices.
Honest scope: this tutorial demonstrates the deterministic scene model and serialization contract, not real freehand Canvas interaction; the real Excalidraw engine and PNG rasterization are not integrated / not verified.