Build an Excalidraw clone

the prompt

Build a hand-drawn-style whiteboard app (an Excalidraw clone) in a single self-contained HTML file. Requirements: an infinite canvas with a rough, sketchy aesthetic; tools for freehand pen, rectangle, ellipse, arrow, and text; selecting and moving shapes; a color and stroke-width picker; pan and zoom; and undo. Persist the drawing to localStorage so it survives a reload. Use <canvas> (you may load rough.js from a CDN for the hand-drawn look; otherwise no libraries). Make it genuinely usable. Return only the HTML.

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