6b0b637636
- Root cause: App.tsx collab sync effect called setLayers(collab.layers) even when collab.layers was empty, wiping out initialLayers - Effect: RenderEngine.render() iterates layers to draw elements; with 0 layers, no elements render (appear to disappear) - Fix: guard against empty collab.layers Fixes: drawing tools work on desktop and mobile, objects persist after release