Funny how I made almost exactly the same but for maps. I needed a way to share a link to a map, with drawings and the ability for the receiver to see their own location on the map. Annotated screenshots solves the first but not the second. Vibe engineered this, with many of the same ideas as OP. Took an evening. Just in time apps for one specific use case is a thing. And because it's so cheap to make and can be hoste…
And if you are open to bug reports.. if I move around the drawings move smoothly with the map, but if I zoom in/out the drawings move only after the map zooming animation ends, rather than smoothly