deedy/qr-data-transfer ? reverse-engineered prompt

Build me a web app that lets me send a file from one device to another through an animated QR code stream, with no file upload to a server. The sender should open on the main page, let me choose a file, then turn it into a fast changing QR stream. The receiver should open on a scan page, use the rear camera, watch the code, and rebuild the file once enough data has been captured.

I want it to be reliable, so if frames are missed or scanned out of order it should still recover and verify everything with checksums before saving. It should support a normal mode and a faster dual lane mode that works best fullscreen and in landscape. Make it feel polished and clear for a regular person to use, with simple instructions on screen and a smooth start and stop flow. If you need current docs for any browser or QR library behavior, look them up online.