Heaps of Learnings here [0] from getting an entire games state into a url or QR code (a pretty damn complex game, 5-10 minute games comfortably fit in a QR code such that games can be replayed exactly as they happened - no server)
[0] - https://github.com/con-dog/snibble/blob/master/README.md
Tnx. HN post discussions include: How to store your app's entire state in the url https://news.ycombinator.com/item?id=34312546 ; Storing State in the URL https://news.ycombinator.com/item?id=31312680 .