> "I also use a lot of "classic" websites where they fall over because of bad server-side state.

An example, a train reservation site, where I choose dates + a destination. The next page, it shows me some results. I decide to change the date. I hit the back button, and it falls over, cuz the state management on the server is messed up."

any idea to not fall into a pit making an website/app/whatever?