I worked a place that did roaming from one AP to another one on a train in Norway in the early 2000 / late 90s, think we was the first in the world to do it.
To don't have a huge network drop we used a VPN connection on the client computer so it had the same IP while jumping from one wifi over to the other one.
https://m.youtube.com/watch?v=Q2X_UATE9-c