What an amazing look into one of the greatest minds in programming!

Thank you for this treasure.

The relevant bits:

I am now allowing the client to guess at the results of the users movement until the authoritative response from the server comes through. This is a biiiig architectural change. The client now needs to know about solidity of objects, friction, gravity, etc. I am sad to see the elegent client-as-terminal setup go away, but I am practical above idealistic.

The server is still the final word, so the client is allways repredicting it's movement based off of the last known good message from the server.