@halome Yup, do it like that you can raise the security bar of your game, if you want to use navagent, you should take a look at Unity headless master server :D

I'm totally new to Colyseus but I've worked on multiplayer games for a while, and here is my idea about your problem: server calculate, client do.

In your particular scenario, it should be step like these:

• Player clicked on location, Client send the action (clicked, [location]) to server
• Server process, so at time 0.2s, player model will be at x, which direction like so, speed like so, send that information (0.2, [x], [dir],[speed]) to user
• Client display those information, and wait for next move from server

Then, no matter how many clients connected to your server, they will received the same game state