PaperMC
Player Loaded World API
With this PR, the in 1.21.4 introduced player_loaded packet can be utilised to send/display messages in-game without needing to guess when the player is actually in the world.
This PR only implements the part when the player joins a server, and not the respawn mechanic, this in my opinion makes sense as there's virtually no reason to fire stuff there on the proxy.
I'm not a fan of having to schedule a task for every player in 1.21.4+, though.
With the current implementation, the proxy waits 1500ms before the event fires as timed out,
which is notchian/paper behaviour, but can be overridden using the velocity.loaded-world-timeout-override system property.
Fixes: #1466
On another note. I think it could be a good idea to remove the timeout mechanism entirely, as plugins could create a similar mechanism by e.g. scheduling in the ServerPostConnectEvent and storing whether the loaded event triggered.
Edit: We could note that in the javadoc if desired