Player Loaded World API (#1541)

Co-authored-by: Emil <12966472+Emilxyz@users.noreply.github.com>
Co-authored-by: Wouter Gritter <wouter@gritter.nl>

api/src/main/java/com/velocitypowered/api/event/player/PlayerClientLoadedWorldEvent.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2018-2026 Velocity Contributors
+ *
+ * The Velocity API is licensed under the terms of the MIT License. For more details,
+ * reference the LICENSE file in the api top-level directory.
+ */
+
+package com.velocitypowered.api.event.player;
+
+import com.google.common.annotations.Beta;
+import com.google.common.base.Preconditions;
+import com.velocitypowered.api.proxy.Player;
+
+/**
+ * Called when a player is marked as loaded by the client.
+ *
+ * <p>This event is fired once per {@link com.velocitypowered.api.proxy.ServerConnection}
+ * when the player explicitly notifies the server after loading the world (closing the downloading terrain screen)
+ *
+ * @implNote Unlike Paper this event will <u>not</u> fire due to a timeout nor respawning.
+ *     Though plugins can implement a timeout by scheduling a task in {@link ServerPostConnectEvent}
+ *     and checking {@link com.velocitypowered.api.proxy.ServerConnection#isClientLoaded()}.
+ * @sinceMinecraft 1.21.4
+ * @since 4.1.0
+ */
+@Beta
+public final class PlayerClientLoadedWorldEvent {
+
+  private final Player player;
+
+  public PlayerClientLoadedWorldEvent(Player player) {
+    this.player = Preconditions.checkNotNull(player, "player");
+  }
+
+  public Player getPlayer() {
+    return player;
+  }
+
+  @Override
+  public String toString() {
+    return "PlayerClientLoadedWorldEvent{"
+        + "player=" + player
+        + '}';
+  }
+}

api/src/main/java/com/velocitypowered/api/proxy/ServerConnection.java

@@ -7,6 +7,7 @@
 
 package com.velocitypowered.api.proxy;
 
+import com.google.common.annotations.Beta;
 import com.velocitypowered.api.proxy.messages.ChannelMessageSink;
 import com.velocitypowered.api.proxy.messages.ChannelMessageSource;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
@@ -40,6 +41,17 @@ public interface ServerConnection extends ChannelMessageSource, ChannelMessageSi
    */
   ServerInfo getServerInfo();
 
+  /**
+   * Returns whether the client notified this connection of having loaded the world.
+   *
+   * @return true if the client has loaded the world
+   * @implNote This is purely client-dependent; see {@link com.velocitypowered.api.event.player.PlayerClientLoadedWorldEvent}.
+   * @sinceMinecraft 1.21.4
+   * @since 4.1.0
+   */
+  @Beta
+  boolean isClientLoaded();
+
   /**
    * Returns the player that this connection is associated with.
    *