Explicitly reject consuming signed command when denied by event

This would fail down the line anyway due to inconsistent chat state (if holding a 'last seen' update)

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/session/SessionCommandHandler.java

@@ -44,11 +44,24 @@ public class SessionCommandHandler implements CommandHandler<SessionPlayerComman
 
   @Nullable
   private MinecraftPacket consumeCommand(SessionPlayerCommandPacket packet) {
-    if (packet.lastSeenMessages != null) {
+    if (packet.lastSeenMessages == null) {
-      return new ChatAcknowledgementPacket(packet.lastSeenMessages.getOffset());
-    }
       return null;
     }
+    if (packet.isSigned()) {
+      // Any signed message produced by the client *must* be passed through to the server in order to maintain a
+      // consistent state for future messages.
+      logger.fatal("A plugin tried to deny a command with signable component(s). "
+          + "This is not supported. "
+          + "Disconnecting player " + player.getUsername() + ". Command packet: " + packet);
+      player.disconnect(Component.text(
+          "A proxy plugin caused an illegal protocol state. "
+              + "Contact your network administrator."));
+      return null;
+    }
+    // An unsigned command with a 'last seen' update will not happen as of 1.20.5+, but for earlier versions - we still
+    // need to pass through the acknowledgement
+    return new ChatAcknowledgementPacket(packet.lastSeenMessages.getOffset());
+  }
 
   @Nullable
   private MinecraftPacket forwardCommand(SessionPlayerCommandPacket packet, String newCommand) {
@@ -83,14 +96,6 @@ public class SessionCommandHandler implements CommandHandler<SessionPlayerComman
     queueCommandResult(this.server, this.player, event -> {
       CommandExecuteEvent.CommandResult result = event.getResult();
       if (result == CommandExecuteEvent.CommandResult.denied()) {
-        if (packet.isSigned()) {
-          logger.fatal("A plugin tried to deny a command with signable component(s). "
-              + "This is not supported. "
-              + "Disconnecting player " + player.getUsername() + ". Command packet: " + packet);
-          player.disconnect(Component.text(
-              "A proxy plugin caused an illegal protocol state. "
-                  + "Contact your network administrator."));
-        }
         return CompletableFuture.completedFuture(consumeCommand(packet));
       }