Disable undo if fastmode

worldedit-core/src/main/java/com/boydti/fawe/config/BBC.java

@@ -93,6 +93,7 @@ public enum BBC {
     COMMAND_HISTORY_OTHER_ERROR("Unable to find session for %s0.", "WorldEdit.History"),
     COMMAND_REDO_SUCCESS("Redo successful%s0.", "WorldEdit.History"),
     COMMAND_UNDO_ERROR("Nothing left to undo. (See also `/inspect` and `/frb`)", "WorldEdit.History"),
+    COMMAND_UNDO_DISABLED("Undo disabled, use: //fast", "WorldEdit.History"),
     COMMAND_UNDO_SUCCESS("Undo successful%s0.", "WorldEdit.History"),
 
     OPERATION("Operation queued (%s0)", "WorldEdit.Operation"),

worldedit-core/src/main/java/com/sk89q/worldedit/command/HistoryCommands.java

@@ -227,6 +227,10 @@ public class HistoryCommands extends MethodCommands {
     )
     @CommandPermissions("worldedit.history.undo")
     public void undo(Player player, LocalSession session, CommandContext context) throws WorldEditException {
+        if (session.hasFastMode()) {
+            BBC.COMMAND_UNDO_DISABLED.send(player);
+            return;
+        }
         int times = Math.max(1, context.getInteger(0, 1));
         FawePlayer.wrap(player).checkConfirmation(() -> {
             EditSession undone = null;