Add XXX

lib/hk-util.js

@@ -893,6 +893,7 @@ HK.onChannelMessage = function (Env, Server, channel, msgStruct, cb) {
         // more straightforward and reliable.
         if (Array.isArray(id) && id[2] && id[2] === channel.lastSavedCp) {
             // Reject duplicate checkpoints
+            // XXX not an error? the checkpoint is already here so we can assume it's stored
             return void cb('DUPLICATE');
         }
     }