add a FIXME note

lib/hk-util.js

@@ -672,6 +672,7 @@ const handleGetHistoryRange = function (Env, Server, seq, userId, parsed) {
 
         if (!Array.isArray(messages)) { messages = []; }
 
+        // FIXME this reduction could be done in the worker instead of the main process
         var toSend = [];
         if (typeof (desiredMessages) === "number") {
             toSend = messages.slice(-desiredMessages);