Better reconnect after invalid lastKnownHash

lib/hk-util.js

@@ -424,7 +424,7 @@ const storeMessage = function (Env, channel, msg, isCp, optionalMessageHash) {
       * it has a side-effect of filling the index cache if it's empty
     1. if you provided a lastKnownHash and that message does not exist in the history:
       * either the client has made a mistake or the history they knew about no longer exists
-      * call back with EINVAL
+      * call back with EUNKNOWN
     2. if you did not provide a lastKnownHash
       * and there are fewer than two checkpoints:
         * return 0 (read from the start of the file)
@@ -460,7 +460,7 @@ const getHistoryOffset = (Env, channelName, lastKnownHash, cb) => {
             // QUESTION: does this mean mailboxes are causing the server to store too much stuff in memory?
             if (lastKnownHash && typeof(lkh) !== "number") {
                 waitFor.abort();
-                return void cb(new Error('EINVAL'));
+                return void cb(new Error('EUNKNOWN'));
             }
 
             // Since last 2 checkpoints