add a FIXME note for a sketchy implementation in history keeper

lib/hk-util.js

@@ -836,6 +836,9 @@ HK.onChannelMessage = function (Env, Server, channel, msgStruct) {
     if (isCp) {
         // id becomes either null or an array or results...
         id = CHECKPOINT_PATTERN.exec(msgStruct[4]);
+        // FIXME relying on this data to be stored on an in-memory structure
+        // managed by a dependency is fragile. We should put this somewhere
+        // more straightforward and reliable.
         if (Array.isArray(id) && id[2] && id[2] === channel.lastSavedCp) {
             // Reject duplicate checkpoints
             return;
@@ -901,6 +904,8 @@ HK.onChannelMessage = function (Env, Server, channel, msgStruct) {
             // FIXME
             if (Array.isArray(id) && id[2]) {
                 // Store new checkpoint hash
+                // there's a FIXME above which concerns a reference to `lastSavedCp`
+                // this is a hacky place to store important data.
                 channel.lastSavedCp = id[2];
             }
         }