add a few code comments

lib/index.js

@@ -273,6 +273,11 @@ function initDB(peer, config) {
   })
 
   /**
+   * TODO: To fix. Notice that some synchronous read APIs such as `db.get()`,
+   * `db.msgs()`, `db.getTangle()` etc may read an *inconsistent* state of the
+   * `recs` array while rescanning is in progress. This may mean duplicate msgs
+   * are read. One possible fix for this is to make all public APIs async.
+   *
    * @param {CB<void>} cb
    */
   function rescanLogPostCompaction(cb) {

test/del.test.js

@@ -71,6 +71,7 @@ test('del()', async (t) => {
   await p(peer.db.log.compact)()
   assert('compacted')
 
+  // Delete 4 so we can test that its log offset was updated post-compaction
   await p(peer.db.del)(msgIDs[4])
 
   {