[lib] Add timestamp check when flipping unread status

Summary:
This diff fixes messages appearing unread by adding a timestamp check when getting new messages.

https://linear.app/comm/issue/ENG-9727/thick-threads-appearing-unread

Test Plan:
1. User A logs to web and mobile
2. User B logs to web
3. User's A mobile is in background
4. User B sends DM to A
5. User A reads the message on web
6. User A brings mobile back to foreground. Verify the last message is not unread.
7. Repeat a few times

Reviewers: kamil, tomek

Reviewed By: tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13766

lib/shared/dm-ops/dm-op-utils.js

@@ -459,16 +459,15 @@ function getThreadUpdatesForNewMessages(
     const time = Math.max(messagesFromOtherPeers.map(message => message.time));
     invariant(threadInfo.thick, 'Thread should be thick');
 
-    // We aren't checking if the unread timestamp is lower than the time.
-    // We're doing this because we want to flip the thread to unread after
-    // any new message from a non-viewer.
-    newUpdateInfos.push({
-      type: updateTypes.UPDATE_THREAD_READ_STATUS,
-      id: uuid.v4(),
-      time,
-      threadID: threadInfo.id,
-      unread: true,
-    });
+    if (threadInfo.timestamps.currentUser.unread < time) {
+      newUpdateInfos.push({
+        type: updateTypes.UPDATE_THREAD_READ_STATUS,
+        id: uuid.v4(),
+        time,
+        threadID: threadInfo.id,
+        unread: true,
+      });
+    }
   }
 
   return newUpdateInfos;