Fix the bug where if we leave and get added back, we get removed again

ts/receiver/closedGroups.ts

@@ -235,6 +235,7 @@ export async function handleNewClosedGroup(
     members: members,
     admins,
     active: true,
+    weWereJustAdded: true,
   };
 
   // be sure to call this before sending the message.
@@ -509,7 +510,8 @@ async function performIfValid(
     lastJoinedTimestamp = aYearAgo;
   }
 
-  if (envelope.timestamp <= lastJoinedTimestamp) {
+  const envelopeTimestamp = _.toNumber(envelope.timestamp);
+  if (envelopeTimestamp <= lastJoinedTimestamp) {
     window.log.warn(
       'Got a group update with an older timestamp than when we joined this group last time. Dropping it.'
     );

ts/session/group/index.ts

@@ -48,6 +48,7 @@ export interface GroupInfo {
   blocked?: boolean;
   admins?: Array<string>;
   secretKey?: Uint8Array;
+  weWereJustAdded?: boolean;
 }
 
 interface UpdatableGroupState {
@@ -243,7 +244,7 @@ export function buildGroupDiff(
 }
 
 export async function updateOrCreateClosedGroup(details: GroupInfo) {
-  const { id } = details;
+  const { id, weWereJustAdded } = details;
 
   const conversation = await ConversationController.getInstance().getOrCreateAndWait(
     id,
@@ -268,7 +269,9 @@ export async function updateOrCreateClosedGroup(details: GroupInfo) {
       updates.timestamp = updates.active_at;
     }
     updates.left = false;
-    updates.lastJoinedTimestamp = updates.active_at;
+    updates.lastJoinedTimestamp = weWereJustAdded
+      ? Date.now()
+      : updates.active_at;
   } else {
     updates.left = true;
   }