write a test to reproduce the issue

bindings_ffi/src/mls.rs

@@ -2303,6 +2303,98 @@ mod tests {
         assert_eq!(client2_members.len(), 2);
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 5)]
+    async fn test_create_new_installations_does_not_fork_group() {
+        let bo_wallet_key = &mut rng();
+        let bo_wallet = xmtp_cryptography::utils::LocalWallet::new(bo_wallet_key);
+
+        // Create clients
+        let alix = new_test_client().await;
+        let bo = new_test_client_with_wallet(bo_wallet.clone()).await;
+        let caro = new_test_client().await;
+
+        let message_callbacks = RustStreamCallback::default();
+        let stream_messages = alix
+            .conversations()
+            .stream_all_messages(Box::new(message_callbacks.clone()))
+            .await;
+        stream_messages.wait_for_ready().await;
+
+        let group = alix
+            .conversations()
+            .create_group(
+                vec![bo.account_address.clone(), caro.account_address.clone()],
+                FfiCreateGroupOptions::default(),
+            )
+            .await
+            .unwrap();
+
+        // Sync groups
+        alix.conversations().sync().await.unwrap();
+        bo.conversations().sync().await.unwrap();
+        caro.conversations().sync().await.unwrap();
+
+        // Find groups for both clients
+        let alix_group = alix.group(group.id()).unwrap();
+        let caro_group = bo.group(group.id()).unwrap();
+
+        // Send messages
+        alix_group
+            .send("First message".as_bytes().to_vec())
+            .await
+            .unwrap();
+
+        caro_group
+            .send("Second message".as_bytes().to_vec())
+            .await
+            .unwrap();
+
+        // Drop and delete local database for client2
+        bo.release_db_connection().unwrap();
+
+        // Recreate client2 (new installation)
+        let bo2 = new_test_client_with_wallet(bo_wallet).await;
+
+        // let bo_message_callbacks = RustStreamCallback::default();
+        // let bo_stream_messages = bo2
+        //     .conversations()
+        //     .stream_all_messages(Box::new(bo_message_callbacks.clone()))
+        //     .await;
+        // bo_stream_messages.wait_for_ready().await;
+
+        // Send a message that will break the group
+        alix_group
+            .send("Third message".as_bytes().to_vec())
+            .await
+            .unwrap();
+
+        let bo_group = bo2.group(group.id()).unwrap();
+
+        bo_group
+            .send("Fourth message".as_bytes().to_vec())
+            .await
+            .unwrap();
+
+        caro_group
+            .send("Fifth message".as_bytes().to_vec())
+            .await
+            .unwrap();
+
+        let caro_messages = caro_group
+            .find_messages(FfiListMessagesOptions::default())
+            .unwrap();
+        let alix_messages = alix_group
+            .find_messages(FfiListMessagesOptions::default())
+            .unwrap();
+        let bo_messages = bo_group
+            .find_messages(FfiListMessagesOptions::default())
+            .unwrap();
+
+        assert_eq!(caro_messages.len(), 5);
+        assert_eq!(alix_messages.len(), 6);
+        assert_eq!(bo_messages.len(), 5);
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 5)]
     async fn test_can_send_messages_when_epochs_behind() {
         let alix = new_test_client().await;