Send and process 'recipient update' sync messages.

SignalServiceKit/src/Devices/OWSRecordTranscriptJob.m

@@ -244,6 +244,11 @@ NS_ASSUME_NONNULL_BEGIN
             continue;
         }
 
+        if (!message.isFromLinkedDevice) {
+            OWSFailDebug(@"Ignoring 'recipient update' for message which was sent locally.");
+            continue;
+        }
+
         OWSLogInfo(@"Processing 'recipient update' transcript in thread: %@, timestamp: %llu, nonUdRecipientIds: %d, "
                    @"udRecipientIds: %d.",
             thread.uniqueId,

SignalServiceKit/src/Messages/DeviceSyncing/OWSIncomingSentMessageTranscript.m

@@ -41,7 +41,9 @@ NS_ASSUME_NONNULL_BEGIN
     if (self.isRecipientUpdate) {
         // Fetch, don't create.  We don't want recipient updates to resurrect messages or threads.
         if (self.dataMessage.group) {
-            _thread = [TSGroupThread fetchObjectWithUniqueID:_dataMessage.group.id transaction:transaction];
+            _thread = [TSGroupThread threadWithGroupId:_dataMessage.group.id transaction:transaction];
+        } else {
+            OWSFailDebug(@"We should never receive a 'recipient update' for messages in contact threads.");
         }
         // Skip the other processing for recipient updates.
     } else {