MM-52600: [Shared Channels] Shared channels do not sync channel membership (#30976)

server/platform/services/sharedchannel/service_api.go

@@ -277,3 +277,41 @@ func (scs *Service) CheckCanInviteToSharedChannel(channelId string) error {
 	}
 	return nil
 }
+
+// updateMembershipSyncCursor updates the LastMembersSyncAt value for the shared channel remote
+// This provides centralized and consistent cursor management
+func (scs *Service) updateMembershipSyncCursor(channelID string, remoteID string, newTimestamp int64) error {
+	// Get the remote record
+	scr, err := scs.server.GetStore().SharedChannel().GetRemoteByIds(channelID, remoteID)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to get shared channel remote for cursor update",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+			mlog.Int("timestamp", int(newTimestamp)),
+			mlog.Err(err),
+		)
+		return fmt.Errorf("failed to get shared channel remote for cursor update: %w", err)
+	}
+
+	if scr == nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Shared channel remote not found for cursor update",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+		)
+		return fmt.Errorf("shared channel remote not found for channel %s and remote %s", channelID, remoteID)
+	}
+
+	// Update the cursor - the store will handle ensuring it only moves forward
+	err = scs.server.GetStore().SharedChannel().UpdateRemoteMembershipCursor(scr.Id, newTimestamp)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update membership cursor",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+			mlog.String("remote_record_id", scr.Id),
+			mlog.Int("timestamp", int(newTimestamp)),
+			mlog.Err(err),
+		)
+	}
+
+	return err
+}