pub(in sync::v3) fn assemble_unread(
notification_count: Option<UInt>,
highlight_count: Option<UInt>,
thread_counts: Option<&BTreeMap<OwnedEventId, (u64, u64)>>,
send_notification_count_filter: impl Fn(&UInt) -> bool,
want_thread_unread: bool,
) -> UnreadNotificationsCount