as we'll need to await a bogus request first thing after opening the txn
funny enough, we originally made it sync to accommodate the same bug
in safari, but that didn't prevent any microtask being awaited
before scheduling a request in the calling code closing the txn.
We'll await a bogus request within the transaction class now so it
doesn't depend on the calling code
we were using the prev_batch of the last sync to pass to
/members, but this points at the timeline *before* the last
sync, so wouldn't contain all members. Use the sync token instead.
