Candidates were derived purely from the event stream, so a read receipt
(or room account data change) in an otherwise quiet room was deferred
until someone spoke in it. Rooms with undelivered receipt/account-data
changes - tracked PREVIOUSLY on the per-connection stream maps, or with
activity in the token range - now count as candidates when the relevant
extension is enabled: the room wakes into the page (usually as an empty,
filtered-out entry) and the extension delivers the data.
Matthew Hodgson
8ec2cde02d