Token expirations cause incorrect timelines (exacerbated by OIDC refreshing tokens)

[kegsay]

because of the gappy syncs, and how initial syncs use timeline limit: 1 to pull in valid prev batch tokens, it means timeline_limit: 20 is pulling in the actual latest event then prepend state events then whatever crap was in the timeline before the last poller expired, see picture.

Ideally we would just return the latest event in this scenario, with a correct prev batch token so the client can backfill the data but that means we need to know where the gaps are, so we can then terminate the timeline fetch at the right spot.

The gap flag is a property of the event in the events table, as that table is the timeline ordering.

[kegsay]

Strictly not limited to OIDC:

i.e A and B in room X, only A using the proxy, send 20 msgs then sign out, some msgs go by, some state events, then B uses the proxy -> prepend the missed state+ see latest event only, then request timeline_limit: 20 and you'll see the same thing.