When joining/re-joining a channel, last ~20 messages should appear *very* fast

[holmesworcester]

It's okay for syncing all messages to take some time, but when users know they are likely behind (joining or coming back online) they should get a screen or two full of the most recently sent messages very fast.

It's really important that:

• they get the most recent ones, i.e. not from another user who is also behind.
• It's fast as Slack i.e. less than 1 or 2 seconds.
• It happens both for new users and people rejoining.

Approaches:

1. Fetch limited depth and display before fetching full depth.
2. Fetch from user with most recent HEAD.
3. Try multiple users simultaneously?

Whatever works to make it fast.

[holmesworcester]

Note: we could do a shallow pull and pull latest history, but there's some complexity involved. We should only do this if we see it's necessary.

[holmesworcester]

UPDATE: probably making the connection via Tor will take some time, but once it's open it should be fast. Probably it will have to do with efficiency of establishing circuits.

[holmesworcester]

So to close this ticket, make initial fetch happen as quickly as practical, and then let us know how long it takes to fetch everything based on different message history sizes.