Synchronize unpromoted chats

[Hocuri]

• Operating System (Linux/Mac/Windows/iOS/Android): Linux
• Core Version: v1.159.4
• Client Version: 1.58.2 (git: flathub)

Problem: Group invite link doesn't work if wrong device answers the securejoin message

Steps to reproduce the problem

1. Alice has two devices, A1 and A2
2. A1 creates a group (without promoting it by sending a message; note that group creation is not synced, i.e. A2 doesn't know about this group), creates a group invite link, and sends it to Bob
3. A1 goes offline
4. Bob clicks on the link, A2 answers
5. A1 goes online again

--> Bob is neither verified nor added to the group.

There are multiple possible solutions to this:

1. Sync group creation (similar to how broadcast creation is synced), so that the second device knows about the group. I think this is what we should implement.
2. After A1 goes online again, let it answer Bob and finish the securejoin protocol. There may be some intricate details here (e.g.: how does A1 know that A2 encountered an error?), so, I wouldn't go for this solution.

[iequidoo]

Sync group creation (similar to how broadcast creation is synced), so that the second device knows about the group. I think this is what we should implement.

+1. Member additions to unpromoted groups are already synced, so it's strange that group creation itself isn't synced.

[iequidoo]

The problem is that an unencrypted group creation can't be synced because they don't have grpid since key-contacts were merged. Changes to unencrypted groups are synced using References to several last messages though. I think that overall using References for synchronization should be avoided, using Subject + To (the list of recipients) is better, moreover it's not possible to add/remove recipients to such groups anymore.

Also now we have a code in receive_imf that assigns messages by Subject + To, so assigning messages by References can be dropped at all (i'd prefer to have separate email threads for different lists of participants), but this is another topic.

[link2xt]

There was also a problem that user reported that "group chat has disappeared" and later found that it was created on another device with a QR code a month earlier, but was in unpromoted state.

[Hocuri]

The problem is that an unencrypted group creation can't be synced

Yes, let's only sync creation of encrypted groups (at least for now).