Missing *new* messages in old threads for new user with history turned off

[igbjnI05bF]

Steps to reproduce

This happens in any Element client with threads enabled, not just desktop app

1. Have a room with history turned off for new users
2. Have discussions in threads
3. New user joins the room, cannot see any history (as expected)
4. Have a different user send a new message in one of the old threads that existed before new user joined

Outcome

What did you expect?

I expect to somehow see the message. I understand that I cannot see entire thread history, but I expect to see new messages. One way to handle this is for the first new message in the thread to create a new thread for the new user. The new user won't really know what the overall topic is about, but at least it's contained in a thread that the new user can participate in.

What happened instead?

I do not see any indication of the message at all. No notification, nothing. Disappears into the abyss. I only see the message if I disable threading in the client, then I see it in the normal timeline.

Operating system

Linux OS and Android have been tested

Application version

No response

How did you install the app?

No response

Homeserver

My new user account is on Conduit but I do not think this is a Conduit specific issue

Will you send logs?

No

[t3chguy]

My new user account is on Conduit but I do not think this is a Conduit specific issue

What makes you think it isn't? The client heavily relies on the server to provide threads as timelines via the /relations and /messages APIs. You unfortunately haven't even included logs so there's not much here to go on.

[igbjnI05bF]

I just tested with two Synapse accounts, same issue. Picture attached, both accounts Synapse. Image attached. Sorry for no logs but this is very easily reproducible:

1. Start a new room
2. Change room settings to only see history after join
3. Start a thread
4. Have new user join room
5. Have original user send a message in thread
6. Watch as absolutely no notification of anything happening happens

[andybalaam]

Chatted with @daniellekirkwood and this should follow the same pattern as element-hq/element-web#26494

[daniellekirkwood]

Yep, when we worked on Threads first time around we discussed a similar thing to this here. If a user doesn't have access to a root message or earlier messages (because it's not yet loaded, not scrolled back to, or restricted due to room events, etc.) then the error message should show: "Unable to load event that was replied to, it either does not exist or you do not have permission to view it."

(Ideally we'd have a different message but for now this is my MVP)