timeline: Warn when constructing thread timeline without threading support in client

[VAWVAW]

The log with level trace.

I am using the latest commit (588d60465) of matrix-sdk-ui in a modified version of iamb.

The only sync running is SyncService without any subscriptions by room id.

I have a room open in two timelines, one with main focus and one with thread focus.

• At 2025-10-13T18:35:12.561343Z I send a new message to the thread timeline. (ignore that is says editing)
• A local echo is inserted at some point in time.
• At 2025-10-13T18:35:12.845689Z the server returns the new event id.
• At 2025-10-13T18:35:12.847761Z the message isn't inserted in the live timeline because it is in a thread.

It seems something is handled incorrectly because the local echo in the thread timeline is not replaced and the thread summary aggregation in the main timeline is not updated.

possibly related to #5773

When creating Timeline with thread focus from a client without ClientBuilder::with_threading_support there should be an indication (error or log entry) that new messages wont be handled correctly.

[bnjbvr]

Thanks for the report.

I'm trying to understand what's going wrong, so double-checking my understanding:

• have you enabled threading support with ClientBuilder::with_threading_support, when creating the Client? Not enabling it would make it so that thread summaries are not updated, and could explain timeline: Thread events received via sync don't update ThreadSummary of root #5773 altogether.
• for a live timeline hiding in-thread events, it's intended that the thread event is not inserted in there, so there's no bug with the message isn't inserted in the live timeline because it is in a thread.; do you agree with that, or did you consider this to be an issue?
• do you have code i could look at, to see how you're creating timelines, etc.?

[VAWVAW]

have you enabled threading support with ClientBuilder::with_threading_support, when creating the Client?

No, I missed that. With this enabled, it works.

Maybe there should be a warning when creating a Timeline with thread focus if the client was built without threading support.

The only thing I noticed is that the thread summary of the thread root as first message in the thread timeline doesn't get updated.

Should I open a new issue for that or edit this one?

[bnjbvr]

We can reuse this issue, but what do you mean exactly by this:

The only thing I noticed is that the thread summary of the thread root as first message in the thread timeline doesn't get updated.

The threaded timeline's root shouldn't have a thread summary at all, unless we did something wrong

[VAWVAW]

The threaded timeline's root shouldn't have a thread summary at all, unless we did something wrong

Currently the oldest message in a thread timeline (the thread root) has a thread summary for me.