The Reply in thread feature does an implicit user mention

[spantaleev]

Steps to reproduce

1. Start in a room view which contains some threaded messages
2. Long-tap on a threaded message
3. Tap "Reply in thread"
4. Type and send a message

Outcome

What did you expect?

A regular message posted to the thread (m.relates_to being populated with the thread / event information).

I don't expect that the message would be mentioning anyone explicitly. I merely wish to post a new threaded message.

What happened instead?

The newly created message event is posted under the thread correctly (m.relates_to is OK), but it also mentions the person you "replied to" (m.mentions is populated).

This affects my usage of baibot, as doing a mention of the bot (as Element X iOS does right now) invokes different behavior than what would have happened when merely continuing the thread and not mentioning anyone.

Your phone model

iPhone 14

Operating system version

iOS 18.1

Application version

Version 1.9.6 (137)

Homeserver

Synapse 1.119.0

Will you send logs?

No

[pixlwave]

Adding some context on this, as mentioned in #2397 (comment), I believe we're going to need MSC4142 (and for the Rust SDK to adopt it) as the app isn't talking threads natively and so we're going to be following the same behaviour for threads as we do replies.