User mention selection only works at the end of text in the compositor

[Jaffex]

Steps to reproduce

When composing a message, write some text, then try to add a mention anywhere in between the text by starting with an @ sign and the beginning of a user's name.

Outcome

What did you expect?

I would expect the @ and any given text after it right to the current cursor position to act exactly as it would act at the end of a given message in the compositor, by suggesting users that start with the already typed text.

After selecting a user, I would expect a space after inserting the user pill if there is not already one after the cursor.

What happened instead?

If you try to mention another user from within anywhere within the text, the user selection does not open at all.
It only works if you're at the end of the text within the compositor.

Here's a little example:

screenrecording.mp4

Your phone model

iPhone 12 mini

Operating system version

iOS 18.1

Application version

1.9.5 (136)

Homeserver

irrelevant

Will you send logs?

Yes