Autogenerated thread title shows <@userid> for @mentions

Reproduction steps

In a channel you have thread creation permissions in, send a message that includes an @mention early on
Click the button to create thread

Expected behaviour

The automatically generated thread title should include the @mention text. e.g. if I create a thread off a message that starts with @Fullest, the autogenerated thread title should start with @Fullest or whatever my nickname is in that community at the time

Actual behaviour

The automatically generated thread title shows the user id. e.g. if I create a thread off a message that starts with @Fullest, the autogenerated thread title starts with <@1471663952882754315>

Build information

Canary Desktop 2026.1018.183012, Web 2026.1018.183012, Linux 7.2.10-200.fc44.x86_64 (x64), Electron 44.4.1, Chrome 152.0.7977.78, Node 24.21.0, Locale en-US

Platform

macOS, Windows, Linux, Web