Keyboard interaction with mentions is broken

[Giszmo]

When doing a "mention" and then hitting the left arrow, the dropdown opens again but hitting to the right, doesn't let you back out of it. When you repeat hitting left beyond the @ you get the full list of profiles. If you now hit enter, it closes but gives you no clue if the last selected mention was added to the tags or what happened.

[Giszmo]

As the displayed name is not an identifier, I think the best UI would be to treat it as one character. If you backspace into a mention, it disappears completely. If you amend it, it adds normal text after the mention. If you left-arrow into it, you skip over the complete mention. Changing a mention to a different mention is not required, so clicking it may position the cursor just right before or after the mention.