Reduce confusion on where events originate from

[dcramer]

In something akin to a Next.js app, all errors will show "JS", and its quite hard at a glance to know if somethings in the UI or on the server.

[dcramer]

Tempted to just say we should add a [UI] or similar annotation but im not sure

[BYK]

@betegon with the recent event source classification, I think we can address this easily on the UI side too, right?

[BYK]

Closed by #1221.