Actually handle errors in pubsub

[A1Liu]

There's a number of errors that can happen everywhere in the pubsub system, and I think maaaaybe 1 of them is handled robustly. To handle we should edit the bad-js extension to be manually triggered, and then add additional UI elements to cause different kinds of errors.

There's an especially worrying error where the whole page freezes, which I can only reproduce accidentally, and that should DEFINITELY NOT happen lol

[A1Liu]

Some of this work is done by #126