WebSocket connection should timeout and report the timeout when system is overloaded

[RalfJung]

To reproduce, open this and click "expand macros". The result after a bit of waiting is this:

I would expect either some sort of error message if the server is overloaded or the invocation timed out, or the macro-expanded output.

[RalfJung]

Of course when I try this again now, the expected output is shown...

But I got the "no output" above at least 3 times. Seems likely that they timed out somewhere in the backend, but that means there's still a bug somewhere where it fails to produce an error message.

[HappiePlant]

For me the entire site is broken right now, running and building does nothing

[shepmaster]

It may not seem like it, but this report is music to my ears!

Here's the child container and process graph of the playground around the time you made this report:

I'm pretty sure that prior to #1090, this would have simply killed the entire machine, so this is useful forward progress.

[RalfJung]

Ah yes, getting no error is certainly better than killing the machine :-)