[Client] emit an event when Playground goes away #2732
Description
Sometimes Playground crashes. There are multiple reasons: out of memory, a bug, or a browser killing the runtime after a few hours of inactivity.
The Playground consumers would benefit from a well specified failure mode, e.g. client emitting a wentaway event and rejecting all calls until remote is reconnected. That would also help the Playground website present useful information to the user.
Cc @draganescu