STS allows to bypass any checked exceptions

[Attila Kelemen]

> The current spec is that handleComplete is not invoked after the scope
> has been shutdown. Calling shutdown means you've got the outcome,
> interrupt the unfinished tasks as you don't care about them. Aside from
> logging, what would your code do?  The equivalent with Executors and
> Future.cancel is Future::get throwing CancellationException - any
> logging needs to be in the task.

Mostly it would be logged, but my issue is a little bit more than
that. Consider the following (non-STS) code:

```
try (var resource = create()) {
  doSomething(resource);
}
```

Suppose `resource.close()` fails with an exception, because of a
cleanup error (say temporary files remain somewhere). In this case,
the whole call fails with an exception, which is the conservative
thing to do. In fact, even is `doSomething` fails as well, the
exception in `close` will not be hidden (too bad `finally` was not
written like this).

However, STS creates a trap, because if you forget to handle the
exception thrown by the task (basically - as is now - it is forcing
you to put everything into a try-catch in each task, otherwise you are
just being hopeful), then likely nobody will notice the problem until
many cleanup issues accumulate and blow up in your face.