RunnableFutureTask is not reusable. Trying to reuse it meant that a
failure in one doWork() call would cause subsequent download() calls
to (a) not block until the runnable has finished executing (does not
apply when using a direct executor), and (b) throw the same failure
as thrown from the first doWork() call.
This could cause #8078 if the initial failure occurred before the
content length was resolved. Retries are not blocked on their work
completing due to (a), and the download would be marked as failed due
to (b). The work itself could then resolve the content length, which
causes the stack trace in this issue.
Issue: #8078
PiperOrigin-RevId: 343498252
1b50071f4f