An untyped pipeline source that is a sync iterable passed each value on
as it came, so a promise reached the next stage as the promise: a
byte-mode destination refused it and an object-mode one received it.
for await over a sync iterator, which Node's pipeline pumps it with,
awaits each value. The source's generator now awaits a value that is
an object (a promise included) before yielding it, and a rejection
closes the source, as Node's async-from-sync iterator does.
Chris Tate
530bd9534f