outgoing-body flush behaviour states

[guybedford]

As far as I can tell, outgoing-body's stream can exist in two different states:

1. unattached to the http request, before the request is made - all writes buffer, and flush is effectively a no-op.
2. attached to the outgoing http request after it has been made - in this state, flush functions correctly.

In state (1), does the subscribe just fail if we exceed the high watermark? Or is the high watermark functionality also disabled?

Effectively, does that mean that a transition from state (1) to state (2) change it from permitting writes over the high watermark to not?