Our streaming endpoint returns 200 and then dies mid-stream, and nothing catches it

The API steps assert on a completed response, which is fine until the response is a stream. Ours opens with a 200, sends a few events and then fails halfway — and

Then the response status should be 200

is perfectly happy with that, because the status was genuinely 200. The failure is in the middle and nothing in the step library can see it.

Has anyone assembled something for server-sent events? What I think I need is an assertion that the stream closed cleanly and one that no error event arrived, and I would rather not invent the vocabulary if someone has already settled on one.