parse_x_response was returning an empty items list whenever xAI returned
a 200 OK with a malformed payload — empty output text, missing "items"
key, or invalid JSON. The pipeline saw "successful response with zero
items" and quietly handed the user a degraded report with no indication
the API had failed. Now raise http.HTTPError on each of those branches
so _retrieve_stream's caller catches it and surfaces the failure in
errors_by_source, giving the user a visible signal that X didn't work.
Closes#155.
Co-authored-by: Kaustav Mishra <km.git007@gmail.com>
Kaustav Mishra