* fix(responses): honor caller stream flag when provider forces SSE
The Responses handlers decided whether to hand back a streaming iterator
from the provider payload's `stream` field, which chatgpt sets
unconditionally because the Codex backend only serves SSE. A caller that
sent `stream: false` therefore received a raw SSE stream on /v1/responses,
and the chat-completions bridge failed with "Unknown items in responses
API response: []" once its recovery path lost the raw SSE it reads from
Transport streaming still follows the provider payload; only the caller's
own `stream` value now decides the response shape. When the provider
forces SSE for a non-streaming caller the body is read and aggregated
through the existing path
* test(chatgpt): inject the authenticator into the responses config so handler tests never log in
* fix(responses): treat an extra_body stream flag as the caller's own and drop a redundant comment
* test(integration): audit the chatgpt caller stream flag across responses, chat and messages
---------
Co-authored-by: SeongWoon Cho <coffee@soylatte.kr>
Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
