The OpenAI images path (/v1/images/*) previously called patchCodexCompletedOutput
to concatenate collected output_item.done items back into the completed event and
then re-parsed that rebuilt JSON to pull out the image results. For multi-megabyte
base64 image payloads this produced two extra full-size copies per request (the
concatenated output array plus the rebuilt completed event), inflating peak memory
under concurrent image generation.
Add codexExtractImageResults, which extracts image_generation_call results directly
from either the completed event's response.output or the collected items, without
the concatenate-and-reparse step. Semantics are preserved: completed output is
preferred and collected items are used only when it is empty, matching the original
patchCodexCompletedOutput behaviour. patchCodexCompletedOutput remains in use by the
text/responses path, which still forwards the patched event downstream.
Adds unit tests covering the completed-output path, the ordered fallback to
collected items, output preference, fallback list, and the wrong-event-type guard.
