The openai-codex image provider rode a Responses call with a hosted
image_generation tool on a pinned chat model (gpt-5.5). Two failure
classes came with that shape: when OpenAI withdrew gpt-5.5 from an
account cohort every image call 404'd while chat kept working
(#105398, #107076), and the host model was free to answer in text
instead of calling the tool, so we streamed SSE, kept partial frames
and retried on empty streams.
Post to chatgpt.com/backend-api/codex/images/generations and
images/edits instead - the route the official Codex client uses
(codex-rs/ext/image-generation). No host model, no SSE, no
partial-frame handling; the response is a plain JSON body with
b64_json. Remote source URLs are fetched client-side and inlined as
data URLs because the backend's own downloader 400s on ordinary
public images.
The backend treats model/quality/size as advisory (#107233), so the
result now reports reported_quality/reported_size next to the
requested values plus the x-codex-imagegen-request-id for support.
GPT Image 2.5 is deliberately not added to this catalog: the backend
accepts any model id, including nonexistent ones, and generates with
its server-managed engine (C2PA reports gpt-image 2.0), so a 2.5 tier
here would be a label with no effect (#106708).
New built-in image_gen backend at plugins/image_gen/openai-codex/ that
exposes the same gpt-image-2 low/medium/high tier catalog as the
existing 'openai' plugin, but routes generation through the ChatGPT/
Codex Responses image_generation tool path. Available whenever the user
has Codex OAuth signed in; no OPENAI_API_KEY required.
The two plugins are independent — users select between them via
'hermes tools' → Image Generation, and image_gen.provider in
config.yaml. The existing 'openai' (API-key) plugin is unchanged.
Reuses _read_codex_access_token() and _codex_cloudflare_headers() from
agent.auxiliary_client so token expiry / cred-pool / Cloudflare
originator handling stays in one place.
Inspired by #14047 by @Hygaard, but re-implemented as a separate
plugin instead of an in-place fork of the openai plugin.
Closes#11195
teknium1