Built-in imagegen immediately returns HTTP 404 for both text-only and reference-image requests

What version of the Codex App are you using?

The task is running in the Codex desktop environment. The exact Codex app build could not be retrieved: the agent cannot access the Codex UI, and /Applications/Codex.app/Contents/Info.plist was not present.

For environment context only (not claimed to be the active Codex runtime): installed ChatGPT.app reports version 26.901.51231, build 8109; standalone codex --version reports codex-cli 0.141.0.

What subscription do you have?

The user intends to use built-in image generation through their Codex/ChatGPT plan, not an external API key. Exact plan tier not collected.

What platform is your computer?

macOS 26.6.2; uname -mprs: Darwin 25.6.0 arm64 arm.

What issue are you seeing?

The built-in image_gen.imagegen tool is advertised as available in the task, but every attempted generation returns immediately with:

image generation failed: http 404 Not Found: Some("")

This occurred with both:

• Reference-image requests using existing local PNG files that had been successfully inspected.
• A text-only image-generation request with no attachments or referenced image paths.

No image or output path was returned. The exposed error contains no request ID, failing endpoint, or actionable explanation. Several attempts across consecutive turns in the same task failed identically. We have not verified reproduction in a fresh task or after restarting the app.

What steps can reproduce the bug?

1. In the Codex desktop task, explicitly request the built-in $imagegen capability.
2. Ask it to generate a simple black-and-white illustration on a white background.
3. The agent invokes the advertised built-in tool with a prompt argument only (no API-key CLI, no reference images).
4. Observe the immediate HTTP 404 above.

The actual text-only prompt from the failed call was:

为户外酒吧棚安装说明书生成一张全新黑白工具插图，白色背景，横向排列七个工具：护目镜、卷尺、十字螺丝刀、工作手套、橡胶锤、稳固的人字梯、充电式电动螺丝刀。统一简洁精确的技术线稿，细黑线、少量浅灰填充，轮廓清晰，间距均匀，无文字、无数字、无品牌、无水印。

In English: generate a new monochrome manual illustration of seven common tools, with white background and no text or branding.

What is the expected behavior?

The built-in tool generates an image and returns the result. If the capability is unavailable for the current client, task, or account, it should report the specific reason and a recovery action instead of an opaque 404.

Additional information

Observed on 2026-09-07 in this task. The user explicitly requested built-in generation; no external image API was called. No claim is made that the request reached a particular image model, that quota was exhausted, or that a particular backend is responsible: the tool exposes too little information to determine this.

Please investigate built-in image-generation routing/capability availability and include a request ID and useful diagnostic message on failure.

No private product documents, credentials, or full session logs are attached. This report was submitted by the user's assistant with the user's explicit authorization.

Start by reproducing the failure through the Codex desktop task's $imagegen or image_gen.imagegen entry point with a prompt-only request, then compare it with a reference-image request. Trace the HTTP 404 failure path; done means successful generation when available or a failure containing a request ID, specific diagnostic reason, and recovery action.