Bug: Unsupported file upload leaves Codex conversation unable to continue

What version of the Codex App are you using (From “About Codex” dialog)?

Codex CLI version from session log: 0.131.0-alpha.9

What subscription do you have?

PRO

What platform is your computer?

Darwin 25.5.0 arm64 arm

What issue are you seeing?

After uploading an unsupported file into a Codex Desktop conversation, the thread stopped responding.

The conversation accepted the next user message, but the assistant produced no visible response. The session log shows the uploaded attachment was serialized as an empty image payload:

{
"type": "input_image",
"image_url": "data:image/png;base64,",
"detail": "high"
}

After that, Codex marked the task as complete with no last_agent_message:

{
"type": "task_complete",
"last_agent_message": null
}
Sending a later text-only message in the same conversation also completed immediately with no assistant response. At that point I could not continue using the conversation.

Feedback ID / session ID:

019e41bf-c551-7d81-ad2d-f6e216dbb4ce

What steps can reproduce the bug?

1. Open an existing Codex Desktop conversation.
2. Upload or paste an unsupported file into the conversation.
3. Send a prompt that references the uploaded file.
4. Observe that the request is accepted, but no assistant response appears.
5. Send another text-only prompt in the same conversation.
6. Observe that Codex still completes the turn without producing an assistant response.

What is the expected behavior?

Codex should reject unsupported files before they are added to the conversation, show a clear error, and keep the conversation usable.

Additional information

The unsupported file appears to be added as an invalid/empty attachment payload. After that, turns complete with no assistant response, and the conversation cannot continue.
The failure happened on May 19, 2026 in Codex Desktop. The affected conversation was working before the unsupported file upload.