Codex CLI renders hook additionalContext as visible developer message

[FasterPHP]

Summary

Codex CLI is rendering hook hookSpecificOutput.additionalContext as a visible developer message in the session transcript.

This appears to contradict the documented behavior used by the Hindsight Codex integration, which says auto-recall should be "invisible to the transcript, visible to Codex".

Environment

• Codex CLI version: 0.118.0
• Platform: Linux
• Hook integration: Hindsight Codex integration

Expected behavior

When a UserPromptSubmit hook returns:

{
  "hookSpecificOutput": {
    "hookEventName": "UserPromptSubmit",
    "additionalContext": "..."
  }
}

the additionalContext should be available to the model without being shown in the user-visible transcript.

Actual behavior

The additionalContext payload is inserted into the session as a visible developer message containing the full Hindsight memory block.

In the same setup, Codex also shows visible UI status like:

• Running Stop hook

The main bug here is the visible transcript rendering of additionalContext.

Reproduction

1. Enable Codex hooks.
2. Configure a UserPromptSubmit hook that returns hookSpecificOutput.additionalContext.
3. Use the Hindsight Codex integration, or any minimal hook that returns hidden context this way.
4. Start a session and submit a prompt.
5. Observe that the hook context is shown in the transcript as a visible developer message.

Relevant docs

Hindsight integration docs state that auto-recall is:

• "invisible to the transcript"
• "visible to Codex"

Reference:

• https://hindsight.vectorize.io/sdks/integrations/codex#features

Local evidence

The Hindsight hook returns additionalContext here:

output = {
    "hookSpecificOutput": {
        "hookEventName": "UserPromptSubmit",
        "additionalContext": context_message,
    }
}
json.dump(output, sys.stdout)

And the resulting session log contains it as a visible developer message:

{"type":"response_item","payload":{"type":"message","role":"developer", ... "<hindsight_memories> ... </hindsight_memories>"}}

Notes

This may be:

• a Codex CLI regression in how hook additionalContext is rendered, or
• a mismatch between current Codex behavior and the documented hook contract relied on by integrations.

[github-actions]

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• Render UserPromptSubmit.additionalContext as multiline hook context in the TUI #16486

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