I was reading this and then realized, I know this person from the other topic.
Most, if not all, of what you are seeking could probably already be done. While I have not performed a full due diligence review, Codex hooks, combined with the fact that much of what Codex does is stored locally in .codex folders, would likely go a long way toward implementing this.
I could not find an official OpenAI page documenting the .codex folder, but the related directory structure for Anthropic Claude Code is described here:
Many advanced users I know create a daemon to monitor and capture updates to these folders, since much of the data is eventually deleted to save space. For your sentinel idea, however, retaining that information could be invaluable.