To decouple this the person would have to broadcast nearly every event and rebuild the observer layers elsewhere.

You could replicate and separate your llm-postgres from the system-of-record-postgres.

And IMO that's what should be done.

Don't get me wrong, I like the idea and all that, but this is another pgsql "solution" that is tied to the database layer, when it should be in the application layer.

I like to be database agnostic, and while I prefer PostgreSQL on production, I prefer SQLite on the dev layer. You should never have to HAVE TO use a specific database to make your APPLICATION work.