If the expectation is not met then it rolls back and fails. I implemented a slipshod version of it years ago for a previous employer (it got the job done with a lousier syntax)

Here's a list of 1,000 postgres extensions, it's not a big deal: https://gist.github.com/joelonsql/e5aa27f8cc9bd22b8999b7de8a...

Things are way more modular than they used to be.

I can probably do it again and just try to get attention for it.