does it come with (or is there any integration with) anything like a rules-engine to control data access? is there an auth component?

Phrag itself does not include auth component, but it has a concept of https://github.com/ykskb/phrag/blob/main/docs/interceptor.md which allows injection of any additional logic per table and operation type. This https://github.com/ykskb/situated-sns-backend has access control implemented with identities from Firebase's ID token like https://github.com/ykskb/situated-sns-backend/blob/main/src/situated_sns/signal.clj#L67.

Nice! Why is only Postgres (and sqlite) supported? The information_schema.query key_column_usage and constraint_column_usage tables are "standard" and should work on other RDBMS? BTW it would be nice if https://github.com/ykskb/phrag/blob/main/docs/mechanism.md linked to the other solutions mentioned and perhaps elaborated a little more on the differences. Where the other solutions too complicated? Too limited?

It's just that I haven't developed a DB adapter for other DBs yet. (That schema usage is specific to Postgres.) I'll probably work on MySQL adapter next, but if you have a demand for any specific DB, plz feel free to raise an issue 🙂 Regarding the feature/design comparison, I agree. I'll look into creating a comparison table between other projects when I get a chance.

Interesting! that "🔚" in a code snippet is confusing, i.e. is that syntax?

Based on https://www.fabricate.site/tutorials/fabricate-for-docs.html > They start with the ✳️ emoji and end with the 🔚 emoji. the answer is yes

For Extended form expressions, I wonder why not ✳( ...)🔚 instead, which I presume would make it easier to have an arbitrary level of nesting?