The necessity of intention for the valid administration of a sacrament is in the Baltimore Catechism. The Baltimore Catechism is (I would say) the most basic, barebones, and common Church-approved instructional docuмent for lay Catholics. It is extremely straightforward, ridiculously accessible (sold in every Catholic bookstore, even diocesan ones, available for free online in probably half a dozen places), written without jargon, etc. And this teaching is in there.
I'm not trying to embarrass anyone. Maybe my judgment of what is "simple" is wrong. And if someone didn't know intention is required for the valid administration of a sacrament, that doesn't mean they're stupid. It's a big Catechism, some things are easy to miss.
But this doctrine is in there, simply and plainly. And I take that as a sign that it's a doctrine the Church expects her adult lay members to know. I think we all make similar judgments about what is or should be common knowledge among serious adult Catholics. If there is a better standard for that judgment than the Baltimore Catechism, I'm all ears.