Tag-awareness for Recoll or other text-based search?

I have a big Calibre library of technical PDFs that I use Recoll (on Linux) to search, and it works very well.

I want to add my collection of pleasure-reading, fiction and whatnot, to my library, but I don't want those books to come up in my Recoll results.

Is there a way to filter, before or after the search, or another tool that would work for that? Or any good solution apart from maintaining two separate Calibre libraries?

Thanks!