1. Thanks
2. I NEVER would have gotten that, ... but
calibredb list -f title --search ^"format:=epub and tags:=^"science fiction^"^"
is only finding tags = "Science" and not "Science Fiction"
Reading the manual about bracketing parameters with spaces with quotes, and assuming that the ^ is treated as a special escape character, what you provided looks like it should work.
It works great on a 'one word tag', but not one with a space
Can you provide a tweak for cmd.exe's insane quoting rules

that works with spaces?