I'd tried that...this has been going on for five days, and I can not describe my level of frustration. But I solved it, literally just now.
Despite systemctl status apparmor.service claiming it was inactive, it was secretly active. audit.log was so full of sudo that I failed to see all of the
That made me realize, when I thought I fixed the apparmor rule, I'd used /etc/bind/dnskey/ rw instead of /etc/bind/dnskey/** rw
The bind manual claims that you don't need to manually create keys or manually include them in your zone file, if you use dnssec-policy default or presumably any other policy with inline-signing. Claims that bind will generate its own keys, write them, and even manage timed rotation or migration to a new policy. I can't confirm or deny that, because it definitely found the keys I had manually created (one of which was $INCLUDEd in the zone file, and one not) and used them. It also edited them and created .state files.
I feel like I should take the rest of the day off and celebrate.