(for some reason, even when DUID generation fails, the package is still tagged as fully-installed, so not even apt-get install -f will finish up the configuration after the dependencies have been manually acquired.)
Thanks for the hint. Actually the package is still built on a Debian 8 because it worked, so it might be a good idea to port the packaging to Debian 9. I will check this asap.
After resolving the DNS issue - does it work at all?
Yeah, it's actually a pretty great server! Once I had generated and inserted the DUID manually, it really works well. 😄👍 (Although, it might be good to at least document which of the three config files scattered across /etc is the one which must be edited to make it actually respond to clients. I figured it out, it's not a massive undertaking; but it's the kind of troubleshooting that doesn't seem like it belongs out-of-the-box.)
Only thing that seemed "off" was that it temporarily semi-broke the OS's default DNS suffix (the IPv4 server WAS advertising it; the IPv6 server was NOT: it showed up in Win10 Task Manager, but most applications seemed not to resolve the domains); I fixed it by hard-coding the network's specific domain $sitexxx$.hsv.al.us.xn--l3h.$mydomain$ into the config file. (The IPv4 server is the canonical/authoritative source of site domain information)
but that (i.e., slaving an aspect of dhcpy6d's configuration to a source) is probably pretty easy to implement with something like a DHCP(v4) client hook, if it ever becomes an issue.