I've redone my network router configuration for Debian. Now based on systemd-networkd and its DHCP server, and unbound for DNS. Previously dnsmasq, but it became problematic (e.g., gave same IP to different MACs at the same time).

So far so good. Missing from new system is automatically adding DNS entries to unbound when DHCP gives a lease and the client provided a hostname. Couldn't figure out how to get the IP/hostname-in-DHCP-request data from the DHCP server. IP/MAC is easy, but not enough.