> Actually, the real problem seems to be that my old hostname.if file, which had > dhcp > up > no longer works with the new thing (dhcpleased) that replaced dhclient.
If you had old file contents it sounds more like you did an upgrade and not as stated below, "installed OpenBSD 7.8" > Installed OpenBSD 7.8. > dhclient was not installed. The change from dhclient to dhcpleased seems to have been around 7.0/7.1 so if you did not install 7.8 but instead upgraded, it would be relevant to add from which version you did upgrade, and if you did or did not follow the upgrade notes for the versions in between. -- May the most significant bit of your life be positive.

