I removed resin entirely and reinstalled it. Inside /etc/resin is -rw-r--r-- 1 resin resin 12284 2009-04-20 19:06 app-default.xml lrwxrwxrwx 1 resin resin 21 2009-04-20 19:06 resin.xml -> /etc/resin/resin.conf resin.conf to which resin.xml points is never installed. (I'm just assuming the reason the resin.xml symlink exists at all is due to resin's quirkiness.) Note that http://bugs.gentoo.org/show_bug.cgi?id=266736 may be caused by this bug.
I can confirm that =www-servers/resin-3.2.1 does not install /etc/resin/resin.conf, but the broken symlink /etc/resin/resin.xml -> /etc/resin/resin.conf.
Fixed in 3.2.1-r1.