New install yields error rendering *head (raw view) and CoffeeScript::SyntaxError

The context is a fresh Wagn installation. When I first go to the home page (localhost:3000) the page shows "error rendering *head (raw view)" at the top of the page, and there is no custom styling -- it appears that no *.css or *.js has been loaded; the Webrick console reports a CoffeeScript::SyntaxError

This is happening on OSX El Capitan using Ruby 2.3.0. The steps I took were as follows. Under rvm and using rubygems, I updated the Wagn gem to 1.18.5. I am trying to configure a core developer setup, so under my local copy of the Wagn source, I did `git pull origin master` to update to the latest Github source. Although the need to do this doesn't seem to be documented, I also copied db/seed from the card-1.18.5 gem into my local source tree, since otherwise `wagn seed` would fail. I ran `wagn new mydeckname --core-dev` specifying the path to my local Wagn source. (The "wagn" command was from the installed wagn gem, rather than in my local source copy.) Then I cd'ed into the mydeckname directory, ran `wagn seed` and `wagn server`.