I removed an old copy of vagrant according to the official HashiCorp docs, and reinstalled using the official OSX universal installer. Now, every vagrant command on the host returns the following warning:
$ vagrant global-status
Ignoring ffi-1.9.10 because its extensions are not built. Try: gem pristine ffi --version 1.9.10
I doublechecked my Ruby setup, and found RVM and rbenv both installed. So, I uninstalled RVM with rvm implode, and deleted ~/.rvm for good measure. Lastly, I installed Ruby 2.3.0 with rbenv, and called rbenv init (and added its output to my shell config).
From here, I have a setup that will let me install any version of ffi. The latest version is newer than 1.9.10, but installing 1.9.10 doesn't affect the warning.
I assume lacking FFI is going to slow things way down. How do I get Vagrant to use the rbenv-managed gems?