The problem on Debian/wheezy is, that foreman-proxy is running under Ruby 1.9 (system default), but puppet is on version 2.7.x, which has no support for ruby >1.8, so the dependency on puppet does pull in only libaugeas-ruby1.8.
Related issues
Bug #4739: Proxy on Debian 7 (wheezy): cannot load such file -- augeas
fixes #4739 - add dependency on libaugeas-ruby
The problem on Debian/wheezy is, that foreman-proxy is running under
Ruby 1.9 (system default), but puppet is on version 2.7.x, which has no
support for ruby >1.8, so the dependency on puppet does pull in only
libaugeas-ruby1.8.