Restore Eclipse subversion project connection
If you are using sublipse as your SVN provider I recommend doing the following
Team -> Share project is usually enough to connect the metadata.
(that is, assuming that the .svn files are still there which they seem to be if you can work on the command line).
Hope this helps as to why this would happen I have no idea
I found an easy way just reimport the project
Just doing Team -> Share Project (per the answer to this question provided by @Paul Whelan) did not work for me. The Share Project wizard acted as though the project was not already in SVN (even though the .svn folder was present for my project).
I ended up resolving the issue by uninstalling the Subversive and JavaHL add-ons (via Help | About Eclipse | Installation Details button | Installed Software tab | Uninstall...), and then reinstalling Subversive. When prompted after restarting Eclipse, I opted to install the SVNKit connector rather than the JavaHL connector.
After having done that, when I once again tried Team -> Share Project..., Eclipse correctly recognized that my project was already present in SVN, and it successfully restored the connection.
Addendum: it turns out that my problem manifests when I start Eclipse outside the company vpn, with a project in the workspace that is attached to a svn repository inside the vpn. Fortunately, switching Eclipse svn plugins from subversive to subclipse did solve it.
Ian