Is there a best practice for preventing mixed eol-styles in a subversion repository.
I know that svn:eol-style=native can be set as an auto-prop, but I would have to ensure that it was set for all committers. I'm also reluctant to do a retrospective, repository-wide change of svn:eol-style if there is a less invasive solution.
You should use pre-commit hooks on server-side.
Here is a hook you need: http://svn.apache.org/repos/asf/subversion/trunk/contrib/hook-scripts/check-mime-type.pl
This hook will enforce users to set correct eol-style.
See svn documentation on how to use them.
Also, you can implement your own hook which will set eol-style automatically.