Want to pin a private repo to a commit or tag in private.txt

I’d like to pin some 3rd party Django apps to a specific commit sha or tag in private.txt. The repos are all private so I’ve cloned them to $(tutor config printroot)/env/build/openedx/requirements

The apps install fine when not pinned but when I use:
-e ./@
or
-e ./@

tutor images build openedx fails with:
ERROR: ./@ is not a valid editable requirement. It should either be a path to a local project or a VCS URL (beginning with svn+, git+, hg+, or bzr+).

Is it possible to pin when using private repos?

Thanks.