I use Git to track all code (core, plugins, themes) in my WordPress install, and the repository is hooked into a CI server for deployment to dev, staging, and production servers.
When trying to activate the Layouts plugin on my dev server after a CI build, I got errors stemming from missing Twig library files. I finally tracked it down to the use of a Git submodule in the vendor library folder within the plugin. The submodule files were not pushed to my repository, and therefore didn't make it to the server.
I would not normally want to independently update a submodule that has not been tested with the plugin, but rather use the version that has been validated and packaged by you. In that regard, I don't think the layouts/vendor/twig/twig/.git folder should be in the official release.
Can advise on the expected handling of the submodule if this is intentional?