I'm starting to use SPM in a CI environment, and I'd like to keep the packages cached / under source control. I've started successfully from Fastlane, by setting the cloned_source_packages_path for my build_ios_app calls.
However, I can't figure out how to "teach" my Xcode project (or workspace) to use the same location. My goals are to (a) prevent Xcode from downloading the packages from their hosts into the "traditional" default location on Xcode launch, and (b) have Xcode fetching and compilation use the new location, so that (for example) if one of our devs builds, an Xcode finds an update, it will download the update AND write that into the repo, NOT into the derived data stash, so that we know to check it in for the next run.
Or, am I just barking entirely up the wrong tree? How do people use SPM with a mix of Xcode and CI?