You don't want to install all dependencies globally. You only want to cache them globally. Each project should resolve its own dependency tree independently. If the wanted version is already in cache, use that, otherwise download from the repository even if an older / newer version is present in cache (unless the user specifically says to use the cache only). As long as your dependencies are inert (they don't mess with the system just by being present), this will work perfectly fine.
For non-inert packages, such as applications installed via the language's dependency manager, that's a different use case and should be handled differently.
For non-inert packages, such as applications installed via the language's dependency manager, that's a different use case and should be handled differently.