[noahmasur]

To add to what rgoulter said, you can use your default system configuration plus whatever the project says you need (and the project's shell will override any conflicts with your default).

However, if you really want to make sure that you're not including anything from your system, you can have direnv pass the `--pure` flag, which will then include only the dependencies from the project and nothing else. This is helpful to make sure that you're not accidentally relying on something already on your system when you declare the project dependencies.