Good point about quietly grabbing env vars, we can warn about that on first run. All it's getting are these:

  var envVars []string
    shellEnvVars := []string{
    "BASH_VERSION",
    "ZSH_VERSION",
    "FISH_VERSION",
    "KSH_VERSION",
    "tcsh",
    "SHELL",
  }

If you want to skip this, running `sprite exec -tty /bin/bash --login` or similar avoids the magic.