these 2 derivations will be built:
  /nix/store/awvbcv5kyajf40qa41vrcpvpa3mnk5m9-resulting-skills-tree.drv
  /nix/store/zmzhhz54990v1a3m0c1waia3arw3vyi8-validate-skills.drv
building '/nix/store/awvbcv5kyajf40qa41vrcpvpa3mnk5m9-resulting-skills-tree.drv'