@astonishing-jelly-60479: winding back up to your "where is the right place to put that requirement so pants itself picks it up? is that something that happens at bootstrap time?" If you list the plugins in pants.ini, pants bootstraps them and adds them to its pythonpath as needed, ie when you change the list:

[DEFAULT]

plugins: [
    'pantsbuild.pants.contrib.go==0.0.45'
  ]