@dazzling-plumber-90795 - there is a bug in that package's setup.py, workaround is:

jsirois@gill /tmp/1.3.x_jax_repro $ cat pants.ini
[GLOBAL]
pants_version: 1.3.1rc1

plugins: [
    'pantsbuild.pants.contrib.jax_ws==%(pants_version)s',
  ]

backend_packages: +[
    "pants.contrib.jax_ws",
  ]