Can't import OpenSCADUtils

[Antony74]

C:\>docker run -it amrit3701/freecad-cli python3
Python 3.6.9 (default, Jul 17 2020, 12:50:27)
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import FreeCAD
>>> import Mesh
>>> import OpenSCADUtils
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Mod/OpenSCAD/OpenSCADUtils.py", line 31, in <module>
    from exportCSG import mesh2polyhedron
  File "/usr/local/Mod/OpenSCAD/exportCSG.py", line 35, in <module>
    try: import FreeCADGui
ModuleNotFoundError: No module named 'FreeCADGui'

Obviously it has a dependency on the front end, and we're trying to run headless, so I doubt this is going to be an easy problem to solve.

Any general advice on how to get the union of two meshes in an automated fashion, please? I've tried pymesh. I've tried converting to a Part.Shape with makeShapeFromMesh and calling fuse. Neither approach yeilds a mesh which is valid according to or repairs correctly in FreeCAD. The OpenSCAD workbench in FreeCAD does it nicely, but is now putting up a fight when I try to automate it