Symptom: setup prints a traceback right after the `FreeCAD lib:` line:

[12:11:52] FreeCAD lib: /usr/lib/freecad-python3/lib | interpreter:
/usr/bin/python3.14 (linked: python3.14)
Traceback (most recent call last):
   File "<stdin>", line 3, in <module>
ModuleNotFoundError: <stdin>(3)<class 'ModuleNotFoundError'>: No module
named 'PartDesign'

Cause. When FreeCAD is imported as a Python library, its home path is
`/usr/lib/freecad-python3/`, so it looks for modules in
`/usr/lib/freecad-python3/Mod`. Debian packages install them in
`/usr/share/freecad/Mod` and don't ship a link between the two. The GUI
finds the modules another way, so only headless and Python use is
affected. `Part` and `Sketcher` still load because they are compiled
modules in `/usr/lib/freecad-python3/lib`. PartDesign is a Python
package under `Mod/`, so it doesn't.

Fix: Add freecad-python3.links with the following line:

usr/share/freecad/Mod usr/lib/freecad-python3/Mod


Using Ubuntu 26.04, kernel: 7.0.0-34-generic