Dockerfile: swap vtk for vtk-osmesa so off-screen rendering works headless

The stock pyvista wheel pulls the stock vtk wheel from PyPI, which is
built with vtkXOpenGLRenderWindow. That render window class needs an
X server even in off_screen mode, so it segfaults the eval worker on
the Space's truly-headless container ("DISPLAY=" with no X11 socket).
The parent ProcessPoolExecutor sees the segfault as BrokenProcessPool
six minutes into the eval, which is exactly the failure mode the
first VTK submission hit.

vtk-osmesa is the same VTK build but compiled against Mesa OSMesa
(pure CPU software rasteriser, statically linked, no display server
required). It shares the `import vtk` namespace so pyvista picks it
up transparently. This is the canonical PyVista headless-Docker fix
(per the PyVista docs + the maintainers' own Docker images). The
wheel lives on Kitware's index, not PyPI proper.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

@@ -43,6 +43,17 @@ ARG CADGENBENCH_SHA=b22a53c
 RUN pip install --no-cache-dir \
         "cadgenbench @ git+https://github.com/huggingface/cadgenbench.git@${CADGENBENCH_SHA}"
 
+# The stock `vtk` wheel that pyvista pulls from PyPI is built with
+# vtkXOpenGLRenderWindow, which needs an X server and segfaults the
+# worker on a truly-headless container (no DISPLAY). Swap it for
+# `vtk-osmesa`, the same VTK build but compiled against OSMesa (pure
+# CPU software rasteriser, self-contained, no display server required).
+# This is the canonical PyVista headless-Docker recipe; the wheel
+# comes from Kitware's index, not PyPI proper.
+RUN pip uninstall -y vtk \
+    && pip install --no-cache-dir \
+        --extra-index-url https://wheels.vtk.org vtk-osmesa
+
 # Drop privileges. HF Spaces conventionally run as uid 1000 with
 # WORKDIR /home/user/app.
 RUN useradd -m -u 1000 user \