diff --git a/src/underworld3/materials.py b/src/underworld3/materials.py
index b9a9be69f..c2f0ca817 100644
--- a/src/underworld3/materials.py
+++ b/src/underworld3/materials.py
@@ -297,7 +297,7 @@ def add_callback(self, callback: Callable):
         Parameters
         ----------
         callback : callable
-            Function called as callback(event_type, \*args)
+            Function called as ``callback(event_type, *args)``
         """
         self._callbacks.append(callback)
 
diff --git a/src/underworld3/model.py b/src/underworld3/model.py
index 7f9795fb8..2a398e57d 100644
--- a/src/underworld3/model.py
+++ b/src/underworld3/model.py
@@ -124,7 +124,7 @@ def __init__(self, name: Optional[str] = None, **kwargs):
         ----------
         name : str, optional
             Human-readable name for this model instance
-        \*\*kwargs : dict
+        **kwargs : dict
             Additional arguments for Pydantic BaseModel
         """
         # Handle name generation before calling super().__init__
@@ -540,7 +540,7 @@ def define_parameter(self, name: str, ptype=None, **kwargs):
             Parameter path (e.g., 'material.viscosity', 'solver.tolerance')
         ptype : ParameterType, optional
             Parameter type for validation (not used yet)
-        \*\*kwargs : dict
+        **kwargs : dict
             Additional arguments
         """
         # TODO: Implement when parameter system is ready
@@ -592,7 +592,7 @@ def set_reference_quantities(self, verbose=False, nondimensional_scaling=True, *
             [0-1] space while user-facing values remain in physical units.
             Set to False for expert mode (dimensional units only, no scaling).
             Disabling this may cause numerical conditioning issues.
-        \*\*quantities : dict
+        **quantities : dict
             Named reference quantities using Pint units or UWQuantity objects,
             e.g. ``domain_depth=uw.quantity(2900, "km")``.
 
diff --git a/tests/test_0800_optional_modules.py b/tests/test_0800_optional_modules.py
index 13d5bfdcc..15ac4f262 100644
--- a/tests/test_0800_optional_modules.py
+++ b/tests/test_0800_optional_modules.py
@@ -49,6 +49,15 @@ def check_module_available(module_name: str) -> bool:
 HAS_GDAL = check_module_available("osgeo.gdal")
 HAS_GEOPANDAS = check_module_available("geopandas")
 HAS_PYVISTA = check_module_available("pyvista")
+
+# Check if a display server is available for rendering.
+# On headless CI (no DISPLAY, no WAYLAND), pyvista.Plotter() calls
+# VTK's OpenGL probe which aborts the entire process — not catchable
+# with try/except. We must skip rendering tests before they run.
+import os
+HAS_DISPLAY = bool(os.environ.get("DISPLAY") or os.environ.get("WAYLAND_DISPLAY")
+                    or os.environ.get("PYVISTA_OFF_SCREEN"))
+HAS_PYVISTA_RENDERING = HAS_PYVISTA and HAS_DISPLAY
 HAS_TRAME = check_module_available("trame")
 
 # Composite feature flags
@@ -98,6 +107,11 @@ def check_petsc_has_pragmatic() -> bool:
     reason="Requires pyvista. Install with: pixi install -e runtime"
 )
 
+requires_pyvista_rendering = pytest.mark.skipif(
+    not HAS_PYVISTA_RENDERING,
+    reason="Requires pyvista and a display server (DISPLAY or PYVISTA_OFF_SCREEN)"
+)
+
 requires_amr = pytest.mark.skipif(
     not HAS_AMR,
     reason="Requires AMR-enabled PETSc. Install with: pixi install -e amr && pixi run -e amr petsc-build"
@@ -233,12 +247,12 @@ def test_pyvista_mesh_conversion(self):
             sphere = pv.Sphere()
             assert sphere is not None
 
-    @requires_pyvista
+    @requires_pyvista_rendering
     def test_pyvista_plotter_available(self):
         """Test pyvista plotter when available."""
         import pyvista as pv
 
-        # Just verify we can create a plotter (off-screen)
+        pv.OFF_SCREEN = True
         plotter = pv.Plotter(off_screen=True)
         assert plotter is not None
         plotter.close()