Add cutout shell and volume node assets for depth volume processing

- Implemented `cutout_shell.py` to build front normals and shell positions for balloon geometry.
- Created `cutout_volume.py` to establish smooth center fields and manage balloon surface attributes.
- Introduced `pisa_sr_export.py` for exporting PiSA-SR components with dependencies and asset finalization.

tests/test_cutout_fine_mesh.py

@@ -228,6 +228,27 @@ def test_cdt_preserves_constraint_split_by_an_interior_vertex():
     assert not g.boundary_vertices_from_faces(len(points), faces)[constraints].any()
 
 
+@pytest.mark.parametrize("offset", [0, 4096, 16384])
+def test_cdt_collinear_outline_samples_do_not_become_sliver_faces(offset):
+    contour = np.asarray(((0., 0.), (240., 0.), (240., 160.), (0., 160.)))
+    contour = contour @ np.asarray(((.763, -.646), (.646, .763)))
+    contour += np.asarray((420.123456, 540.234567)) + offset
+    contours, spine, edges = fine.subdivide_constraints(
+        [contour], np.empty((0, 2)), [], 16
+    )
+    free = g.uniform_interior_points_for_contours(contours, 16)
+    points, faces, _ = fine.triangulate(contours, spine, edges, free, 16)
+    triangles = points[faces]
+    area = abs(np.cross(triangles[:, 1] - triangles[:, 0], triangles[:, 2] - triangles[:, 0]))
+    longest_squared = np.max(np.sum((triangles - np.roll(triangles, 1, axis=1))**2, axis=2), axis=1)
+    assert np.min(area / longest_squared) > 1e-4
+    assert area.sum() / 2 == pytest.approx(abs(g.contour_area(contour)), rel=1e-9)
+    boundary = g.boundary_vertices_from_faces(len(points), faces)
+    np.testing.assert_allclose(fine.ContourDomain([contour]).clearance(points[boundary]), 0, atol=1e-9)
+    # Every subdivided outline point survives; removing slivers must not skip it.
+    assert cKDTree(points[boundary]).query(contours[0])[0].max() < 1e-9
+
+
 def test_contour_validation_accepts_pixel_contacts_and_rejects_crossings():
     crossing = np.asarray(((0, 0), (4, 4), (0, 4), (4, 0)))
     assert not fine.valid_contours([crossing])