Viewport association fixture
viewport_associations.dxf is a synthetic paper-space fixture for line, circle,
arc, polyline, spline, block-instance, and intersection references through one
1:2 viewport. src/app/viewport_dimension_tests.rs loads it and exercises actual
association refresh and an edit to the second intersection source.
Each dimension carries DIMLFAC=-2 and ACAD_DIMASSOC_CALC_DIMLFAC=-2. These are
necessary for its paper definition points and saved model measurements to agree;
the original fixture omitted both factors. The spline tangent also uses the
actual touch point (90, 283.125) at parameter 0.75, measured from (0, 300).
The original endpoint (120, 300) was not tangent. Tests verify the cross product
with the spline derivative and preservation after an unsupported reference edit.
The larger original 115448.dxf is private and is not included. An opt-in test
uses OPENCAD_VIEWPORT_REGRESSION_DXF to read a local copy without modifying it.