Track mixed paper and viewport dimension references

tests/fixtures/dim_assoc/README.md

@@ -1,16 +1,10 @@
 # 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.
+`viewport_associations.dxf` contains line, circle, arc, polyline, spline,
+block-instance, and intersection references through a 1:2 viewport.
+`src/app/viewport_dimension_tests.rs` tests refresh and intersection source edits.
 
-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.
+Each dimension stores `DIMLFAC=-2` and `ACAD_DIMASSOC_CALC_DIMLFAC=-2` so its paper
+definition points measure in model units. The spline tangent from `(0, 300)`
+touches `(90, 283.125)` at parameter `0.75`; tests verify its tangency and preserve
+the dimension if an edited reference cannot resolve.