Resolve viewport dimension features and preserve valid measurements on refresh

docs/viewport-dimensions.md

@@ -34,10 +34,46 @@ user's unit conversion separate from viewport scale. The ordinary `DIMLFAC`
 override remains sufficient for displaying the saved measurement in other CAD
 readers. The data survives DXF/DWG saves and undo/redo.
 
-The dependent association change uses this metadata when viewport scale changes.
-This creation change alone creates nonassociative viewport dimensions and leaves
-the drawing's `DIMASSOC` setting unchanged. Direct model/paper associations retain
-their existing behavior.
+With `DIMASSOC=2`, acquired features attach a dimension to its viewport, each
+block instance, and the source entity. Intersections retain both source chains.
+Source edits and viewport changes update the definition points and recompute
+compensation while preserving explicit user-positioned sheet text and dimension
+style overrides. A successful update invalidates the saved picture block so the
+new geometry and number are rendered and exported. Undo restores both the
+reference data and the previous picture.
+
+Properties reports whether the dimension is associated, partially associated,
+unresolved, broken, or nonassociative. A broken or unsupported required reference
+preserves the entire dimension's last valid appearance and its original records.
+Creating another dimension does not announce geometry changes to its sources.
+
+## Imported references and support limits
+
+The resolver distinguishes the application's vertex/parameter convention from
+imported edge references. Imported start/end and midpoint modes use their edge
+marker and parameter together. The original regression drawing's first-edge
+start/end pair now reproduces its `0.128` measurement. An imported polyline
+endpoint beyond the first edge requires a usable stored point to validate the
+marker; zero/sentinel data cannot establish that identity. Ambiguous imports
+remain unresolved. Imported viewport scale is updated only when existing OCS
+metadata or `ACAD_DIMASSOC_CALC_DIMLFAC` separates compensation from user scaling.
+
+Unsupported cases retain their saved data and appearance:
+
+- Perspective/oblique viewport projections and malformed/missing reference chains.
+- Ambiguous intersections within one batched block; they are not attached to a
+  guessed pair of children. Intersections between separate identified chains work.
+- Array inserts without an addressable instance index, nesting beyond eight levels,
+  and radial measurements of nonuniformly transformed circular geometry.
+- Imported quadrant references whose moved geometry no longer validates the stored
+  point; newly acquired circle/arc quadrants keep their source-local angle.
+- Tangency with no verified solution, two dependent perpendicular/tangent references
+  requiring a coupled solve, unsupported snap modes, and imported measurement data that does not identify the old viewport compensation.
+
+The osnap codes and reference fields follow the
+[Autodesk DIMASSOC reference](https://help.autodesk.com/cloudhelp/2024/ENU/AutoCAD-DXF/files/GUID-C0B96256-A911-4B4D-85E6-EB4AF2C91E27.htm).
+The restricted imported-marker interpretation above is validated by fixtures;
+it is not a claim that every exporter uses an interchangeable marker scheme.
 
 ## Validation
 
@@ -46,3 +82,17 @@ commits for all five commands, object picks, input retries, active positive and
 negative style factors, exploded dimensions, undo/redo, DXF/DWG persistence,
 clipping, overlapping viewports, pan, scale, and twist. These are headless tests;
 they do not establish visual acceptance in the desktop UI.
+
+Association tests also exercise regeneration, nearest and quadrant parameters,
+angular arc/polyline object picks, spline tangency,
+perpendicularity under nonuniform block scale, nested paths, intersection source
+edits, preserved overrides, erased sources, copy detachment, saved picture
+invalidation, and history. The checked-in DXF fixture is exercised directly.
+The original private drawing can be checked separately:
+
+```powershell
+$env:OPENCAD_VIEWPORT_REGRESSION_DXF = 'C:\path\to\115448.dxf'
+cargo test --locked --offline --lib viewport_dimension_original -- --ignored --nocapture
+```
+
+Do not treat passing headless checks as completed desktop visual acceptance.