Dimensional constraints: dynamic dimension persistence, lock mark, display variables, DIMCONSTRAINT

The dynamic dimension of a dimensional constraint is now linked in the
drawing file (AcDbAssocDependency + AcDbAssocDimDependencyBody on the
constraint node), reread on load, hidden by DCHIDE/DYNCONSTRAINTDISPLAY
and never plotted; it carries a lock mark before its text. New
CONSTRAINTNAMEFORMAT and DYNCONSTRAINTDISPLAY variables and the
DIMCONSTRAINT option front end. A transformed entity whose own end points
a driving dimension measures keeps only the first constraint point, so a
scaled line returns to its dimension value.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/scene/parametric_solve.rs

@@ -2441,7 +2441,31 @@ fn solve_scope(
             })
         })
         .flatten();
-        let pinned = axis_pin.unwrap_or(*reference);
+        // A transformed entity whose own end points a driving dimension
+        // measures keeps only the first constraint point where the transform
+        // put it; the dimension pulls the other end back to its value (a
+        // scaled line keeps its d1), as in the reference.
+        let dimension_pin = (reference.marker.is_none() && axis_pin.is_none())
+            .then(|| {
+                constraints.iter().find_map(|c| {
+                    (c.enabled
+                        && c.driving_param.is_some()
+                        && matches!(
+                            c.kind,
+                            ConstraintKind::Distance
+                                | ConstraintKind::DistanceX
+                                | ConstraintKind::DistanceY
+                                | ConstraintKind::DistanceDirected
+                        )
+                        && c.refs.len() >= 2
+                        && c.refs
+                            .iter()
+                            .all(|r| r.entity == reference.entity && r.marker.is_some()))
+                    .then(|| c.refs[0])
+                })
+            })
+            .flatten();
+        let pinned = axis_pin.or(dimension_pin).unwrap_or(*reference);
         // The re-aligned entity keeps the length the transform gave it (a
         // scaled vertical line stays scaled), not its pre-edit length.
         if axis_pin.is_some() {