DCRADIUS: reference radial dimensional constraint with a dynamic radial dimension

Select arc or circle / Dimension text / dimension line location / value or
name prompts with a radN parameter, invalid-selection, miss, duplicate and
invalid-expression messages, negative values as magnitudes, a dynamic radial
dimension on the constraints layer drawn as the reference does (mid-radius
text on the center-to-rim line, no hook, no center mark, one text grip), the
stored text position following the radius, center-anchored resizing, the
Properties title and Constraint section, DIMCONSTRAINT's Radius default,
the small-button Dimensional ribbon grid and tooltip descriptions.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/app/commands/draw.rs

@@ -1891,10 +1891,20 @@ impl OpenCADStudio {
                 self.tabs[i].active_cmd = Some(Box::new(command));
             }
 
-            "DCONSTRAINT" | "DCRADIUS" | "DCDIAMETER" => {
-                if cmd == "DCRADIUS" {
-                    self.dim_constraint_last = "Radius";
-                } else if cmd == "DCDIAMETER" {
+            "DCRADIUS" => {
+                use crate::modules::parametric::{DimConstraintAxis, DimConstraintCommand};
+                use crate::scene::parametric_constraints::next_radial_parameter_name;
+                // Run on its own it leaves DIMCONSTRAINT's default alone.
+                let name = next_radial_parameter_name(self.tabs[i].scene.named_parameters());
+                // The circle or arc is picked inside the command.
+                self.tabs[i].scene.deselect_all();
+                let command = DimConstraintCommand::new(DimConstraintAxis::Radius, name);
+                self.command_line.push_info(&command.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(command));
+            }
+
+            "DCONSTRAINT" | "DCDIAMETER" => {
+                if cmd == "DCDIAMETER" {
                     self.dim_constraint_last = "Diameter";
                 }
                 let handles = self.tabs[i].scene.selected_handles_in_order();