DCDIAMETER/DCRADIUS: the reference flow with a real radial dimension

The commands ask for the circle or arc themselves, report the measured
size, take a dimension line location and then the value or name and
value, creating a radius or diameter dimension as the constraint's
dynamic dimension with a radN/diaN parameter, refusing a second radial
constraint on the same object and any non-positive value.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/commands/draw.rs

@@ -1891,12 +1891,30 @@ 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" {
-                    self.dim_constraint_last = "Diameter";
-                }
+            "DCRADIUS" | "DCDIAMETER" => {
+                use crate::modules::parametric::{DimConstraintAxis, DimConstraintCommand};
+                use crate::scene::parametric_constraints::next_radial_parameter_name;
+                let diameter = cmd == "DCDIAMETER";
+                self.dim_constraint_last = if diameter { "Diameter" } else { "Radius" };
+                // The reference asks for the circle itself, whatever is
+                // selected, so a pick-first set is left alone.
+                let name = next_radial_parameter_name(
+                    self.tabs[i].scene.named_parameters(),
+                    diameter,
+                );
+                let command = DimConstraintCommand::new(
+                    if diameter {
+                        DimConstraintAxis::Diameter
+                    } else {
+                        DimConstraintAxis::Radius
+                    },
+                    name,
+                );
+                self.command_line.push_info(&command.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(command));
+            }
+
+            "DCONSTRAINT" => {
                 let handles = self.tabs[i].scene.selected_handles_in_order();
                 if handles.is_empty() {
                     use crate::modules::draw::select::SelectObjectsCommand;
@@ -1914,8 +1932,6 @@ impl OpenCADStudio {
                         "DCHORIZONTAL" => ("DCHORIZONTAL", DistanceMode::X),
                         "DCVERTICAL" => ("DCVERTICAL", DistanceMode::Y),
                         "DCALIGNED" => ("DCALIGNED", DistanceMode::Aligned),
-                        "DCRADIUS" => ("DCRADIUS", DistanceMode::Radius),
-                        "DCDIAMETER" => ("DCDIAMETER", DistanceMode::Diameter),
                         _ => ("DCONSTRAINT", DistanceMode::Auto),
                     };
                     match DistanceConstraintCommand::with_mode(