Merge pull request #1332 from ramox81/codex/concentric-constraint-parity

# Conflicts:
#	src/entities/arc.rs
#	src/entities/ellipse.rs
#	src/modules/parametric/mod.rs
#	src/scene/parametric_solve.rs
#	src/ui/overlay.rs

src/app/command_driver.rs

@@ -3372,6 +3372,88 @@ impl OpenCADStudio {
                     self.commit_undo_delta(i, pd);
                 }
             }
+            CmdResult::AddConcentricConstraint {
+                first,
+                second,
+                label,
+            } => {
+                use crate::scene::parametric_constraints::ConstraintKind;
+
+                let refs = vec![first, second];
+                if let Err(message) = self.tabs[i].scene.validate_parametric_constraint(
+                    ConstraintKind::Concentric,
+                    &refs,
+                    None,
+                ) {
+                    self.tabs[i].active_cmd = None;
+                    self.tabs[i].snap_result = None;
+                    self.command_line.push_error(message);
+                    return Task::none();
+                }
+                let scope = self.tabs[i].current_parametric_scope();
+                let duplicate = self.tabs[i]
+                    .scene
+                    .parametric_constraint_set(scope)
+                    .is_some_and(|set| {
+                        set.constraints.iter().any(|constraint| {
+                            constraint.enabled
+                                && constraint.kind == ConstraintKind::Concentric
+                                && matches!(constraint.refs.as_slice(), [a, b]
+                                    if (*a == first && *b == second)
+                                        || (*a == second && *b == first))
+                        })
+                    });
+                if duplicate {
+                    self.tabs[i].active_cmd = None;
+                    self.tabs[i].snap_result = None;
+                    self.command_line
+                        .push_output("The Concentric constraint already exists.");
+                    return Task::none();
+                }
+                let constraints_before = self.tabs[i]
+                    .scene
+                    .parametric_constraint_set(scope)
+                    .cloned()
+                    .unwrap_or_else(|| {
+                        crate::scene::parametric_constraints::ParametricConstraintSet::new(scope)
+                    });
+                let touched = if first.entity == second.entity {
+                    vec![first.entity]
+                } else {
+                    vec![first.entity, second.entity]
+                };
+                let pending = self.begin_undo(i, label, touched.len(), true);
+                self.tabs[i]
+                    .scene
+                    .record_undo_parametric_constraints_before(scope, constraints_before);
+                let id = self.tabs[i].scene.parametric_constraint_set_mut(scope).add(
+                    ConstraintKind::Concentric,
+                    refs,
+                    None,
+                );
+                self.tabs[i].scene.note_parametric_constraint_applied(
+                    scope,
+                    id,
+                    self.constraint_bar_display,
+                );
+                let changes = touched
+                    .into_iter()
+                    .map(|handle| (handle, crate::scene::ChangeKind::Modified))
+                    .collect::<Vec<_>>();
+                self.tabs[i].scene.bump_entities_with_initial_parametric_policy(
+                    &changes,
+                    &[first],
+                    true,
+                );
+                self.tabs[i].dirty = true;
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.command_line.push_output("Constraint applied.");
+                self.refresh_properties();
+                if let Some(pd) = pending {
+                    self.commit_undo_delta(i, pd);
+                }
+            }
             CmdResult::AddCoincidentConstraint {
                 first,
                 second,