Turn an object onto its Horizontal/Vertical axis before solving

The solver cannot start from an axis lying exactly across the datum: the
distance and direction equations are singular there, so a horizontal line,
a text at 0 degrees or an ellipse whose major axis is horizontal stayed
put when Vertical was applied. The command now turns the object about its
anchor (line start, picked segment's first vertex, text insertion point,
ellipse center) onto the axis first — a polyline moves only the segment's
end vertex — and lets the constraint hold what already fits. Two points on
one entity follow the same rule about the first point.

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

src/app/command_driver.rs

@@ -3486,6 +3486,53 @@ impl OpenCADStudio {
                         }
                     }
                 }
+                // The solver cannot start from an axis lying exactly across
+                // the datum (its equations are singular there), so turn the
+                // object onto the axis about its anchor first — the
+                // reference turns it about that anchor too — and let the
+                // constraint hold what already fits.
+                if let Some((handle, anchor, end, vertex)) =
+                    crate::scene::parametric_constraints::axis_alignment_target(
+                        &self.tabs[i].scene.document,
+                        &refs,
+                    )
+                {
+                    let axis = (end.x - anchor.x, end.y - anchor.y);
+                    let length = axis.0.hypot(axis.1);
+                    let target = if axis.0 * direction.x + axis.1 * direction.y >= 0.0 {
+                        (direction.x, direction.y)
+                    } else {
+                        (-direction.x, -direction.y)
+                    };
+                    let angle = (axis.0 * target.1 - axis.1 * target.0)
+                        .atan2(axis.0 * target.0 + axis.1 * target.1);
+                    if length > 1.0e-9 && angle.abs() > 1.0e-9 {
+                        match vertex {
+                            Some(index) => {
+                                let moved =
+                                    self.tabs[i].scene.document.get_entity(handle).cloned();
+                                if let Some(mut entity) = moved {
+                                    if crate::scene::parametric_constraints::set_polyline_vertex(
+                                        &mut entity,
+                                        index,
+                                        anchor.x + length * target.0,
+                                        anchor.y + length * target.1,
+                                    ) {
+                                        self.tabs[i].scene.update_entity(entity);
+                                    }
+                                }
+                            }
+                            None => self.tabs[i].scene.transform_entities(
+                                &[handle],
+                                &EntityTransform::Rotate {
+                                    center: glam::DVec3::new(anchor.x, anchor.y, anchor.z),
+                                    axis: glam::DVec3::Z,
+                                    angle_rad: angle,
+                                },
+                            ),
+                        }
+                    }
+                }
                 let id = self.tabs[i]
                     .scene
                     .parametric_constraint_set_mut(scope)