fix: prepend_child causes negative order values when reordering within same parent (#488)

Author: navaneethkp36

lib/closure_tree/hierarchy_maintenance.rb

@@ -49,7 +49,8 @@ def _ct_after_save
           _ct_reorder_prior_siblings_if_parent_changed
           _ct_reorder_siblings
         elsif saved_changes[_ct.order_column_sym]
-          _ct_reorder_siblings(saved_changes[_ct.order_column_sym].min)
+          min = saved_changes[_ct.order_column_sym].min
+          _ct_reorder_siblings(min.negative? ? nil : min)
         end
       end
       if saved_changes[_ct.parent_column_name] && !@was_new_record

test/closure_tree/label_order_value_test.rb

@@ -38,6 +38,24 @@ def setup
     assert_equal 1, c.reload.order_value
   end
 
+  test 'prepend_child should produce 0-based order values when reordering within the same parent' do
+    root = Label.create(name: 'root')
+    a = root.children.create(name: 'a')
+    b = root.children.create(name: 'b')
+    c = root.children.create(name: 'c')
+
+    assert_equal 0, a.order_value
+    assert_equal 1, b.order_value
+    assert_equal 2, c.order_value
+
+    # Move c to be the first child (same parent, reorder only)
+    root.prepend_child(c)
+
+    assert_equal 0, c.reload.order_value
+    assert_equal 1, a.reload.order_value
+    assert_equal 2, b.reload.order_value
+  end
+
   test 'should set order_value on roots for LabelWithoutRootOrdering' do
     root = LabelWithoutRootOrdering.create(name: 'root')
     assert_nil root.order_value