Issue #3029061 by tim.plunkett, phenaproxima: New layouts are missing config schema

core/modules/layout_builder/config/schema/layout_builder.schema.yml

@@ -64,3 +64,16 @@ inline_block:
 
 block.settings.inline_block:*:
   type: inline_block
+
+layout_builder_multi_width:
+  type: layout_plugin.settings
+  mapping:
+    column_widths:
+      type: string
+      label: 'Column widths'
+
+layout_plugin.settings.layout_twocol_section:
+  type: layout_builder_multi_width
+
+layout_plugin.settings.layout_threecol_section:
+  type: layout_builder_multi_width

core/modules/layout_builder/tests/src/FunctionalJavascript/TestMultiWidthLayoutsTest.php

@@ -100,6 +100,12 @@ public function testWidthChange() {
         $page->findField('layout_settings[column_widths]')->setValue($width);
         $page->pressButton("Update");
         $this->assertWidthClassApplied($width_class);
+
+        // Save the layout and return to the Layout Builder UI for more changes.
+        $assert_session->pageTextContains('You have unsaved changes.');
+        $page->clickLink('Save Layout');
+        $assert_session->pageTextNotContains('You have unsaved changes.');
+        $this->clickLink('Manage layout');
       }
       $assert_session->linkExists('Remove section');
       $this->clickLink('Remove section');