fix(site-builder): Container 40px drop-zone min-height only when empty

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

craft/src/components/layout/Container.dropZone.test.tsx

@@ -0,0 +1,33 @@
+import { describe, test, expect, afterEach } from 'vitest';
+import { renderEditorHarness, EditorHarness } from '../../test-utils/editorHarness';
+
+// The 40px min-height is an editor-only DROP ZONE for EMPTY containers. A container that has
+// content must lay out like the published page (no injected min-height).
+const node = (type: string, props: Record<string, unknown>, nodes: string[] = [], extra: Record<string, unknown> = {}) => ({
+  type: { resolvedName: type }, isCanvas: type === 'Container' || type === 'Text', props, displayName: type, custom: {}, hidden: false, nodes, linkedNodes: {}, ...extra,
+});
+let h: EditorHarness | null = null;
+afterEach(() => { h?.unmount(); h = null; });
+const mount = (inner: Record<string, any>, withChild: boolean) => {
+  h = renderEditorHarness({
+    initialState: JSON.stringify({
+      ROOT: node('Container', { tag: 'div', style: {} }, ['c1']),
+      c1: node('Container', { tag: 'section', ...inner }, withChild ? ['t1'] : [], { parent: 'ROOT' }),
+      ...(withChild ? { t1: node('TextBlock', { text: 'hi', style: {} }, [], { parent: 'c1' }) } : {}),
+    }),
+  });
+  return h.container.querySelector('section') as HTMLElement;
+};
+
+describe('Container empty-only drop zone', () => {
+  test('empty container keeps the 40px drop zone', () => {
+    expect(mount({ style: {} }, false).style.minHeight).toBe('40px');
+  });
+  test('non-empty container does NOT get an injected min-height', () => {
+    expect(mount({ style: {} }, true).style.minHeight).toBe('');
+  });
+  test('an explicit style.minHeight always wins', () => {
+    expect(mount({ style: { minHeight: '100px' } }, true).style.minHeight).toBe('100px');
+    expect(mount({ style: { minHeight: '100px' } }, false).style.minHeight).toBe('100px');
+  });
+});

craft/src/components/layout/Container.tsx

@@ -95,8 +95,11 @@ export const Container: UserComponent<ContainerProps> = ({
   // follows the current device's Alignment / Vertical alignment.
   const layout = containerLayout(style, needsBoxedWrapper);
 
+  // 40px min-height = editor-only DROP ZONE, so only an EMPTY container gets it. A container with
+  // content must size like the published page (toHtml adds no min-height).
+  const isEmpty = React.Children.count(children) === 0;
   const outerStyle: CSSProperties = {
-    minHeight: '40px',
+    ...(isEmpty ? { minHeight: '40px' } : {}),
     ...style,
     ...(fullWidth ? { width: '100vw', marginLeft: 'calc(-50vw + 50%)' } : {}),
     ...layout.outer,