fix(overlays): presenting an overlay does not create nested elements (#26154)

Resolves #26117

core/src/components/datetime-button/test/basic/datetime-button.e2e.ts

@@ -17,6 +17,7 @@ test.describe('datetime-button: switching to correct view', () => {
     expect(datetime).toHaveJSProperty('presentation', 'date-time');
 
     await page.locator('#date-button').click();
+    await page.waitForChanges();
 
     expect(datetime).toHaveJSProperty('presentation', 'date');
   });
@@ -25,6 +26,7 @@ test.describe('datetime-button: switching to correct view', () => {
     expect(datetime).toHaveJSProperty('presentation', 'date-time');
 
     await page.locator('#time-button').click();
+    await page.waitForChanges();
 
     expect(datetime).toHaveJSProperty('presentation', 'time');
   });

core/src/components/modal/test/inline/modal.e2e.ts

@@ -21,4 +21,44 @@ test.describe('modal: inline', () => {
 
     expect(await page.screenshot()).toMatchSnapshot(`modal-inline-dismiss-${page.getSnapshotSettings()}.png`);
   });
+
+  test('presenting should create a single root element with the ion-page class', async ({ page, skip }, testInfo) => {
+    skip.mode('md');
+    skip.rtl();
+
+    testInfo.annotations.push({
+      type: 'issue',
+      description: 'https://github.com/ionic-team/ionic-framework/issues/26117',
+    });
+
+    await page.setContent(`
+    <ion-datetime-button datetime="datetime"></ion-datetime-button>
+
+    <ion-modal>
+      <ion-datetime id="datetime" presentation="date-time"></ion-datetime>
+    </ion-modal>
+    `);
+
+    const ionModalDidPresent = await page.spyOnEvent('ionModalDidPresent');
+    const ionModalDidDismiss = await page.spyOnEvent('ionModalDidDismiss');
+    const modal = page.locator('ion-modal');
+
+    await page.locator('#date-button').click();
+    await ionModalDidPresent.next();
+
+    // Verifies that the host element exists with the .ion-page class
+    expect(await modal.evaluate((el: HTMLIonModalElement) => el.firstElementChild!.className)).toContain('ion-page');
+
+    await modal.evaluate((el: HTMLIonModalElement) => el.dismiss());
+    await ionModalDidDismiss.next();
+
+    await page.locator('#date-button').click();
+    await ionModalDidPresent.next();
+
+    // Verifies that presenting the overlay again does not create a new host element
+    expect(await modal.evaluate((el: HTMLIonModalElement) => el.firstElementChild!.className)).toContain('ion-page');
+    expect(
+      await modal.evaluate((el: HTMLIonModalElement) => el.firstElementChild!.firstElementChild!.className)
+    ).not.toContain('ion-page');
+  });
 });

core/src/utils/framework-delegate.ts

@@ -87,15 +87,23 @@ export const CoreDelegate = () => {
 
       await new Promise((resolve) => componentOnReady(el, resolve));
     } else if (BaseComponent.children.length > 0) {
-      // If there is no component, then we need to create a new parent
-      // element to apply the css classes to.
+      const root = BaseComponent.children[0] as HTMLElement;
+      if (!root.classList.contains('ion-delegate-host')) {
+        /**
+         * If the root element is not a delegate host, it means
+         * that the overlay has not been presented yet and we need
+         * to create the containing element with the specified classes.
+         */
         const el = BaseComponent.ownerDocument?.createElement('div');
+        // Add a class to track if the root element was created by the delegate.
+        el.classList.add('ion-delegate-host');
         cssClasses.forEach((c) => el.classList.add(c));
         // Move each child from the original template to the new parent element.
         el.append(...BaseComponent.children);
         // Append the new parent element to the original parent element.
         BaseComponent.appendChild(el);
       }
+    }
 
     /**
      * Get the root of the app and