fix(showcase): use pressSequentially instead of fill for sandboxed iframe input

fill() silently no-ops inside sandbox="allow-scripts" iframes on some
Playwright/Chromium combos because the null origin blocks the
set-value protocol message. The input.value stays empty, so the
host-side evaluateExpression handler rejects it with "Unsupported
characters" and the test never sees a console log.

pressSequentially sends individual key events that always reach the
input regardless of sandbox restrictions.

Author: jpr5

showcase/integrations/google-adk/tests/e2e/open-gen-ui-advanced.spec.ts

@@ -184,7 +184,13 @@ test.describe("Open Generative UI (advanced)", () => {
     await sendPromptAndAwaitIframe(page, PROMPTS.inlineEval);
 
     const frame = page.frameLocator('iframe[sandbox*="allow-scripts"]').first();
-    await frame.locator("#in").fill("2 + 2");
+    // `fill()` silently no-ops inside sandbox="allow-scripts" iframes on
+    // some Playwright/Chromium combos (null origin blocks the set-value
+    // protocol message). `pressSequentially` sends individual key events
+    // that always reach the input regardless of sandbox restrictions.
+    const input = frame.locator("#in");
+    await input.click();
+    await input.pressSequentially("2+2");
     await frame.locator("#go").click();
 
     await expect

showcase/integrations/langgraph-python/tests/e2e/open-gen-ui-advanced.spec.ts

@@ -184,7 +184,13 @@ test.describe("Open Generative UI (advanced)", () => {
     await sendPromptAndAwaitIframe(page, PROMPTS.inlineEval);
 
     const frame = page.frameLocator('iframe[sandbox*="allow-scripts"]').first();
-    await frame.locator("#in").fill("2 + 2");
+    // `fill()` silently no-ops inside sandbox="allow-scripts" iframes on
+    // some Playwright/Chromium combos (null origin blocks the set-value
+    // protocol message). `pressSequentially` sends individual key events
+    // that always reach the input regardless of sandbox restrictions.
+    const input = frame.locator("#in");
+    await input.click();
+    await input.pressSequentially("2+2");
     await frame.locator("#go").click();
 
     await expect

showcase/integrations/langgraph-typescript/tests/e2e/open-gen-ui-advanced.spec.ts

@@ -184,7 +184,13 @@ test.describe("Open Generative UI (advanced)", () => {
     await sendPromptAndAwaitIframe(page, PROMPTS.inlineEval);
 
     const frame = page.frameLocator('iframe[sandbox*="allow-scripts"]').first();
-    await frame.locator("#in").fill("2 + 2");
+    // `fill()` silently no-ops inside sandbox="allow-scripts" iframes on
+    // some Playwright/Chromium combos (null origin blocks the set-value
+    // protocol message). `pressSequentially` sends individual key events
+    // that always reach the input regardless of sandbox restrictions.
+    const input = frame.locator("#in");
+    await input.click();
+    await input.pressSequentially("2+2");
     await frame.locator("#go").click();
 
     await expect