test(ai): cover AI menu item sizing

The AI menu had no coverage that could catch this: the one AI screenshot
(`ai_menu_scroll_position`) is a `document.body` shot on an 800x400 viewport
where the menu is clipped just below the first item, which is why #2909 only
needed to update the *slash* menu baselines.

Screenshots the AI menu in its prompt and error states. Without the fix the
menu is 88px taller, so both fail on all three browsers before pixels are
even compared: "Expected image dimensions to be 623x200px, but received
623x288px".

Author: YousefED

tests/src/end-to-end/ai/__screenshots__/aiMenuAppearance.test.tsx/ai-menu-error-items-chromium-linux.png

@@ -0,0 +1,42 @@
+import App from "@examples/09-ai/01-minimal/src/App";
+import { beforeEach, describe, test } from "vite-plus/test";
+import { render } from "vitest-browser-react";
+import { userEvent } from "../../utils/context.js";
+import {
+  EDITOR_SELECTOR,
+  PARAGRAPH_SELECTOR,
+  SLASH_MENU_SELECTOR,
+} from "../../utils/const.js";
+import { expectElement, sleep, waitForSelector } from "../../utils/editor.js";
+
+beforeEach(async () => {
+  await render(<App />);
+  await waitForSelector(EDITOR_SELECTOR);
+});
+
+describe("AI menu appearance", () => {
+  // Every AI menu item is `size: "small"`. A `min-height` meant for full-size
+  // items used to clamp them to the full row height, stretching the whole menu
+  // (#2909) - these baselines are what catches that.
+  test("renders compact items while prompting and after an error", async () => {
+    // Work from the first block, so the menu opens near the top of the tester
+    // iframe rather than below its fold.
+    await userEvent.click(
+      await waitForSelector(`${EDITOR_SELECTOR} ${PARAGRAPH_SELECTOR}`),
+    );
+    await userEvent.keyboard("{End}/");
+    await waitForSelector(SLASH_MENU_SELECTOR);
+    await userEvent.keyboard("ai{Enter}");
+
+    const aiMenu = await waitForSelector(".bn-combobox");
+    await sleep(500); // The menu's open transition.
+    await expectElement(aiMenu).toMatchScreenshot("ai-menu-prompt-items");
+
+    // The example points at a local AI backend that isn't running in the test
+    // container, so any prompt fails into the error state (Retry / Cancel).
+    await userEvent.keyboard("Write a poem{Enter}");
+    await waitForSelector(".bn-combobox-error", { timeout: 15000 });
+    await sleep(500);
+    await expectElement(aiMenu).toMatchScreenshot("ai-menu-error-items");
+  });
+});