diff --git a/tools/ui/tests/stories/a11y/ChatScreenForm.a11y.stories.svelte b/tools/ui/tests/stories/a11y/ChatScreenForm.a11y.stories.svelte
index 6fa5924e08..826e0d4aa1 100644
--- a/tools/ui/tests/stories/a11y/ChatScreenForm.a11y.stories.svelte
+++ b/tools/ui/tests/stories/a11y/ChatScreenForm.a11y.stories.svelte
@@ -2,8 +2,25 @@
 	import { defineMeta } from '@storybook/addon-svelte-csf';
 	import ChatScreenForm from '$lib/components/app/chat/ChatScreen/ChatScreenForm.svelte';
 	import { ATTACHMENT_TOOLTIP_TEXT } from '$lib/constants';
+	import { ServerRole } from '$lib/enums';
+	import { serverStore } from '$lib/stores';
+	import type { ApiLlamaCppServerProps } from '$lib/types';
 	import { expect, screen, waitFor } from 'storybook/test';
 
+	/**
+	 * The add menu mounts the reasoning submenu only outside router mode, and the
+	 * dev server proxies /props to whichever server happens to be running, so pin
+	 * the mode this story asserts instead of inheriting it from the environment.
+	 */
+	function pinSingleModelMode(): void {
+		serverStore.props = {
+			...(serverStore.props ?? {}),
+			role: ServerRole.MODEL
+		} as ApiLlamaCppServerProps;
+
+		serverStore.role = ServerRole.MODEL;
+	}
+
 	const { Story } = defineMeta({
 		component: ChatScreenForm,
 		parameters: {
@@ -38,6 +55,8 @@
 	args={{ class: 'max-w-[56rem] w-[calc(100vw-2rem)]' }}
 	name="AddDropdownFocusesFirstEnabled"
 	play={async ({ canvas, userEvent }) => {
+		pinSingleModelMode();
+
 		const trigger = await canvas.findByRole('button', { name: ATTACHMENT_TOOLTIP_TEXT });
 
 		trigger.focus();