diff --git a/web/src/lib/chat/__tests__/composer-shortcuts.test.ts b/web/src/lib/chat/__tests__/composer-shortcuts.test.ts
index 4c6e88095..7523d15f2 100644
--- a/web/src/lib/chat/__tests__/composer-shortcuts.test.ts
+++ b/web/src/lib/chat/__tests__/composer-shortcuts.test.ts
@@ -86,7 +86,7 @@ describe('shouldSubmitOnEnter', () => {
 		).toBe(false);
 	});
 
-	it('never submits on mobile (Enter inserts newline)', () => {
+	it('uses the setting as the only Enter/Shift+Enter mode switch', () => {
 		expect(
 			shouldSubmitOnEnter({
 				sendByShiftEnter: false,
@@ -94,12 +94,8 @@ describe('shouldSubmitOnEnter', () => {
 				ctrlKey: false,
 				metaKey: false,
 				isComposing: false,
-				isMobile: true,
 			})
-		).toBe(false);
-	});
-
-	it('never submits on mobile even with Shift+Enter', () => {
+		).toBe(true);
 		expect(
 			shouldSubmitOnEnter({
 				sendByShiftEnter: true,
@@ -107,9 +103,8 @@ describe('shouldSubmitOnEnter', () => {
 				ctrlKey: false,
 				metaKey: false,
 				isComposing: false,
-				isMobile: true,
 			})
-		).toBe(false);
+		).toBe(true);
 	});
 });
 
diff --git a/web/src/lib/chat/composer-shortcuts.ts b/web/src/lib/chat/composer-shortcuts.ts
index 21c1cbbfd..56d389945 100644
--- a/web/src/lib/chat/composer-shortcuts.ts
+++ b/web/src/lib/chat/composer-shortcuts.ts
@@ -4,16 +4,13 @@ interface EnterSubmissionParams {
 	ctrlKey: boolean;
 	metaKey: boolean;
 	isComposing: boolean;
-	isMobile?: boolean;
 }
 
 /**
  * Returns true when an Enter keypress should submit the composer.
- * On mobile, Enter always inserts a newline (submit via send button).
  * Ctrl/Cmd+Enter stays unbound regardless of preference.
  */
 export function shouldSubmitOnEnter(params: EnterSubmissionParams): boolean {
-	if (params.isMobile) return false;
 	if (params.isComposing) return false;
 	if (params.ctrlKey || params.metaKey) return false;
 	return params.sendByShiftEnter ? params.shiftKey : !params.shiftKey;
diff --git a/web/src/lib/components/chat/PromptComposer.svelte b/web/src/lib/components/chat/PromptComposer.svelte
index 640174c97..ca9a745ec 100644
--- a/web/src/lib/components/chat/PromptComposer.svelte
+++ b/web/src/lib/components/chat/PromptComposer.svelte
@@ -107,7 +107,6 @@
 				ctrlKey: event.ctrlKey,
 				metaKey: event.metaKey,
 				isComposing: event.isComposing,
-				isMobile: appShell.isMobile,
 			})
 		) return;
 
diff --git a/web/src/lib/components/chat/__tests__/NewChatForm.test.ts b/web/src/lib/components/chat/__tests__/NewChatForm.test.ts
index 412d0d7b3..52a30e6f2 100644
--- a/web/src/lib/components/chat/__tests__/NewChatForm.test.ts
+++ b/web/src/lib/components/chat/__tests__/NewChatForm.test.ts
@@ -1,6 +1,7 @@
 import { fireEvent, render, screen, waitFor } from '@testing-library/svelte';
-import { describe, expect, it, vi } from 'vitest';
+import { beforeEach, describe, expect, it, vi } from 'vitest';
 import NewChatFormTestHarness from './NewChatFormTestHarness.svelte';
+import * as chatsApi from '$lib/api/chats';
 import * as settingsApi from '$lib/api/settings';
 import * as gitApi from '$lib/api/git';
 import type { RemoteSettingsSnapshot } from '$shared/settings';
@@ -18,6 +19,22 @@ vi.mock('$lib/api/settings', () => ({
 	updateRemoteSettings: vi.fn(),
 }));
 
+function installMatchMedia(matches: boolean): void {
+	Object.defineProperty(window, 'matchMedia', {
+		configurable: true,
+		value: vi.fn().mockImplementation((query: string) => ({
+			matches,
+			media: query,
+			onchange: null,
+			addEventListener: vi.fn(),
+			removeEventListener: vi.fn(),
+			addListener: vi.fn(),
+			removeListener: vi.fn(),
+			dispatchEvent: vi.fn(),
+		})),
+	});
+}
+
 function deferred<T>() {
 	let resolve!: (value: T) => void;
 	const promise = new Promise<T>((res) => {
@@ -49,7 +66,46 @@ function makeSnapshot(overrides: Partial<RemoteSettingsSnapshot> = {}): RemoteSe
 	};
 }
 
+async function renderReadyNewChatForm(options: {
+	sendByShiftEnter?: boolean;
+	isMobile?: boolean;
+} = {}) {
+	const onStartChat = vi.fn();
+	vi.mocked(settingsApi.getRemoteSettings).mockResolvedValueOnce(makeSnapshot({
+		lastProjectPath: '/workspace/project',
+	}));
+	vi.mocked(chatsApi.validateStart).mockResolvedValue({
+		valid: true,
+		isGitRepo: false
+	});
+
+	render(NewChatFormTestHarness, {
+		props: {
+			...options,
+			onStartChat,
+		}
+	});
+
+	const messageInput = await screen.findByPlaceholderText('How can I help you today?') as HTMLTextAreaElement;
+	await waitFor(() => {
+		expect(screen.queryByRole('status', { name: 'Loading chat defaults...' })).toBeNull();
+	});
+	await fireEvent.input(messageInput, { target: { value: 'Start this session' } });
+
+	const sendButton = screen.getByTitle('Start session') as HTMLButtonElement;
+	await waitFor(() => {
+		expect(sendButton.disabled).toBe(false);
+	});
+
+	return { messageInput, onStartChat };
+}
+
 describe('NewChatForm', () => {
+	beforeEach(() => {
+		vi.clearAllMocks();
+		installMatchMedia(false);
+	});
+
 	it('shows a centered spinner and hides the composer until settings load', async () => {
 		const pending = deferred<Awaited<ReturnType<typeof settingsApi.getRemoteSettings>>>();
 		vi.mocked(settingsApi.getRemoteSettings).mockReturnValueOnce(pending.promise);
@@ -109,4 +165,45 @@ describe('NewChatForm', () => {
 		expect(worktreeDialog.textContent).toContain('New worktree');
 	});
 
+	it('starts on Enter when send by Shift+Enter is disabled', async () => {
+		const { messageInput, onStartChat } = await renderReadyNewChatForm({
+			sendByShiftEnter: false,
+		});
+
+		await fireEvent.keyDown(messageInput, { key: 'Enter' });
+
+		expect(onStartChat).toHaveBeenCalledTimes(1);
+	});
+
+	it('keeps Enter as a newline when send by Shift+Enter is enabled', async () => {
+		const { messageInput, onStartChat } = await renderReadyNewChatForm({
+			sendByShiftEnter: true,
+		});
+
+		await fireEvent.keyDown(messageInput, { key: 'Enter' });
+
+		expect(onStartChat).not.toHaveBeenCalled();
+	});
+
+	it('starts on Shift+Enter when send by Shift+Enter is enabled', async () => {
+		const { messageInput, onStartChat } = await renderReadyNewChatForm({
+			sendByShiftEnter: true,
+		});
+
+		await fireEvent.keyDown(messageInput, { key: 'Enter', shiftKey: true });
+
+		expect(onStartChat).toHaveBeenCalledTimes(1);
+	});
+
+	it('does not let the mobile viewport override the Enter setting', async () => {
+		installMatchMedia(true);
+		const { messageInput, onStartChat } = await renderReadyNewChatForm({
+			sendByShiftEnter: false,
+			isMobile: true,
+		});
+
+		await fireEvent.keyDown(messageInput, { key: 'Enter' });
+
+		expect(onStartChat).toHaveBeenCalledTimes(1);
+	});
 });
diff --git a/web/src/lib/components/chat/__tests__/NewChatFormTestHarness.svelte b/web/src/lib/components/chat/__tests__/NewChatFormTestHarness.svelte
index 2c73e9f74..97f9e4e84 100644
--- a/web/src/lib/components/chat/__tests__/NewChatFormTestHarness.svelte
+++ b/web/src/lib/components/chat/__tests__/NewChatFormTestHarness.svelte
@@ -2,9 +2,24 @@
 	import NewChatForm from '../NewChatForm.svelte';
 	import { setAppShell, setModelCatalog, setLocalSettings, setRemoteSettings, setChatSessions } from '$lib/context';
 	import { createRemoteSettingsStore } from '$lib/stores/remote-settings.svelte';
+	import type { NewChatConfig } from '$lib/types/app';
+
+	interface Props {
+		sendByShiftEnter?: boolean;
+		isMobile?: boolean;
+		onStartChat?: (config: NewChatConfig) => void;
+	}
+
+	let {
+		sendByShiftEnter = false,
+		isMobile = false,
+		onStartChat = () => {},
+	}: Props = $props();
 
 	setLocalSettings({
-		sendByShiftEnter: false
+		get sendByShiftEnter() {
+			return sendByShiftEnter;
+		}
 	} as never);
 
 	setRemoteSettings(createRemoteSettingsStore());
@@ -15,6 +30,9 @@
 
 	setAppShell({
 		projectBasePath: '/workspace',
+		get isMobile() {
+			return isMobile;
+		},
 		onNewChatDialogSeed() {
 			return () => {};
 		}
@@ -86,4 +104,4 @@
 			} as never);
 	</script>
 
-<NewChatForm onStartChat={() => {}} />
+	<NewChatForm {onStartChat} />