fix(ui): removed double padding on rendered content (#21029)

packages/cli/src/ui/components/MainContent.test.tsx

@@ -8,7 +8,7 @@ import { renderWithProviders } from '../../test-utils/render.js';
 import { waitFor } from '../../test-utils/async.js';
 import { MainContent } from './MainContent.js';
 import { getToolGroupBorderAppearance } from '../utils/borderStyles.js';
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import { Box, Text } from 'ink';
 import { act, useState, type JSX } from 'react';
 import { useAlternateBuffer } from '../hooks/useAlternateBuffer.js';
@@ -56,10 +56,6 @@ vi.mock('./AppHeader.js', () => ({
   ),
 }));
 
-vi.mock('./ShowMoreLines.js', () => ({
-  ShowMoreLines: () => <Text>ShowMoreLines</Text>,
-}));
-
 vi.mock('./shared/ScrollableList.js', () => ({
   ScrollableList: ({
     data,
@@ -339,6 +335,10 @@ describe('MainContent', () => {
     vi.mocked(useAlternateBuffer).mockReturnValue(false);
   });
 
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
   it('renders in normal buffer mode', async () => {
     const { lastFrame, unmount } = renderWithProviders(<MainContent />, {
       uiState: defaultMockUiState as Partial<UIState>,
@@ -457,6 +457,60 @@ describe('MainContent', () => {
     unmount();
   });
 
+  it('renders multiple history items with single line padding between them', async () => {
+    vi.mocked(useAlternateBuffer).mockReturnValue(true);
+    const uiState = {
+      ...defaultMockUiState,
+      history: [
+        { id: 1, type: 'gemini', text: 'Gemini message 1\n'.repeat(10) },
+        { id: 2, type: 'gemini', text: 'Gemini message 2\n'.repeat(10) },
+      ],
+      constrainHeight: true,
+      staticAreaMaxItemHeight: 5,
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <MainContent />,
+      {
+        uiState: uiState as Partial<UIState>,
+        useAlternateBuffer: true,
+      },
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toMatchSnapshot();
+    unmount();
+  });
+
+  it('renders mixed history items (user + gemini) with single line padding between them', async () => {
+    vi.mocked(useAlternateBuffer).mockReturnValue(true);
+    const uiState = {
+      ...defaultMockUiState,
+      history: [
+        { id: 1, type: 'user', text: 'User message' },
+        { id: 2, type: 'gemini', text: 'Gemini response\n'.repeat(10) },
+      ],
+      constrainHeight: true,
+      staticAreaMaxItemHeight: 5,
+    };
+
+    const { lastFrame, waitUntilReady, unmount } = renderWithProviders(
+      <MainContent />,
+      {
+        uiState: uiState as unknown as Partial<UIState>,
+        useAlternateBuffer: true,
+      },
+    );
+
+    await waitUntilReady();
+
+    const output = lastFrame();
+    expect(output).toMatchSnapshot();
+    unmount();
+  });
+
   it('renders a split tool group without a gap between static and pending areas', async () => {
     const toolCalls = [
       {