diff --git a/tests/integration/phase5-smoke.test.tsx b/tests/integration/phase5-smoke.test.tsx
new file mode 100644
index 0000000..7b9494b
--- /dev/null
+++ b/tests/integration/phase5-smoke.test.tsx
@@ -0,0 +1,162 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { render, screen, fireEvent, act } from '@testing-library/react';
+import { AppShell } from '@/components/layout/AppShell';
+import { useFileStore } from '@/stores/file-store';
+import { useEditorStore } from '@/stores/editor-store';
+import { useAppStore } from '@/stores/app-store';
+
+// Mock react-resizable-panels for jsdom (same pattern as AppShell.test.tsx)
+vi.mock('@/components/ui/resizable', () => ({
+  ResizablePanelGroup: ({ children, direction }: any) => (
+    <div data-testid="resizable-panel-group" data-direction={direction}>
+      {children}
+    </div>
+  ),
+  ResizablePanel: ({ children, defaultSize }: any) => (
+    <div data-testid="resizable-panel" data-size={defaultSize}>
+      {children}
+    </div>
+  ),
+  ResizableHandle: () => <div data-testid="resizable-handle" />,
+}));
+
+vi.mock('@/lib/ipc', () => ({
+  ipc: {
+    file: {
+      open: vi.fn().mockResolvedValue({ ok: false, error: { code: 'NO_BRIDGE', message: 'mock' } }),
+      read: vi.fn().mockResolvedValue({ ok: true, data: '# hello' }),
+      write: vi.fn().mockResolvedValue({ ok: true, data: undefined }),
+      list: vi.fn().mockResolvedValue({
+        ok: true,
+        data: [
+          { name: 'README.md', path: '/root/README.md', isDirectory: false },
+          { name: 'src', path: '/root/src', isDirectory: true },
+        ],
+      }),
+      pickFolder: vi.fn().mockResolvedValue({ ok: true, data: '/root' }),
+      pickFile: vi.fn().mockResolvedValue({ ok: true, data: '/root/README.md' }),
+      onChange: vi.fn(() => () => {}),
+    },
+  },
+}));
+
+describe('Phase 5 integration', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useFileStore.setState({
+      tree: null,
+      rootPath: null,
+      expanded: new Set(),
+      openTabs: [],
+      activeTabId: null,
+    });
+    useEditorStore.setState({ buffers: new Map(), activeId: null });
+    useAppStore.setState({
+      sidebarVisible: true,
+      previewVisible: true,
+      zenMode: false,
+      paneSizes: { sidebar: 20, editor: 50, preview: 30 },
+    });
+  });
+
+  it('AppShell renders Sidebar (Files + Outline sections) and TabBar', () => {
+    render(<AppShell />);
+    expect(screen.getByText('Files')).toBeInTheDocument();
+    expect(screen.getByText('Outline')).toBeInTheDocument();
+    expect(screen.getByText(/no files open/i)).toBeInTheDocument();
+  });
+
+  it('opening a folder via the Open Folder button populates the tree', async () => {
+    render(<AppShell />);
+    const openBtn = screen.getByRole('button', { name: /open folder/i });
+    await act(async () => {
+      fireEvent.click(openBtn);
+    });
+    // After openFolder, the tree should have children
+    const state = useFileStore.getState();
+    expect(state.tree).not.toBeNull();
+    expect(state.tree?.children).toHaveLength(2);
+    expect(state.rootPath).toBe('/root');
+  });
+
+  it('clicking a file in the tree opens it as a tab and populates the editor buffer', async () => {
+    // Seed the tree directly
+    useFileStore.setState({
+      tree: {
+        name: 'root',
+        path: '/root',
+        isDirectory: true,
+        loaded: true,
+        children: [
+          { name: 'README.md', path: '/root/README.md', isDirectory: false, children: null },
+        ],
+      },
+      rootPath: '/root',
+      openTabs: [],
+      activeTabId: null,
+    });
+
+    render(<AppShell />);
+    const fileButton = screen.getByText('README.md').closest('button')!;
+    await act(async () => {
+      fireEvent.click(fileButton);
+    });
+
+    const state = useFileStore.getState();
+    expect(state.openTabs).toHaveLength(1);
+    expect(state.openTabs[0].id).toBe('/root/README.md');
+    expect(state.activeTabId).toBe('/root/README.md');
+
+    // Editor buffer should have the file content
+    const buf = useEditorStore.getState().buffers.get('/root/README.md');
+    expect(buf?.content).toBe('# hello');
+  });
+
+  it('TabBar shows the open tab and switches active on click', async () => {
+    useFileStore.setState({
+      tree: null,
+      rootPath: null,
+      expanded: new Set(),
+      openTabs: [
+        { id: '/a.md', path: '/a.md', title: 'a.md', dirty: false },
+        { id: '/b.md', path: '/b.md', title: 'b.md', dirty: false },
+      ],
+      activeTabId: '/a.md',
+    });
+    render(<AppShell />);
+    const aTab = screen.getByText('a.md').closest('[role="tab"]')!;
+    const bTab = screen.getByText('b.md').closest('[role="tab"]')!;
+    expect(aTab).toHaveAttribute('aria-current', 'page');
+    await act(async () => {
+      fireEvent.click(bTab);
+    });
+    expect(useFileStore.getState().activeTabId).toBe('/b.md');
+  });
+
+  it('keyboard shortcut Ctrl+S triggers saveActiveBuffer (no-op when no active tab)', () => {
+    render(<AppShell />);
+    fireEvent.keyDown(window, { key: 's', ctrlKey: true });
+    // No assertion on side effect, just confirms it doesn't throw
+    expect(useFileStore.getState().openTabs).toHaveLength(0);
+  });
+
+  it('drag-reorder updates the openTabs order', () => {
+    useFileStore.setState({
+      tree: null,
+      rootPath: null,
+      expanded: new Set(),
+      openTabs: [
+        { id: '/a.md', path: '/a.md', title: 'a.md', dirty: false },
+        { id: '/b.md', path: '/b.md', title: 'b.md', dirty: false },
+        { id: '/c.md', path: '/c.md', title: 'c.md', dirty: false },
+      ],
+      activeTabId: '/a.md',
+    });
+    render(<AppShell />);
+    act(() => {
+      useFileStore.getState().reorderTabs(0, 2);
+    });
+    const order = useFileStore.getState().openTabs.map((t) => t.id);
+    expect(order).toEqual(['/b.md', '/c.md', '/a.md']);
+  });
+});