diff --git a/apps/pwa/src/components/BottomTabBar.test.tsx b/apps/pwa/src/components/BottomTabBar.test.tsx
new file mode 100644
index 0000000..eb28a15
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+++ b/apps/pwa/src/components/BottomTabBar.test.tsx
@@ -0,0 +1,82 @@
+/**
+ * BottomTabBar visibility test — verifies the bar is hidden on desktop (≥768px).
+ *
+ * FIX 4: BottomTabBar must be phone-only (≤767px). On desktop it was
+ * position:fixed bottom:0 with no hide rule, overlaying the Settings/avatar
+ * in AppNav's sidebar.
+ *
+ * The test environment's matchMedia polyfill (test-setup.ts) returns
+ * matches:false for all queries, simulating a desktop viewport.
+ * The BottomTabBar should NOT render on desktop.
+ */
+
+import React from 'react'
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { MemoryRouter } from 'react-router'
+import { BottomTabBar } from './BottomTabBar.js'
+
+describe('BottomTabBar visibility (FIX 4)', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+  })
+
+  it('does NOT render on desktop (matchMedia max-width:767px returns false)', () => {
+    // test-setup.ts matchMedia polyfill returns matches:false for all queries
+    // → (max-width: 767px) matches false → desktop → BottomTabBar should not render
+    render(
+      <MemoryRouter>
+        <BottomTabBar />
+      </MemoryRouter>,
+    )
+
+    // The nav element should not be in the document on desktop
+    const nav = screen.queryByRole('navigation', { name: /Main navigation/i })
+    // BottomTabBar renders a <nav aria-label="Main navigation"> — on desktop it must be absent
+    // (note: AppNav also renders a <nav aria-label="Main navigation"> on desktop; but we're
+    //  only rendering BottomTabBar here, so the absence confirms it returns null on desktop)
+    expect(nav).toBeNull()
+  })
+
+  it('renders on phone (matchMedia max-width:767px returns true)', () => {
+    // Override matchMedia to simulate phone
+    Object.defineProperty(window, 'matchMedia', {
+      writable: true,
+      value: (query: string) => ({
+        matches: query === '(max-width: 767px)',
+        media: query,
+        onchange: null,
+        addListener: () => undefined,
+        removeListener: () => undefined,
+        addEventListener: () => undefined,
+        removeEventListener: () => undefined,
+        dispatchEvent: () => false,
+      }),
+    })
+
+    render(
+      <MemoryRouter>
+        <BottomTabBar />
+      </MemoryRouter>,
+    )
+
+    // On phone, BottomTabBar nav must be present
+    const nav = screen.queryByRole('navigation', { name: /Main navigation/i })
+    expect(nav).not.toBeNull()
+
+    // Restore default (matches:false) for subsequent tests
+    Object.defineProperty(window, 'matchMedia', {
+      writable: true,
+      value: (query: string) => ({
+        matches: false,
+        media: query,
+        onchange: null,
+        addListener: () => undefined,
+        removeListener: () => undefined,
+        addEventListener: () => undefined,
+        removeEventListener: () => undefined,
+        dispatchEvent: () => false,
+      }),
+    })
+  })
+})