diff --git a/apps/pwa/src/components/SyncStateToast.test.tsx b/apps/pwa/src/components/SyncStateToast.test.tsx
new file mode 100644
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+++ b/apps/pwa/src/components/SyncStateToast.test.tsx
@@ -0,0 +1,232 @@
+/**
+ * SyncStateToast tests — Task 2 (TDD RED → GREEN)
+ *
+ * Covers all states from UI-SPEC §SyncStateToast:
+ *   - pending: "Syncing…" + spinner role="status"
+ *   - done: "Saved" + Check icon, auto-dismiss after 2s, invalidates ['events']
+ *   - failed (generic): "Didn't save. Try again." role="alert", persists with dismiss button
+ *   - failed (conflict/412): conflict copy, invalidates ['events']
+ *   - dead: "Not saved. Check your connection." role="alert"
+ *   - refetchInterval active only while pending
+ *   - renders nothing when lastSyncedUid is null
+ */
+
+import 'temporal-polyfill/global'
+import React from 'react'
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { render, screen, waitFor, act, fireEvent } from '@testing-library/react'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+
+// ── Module mocks ──────────────────────────────────────────────────────────────
+// vi.hoisted() required for variables referenced inside vi.mock() factories (D-03-04-hoisting)
+
+const {
+  mockLastSyncedUid,
+  mockSetLastSyncedUid,
+  mockFetchSyncStatus,
+} = vi.hoisted(() => ({
+  mockLastSyncedUid: { value: 'test-uid-123' as string | null },
+  mockSetLastSyncedUid: vi.fn(),
+  mockFetchSyncStatus: vi.fn(),
+}))
+
+vi.mock('../store/calendarStore.js', () => ({
+  useCalendarStore: (selector: (s: Record<string, unknown>) => unknown) => {
+    const state = {
+      lastSyncedUid: mockLastSyncedUid.value,
+      setLastSyncedUid: mockSetLastSyncedUid,
+    }
+    return selector(state)
+  },
+}))
+
+vi.mock('../api/client.js', () => ({
+  fetchSyncStatus: mockFetchSyncStatus,
+}))
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeQueryClient() {
+  return new QueryClient({
+    defaultOptions: {
+      queries: { retry: false },
+    },
+  })
+}
+
+function renderToast(queryClient: QueryClient) {
+  const { SyncStateToast } = require('./SyncStateToast.js')
+  return render(
+    <QueryClientProvider client={queryClient}>
+      <SyncStateToast />
+    </QueryClientProvider>,
+  )
+}
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('SyncStateToast', () => {
+  let queryClient: QueryClient
+
+  beforeEach(() => {
+    vi.clearAllMocks()
+    vi.useFakeTimers()
+    queryClient = makeQueryClient()
+    mockLastSyncedUid.value = 'test-uid-123'
+  })
+
+  afterEach(() => {
+    vi.useRealTimers()
+    vi.resetModules()
+  })
+
+  it('renders nothing when lastSyncedUid is null', async () => {
+    mockLastSyncedUid.value = null
+    const { container } = renderToast(queryClient)
+    expect(container.firstChild).toBeNull()
+  })
+
+  it('pending: renders "Syncing…" with role="status"', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'pending' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByRole('status')).toBeInTheDocument()
+    })
+    expect(screen.getByText('Syncing…')).toBeInTheDocument()
+  })
+
+  it('done: renders "Saved" and auto-dismisses after 2s', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'done' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByText('Saved')).toBeInTheDocument()
+    })
+
+    // Auto-dismiss after 2 seconds
+    act(() => {
+      vi.advanceTimersByTime(2000)
+    })
+
+    await waitFor(() => {
+      expect(mockSetLastSyncedUid).toHaveBeenCalledWith(null)
+    })
+  })
+
+  it('done: calls queryClient.invalidateQueries for ["events"]', async () => {
+    const invalidateSpy = vi.spyOn(queryClient, 'invalidateQueries')
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'done' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByText('Saved')).toBeInTheDocument()
+    })
+
+    expect(invalidateSpy).toHaveBeenCalledWith(
+      expect.objectContaining({ queryKey: ['events'] }),
+    )
+  })
+
+  it('failed (generic): renders "Didn\'t save. Try again." with role="alert"', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'failed' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByRole('alert')).toBeInTheDocument()
+    })
+    expect(screen.getByText("Didn't save. Try again.")).toBeInTheDocument()
+  })
+
+  it('failed (generic): persists and has a dismiss button', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'failed' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByRole('alert')).toBeInTheDocument()
+    })
+
+    // Should not auto-dismiss after 2s
+    act(() => {
+      vi.advanceTimersByTime(3000)
+    })
+    expect(screen.getByRole('alert')).toBeInTheDocument()
+
+    // Should have a dismiss button
+    const dismissBtn = screen.getByRole('button', { name: /dismiss/i })
+    expect(dismissBtn).toBeInTheDocument()
+  })
+
+  it('failed (conflict/412): renders conflict copy and invalidates ["events"]', async () => {
+    const invalidateSpy = vi.spyOn(queryClient, 'invalidateQueries')
+    mockFetchSyncStatus.mockResolvedValue({
+      uid: 'test-uid-123',
+      status: 'failed',
+      error: '412 Conflict',
+    })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(
+        screen.getByText('This event changed elsewhere — review the latest version'),
+      ).toBeInTheDocument()
+    })
+
+    expect(invalidateSpy).toHaveBeenCalledWith(
+      expect.objectContaining({ queryKey: ['events'] }),
+    )
+  })
+
+  it('dead: renders "Not saved. Check your connection." with role="alert"', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'dead' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByRole('alert')).toBeInTheDocument()
+    })
+    expect(screen.getByText('Not saved. Check your connection.')).toBeInTheDocument()
+  })
+
+  it('refetchInterval is active (3000ms) while pending', async () => {
+    let callCount = 0
+    mockFetchSyncStatus.mockImplementation(() => {
+      callCount++
+      return Promise.resolve({ uid: 'test-uid-123', status: 'pending' })
+    })
+
+    renderToast(queryClient)
+
+    // Wait for first fetch
+    await waitFor(() => expect(callCount).toBeGreaterThanOrEqual(1))
+
+    // Advance time and verify refetch happens
+    act(() => {
+      vi.advanceTimersByTime(3000)
+    })
+
+    await waitFor(() => expect(callCount).toBeGreaterThanOrEqual(2))
+  })
+
+  it('dismiss button on failed toast calls setLastSyncedUid(null)', async () => {
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'failed' })
+
+    renderToast(queryClient)
+
+    await waitFor(() => {
+      expect(screen.getByRole('alert')).toBeInTheDocument()
+    })
+
+    const dismissBtn = screen.getByRole('button', { name: /dismiss/i })
+    fireEvent.click(dismissBtn)
+
+    expect(mockSetLastSyncedUid).toHaveBeenCalledWith(null)
+  })
+
+})