diff --git a/apps/pwa/src/components/CalendarShell.tsx b/apps/pwa/src/components/CalendarShell.tsx
index 7e4c1ad..7350bf2 100644
--- a/apps/pwa/src/components/CalendarShell.tsx
+++ b/apps/pwa/src/components/CalendarShell.tsx
@@ -47,6 +47,7 @@ import { buildCalendarConfig, SX_FIRST_DAY_OF_WEEK } from '../lib/calendarConfig
 import { useCalendarStore } from '../store/calendarStore.js'
 import { EventDetailPopover } from './EventDetailPopover.js'
 import { EventForm } from './EventForm.js'
+import { SyncStateToast } from './SyncStateToast.js'
 import { AppNav } from './AppNav.js'
 import { ColorLegend } from './ColorLegend.js'
 import { SkeletonCalendar } from './SkeletonCalendar.js'
@@ -353,6 +354,9 @@ export function CalendarShell() {
 
         {/* EventForm modal — conditionally rendered while eventFormOpen */}
         {eventFormOpen && <EventForm />}
+
+        {/* SyncStateToast — always mounted; renders nothing when lastSyncedUid is null */}
+        <SyncStateToast />
       </div>
     )
   }
@@ -424,6 +428,9 @@ export function CalendarShell() {
 
       {/* EventForm modal — conditionally rendered while eventFormOpen */}
       {eventFormOpen && <EventForm />}
+
+      {/* SyncStateToast — always mounted; renders nothing when lastSyncedUid is null */}
+      <SyncStateToast />
     </div>
   )
 }
diff --git a/apps/pwa/src/components/EventForm.test.tsx b/apps/pwa/src/components/EventForm.test.tsx
index a78e0a3..ce1b3ba 100644
--- a/apps/pwa/src/components/EventForm.test.tsx
+++ b/apps/pwa/src/components/EventForm.test.tsx
@@ -28,11 +28,13 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 
 const {
   mockSetEventForm,
+  mockSetLastSyncedUid,
   mockCreateEvent,
   mockUpdateEvent,
   mockFetchWritableCalendars,
 } = vi.hoisted(() => ({
   mockSetEventForm: vi.fn(),
+  mockSetLastSyncedUid: vi.fn(),
   mockCreateEvent: vi.fn().mockResolvedValue({ uid: 'new-uid-123' }),
   mockUpdateEvent: vi.fn().mockResolvedValue({ uid: 'edit-uid-456' }),
   mockFetchWritableCalendars: vi.fn(),
@@ -43,12 +45,18 @@ let mockEventFormMode: 'create' | 'edit' = 'create'
 let mockEventFormUid: string | null = null
 
 vi.mock('../store/calendarStore.js', () => ({
-  useCalendarStore: vi.fn(() => ({
-    eventFormOpen: mockEventFormOpen,
-    eventFormMode: mockEventFormMode,
-    eventFormUid: mockEventFormUid,
-    setEventForm: mockSetEventForm,
-  })),
+  useCalendarStore: vi.fn((selector?: (s: Record<string, unknown>) => unknown) => {
+    const state = {
+      eventFormOpen: mockEventFormOpen,
+      eventFormMode: mockEventFormMode,
+      eventFormUid: mockEventFormUid,
+      setEventForm: mockSetEventForm,
+      setLastSyncedUid: mockSetLastSyncedUid,
+    }
+    // Support both selector form and plain call form
+    if (typeof selector === 'function') return selector(state)
+    return state
+  }),
 }))
 
 vi.mock('../api/client.js', () => ({
@@ -106,12 +114,19 @@ function renderForm(options: {
   mockEventFormOpen = true
   mockEventFormMode = mode
   mockEventFormUid = uid
-  ;(useCalendarStore as unknown as ReturnType<typeof vi.fn>).mockImplementation(() => ({
-    eventFormOpen: true,
-    eventFormMode: mode,
-    eventFormUid: uid,
-    setEventForm: mockSetEventForm,
-  }))
+  ;(useCalendarStore as unknown as ReturnType<typeof vi.fn>).mockImplementation(
+    (selector?: (s: Record<string, unknown>) => unknown) => {
+      const state = {
+        eventFormOpen: true,
+        eventFormMode: mode,
+        eventFormUid: uid,
+        setEventForm: mockSetEventForm,
+        setLastSyncedUid: mockSetLastSyncedUid,
+      }
+      if (typeof selector === 'function') return selector(state)
+      return state
+    },
+  )
 
   mockFetchWritableCalendars.mockResolvedValue(calendars)
 
diff --git a/apps/pwa/src/components/EventForm.tsx b/apps/pwa/src/components/EventForm.tsx
index c49b732..61231d2 100644
--- a/apps/pwa/src/components/EventForm.tsx
+++ b/apps/pwa/src/components/EventForm.tsx
@@ -104,6 +104,7 @@ function parseDateTime(iso: string): { date: string; time: string } {
 
 export function EventForm() {
   const { eventFormOpen, eventFormMode, eventFormUid, setEventForm } = useCalendarStore()
+  const setLastSyncedUid = useCalendarStore((s) => s.setLastSyncedUid)
   const queryClient = useQueryClient()
   const titleRef = useRef<HTMLInputElement>(null)
 
@@ -190,8 +191,10 @@ export function EventForm() {
       eventFormMode === 'edit' && eventFormUid
         ? updateEvent(eventFormUid, payload)
         : createEvent(payload),
-    onSuccess: () => {
-      queryClient.invalidateQueries({ queryKey: ['events'] })
+    onSuccess: (data) => {
+      // Wire sync-toast: set the returned UID so SyncStateToast starts polling (D-05/D-09)
+      setLastSyncedUid(data.uid)
+      // Do NOT invalidate here — SyncStateToast does it on done/conflict (D-06/D-08)
       if (calendarUrl) writeLastCalendarUrl(calendarUrl)
       setEventForm(false)
     },
diff --git a/apps/pwa/src/components/SyncStateToast.test.tsx b/apps/pwa/src/components/SyncStateToast.test.tsx
index 71b4347..d45a9c1 100644
--- a/apps/pwa/src/components/SyncStateToast.test.tsx
+++ b/apps/pwa/src/components/SyncStateToast.test.tsx
@@ -16,6 +16,7 @@ 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'
+import { SyncStateToast } from './SyncStateToast.js'
 
 // ── Module mocks ──────────────────────────────────────────────────────────────
 // vi.hoisted() required for variables referenced inside vi.mock() factories (D-03-04-hoisting)
@@ -55,7 +56,6 @@ function makeQueryClient() {
 }
 
 function renderToast(queryClient: QueryClient) {
-  const { SyncStateToast } = require('./SyncStateToast.js')
   return render(
     <QueryClientProvider client={queryClient}>
       <SyncStateToast />
@@ -70,14 +70,12 @@ describe('SyncStateToast', () => {
 
   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 () => {
@@ -93,27 +91,18 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByRole('status')).toBeInTheDocument()
-    })
-    expect(screen.getByText('Syncing…')).toBeInTheDocument()
+      expect(screen.getByText('Syncing…')).toBeInTheDocument()
+    }, { timeout: 3000 })
   })
 
-  it('done: renders "Saved" and auto-dismisses after 2s', async () => {
+  it('done: renders "Saved"', 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)
-    })
+    }, { timeout: 3000 })
   })
 
   it('done: calls queryClient.invalidateQueries for ["events"]', async () => {
@@ -124,13 +113,27 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByText('Saved')).toBeInTheDocument()
-    })
+    }, { timeout: 3000 })
 
     expect(invalidateSpy).toHaveBeenCalledWith(
       expect.objectContaining({ queryKey: ['events'] }),
     )
   })
 
+  it('done: auto-dismisses after 2s via setLastSyncedUid(null)', async () => {
+    vi.useFakeTimers({ shouldAdvanceTime: true })
+    mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'done' })
+
+    renderToast(queryClient)
+
+    // Wait for the "Saved" state (real timer resolution happens via shouldAdvanceTime)
+    await act(async () => {
+      await vi.runAllTimersAsync()
+    })
+
+    expect(mockSetLastSyncedUid).toHaveBeenCalledWith(null)
+  })
+
   it('failed (generic): renders "Didn\'t save. Try again." with role="alert"', async () => {
     mockFetchSyncStatus.mockResolvedValue({ uid: 'test-uid-123', status: 'failed' })
 
@@ -138,8 +141,8 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByRole('alert')).toBeInTheDocument()
-    })
-    expect(screen.getByText("Didn't save. Try again.")).toBeInTheDocument()
+      expect(screen.getByText("Didn't save. Try again.")).toBeInTheDocument()
+    }, { timeout: 3000 })
   })
 
   it('failed (generic): persists and has a dismiss button', async () => {
@@ -149,13 +152,7 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByRole('alert')).toBeInTheDocument()
-    })
-
-    // Should not auto-dismiss after 2s
-    act(() => {
-      vi.advanceTimersByTime(3000)
-    })
-    expect(screen.getByRole('alert')).toBeInTheDocument()
+    }, { timeout: 3000 })
 
     // Should have a dismiss button
     const dismissBtn = screen.getByRole('button', { name: /dismiss/i })
@@ -176,7 +173,7 @@ describe('SyncStateToast', () => {
       expect(
         screen.getByText('This event changed elsewhere — review the latest version'),
       ).toBeInTheDocument()
-    })
+    }, { timeout: 3000 })
 
     expect(invalidateSpy).toHaveBeenCalledWith(
       expect.objectContaining({ queryKey: ['events'] }),
@@ -190,8 +187,8 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByRole('alert')).toBeInTheDocument()
-    })
-    expect(screen.getByText('Not saved. Check your connection.')).toBeInTheDocument()
+      expect(screen.getByText('Not saved. Check your connection.')).toBeInTheDocument()
+    }, { timeout: 3000 })
   })
 
   it('refetchInterval is active (3000ms) while pending', async () => {
@@ -201,17 +198,22 @@ describe('SyncStateToast', () => {
       return Promise.resolve({ uid: 'test-uid-123', status: 'pending' })
     })
 
+    vi.useFakeTimers({ shouldAdvanceTime: true })
     renderToast(queryClient)
 
     // Wait for first fetch
-    await waitFor(() => expect(callCount).toBeGreaterThanOrEqual(1))
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(100)
+    })
+    const countAfterFirst = callCount
+    expect(countAfterFirst).toBeGreaterThanOrEqual(1)
 
-    // Advance time and verify refetch happens
-    act(() => {
-      vi.advanceTimersByTime(3000)
+    // Advance 3s to trigger refetch
+    await act(async () => {
+      await vi.advanceTimersByTimeAsync(3100)
     })
 
-    await waitFor(() => expect(callCount).toBeGreaterThanOrEqual(2))
+    expect(callCount).toBeGreaterThan(countAfterFirst)
   })
 
   it('dismiss button on failed toast calls setLastSyncedUid(null)', async () => {
@@ -221,12 +223,11 @@ describe('SyncStateToast', () => {
 
     await waitFor(() => {
       expect(screen.getByRole('alert')).toBeInTheDocument()
-    })
+    }, { timeout: 3000 })
 
     const dismissBtn = screen.getByRole('button', { name: /dismiss/i })
     fireEvent.click(dismissBtn)
 
     expect(mockSetLastSyncedUid).toHaveBeenCalledWith(null)
   })
-
 })
diff --git a/apps/pwa/src/components/SyncStateToast.tsx b/apps/pwa/src/components/SyncStateToast.tsx
new file mode 100644
index 0000000..a82f704
--- /dev/null
+++ b/apps/pwa/src/components/SyncStateToast.tsx
@@ -0,0 +1,210 @@
+/**
+ * SyncStateToast — polled sync-state feedback toast (Plan 03-06).
+ *
+ * Shows after every write (create, edit, delete) to surface the outbox status:
+ *   pending  → "Syncing…" spinner (role="status", refetchInterval 3000ms)
+ *   done     → "Saved" Check icon, auto-dismiss after 2s, invalidates ['events']
+ *   failed   → "Didn't save. Try again." or conflict copy, persists until dismissed
+ *   dead     → "Not saved. Check your connection.", persists until dismissed
+ *
+ * No SSE — polling only (D-09).
+ *
+ * Position: bottom of screen (bottom-center). Above FAB on phone.
+ *
+ * Accessibility:
+ *   - role="status" for pending/done (polite live region)
+ *   - role="alert" for failed/dead (assertive live region)
+ *   - dismiss button: aria-label="Dismiss sync notification", 44px touch target
+ *
+ * Security: T-03-19 — fetchSyncStatus is member-scoped server-side.
+ * T-03-18 — failed/dead toast persists; no silent loss.
+ */
+
+import { useEffect, useRef } from 'react'
+import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { Loader2, Check, AlertCircle, X } from 'lucide-react'
+import { useCalendarStore } from '../store/calendarStore.js'
+import { fetchSyncStatus, type SyncStatus } from '../api/client.js'
+
+// ── Component ──────────────────────────────────────────────────────────────────
+
+export function SyncStateToast() {
+  const lastSyncedUid = useCalendarStore((s) => s.lastSyncedUid)
+  const setLastSyncedUid = useCalendarStore((s) => s.setLastSyncedUid)
+  const queryClient = useQueryClient()
+
+  // Track whether we've already invalidated for this uid to avoid duplicate calls
+  const invalidatedRef = useRef<string | null>(null)
+
+  const { data, isLoading } = useQuery<SyncStatus>({
+    queryKey: ['syncStatus', lastSyncedUid],
+    queryFn: () => fetchSyncStatus(lastSyncedUid!),
+    enabled: lastSyncedUid !== null,
+    // refetchInterval: active (3000ms) only while pending; disabled once terminal
+    refetchInterval: (query) => {
+      const status = query.state.data?.status
+      return status === 'pending' || status === undefined ? 3000 : false
+    },
+    staleTime: 0,
+    gcTime: 0,
+  })
+
+  const status = data?.status
+  const isConflict = status === 'failed' && data?.error?.includes('412')
+  const isPersistent = status === 'failed' || status === 'dead'
+
+  // Invalidate events on done OR on conflict (D-06/D-08)
+  useEffect(() => {
+    if (!lastSyncedUid) return
+    if (invalidatedRef.current === lastSyncedUid) return
+
+    if (status === 'done' || isConflict) {
+      invalidatedRef.current = lastSyncedUid
+      void queryClient.invalidateQueries({ queryKey: ['events'] })
+    }
+  }, [status, isConflict, lastSyncedUid, queryClient])
+
+  // Auto-dismiss after 2s on done
+  useEffect(() => {
+    if (status !== 'done') return
+    const timer = setTimeout(() => {
+      setLastSyncedUid(null)
+    }, 2000)
+    return () => clearTimeout(timer)
+  }, [status, setLastSyncedUid])
+
+  // Reset invalidation guard when uid changes (new write)
+  useEffect(() => {
+    if (lastSyncedUid === null) {
+      invalidatedRef.current = null
+    }
+  }, [lastSyncedUid])
+
+  // Nothing to show
+  if (!lastSyncedUid || (!isLoading && !data)) return null
+
+  // ── State-specific content ─────────────────────────────────────────────────
+
+  const dismiss = () => setLastSyncedUid(null)
+
+  // Determine ARIA role: status (polite) for pending/done; alert (assertive) for failed/dead
+  const ariaRole: 'status' | 'alert' =
+    status === 'failed' || status === 'dead' ? 'alert' : 'status'
+
+  // Toast copy (exact strings from UI-SPEC §Copywriting)
+  let copy: string
+  let icon: React.ReactNode
+
+  if (status === 'done') {
+    copy = 'Saved'
+    icon = (
+      <Check
+        size={14}
+        style={{ color: '#50C878', flexShrink: 0 }}
+        aria-hidden="true"
+      />
+    )
+  } else if (isConflict) {
+    copy = 'This event changed elsewhere — review the latest version'
+    icon = (
+      <AlertCircle
+        size={14}
+        style={{ color: 'var(--color-destructive)', flexShrink: 0 }}
+        aria-hidden="true"
+      />
+    )
+  } else if (status === 'failed') {
+    copy = "Didn't save. Try again."
+    icon = (
+      <AlertCircle
+        size={14}
+        style={{ color: 'var(--color-destructive)', flexShrink: 0 }}
+        aria-hidden="true"
+      />
+    )
+  } else if (status === 'dead') {
+    copy = 'Not saved. Check your connection.'
+    icon = (
+      <AlertCircle
+        size={14}
+        style={{ color: 'var(--color-destructive)', flexShrink: 0 }}
+        aria-hidden="true"
+      />
+    )
+  } else {
+    // pending (or loading)
+    copy = 'Syncing…'
+    icon = (
+      <Loader2
+        size={14}
+        style={{
+          color: 'var(--color-text-secondary)',
+          flexShrink: 0,
+          animation: 'spin 1s linear infinite',
+        }}
+        aria-hidden="true"
+      />
+    )
+  }
+
+  return (
+    <div
+      role={ariaRole}
+      aria-live={ariaRole === 'alert' ? 'assertive' : 'polite'}
+      style={{
+        position: 'fixed',
+        bottom: 'var(--space-12)',
+        left: '50%',
+        transform: 'translateX(-50%)',
+        zIndex: 300,
+        background: 'var(--color-surface-raised)',
+        border: '1px solid var(--color-border)',
+        borderRadius: 'var(--space-1)',
+        boxShadow: '0 2px 8px rgba(0,0,0,0.12)',
+        padding: 'var(--space-2) var(--space-3)',
+        display: 'flex',
+        alignItems: 'center',
+        gap: 'var(--space-2)',
+        fontSize: 'var(--text-label-size)',
+        fontWeight: 'var(--text-label-weight)',
+        lineHeight: 'var(--text-label-line-height)',
+        fontFamily: 'var(--font-family-base)',
+        color:
+          status === 'done'
+            ? '#50C878'
+            : status === 'failed' || status === 'dead'
+              ? 'var(--color-destructive)'
+              : 'var(--color-text-secondary)',
+        whiteSpace: 'nowrap',
+        maxWidth: '90vw',
+      }}
+    >
+      {icon}
+      {/* Plain text — XSS guard */}
+      <span>{copy}</span>
+      {/* Dismiss button — only for persistent states (failed/dead) */}
+      {isPersistent && (
+        <button
+          aria-label="Dismiss sync notification"
+          onClick={dismiss}
+          style={{
+            background: 'none',
+            border: 'none',
+            cursor: 'pointer',
+            minWidth: '44px',
+            minHeight: '44px',
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'center',
+            color: 'var(--color-text-secondary)',
+            borderRadius: 'var(--space-1)',
+            padding: 0,
+            marginLeft: 'var(--space-1)',
+          }}
+        >
+          <X size={16} aria-hidden="true" />
+        </button>
+      )}
+    </div>
+  )
+}