diff --git a/apps/pwa/src/components/CalendarShell.tsx b/apps/pwa/src/components/CalendarShell.tsx
index fea479b..6cee341 100644
--- a/apps/pwa/src/components/CalendarShell.tsx
+++ b/apps/pwa/src/components/CalendarShell.tsx
@@ -28,7 +28,7 @@
  *   success + events → ScheduleXCalendar
  */
 
-import { useState, useEffect, useMemo } from 'react'
+import { useState, useEffect, useMemo, useRef } from 'react'
 import { useQuery, useQueryClient } from '@tanstack/react-query'
 import { ScheduleXCalendar, useCalendarApp } from '@schedule-x/react'
 import {
@@ -83,8 +83,11 @@ export function CalendarShell({ onOpenSettings }: { onOpenSettings?: () => void
   const selectedView = useCalendarStore((s) => s.selectedView)
   const setEventForm = useCalendarStore((s) => s.setEventForm)
   const eventFormOpen = useCalendarStore((s) => s.eventFormOpen)
+  const sessionExpired = useCalendarStore((s) => s.sessionExpired)
   const { start, end } = calendarRange
   const queryClient = useQueryClient()
+  // Ref to ensure the session-expiry redirect timer fires only once per expiry
+  const sessionExpiredRedirectFired = useRef(false)
 
   // Fetch current user to build per-member color config
   const meQuery = useQuery({
@@ -208,6 +211,26 @@ export function CalendarShell({ onOpenSettings }: { onOpenSettings?: () => void
     }
   }, [meQuery.isSuccess])
 
+  // Session-expiry redirect (D-11) — fires when a mid-use 401 is detected by the
+  // global QueryCache/MutationCache handler and arms the Zustand sessionExpired flag.
+  // Re-arms the one-shot guard (clearLoginRedirect) so maybeRedirectToLogin fires
+  // afresh, then schedules the top-level navigation after ~1.5s (UI-SPEC §Surface 2
+  // "≤2s before redirect, no dismiss button").
+  useEffect(() => {
+    if (!sessionExpired) return
+    if (sessionExpiredRedirectFired.current) return
+    sessionExpiredRedirectFired.current = true
+
+    clearLoginRedirect()
+    const timer = setTimeout(() => {
+      maybeRedirectToLogin()
+    }, 1500)
+
+    return () => {
+      clearTimeout(timer)
+    }
+  }, [sessionExpired])
+
   // ── Render helpers ────────────────────────────────────────────────────────
 
   // Determine which content to show in the calendar area.
@@ -238,6 +261,20 @@ export function CalendarShell({ onOpenSettings }: { onOpenSettings?: () => void
     return <AuthSplash state="redirecting" />
   }
 
+  // ── Session-expiry interstitial (D-11) ─────────────────────────────────────
+  // When a mid-use query or mutation returns 401, the global QueryCache/MutationCache
+  // handler sets sessionExpired=true. Show the "Session expired" interstitial while the
+  // 1.5s timer fires (wired above in the sessionExpired useEffect).
+  if (sessionExpired) {
+    return (
+      <AuthSplash
+        state="redirecting"
+        heading="Session expired"
+        body="Signing you back in…"
+      />
+    )
+  }
+
   // ── Calendar content ───────────────────────────────────────────────────────
 
   // The content panel (right of sidebar on desktop, full-width on phone).
diff --git a/apps/pwa/src/main.tsx b/apps/pwa/src/main.tsx
index cd42445..dd5c0ab 100644
--- a/apps/pwa/src/main.tsx
+++ b/apps/pwa/src/main.tsx
@@ -10,11 +10,32 @@ import './styles/index.css'
 
 import React from 'react'
 import ReactDOM from 'react-dom/client'
-import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { QueryClient, QueryClientProvider, QueryCache, MutationCache } from '@tanstack/react-query'
 import App from './App.js'
 import { ErrorBoundary } from './components/ErrorBoundary.js'
+import { SessionExpiredError } from './api/client.js'
+import { useCalendarStore } from './store/calendarStore.js'
+
+/**
+ * Global session-expiry error handler (D-11, Plan 06-05).
+ *
+ * When any query or mutation throws a SessionExpiredError, arm the interstitial
+ * via the Zustand store's imperative getter — safe to call outside React since
+ * Zustand's create() returns a store with a .getState() API.
+ *
+ * QueryCache and MutationCache onError callbacks are the correct v5 pattern for
+ * global error handling (NOT defaultOptions.onError, which was removed in v5).
+ * Confirmed via Context7 /tanstack/query docs for v5.101.0.
+ */
+function onGlobalError(error: unknown): void {
+  if (error instanceof SessionExpiredError) {
+    useCalendarStore.getState().setSessionExpired(true)
+  }
+}
 
 const queryClient = new QueryClient({
+  queryCache: new QueryCache({ onError: onGlobalError }),
+  mutationCache: new MutationCache({ onError: onGlobalError }),
   defaultOptions: {
     queries: {
       retry: 1,
diff --git a/apps/pwa/src/store/calendarStore.ts b/apps/pwa/src/store/calendarStore.ts
index 7c07dfb..34fa668 100644
--- a/apps/pwa/src/store/calendarStore.ts
+++ b/apps/pwa/src/store/calendarStore.ts
@@ -50,6 +50,12 @@ export interface CalendarStore {
   /** UID of the most recently enqueued write. SyncStateToast polls sync-status for this. */
   lastSyncedUid: string | null
 
+  // ── Session-expiry flag (Plan 06-05 / D-11) ─────────────────────────────
+  // Set to true by the global QueryCache/MutationCache onError handler in main.tsx
+  // when a SessionExpiredError is detected from any query or mutation.
+  // Drives the "Session expired / Signing you back in…" interstitial in CalendarShell.
+  sessionExpired: boolean
+
   setSelectedView: (view: string) => void
   setSelectedDate: (date: string) => void
   setOpenEventId: (id: string | null) => void
@@ -77,6 +83,14 @@ export interface CalendarStore {
    * Pass null to dismiss the toast.
    */
   setLastSyncedUid: (uid: string | null) => void
+
+  /**
+   * Arm the session-expiry interstitial (D-11).
+   * Called imperatively from the global QueryCache/MutationCache onError handler
+   * (outside React, via getState().setSessionExpired) when a SessionExpiredError
+   * is caught from any query or mutation.
+   */
+  setSessionExpired: (expired: boolean) => void
 }
 
 // ── Helpers ────────────────────────────────────────────────────────────────
@@ -141,6 +155,9 @@ export const useCalendarStore = create<CalendarStore>((set) => ({
   deleteDialogUid: null,
   lastSyncedUid: null,
 
+  // Session-expiry flag — false by default; set by global QueryCache/MutationCache handler
+  sessionExpired: false,
+
   setSelectedView: (view: string) => {
     set({ selectedView: view })
     // Persist to localStorage keyed by breakpoint group
@@ -166,4 +183,6 @@ export const useCalendarStore = create<CalendarStore>((set) => ({
     set({ deleteDialogOpen: open, deleteDialogUid: uid }),
 
   setLastSyncedUid: (uid: string | null) => set({ lastSyncedUid: uid }),
+
+  setSessionExpired: (expired: boolean) => set({ sessionExpired: expired }),
 }))