diff --git a/apps/pwa/src/App.tsx b/apps/pwa/src/App.tsx
index c11e6ea..719b957 100644
--- a/apps/pwa/src/App.tsx
+++ b/apps/pwa/src/App.tsx
@@ -44,7 +44,7 @@
  *   - /api/me query shared so AppNav has user data on all routes.
  */
 
-import { useState, useMemo } from 'react';
+import { useState, useMemo, useEffect } from 'react';
 import { BrowserRouter, Routes, Route, Navigate } from 'react-router';
 import { useQuery } from '@tanstack/react-query';
 import { CalendarShell } from './components/CalendarShell.js';
@@ -59,12 +59,9 @@ import { PushPermissionPrompt } from './components/PushPermissionPrompt.js';
 import { PermissionDeniedBanner } from './components/PermissionDeniedBanner.js';
 import { SetupBanner } from './components/SetupBanner.js';
 import { SettingsSheet } from './components/SettingsSheet.js';
+import { useIsPhone } from './hooks/useIsPhone.js';
 import { fetchMe, fetchSetupStatus, fetchAuthMode } from './api/client.js';
 
-function isPhone(): boolean {
-  return typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
-}
-
 /**
  * OidcRedirect — tiny helper that triggers a top-level navigation to /api/login.
  *
@@ -75,13 +72,18 @@ function isPhone(): boolean {
  * which browsers cannot follow as a fetch/XHR (T-07-04).
  */
 function OidcRedirect() {
-  window.location.replace('/api/login');
+  // IN-01: navigate from an effect, not during render. React may invoke a
+  // component body more than once (StrictMode double-invoke, concurrent
+  // re-renders); side effects belong in useEffect.
+  useEffect(() => {
+    window.location.replace('/api/login');
+  }, []);
   return <div aria-hidden="true" />;
 }
 
 export default function App() {
   const [settingsOpen, setSettingsOpen] = useState(false);
-  const phone = isPhone();
+  const phone = useIsPhone();
 
   // Setup status query — staleTime 0 so the wizard gate is always fresh (D-10 spirit).
   // Must be fetched before rendering any authenticated route to gate the app on /setup.
diff --git a/apps/pwa/src/components/CalendarShell.tsx b/apps/pwa/src/components/CalendarShell.tsx
index cc7f0de..75a829e 100644
--- a/apps/pwa/src/components/CalendarShell.tsx
+++ b/apps/pwa/src/components/CalendarShell.tsx
@@ -55,6 +55,7 @@ import { SyncStateToast } from './SyncStateToast.js';
 import { ColorLegend } from './ColorLegend.js';
 import { SkeletonCalendar } from './SkeletonCalendar.js';
 import { InstallPrompt } from './InstallPrompt.js';
+import { useIsPhone } from '../hooks/useIsPhone.js';
 
 // ── Helpers ────────────────────────────────────────────────────────────────
 
@@ -71,10 +72,6 @@ function resolveDefaultView(persistedView: string): string {
   return persistedView;
 }
 
-function isPhone(): boolean {
-  return typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
-}
-
 // ── Component ──────────────────────────────────────────────────────────────
 
 export function CalendarShell() {
@@ -249,7 +246,7 @@ export function CalendarShell() {
   const isInitialLoading = eventsQuery.isLoading && !eventsQuery.data;
   const isEventsError = eventsQuery.isError;
 
-  const phone = isPhone();
+  const phone = useIsPhone();
 
   // ── Auth splash (D-10) ────────────────────────────────────────────────────
   // Gate the calendar render on auth state so no calendar shell, skeleton, or
diff --git a/apps/pwa/src/components/CredentialSheet.tsx b/apps/pwa/src/components/CredentialSheet.tsx
index f1ded69..8c9cef2 100644
--- a/apps/pwa/src/components/CredentialSheet.tsx
+++ b/apps/pwa/src/components/CredentialSheet.tsx
@@ -31,6 +31,7 @@ import {
   type SaveCredentialPayload,
   type SaveMyCredentialPayload,
 } from '../api/client.js';
+import { useIsPhone } from '../hooks/useIsPhone.js';
 
 export type CredentialSheetMode = 'admin-rotate' | 'admin-add' | 'self-service';
 
@@ -76,6 +77,7 @@ export function CredentialSheet({
   triggerRef,
 }: CredentialSheetProps) {
   const queryClient = useQueryClient();
+  const phone = useIsPhone();
   const [password, setPassword] = useState('');
   const [email, setEmail] = useState('');
   const [validationError, setValidationError] = useState<string | null>(null);
@@ -153,7 +155,6 @@ export function CredentialSheet({
   const heading = headingFor(mode);
   const isPending = credentialMutation.isPending;
   const saveDisabled = isPending || password.trim().length === 0 || email.trim().length === 0;
-  const phone = window.matchMedia('(max-width: 767px)').matches;
 
   return (
     <>
diff --git a/apps/pwa/src/components/SettingsSheet.tsx b/apps/pwa/src/components/SettingsSheet.tsx
index a40e54c..8a7a808 100644
--- a/apps/pwa/src/components/SettingsSheet.tsx
+++ b/apps/pwa/src/components/SettingsSheet.tsx
@@ -26,6 +26,7 @@ import { X, Bell, AlertCircle, Loader2, LogOut } from 'lucide-react';
 import { useQuery, useMutation } from '@tanstack/react-query';
 import { useNavigate } from 'react-router';
 import { usePushSubscription } from '../hooks/usePushSubscription.js';
+import { useIsPhone } from '../hooks/useIsPhone.js';
 import { InstructionSheet } from './InstructionSheet.js';
 import { fetchMe, fetchAuthMode, fetchChangePassword, fetchLinkOidc, fetchLocalLogout } from '../api/client.js';
 
@@ -55,6 +56,8 @@ interface SettingsSheetProps {
 export function SettingsSheet({ isOpen, onClose }: SettingsSheetProps) {
   const { subscribe, permission, isSubscribed, setEnabled } = usePushSubscription();
   const navigate = useNavigate();
+  // WR-05: resize-aware so an iPad rotation across 767px reflows the sheet.
+  const phone = useIsPhone();
   const [isTogglingOn, setIsTogglingOn] = useState(false);
   const [instructionsOpen, setInstructionsOpen] = useState(false);
 
@@ -132,8 +135,6 @@ export function SettingsSheet({ isOpen, onClose }: SettingsSheetProps) {
 
   if (!isOpen) return null;
 
-  const phone = window.matchMedia('(max-width: 767px)').matches;
-
   // D-07: fire-and-best-effort logout — navigate to /login regardless of API success/failure
   const handleSignOut = async () => {
     try {
@@ -589,6 +590,7 @@ interface ChangePasswordSheetProps {
 }
 
 function ChangePasswordSheet({ isOpen, onClose }: ChangePasswordSheetProps) {
+  const phone = useIsPhone();
   const [currentPassword, setCurrentPassword] = useState('');
   const [newPassword, setNewPassword] = useState('');
   const [confirmPassword, setConfirmPassword] = useState('');
@@ -647,8 +649,6 @@ function ChangePasswordSheet({ isOpen, onClose }: ChangePasswordSheetProps) {
 
   if (!isOpen) return null;
 
-  const phone = window.matchMedia('(max-width: 767px)').matches;
-
   return (
     <>
       {/* Backdrop */}
@@ -921,6 +921,7 @@ interface LinkOidcSheetProps {
 }
 
 function LinkOidcSheet({ isOpen, onClose }: LinkOidcSheetProps) {
+  const phone = useIsPhone();
   const [error, setError] = useState<string | null>(null);
   const headingRef = useRef<HTMLHeadingElement>(null);
 
@@ -959,8 +960,6 @@ function LinkOidcSheet({ isOpen, onClose }: LinkOidcSheetProps) {
 
   if (!isOpen) return null;
 
-  const phone = window.matchMedia('(max-width: 767px)').matches;
-
   return (
     <>
       {/* Backdrop */}
diff --git a/apps/pwa/src/hooks/useIsPhone.ts b/apps/pwa/src/hooks/useIsPhone.ts
new file mode 100644
index 0000000..e99b5c2
--- /dev/null
+++ b/apps/pwa/src/hooks/useIsPhone.ts
@@ -0,0 +1,50 @@
+/**
+ * useIsPhone / useMediaQuery — resize-aware breakpoint hooks (WR-05, IN-03).
+ *
+ * The previous pattern read `window.matchMedia('(max-width: 767px)').matches`
+ * synchronously at render time with no `change` listener, so rotating an iPad
+ * across the 767px breakpoint (or resizing a desktop window) left the layout
+ * stale until an unrelated re-render. These hooks subscribe to the media query
+ * via `matchMedia.addEventListener('change', …)` so components re-render on
+ * breakpoint crossings.
+ *
+ * The phone breakpoint is centralised here (PHONE_MAX_QUERY) so the JS constant
+ * stays in one place. It corresponds to one pixel below `--bp-tablet: 768px`
+ * in tokens.css.
+ */
+import { useEffect, useState } from 'react';
+
+/** Phone breakpoint: ≤767px (one below --bp-tablet: 768px). */
+export const PHONE_MAX_QUERY = '(max-width: 767px)';
+
+/**
+ * useMediaQuery — subscribe to a media query and re-render on change.
+ *
+ * SSR-safe: returns `false` when `window`/`matchMedia` is unavailable.
+ */
+export function useMediaQuery(query: string): boolean {
+  const [matches, setMatches] = useState<boolean>(() => {
+    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') return false;
+    return window.matchMedia(query).matches;
+  });
+
+  useEffect(() => {
+    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') return;
+    const mql = window.matchMedia(query);
+    // Sync immediately in case the query changed between render and effect.
+    setMatches(mql.matches);
+    const onChange = (e: MediaQueryListEvent) => setMatches(e.matches);
+    mql.addEventListener('change', onChange);
+    return () => mql.removeEventListener('change', onChange);
+  }, [query]);
+
+  return matches;
+}
+
+/**
+ * useIsPhone — true when the viewport is at or below the phone breakpoint.
+ * Re-renders on breakpoint crossings (resize / orientation change).
+ */
+export function useIsPhone(): boolean {
+  return useMediaQuery(PHONE_MAX_QUERY);
+}
diff --git a/apps/pwa/src/routes/AdminPage.tsx b/apps/pwa/src/routes/AdminPage.tsx
index 14a8e5b..54bf5d5 100644
--- a/apps/pwa/src/routes/AdminPage.tsx
+++ b/apps/pwa/src/routes/AdminPage.tsx
@@ -38,6 +38,7 @@ import {
   type AdminCalendar,
 } from '../api/client.js';
 import { CredentialSheet, type CredentialSheetMode } from '../components/CredentialSheet.js';
+import { useIsPhone } from '../hooks/useIsPhone.js';
 
 // ── Styles ─────────────────────────────────────────────────────────────────
 
@@ -55,8 +56,8 @@ const sectionLabelStyle: React.CSSProperties = {
 export function AdminPage() {
   const queryClient = useQueryClient();
 
-  // Phone detection for toast bottom offset
-  const phone = typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
+  // Phone detection for toast bottom offset (WR-05: resize-aware)
+  const phone = useIsPhone();
 
   // Success toast state (D-08)
   const [toast, setToast] = useState<string | null>(null);
@@ -1345,6 +1346,8 @@ interface ResetPasswordSheetProps {
 }
 
 function ResetPasswordSheet({ isOpen, onClose, onSuccess, member }: ResetPasswordSheetProps) {
+  // WR-05: resize-aware phone detection.
+  const sheetPhone = useIsPhone();
   const [newPassword, setNewPassword] = useState('');
   const [confirmPassword, setConfirmPassword] = useState('');
   const [error, setError] = useState<string | null>(null);
@@ -1374,10 +1377,6 @@ function ResetPasswordSheet({ isOpen, onClose, onSuccess, member }: ResetPasswor
     onClose();
   }
 
-  // Phone detection for desktop centering
-  const sheetPhone =
-    typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
-
   const resetMutation = useMutation({
     mutationFn: async () => {
       if (newPassword !== confirmPassword) throw new Error('mismatch');