diff --git a/Docs/DesignLanguage.md b/Docs/DesignLanguage.md
index f6a699687..b9c38c7d6 100644
--- a/Docs/DesignLanguage.md
+++ b/Docs/DesignLanguage.md
@@ -300,6 +300,27 @@ presence. Rings compete with the artwork and are hard to read at small sizes.
 Where an icon appears without a row, such as in a planet folder, a small dot at
 the top right marks unread activity.
 
+## Phone and wide layouts
+
+Valour has two layouts. The phone layout shows one window at a time, with the
+sidebar sliding in from the left. The wide layout keeps the sidebar open and
+lets windows sit side by side in tabs and splits. Components read
+`DeviceInfo.IsMobile` to choose between them.
+
+Browsers, desktop apps, and the Android app choose once at startup from the
+device type. The iPhone and iPad app choose from the window size instead: the
+wide layout needs a window at least 680 points wide and 500 points tall, which
+roughly matches iOS regular width and height size classes. When the window
+crosses that line, such as when an iPhone Duo opens or closes or an iPad enters
+Split View, the page shell rebuilds itself in the new layout. The dock saves its
+windows first and restores them afterward; the phone layout keeps only the
+focused tab.
+
+On iOS, the app shell stays inside the left and right safe areas. On iPhone Duo
+the status bar becomes a rail along one edge, and on other iPhones in landscape
+the camera housing takes one side. The page background shows through those
+insets.
+
 ## Victor and scenes
 
 Victor is drawn as himself, the dog from the logo, in a few poses: `astronaut`,
diff --git a/Valour/Client.Maui/wwwroot/app.css b/Valour/Client.Maui/wwwroot/app.css
index 6222b37f6..16f254eec 100644
--- a/Valour/Client.Maui/wwwroot/app.css
+++ b/Valour/Client.Maui/wwwroot/app.css
@@ -61,3 +61,14 @@ h1:focus {
         background-color: var(--surface-canvas);
     }
 }
+
+/* Keeps the app clear of the side safe areas: the status bar rail that the
+   iPhone Duo draws along one edge, and the camera housing on iPhones in
+   landscape. The page background shows through the inset. */
+@supports (-webkit-touch-callout: none) {
+    .mobile-holder {
+        box-sizing: border-box;
+        padding-left: env(safe-area-inset-left);
+        padding-right: env(safe-area-inset-right);
+    }
+}
diff --git a/Valour/Client/Device/DeviceInfo.cs b/Valour/Client/Device/DeviceInfo.cs
index d0ce9c427..f38555ea7 100644
--- a/Valour/Client/Device/DeviceInfo.cs
+++ b/Valour/Client/Device/DeviceInfo.cs
@@ -2,7 +2,31 @@
 
 public class DeviceInfo
 {   
+    /// <summary>
+    /// True when the app shows the phone layout: one window at a time and a
+    /// slide-out sidebar. The iPhone and iPad app can switch layouts while it
+    /// runs (see <see cref="SetMobileLayout"/>); elsewhere it is set once.
+    /// </summary>
     public static bool IsMobile { get; set; }
+
+    /// <summary>
+    /// Raised after <see cref="IsMobile"/> changes while the app runs, with the
+    /// new value. The page shell rebuilds the layout when it fires.
+    /// </summary>
+    public static event Action<bool> LayoutModeChanged;
+
+    /// <summary>
+    /// Switches between the phone and wide layouts, such as when a foldable
+    /// iPhone opens or closes or an iPad enters Split View.
+    /// </summary>
+    public static void SetMobileLayout(bool mobile)
+    {
+        if (IsMobile == mobile)
+            return;
+
+        IsMobile = mobile;
+        LayoutModeChanged?.Invoke(mobile);
+    }
     public static bool IsEmbedded { get; set; }
 
     /// <summary>
diff --git a/Valour/Client/Device/LayoutModeWatcher.cs b/Valour/Client/Device/LayoutModeWatcher.cs
new file mode 100644
index 000000000..8c5dd0ab9
--- /dev/null
+++ b/Valour/Client/Device/LayoutModeWatcher.cs
@@ -0,0 +1,33 @@
+using Microsoft.JSInterop;
+
+namespace Valour.Client.Device;
+
+/// <summary>
+/// Chooses the phone or wide layout from the window size in the iPhone and iPad
+/// app, and switches it when the window changes size, such as when an iPhone Duo
+/// opens or closes. The size rule lives in valourLayout in main.js.
+/// </summary>
+public sealed class LayoutModeWatcher
+{
+    private static DotNetObjectReference<LayoutModeWatcher> _reference;
+
+    /// <summary>
+    /// Returns whether the window currently fits the phone layout, and starts
+    /// reporting changes to <see cref="DeviceInfo.SetMobileLayout"/>.
+    /// </summary>
+    public static async Task<bool> StartAsync(IJSRuntime js)
+    {
+        var wide = await js.InvokeAsync<bool>("valourLayout.isWide");
+
+        if (_reference is null)
+        {
+            _reference = DotNetObjectReference.Create(new LayoutModeWatcher());
+            await js.InvokeVoidAsync("valourLayout.watch", _reference);
+        }
+
+        return !wide;
+    }
+
+    [JSInvokable]
+    public void OnWideLayoutChanged(bool wide) => DeviceInfo.SetMobileLayout(!wide);
+}
diff --git a/Valour/Client/Pages/Index.razor b/Valour/Client/Pages/Index.razor
index 6cb0c9fda..53841e1c8 100644
--- a/Valour/Client/Pages/Index.razor
+++ b/Valour/Client/Pages/Index.razor
@@ -6,6 +6,7 @@
 @page "/planetwiki/{StartPlanetId:long}/{StartPageId:long}"
 @page "/planetwiki/{StartPlanetId:long}"
 @using Valour.Sdk.Services
+@implements IDisposable
 
 @inject ValourClient Client
 @inject AuthService AuthService
@@ -30,6 +31,9 @@
 <ProfilePopup />
 <CustomDropdownContent />
 
+@* Removed for one render while the layout switches; see OnLayoutModeChanged. *@
+@if (!_rebuildingShell)
+{
 <div class="mobile-holder @MobileClass @EmbeddedClass">
 	<ToastContainer>
 		<!-- Modal management -->
@@ -75,6 +79,7 @@
 		</ModalRoot>
 	</ToastContainer>
 </div>
+}
 
 @* Ctrl+/ or Cmd+/ swaps the app for the ValourOS terminal. *@
 <ValourTerminal />
@@ -103,6 +108,8 @@
 	[Parameter]
 	public long? StartPageId { get; set; }
 
+	private bool _rebuildingShell;
+
 	private string MobileClass => DeviceInfo.IsMobile ? "mobile" : "desktop";
 	
 	private string EmbeddedClass => DeviceInfo.IsEmbedded ? "embedded" : "";
@@ -115,6 +122,7 @@
 
 		WindowService.FocusedPlanetChanged += OnPlanetChange;
 		AuthService.LoggedIn += OnLoginAsync;
+		DeviceInfo.LayoutModeChanged += OnLayoutModeChanged;
 	}
 
 	private async Task OnLoginAsync(User user)
@@ -122,9 +130,40 @@
 		await InvokeAsync(StateHasChanged);
 	}
 
+	// Folding an iPhone Duo or resizing an iPad window can switch between the
+	// phone and wide layouts. Components read DeviceInfo.IsMobile when they are
+	// created, so the shell is rebuilt instead of updated in place. The dock
+	// saves its layout first and restores it on load, collapsing it to the
+	// focused tab for the phone layout. The shell is removed for one render
+	// before it returns, so the old dock is disposed before the new one
+	// registers as the main dock.
+	private void OnLayoutModeChanged(bool mobile) => _ = InvokeAsync(RebuildShellAsync);
+
+	private async Task RebuildShellAsync()
+	{
+		if (_rebuildingShell)
+			return;
+
+		var dock = WindowService.MainDock;
+		if (dock?.Layout is not null)
+			await dock.SaveLayout();
+
+		// The launch route was already opened; reopening it would undo where the user went since.
+		_startRoute = null;
+
+		_rebuildingShell = true;
+		StateHasChanged();
+		await Task.Yield();
+
+		_rebuildingShell = false;
+		StateHasChanged();
+	}
+
 	public void Dispose()
 	{
 		WindowService.FocusedPlanetChanged -= OnPlanetChange;
+		DeviceInfo.LayoutModeChanged -= OnLayoutModeChanged;
+		AuthService.LoggedIn -= OnLoginAsync;
 	}
 
 	private Task OnPlanetChange(Planet planet)
diff --git a/Valour/Client/ValourApp.razor b/Valour/Client/ValourApp.razor
index eadb9469f..ad8a13e60 100644
--- a/Valour/Client/ValourApp.razor
+++ b/Valour/Client/ValourApp.razor
@@ -1,4 +1,4 @@
-@using Microsoft.Extensions.DependencyInjection
+@using Microsoft.Extensions.DependencyInjection
 @inject ValourClient Client
 @inject LoggingService Logger
 @inject IJSRuntime JsRuntime
@@ -217,7 +217,11 @@
     {
         if (firstRender)
         {
-            var isMobile = await JsRuntime.InvokeAsync<bool>("IsMobile");
+            // The iPhone and iPad app pick the layout from the window size and
+            // switch it live; other hosts decide once from the device type.
+            var isMobile = DeviceInfo.IsIosApp
+                ? await LayoutModeWatcher.StartAsync(JsRuntime)
+                : await JsRuntime.InvokeAsync<bool>("IsMobile");
             var isEmbedded = await JsRuntime.InvokeAsync<bool>("IsEmbedded");
 
             DeviceInfo.IsMobile = isMobile;
diff --git a/Valour/Client/wwwroot/js/main.js b/Valour/Client/wwwroot/js/main.js
index 5e2444cb9..2d4502159 100644
--- a/Valour/Client/wwwroot/js/main.js
+++ b/Valour/Client/wwwroot/js/main.js
@@ -72,6 +72,39 @@ function IsEmbedded() {
     return embedded;
 }
 
+// The iPhone and iPad app choose between the phone and wide layouts from the
+// window size instead of the device, so an unfolded iPhone Duo or a full-screen
+// iPad gets the wide layout, while a folded phone, a phone in landscape, or a
+// narrow Split View window gets the phone layout. The thresholds approximate
+// Apple's regular width and height size classes.
+window.valourLayout = (() => {
+    const wideQuery = '(min-width: 680px) and (min-height: 500px)';
+    // Folding animates the window through several sizes; report only where it settles.
+    const settleMs = 250;
+    let media = null;
+    let timer = null;
+
+    function isWide() {
+        return window.matchMedia(wideQuery).matches;
+    }
+
+    function watch(dotnetRef) {
+        if (media)
+            return;
+
+        media = window.matchMedia(wideQuery);
+        media.addEventListener('change', () => {
+            clearTimeout(timer);
+            timer = setTimeout(() => {
+                dotnetRef.invokeMethodAsync('OnWideLayoutChanged', media.matches)
+                    .catch(() => { });
+            }, settleMs);
+        });
+    }
+
+    return { isWide, watch };
+})();
+
 // A readable name for this device, shown in the account's device list when
 // linking devices for end-to-end encryption.
 function getValourDeviceName(isHybrid) {