Back closes what is open

On a phone the Back button left the page under an open menu, sheet or dialog. An open overlay now says so (new
IDOverlayHost, cascaded by MainLayout; OverlayService keeps them newest last): DModal and DDropdown through the
cascade, so the D components stay free of app services, and the nav menu, PhoneSheet and the full-screen globe through
the service. MainLayout's location-changing handler lets Back close the newest overlay instead of leaving the page; a
link followed or the app's own navigation (signing out after its question, say) closes them all and goes on. Blazor
can't tell Back from the app's navigation, so a capture-phase popstate listener in main.js marks Back
(AppStatusService.TookBack). No history entries are pushed. Phone flow: Back closes the menu, a card's More sheet, the
composer and the full-screen globe one after another without leaving the feed, and with nothing open goes back.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

Shared/MainLayout.razor

@@ -1,15 +1,47 @@
-@inherits LayoutComponentBase
+@inherits LayoutComponentBase
+@implements IDisposable
 
-<div class="relative flex flex-col md:flex-row w-full h-full">
-	<NavMenu />
+@* The page and its menu. The overlays it holds (dialogs, menus, sheets: IDOverlayHost, cascaded) close with the phone's
+   Back button: while one is open, Back closes the newest instead of leaving the page; a link followed or the app's own
+   navigation closes them all and goes on. *@
+<CascadingValue Value="(IDOverlayHost)Overlays" IsFixed="true">
+	<div class="relative flex flex-col md:flex-row w-full h-full">
+		<NavMenu />
 
-	<div class="block flex-1 relative w-full h-full">
-		<div class="block absolute overflow-y-auto w-full h-full p-3 md:py-4 md:pl-2 md:pr-4">
-			@Body
+		<div class="block flex-1 relative w-full h-full">
+			<div class="block absolute overflow-y-auto w-full h-full p-3 md:py-4 md:pl-2 md:pr-4">
+				@Body
+			</div>
 		</div>
 	</div>
-</div>
 
-<ToastHost />
-<PublicNoticeHost />
-<ConfirmHost />
+	<ToastHost />
+	<PublicNoticeHost />
+	<ConfirmHost />
+</CascadingValue>
+
+@code {
+	[Inject] OverlayService Overlays { get; set; }
+	[Inject] NavigationManager Navigation { get; set; }
+	[Inject] AppStatusService Status { get; set; }
+
+	IDisposable changing;
+
+	protected override void OnInitialized() => changing = Navigation.RegisterLocationChangingHandler(OnLocationChanging);
+
+	async ValueTask OnLocationChanging(LocationChangingContext context)
+	{
+		var back = !context.IsNavigationIntercepted && Status.TookBack();
+		if (!Overlays.HasOpen)
+			return;
+		if (back)
+		{
+			context.PreventNavigation();
+			await Overlays.CloseTop(context.CancellationToken);
+			return;
+		}
+		await Overlays.CloseAll(context.CancellationToken);
+	}
+
+	public void Dispose() => changing?.Dispose();
+}

Shared/NavMenu.razor

@@ -141,7 +141,27 @@
 @code {
 	[Inject] ConfirmService Confirm { get; set; }
 
+	[Inject] OverlayService Overlays { get; set; }
+
 	bool isMenuOpen;
+	IDisposable overlay;
+
+	// open, the Back button closes it
+	void SetMenu(bool open)
+	{
+		isMenuOpen = open;
+		if (open && overlay is null)
+			overlay = Overlays.Open(() => InvokeAsync(() =>
+			{
+				SetMenu(false);
+				StateHasChanged();
+			}));
+		else if (!open && overlay is not null)
+		{
+			overlay.Dispose();
+			overlay = null;
+		}
+	}
 	bool isPersonaMenuOpen;
 
 	string PersonaBackground => CascadingState.Persona?.Header is { Length: > 0 } header && !header.Contains("/missing-")
@@ -162,37 +182,38 @@
 	{
 		if (!isMenuOpen)
 			return;
-		isMenuOpen = false;
+		SetMenu(false);
 		InvokeAsync(StateHasChanged);
 	}
 
-	void CloseMenu() => isMenuOpen = false;
+	void CloseMenu() => SetMenu(false);
 
 	void OnKeyDown(KeyboardEventArgs e)
 	{
 		if (e.Key == "Escape")
-			isMenuOpen = false;
+			SetMenu(false);
 	}
 
 	public override async ValueTask DisposeAsync()
 	{
 		Navigation.LocationChanged -= OnLocationChanged;
+		overlay?.Dispose();
 		await base.DisposeAsync();
 	}
 
 	async Task SwitchPersona(string personaId)
 	{
-		isMenuOpen = false;
+		SetMenu(false);
 		var result = await CascadingState.SwitchPersona(personaId);
 		if (result.IsInvalid)
 			Toast.AddResponseError(result);
 	}
 
-	private void ToggleNavMenu() => isMenuOpen = !isMenuOpen;
+	private void ToggleNavMenu() => SetMenu(!isMenuOpen);
 
 	async Task Logout()
 	{
-		isMenuOpen = false;
+		SetMenu(false);
 		if (!await Confirm.Ask(Localizer["Log out?"], Localizer["Every persona of this login is signed out on this device."], Localizer["Logout"], true))
 			return;
 		Navigation.NavigateTo("logout");