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

Components/Daisy/Actions/DDropdown.razor

@@ -1,4 +1,5 @@
 @inherits DComponentBase
+@implements IDisposable
 
 @* daisyUI Dropdown: https://daisyui.com/components/dropdown/ . The open state lives in C# (@bind-IsOpen):
    dropdown-open shows the content and dropdown-close keeps the focus-within rule from showing it while closed.
@@ -42,8 +43,12 @@
 		+ "max-md:overflow-y-auto max-md:overscroll-contain max-md:rounded-b-none max-md:translate-none max-md:scale-100 "
 		+ "max-md:p-3 max-md:pb-[max(0.75rem,env(safe-area-inset-bottom))]";
 
+	/// <summary>Where it says it is open, so the Back button closes it (cascaded by the app; none, none said).</summary>
+	[CascadingParameter] IDOverlayHost Overlays { get; set; }
+
 	ElementReference trigger;
 	ElementReference content;
+	IDisposable overlay;
 	bool focusContent;
 	bool focusTrigger;
 
@@ -65,6 +70,25 @@
 		_ => null
 	};
 
+	protected override void OnParametersSet() => TrackOverlay();
+
+	void TrackOverlay()
+	{
+		if (IsOpen && overlay is null)
+			overlay = Overlays?.Open(() => InvokeAsync(async () =>
+			{
+				await SetOpen(false, true);
+				StateHasChanged();
+			}));
+		else if (!IsOpen && overlay is not null)
+		{
+			overlay.Dispose();
+			overlay = null;
+		}
+	}
+
+	public void Dispose() => overlay?.Dispose();
+
 	protected override async Task OnAfterRenderAsync(bool firstRender)
 	{
 		if (focusContent)
@@ -93,6 +117,7 @@
 		focusContent = isOpen && !IsOpen;
 		focusTrigger = !isOpen && IsOpen && giveFocusBack;
 		IsOpen = isOpen;
+		TrackOverlay();
 		await IsOpenChanged.InvokeAsync(isOpen);
 	}
 }

Components/Daisy/Actions/DModal.razor

@@ -1,4 +1,5 @@
 @inherits DComponentBase
+@implements IDisposable
 
 @* daisyUI Modal: https://daisyui.com/components/modal/ . Always rendered; the open state lives in C# (@bind-IsOpen)
    and shows as modal-open. On opening, the box takes the focus (Blazor's FocusAsync) so that Escape, handled on the
@@ -58,7 +59,11 @@
 	[Parameter] public bool ShowClose { get; set; } = true;
 	[Parameter] public string BoxClass { get; set; }
 
+	/// <summary>Where it says it is open, so the Back button closes it (cascaded by the app; none, none said).</summary>
+	[CascadingParameter] IDOverlayHost Overlays { get; set; }
+
 	readonly string uid = "d" + Guid.NewGuid().ToString("N")[..8];
+	IDisposable overlay;
 	ElementReference box;
 	bool wasOpen;
 	bool focusPending;
@@ -80,8 +85,26 @@
 		if (IsOpen && !wasOpen)
 			focusPending = true;
 		wasOpen = IsOpen;
+		TrackOverlay();
 	}
 
+	void TrackOverlay()
+	{
+		if (IsOpen && overlay is null)
+			overlay = Overlays?.Open(() => InvokeAsync(async () =>
+			{
+				await SetOpen(false);
+				StateHasChanged();
+			}));
+		else if (!IsOpen && overlay is not null)
+		{
+			overlay.Dispose();
+			overlay = null;
+		}
+	}
+
+	public void Dispose() => overlay?.Dispose();
+
 	protected override async Task OnAfterRenderAsync(bool firstRender)
 	{
 		if (!focusPending)
@@ -98,6 +121,7 @@
 	{
 		IsOpen = isOpen;
 		wasOpen = isOpen;
+		TrackOverlay();
 		await IsOpenChanged.InvokeAsync(isOpen);
 	}
 }

Components/Daisy/IDOverlayHost.cs

@@ -0,0 +1,11 @@
+namespace decePubClient.Components.Daisy;
+
+/// <summary>
+/// Where an open overlay (a dialog, a menu, a sheet) says it is open, so that the phone's Back button closes it instead
+/// of leaving the page: Open registers how to close it and returns what ends the registration once it is closed. The
+/// app cascades one (OverlayService, from MainLayout); a component without one simply doesn't register.
+/// </summary>
+public interface IDOverlayHost
+{
+	IDisposable Open(Func<Task> close);
+}

Components/Feed/GlobePanel.razor

@@ -82,8 +82,11 @@
 	[Parameter] public bool Expanded { get; set; }
 	[Parameter] public EventCallback<bool> ExpandedChanged { get; set; }
 
+	[Inject] OverlayService Overlays { get; set; }
+
 	ElementReference closeButton;
 	ElementReference expandButton;
+	IDisposable overlay;
 	bool focusClose;
 	bool focusExpand;
 
@@ -115,7 +118,18 @@
 
 	protected override void OnInitialized() => IsLoading = false;
 
-	protected override void OnParametersSet() => postsHandedOver = true;
+	protected override void OnParametersSet()
+	{
+		postsHandedOver = true;
+		// full screen, the Back button closes it
+		if (Expanded && overlay is null)
+			overlay = Overlays.Open(() => InvokeAsync(Close));
+		else if (!Expanded && overlay is not null)
+		{
+			overlay.Dispose();
+			overlay = null;
+		}
+	}
 
 	protected override async Task OnAfterRenderAsync(bool firstRender)
 	{
@@ -323,6 +337,7 @@
 
 	public override async ValueTask DisposeAsync()
 	{
+		overlay?.Dispose();
 		await cancellation.CancelAsync();
 		cancellation.Dispose();
 		statsTimer?.Dispose();

Components/PhoneSheet.razor

@@ -29,8 +29,30 @@
 	[Parameter] public RenderFragment ChildContent { get; set; }
 	[Parameter] public string Class { get; set; }
 
+	[Inject] OverlayService Overlays { get; set; }
+
+	IDisposable overlay;
+
 	protected override void OnInitialized() => IsLoading = false;
 
+	// open, the Back button closes it
+	protected override void OnParametersSet()
+	{
+		if (IsOpen && overlay is null)
+			overlay = Overlays.Open(() => InvokeAsync(Close));
+		else if (!IsOpen && overlay is not null)
+		{
+			overlay.Dispose();
+			overlay = null;
+		}
+	}
+
+	public override async ValueTask DisposeAsync()
+	{
+		overlay?.Dispose();
+		await base.DisposeAsync();
+	}
+
 	Task Close() => OnClose.InvokeAsync();
 
 	Task OnKeyDown(KeyboardEventArgs e) => e.Key == "Escape" ? Close() : Task.CompletedTask;

Program.cs

@@ -51,6 +51,7 @@ builder.Services.AddOptions()
 	.AddScoped<StreamingService>()
 	.AddScoped<PublicNoticeService>()
 	.AddScoped<ConfirmService>()
+	.AddScoped<OverlayService>()
 	.AddScoped<MediaService>()
 	.AddScoped<GroupService>()
 	.AddScoped<InstanceService>()

Services/AppStatusService.cs

@@ -42,6 +42,9 @@ public class AppStatusService(IJSRuntime jsRuntime)
 
 		public bool IsMobileMedia() => JsSyncRuntime.Invoke<bool>("isMobileMedia");
 
+		// whether the navigation being decided came from the Back (or Forward) button
+		public bool TookBack() => JsSyncRuntime.Invoke<bool>("tookBack");
+
 		// whether the pointer can hover (a mouse); a touch screen can't, so what shows on hover there opens on a tap
 		public bool CanHover() => JsSyncRuntime.Invoke<bool>("canHover");
 

Services/OverlayService.cs

@@ -0,0 +1,64 @@
+using decePubClient.Components.Daisy;
+
+namespace decePubClient.Services
+{
+	/// <summary>
+	/// The overlays open now, newest last (IDOverlayHost): MainLayout closes the newest when the Back button is pressed
+	/// while one is open, and all of them when the app goes elsewhere.
+	/// </summary>
+	public class OverlayService : IDOverlayHost
+	{
+		readonly List<Entry> open = [];
+
+		public bool HasOpen
+		{
+			get
+			{
+				lock (open)
+					return open.Count > 0;
+			}
+		}
+
+		public IDisposable Open(Func<Task> close)
+		{
+			var entry = new Entry(this, close);
+			lock (open)
+				open.Add(entry);
+			return entry;
+		}
+
+		public async Task CloseTop(CancellationToken cancellationToken = default)
+		{
+			Entry top;
+			lock (open)
+				top = open.LastOrDefault();
+			if (top is null)
+				return;
+			top.Dispose();
+			await top.Close();
+		}
+
+		public async Task CloseAll(CancellationToken cancellationToken = default)
+		{
+			Entry[] all;
+			lock (open)
+			{
+				all = [.. open];
+				open.Clear();
+			}
+			foreach (var entry in all.Reverse())
+				await entry.Close();
+		}
+
+		sealed class Entry(OverlayService owner, Func<Task> close) : IDisposable
+		{
+			public Func<Task> Close { get; } = close;
+
+			public void Dispose()
+			{
+				lock (owner.open)
+					owner.open.Remove(this);
+			}
+		}
+	}
+}

Shared/MainLayout.razor

@@ -1,6 +1,11 @@
-@inherits LayoutComponentBase
+@inherits LayoutComponentBase
+@implements IDisposable
 
-<div class="relative flex flex-col md:flex-row w-full h-full">
+@* 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">
@@ -8,8 +13,35 @@
 				@Body
 			</div>
 		</div>
-</div>
+	</div>
 
-<ToastHost />
+	<ToastHost />
-<PublicNoticeHost />
+	<PublicNoticeHost />
-<ConfirmHost />
+	<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");

tests/e2e/Mobile/FlowTests.cs

@@ -310,6 +310,51 @@ namespace decePubClient.E2E.Mobile
 			});
 		}
 
+		// the Back button closes what is open, one at a time, and stays on the page
+		[Fact]
+		public async Task Back_closes_what_is_open()
+		{
+			await using var session = await SignIn.As(browser, Persona(), Phone);
+			await Flow(session, "back", async page =>
+			{
+				var home = page.Url;
+				// a page to go back to, so a Back that isn't held would leave the feed
+				await page.Locator("[data-nav-toggle]").TapAsync();
+				await page.Locator("[data-nav-panel] a[href='explore']").TapAsync();
+				await page.WaitForURLAsync(url => new Uri(url).AbsolutePath == "/explore");
+				await page.Locator("[data-nav-toggle]").TapAsync();
+				await page.Locator("[data-nav-panel] a[href='/']").First.TapAsync();
+				await page.WaitForURLAsync(url => new Uri(url).AbsolutePath == "/");
+				await page.Locator("#feed-scroll article[data-uri]").First.WaitForAsync();
+
+				async Task BackCloses(ILocator open, string what)
+				{
+					await Assertions.Expect(open).ToBeVisibleAsync();
+					await page.GoBackAsync();
+					await Assertions.Expect(open).ToBeHiddenAsync(new() { Timeout = 5000 });
+					Assert.True(new Uri(page.Url).AbsolutePath == "/", $"Back after the {what} left the feed for {page.Url}");
+				}
+
+				await page.Locator("[data-nav-toggle]").TapAsync();
+				await BackCloses(page.Locator("[data-nav-panel]"), "menu");
+
+				var card = Card(page, "footer [title='Other']");
+				await card.Locator("footer [title='Other'] > [role=button]").TapAsync();
+				await BackCloses(card.Locator(".dropdown-open > [data-sheet]"), "More sheet");
+
+				await page.Locator("[data-compose-open]").TapAsync();
+				await BackCloses(page.Locator("[data-sheet]:has(textarea[data-compose])"), "composer");
+
+				await page.Locator("button[title='Globe']").TapAsync();
+				await page.Locator("[data-globe-expand]").TapAsync();
+				await BackCloses(page.Locator("aside[role=dialog]"), "full-screen globe");
+
+				// with nothing open, Back leaves the feed as before
+				await page.GoBackAsync();
+				await page.WaitForURLAsync(url => new Uri(url).AbsolutePath == "/explore", new() { Timeout = 10000 });
+			});
+		}
+
 		static async Task<JsonNode> Latest(Pasture.Persona persona) =>
 			(await PersonaApi.Call(persona, $"/api/v1/accounts/{persona.LocalId}/statuses?limit=1"))!.AsArray().FirstOrDefault();
 	}

wwwroot/main.js

@@ -140,6 +140,16 @@ document.addEventListener("click", event => {
 		window.logFromJs(e.message, "openThread")
 	}
 })
+// The Back button (a popstate) as opposed to the app's own navigation: Blazor's location-changing handlers can't tell
+// them apart, and MainLayout lets Back close an open overlay but lets the app's navigation through. Registered for the
+// capture phase, so it runs before Blazor's own listener.
+let backAt = 0
+window.addEventListener("popstate", () => backAt = Date.now(), { capture: true })
+window.tookBack = () => {
+	const back = Date.now() - backAt < 1000
+	backAt = 0
+	return back
+}
 window.canHover = () => {
 	try {
 		return window.matchMedia("(hover: hover)").matches