fix(mobile): width and swipe

src/OpenIPC.Viewer.App/Services/IBackNavigable.cs

@@ -0,0 +1,12 @@
+namespace OpenIPC.Viewer.App.Services;
+
+/// <summary>
+/// A page view model or overlay dialog with levels of its own (a settings
+/// section over its list, a remote folder over its parent). System Back asks
+/// it first and only leaves the page or closes the sheet once it says no.
+/// </summary>
+public interface IBackNavigable
+{
+    /// <summary>Steps one level up inside; false when already at the top.</summary>
+    bool TryGoBack();
+}

src/OpenIPC.Viewer.App/Services/OverlayDialogPresenter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 using Avalonia;
 using Avalonia.Animation;
@@ -20,7 +21,7 @@ namespace OpenIPC.Viewer.App.Services;
 // returns null). This presenter adds a dim background + a bottom-sheet card
 // holding the dialog Content to the active TopLevel's OverlayLayer and awaits
 // a caller-provided TaskCompletionSource. Result is delivered when the content
-// closes itself via its TCS.
+// closes itself via its TCS, or when the dialog is dismissed (system Back).
 //
 // Layout is a bottom sheet: the card stretches full width and pins to the
 // bottom edge with rounded top corners, the native mobile pattern. Its height
@@ -45,18 +46,39 @@ public static class OverlayDialogPresenter
     // Air between a sheet's last row and the navigation bar / gesture pill.
     private const double SheetBottomGap = 14;
 
-    // Number of overlay dialogs currently on screen. Mobile dialogs live in the
+    // Dialogs currently on screen, oldest first. Mobile dialogs live in the
     // TopLevel.OverlayLayer; the dim Border does not reliably intercept taps on
     // the bottom nav, so the shell gates navigation on this instead. Desktop
     // uses real modal Windows (ShowDialog) and never goes through here.
-    private static int _activeCount;
+    private static readonly List<OpenDialog> Open = new();
 
     /// <summary>True while at least one overlay (mobile modal) dialog is open.</summary>
-    public static bool IsAnyOpen => _activeCount > 0;
+    public static bool IsAnyOpen => Open.Count > 0;
 
     /// <summary>Raised on the UI thread whenever <see cref="IsAnyOpen"/> may have changed.</summary>
     public static event Action? ActiveChanged;
 
+    /// <summary>
+    /// System Back over the overlays: the topmost dialog first steps up its own
+    /// levels (<see cref="IBackNavigable"/>, e.g. the file manager's folders),
+    /// then is cancelled as if the user had hit Cancel. False when none is open.
+    /// The caller is parked on the dialog's TaskCompletionSource, so tearing the
+    /// sheet down any other way would leave every command that awaits a dialog
+    /// (Add camera, Discover, …) disabled for good.
+    /// </summary>
+    public static bool TryDismissTopmost()
+    {
+        if (Open.Count == 0)
+            return false;
+        var top = Open[^1];
+        var inner = top.Content as IBackNavigable ?? top.Content.DataContext as IBackNavigable;
+        if (inner?.TryGoBack() != true)
+            top.Dismissed.TrySetResult();
+        return true;
+    }
+
+    private sealed record OpenDialog(Control Content, TaskCompletionSource Dismissed);
+
     // fullScreen → fill the whole TopLevel (no bottom-sheet card / scroll wrapper).
     // Used for the SSH terminal and file manager, which are full-screen pages on
     // mobile, not sheets (phase-13 §13.3).
@@ -167,8 +189,9 @@ void ApplySize(Size s)
             sizeSub = top.GetObservable(TopLevel.ClientSizeProperty).Subscribe(ApplySize);
         }
 
+        var entry = new OpenDialog(content, new TaskCompletionSource());
         overlay.Children.Add(dim);
-        _activeCount++;
+        Open.Add(entry);
         ActiveChanged?.Invoke();
         // Kick the transitions after the first layout pass — set synchronously
         // the Avalonia renderer treats them as initial state and skips the
@@ -182,13 +205,17 @@ void ApplySize(Size s)
 
         try
         {
-            return await completion.ConfigureAwait(true);
+            var finished = await Task.WhenAny(completion, entry.Dismissed.Task).ConfigureAwait(true);
+            // Dismissed (Back) delivers the same "no result" the Cancel button does.
+            return ReferenceEquals(finished, completion)
+                ? await completion.ConfigureAwait(true)
+                : default!;
         }
         finally
         {
             sizeSub?.Dispose();
             overlay.Children.Remove(dim);
-            _activeCount--;
+            Open.Remove(entry);
             ActiveChanged?.Invoke();
         }
     }

src/OpenIPC.Viewer.App/ViewModels/FileManagerViewModel.cs

@@ -21,7 +21,7 @@ namespace OpenIPC.Viewer.App.ViewModels;
 /// the OS file pickers (no local FS panel) so there are no desktop-only paths
 /// or mobile sandbox issues. Root-level deletes are refused.
 /// </summary>
-public sealed partial class FileManagerViewModel : ViewModelBase, IAsyncDisposable
+public sealed partial class FileManagerViewModel : ViewModelBase, IAsyncDisposable, IBackNavigable
 {
     private readonly Camera _camera;
     private readonly CameraDirectoryService _directory;
@@ -93,6 +93,15 @@ private Task NavigateUpAsync()
         return LoadEntriesAsync();
     }
 
+    // System Back climbs to the parent folder; at "/" it closes the manager.
+    public bool TryGoBack()
+    {
+        if ((RemotePath ?? "/").Trim('/').Length == 0)
+            return false;
+        _ = NavigateUpAsync();
+        return true;
+    }
+
     [RelayCommand]
     private async Task OpenEntryAsync(RemoteEntryViewModel? entry)
     {

src/OpenIPC.Viewer.App/ViewModels/MainWindowViewModel.cs

@@ -32,6 +32,9 @@ public sealed partial class MainWindowViewModel : ViewModelBase,
     // Back returns there instead of always dropping to the library list.
     private ViewModelBase? _singleCameraOrigin;
 
+    // Settings → Start page: the root the system Back gesture unwinds to.
+    private readonly ViewModelBase _startPage;
+
     public GridPageViewModel Live { get; }
     public CameraLibraryPageViewModel Library { get; }
     public RecordingsPageViewModel Recordings { get; }
@@ -96,7 +99,8 @@ public MainWindowViewModel(
         _playerFactory = playerFactory;
         _logger = logger;
         // Settings → Start page (#70): open straight into the live grid if asked.
-        _currentPage = userSettings.Current.StartupPage == "live" ? live : library;
+        _startPage = userSettings.Current.StartupPage == "live" ? live : library;
+        _currentPage = _startPage;
 
         WeakReferenceMessenger.Default.Register<OpenCameraMessage>(this);
         WeakReferenceMessenger.Default.Register<GoBackToLibraryMessage>(this);
@@ -187,6 +191,52 @@ private void ExitKiosk()
         UpdateFullscreen();
     }
 
+    /// <summary>
+    /// System Back (Android button / edge swipe, mouse back button) walks up one
+    /// level: the topmost sheet, then fullscreen, then the page a camera or
+    /// recording was opened from, then the page's own levels (a settings section
+    /// back to its list), then the start page. False at the root, so the platform takes over
+    /// (Android sends the app to the background).
+    /// </summary>
+    public bool TryGoBack()
+    {
+        if (OverlayDialogPresenter.TryDismissTopmost())
+            return true;
+
+        if (_playerFullscreen && CurrentPage is RecordingPlayerPageViewModel)
+        {
+            Receive(new SetPlayerFullscreenMessage(false));
+            return true;
+        }
+
+        if (KioskMode)
+        {
+            KioskMode = false;
+            UpdateFullscreen();
+            return true;
+        }
+
+        switch (CurrentPage)
+        {
+            case RecordingPlayerPageViewModel:
+                Receive(new GoBackToRecordingsMessage());
+                return true;
+            case SingleCameraPageViewModel:
+                Receive(new GoBackToLibraryMessage());
+                return true;
+            case IBackNavigable page when page.TryGoBack():
+                return true;
+        }
+
+        if (!ReferenceEquals(CurrentPage, _startPage))
+        {
+            CurrentPage = _startPage;
+            return true;
+        }
+
+        return false;
+    }
+
     private static bool CanNavigate() => !OverlayDialogPresenter.IsAnyOpen;
 
     [RelayCommand(CanExecute = nameof(CanNavigate))]

src/OpenIPC.Viewer.App/ViewModels/RecordingsPageViewModel.cs

@@ -22,7 +22,7 @@ public enum MediaTab { Recordings, Snapshots }
 
 public enum RecordingPeriod { All, Today, Days7, Days30 }
 
-public sealed partial class RecordingsPageViewModel : ViewModelBase
+public sealed partial class RecordingsPageViewModel : ViewModelBase, IBackNavigable
 {
     private readonly IRecordingRepository _repo;
     private readonly CameraDirectoryService _cameras;
@@ -39,6 +39,16 @@ public sealed partial class RecordingsPageViewModel : ViewModelBase
     // Phase 16.3: archive activity calendar. Selecting a day filters the list.
     public ArchiveCalendarViewModel Calendar { get; }
 
+    // Phone: Back folds an expanded month calendar back to its week strip
+    // before leaving the page.
+    public bool TryGoBack()
+    {
+        if (!ShowRecordings || !Calendar.IsExpanded)
+            return false;
+        Calendar.IsExpanded = false;
+        return true;
+    }
+
     // Phase 14: the Recordings page doubles as the captured-media browser. A
     // segmented header flips between the recordings list and the snapshot
     // gallery; the snapshot tab loads lazily on first view.

src/OpenIPC.Viewer.App/ViewModels/SettingsPageViewModel.cs

@@ -16,7 +16,7 @@
 
 namespace OpenIPC.Viewer.App.ViewModels;
 
-public sealed partial class SettingsPageViewModel : ViewModelBase
+public sealed partial class SettingsPageViewModel : ViewModelBase, IBackNavigable
 {
     private readonly UserSettingsService _settings;
     private readonly IFileSystem _fs;
@@ -136,6 +136,16 @@ partial void OnIsWideChanged(bool value)
     [RelayCommand]
     private void BackToList() => SelectedSectionIndex = -1;
 
+    // Phone: an open section returns to the section list. Wide shows both panes,
+    // so there is no level to step up.
+    public bool TryGoBack()
+    {
+        if (!ShowBackButton)
+            return false;
+        BackToList();
+        return true;
+    }
+
     // Deep-link target for the tray "About" item — keeps the section index in
     // one place (it shifts between editions with different section sets).
     public void SelectAboutSection() => SelectedSectionIndex = 6;

src/OpenIPC.Viewer.App/Views/Dialogs/HealthCenterContent.axaml

@@ -11,7 +11,7 @@
              FontSize="{StaticResource FontSizeBase}"
              Foreground="{StaticResource TextPrimaryBrush}">
 
-  <Grid RowDefinitions="Auto,Auto,*,Auto" Margin="24" MinWidth="420">
+  <Grid RowDefinitions="Auto,Auto,*,Auto" Margin="24" MinWidth="300">
 
     <!-- Header: title + refresh -->
     <Grid Grid.Row="0" ColumnDefinitions="*,Auto">

src/OpenIPC.Viewer.App/Views/MainView.axaml.cs

@@ -3,6 +3,7 @@
 using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Controls.Platform;
+using Avalonia.Interactivity;
 using OpenIPC.Viewer.App.ViewModels;
 
 namespace OpenIPC.Viewer.App.Views;
@@ -49,6 +50,7 @@ public partial class MainView : UserControl
     private Thickness _contentPadding = WidePadding;
     private MainWindowViewModel? _vm;
     private IInsetsManager? _insets;
+    private TopLevel? _topLevel;
 
     public bool ShowSidebar => _showSidebar;
     public bool ShowBottomNav => _showBottomNav;
@@ -72,7 +74,10 @@ public MainView()
     protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
     {
         base.OnAttachedToVisualTree(e);
-        _insets = TopLevel.GetTopLevel(this)?.InsetsManager;
+        _topLevel = TopLevel.GetTopLevel(this);
+        if (_topLevel is not null)
+            _topLevel.BackRequested += OnBackRequested;
+        _insets = _topLevel?.InsetsManager;
         if (_insets is not null)
         {
             _insets.SafeAreaChanged += OnSafeAreaChanged;
@@ -83,6 +88,11 @@ protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
     protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
     {
         base.OnDetachedFromVisualTree(e);
+        if (_topLevel is not null)
+        {
+            _topLevel.BackRequested -= OnBackRequested;
+            _topLevel = null;
+        }
         if (_insets is not null)
         {
             _insets.SafeAreaChanged -= OnSafeAreaChanged;
@@ -92,6 +102,14 @@ protected override void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e
 
     private void OnSafeAreaChanged(object? sender, SafeAreaChangedArgs e) => ApplySafeArea();
 
+    // Android Back (button or edge swipe) and the mouse back button arrive here.
+    // Left unhandled at the root, Android sends the app to the background.
+    private void OnBackRequested(object? sender, RoutedEventArgs e)
+    {
+        if (!e.Handled && _vm?.TryGoBack() == true)
+            e.Handled = true;
+    }
+
     private void ApplySafeArea() =>
         Padding = _isFullscreen ? default : _insets?.SafeAreaPadding ?? default;
 

src/OpenIPC.Viewer.App/Views/Pages/RecordingPlayerPage.axaml

@@ -343,8 +343,8 @@
             </StackPanel>
           </Border>
 
-          <ScrollViewer Grid.Row="2" Padding="4,0,4,6">
-            <ItemsControl ItemsSource="{Binding EventList}">
+          <ScrollViewer Grid.Row="2">
+            <ItemsControl ItemsSource="{Binding EventList}" Margin="4,0,4,6">
               <ItemsControl.ItemTemplate>
                 <DataTemplate x:DataType="vm:PlayerEventRow">
                   <Button Classes="evrow"

src/OpenIPC.Viewer.App/Views/Pages/SettingsPage.axaml

@@ -82,9 +82,12 @@
     <!-- ===== Master / list pane (column 0) ===== -->
     <ScrollViewer Grid.Column="0"
                   IsVisible="{Binding ShowList}"
-                  Padding="0,0,8,24"
                   HorizontalScrollBarVisibility="Disabled">
-      <StackPanel Spacing="12">
+      <!-- ALL inset lives on the content, never on ScrollViewer.Padding: the
+           padding is deducted from the viewport but never added to the extent,
+           so the content kept its full width and hung off the right edge, and
+           the last row could not be scrolled clear of the bottom. -->
+      <StackPanel Spacing="12" Margin="0,0,8,24">
         <TextBlock Text="{Binding [Settings.Title], Source={x:Static svc:Localizer.Instance}}"
                    FontSize="{StaticResource FontSizeXl}"
                    FontWeight="SemiBold"
@@ -191,9 +194,10 @@
     <!-- ===== Detail pane (column 1) ===== -->
     <ScrollViewer Grid.Column="1"
                   IsVisible="{Binding ShowDetail}"
-                  Padding="16,0,8,24"
                   HorizontalScrollBarVisibility="Disabled">
-      <StackPanel Spacing="20">
+      <!-- See the master pane above: every inset goes on the content, or combo
+           boxes and wrapped paragraphs run past the right edge on a phone. -->
+      <StackPanel Spacing="20" Margin="16,0,8,24">
 
         <!-- Back link — narrow only -->
         <Button Classes="back-link"

src/OpenIPC.Viewer.App/Views/Pages/SingleCameraPage.axaml

@@ -488,8 +488,10 @@
                 BorderThickness="1"
                 CornerRadius="4">
           <StackPanel Spacing="6" Margin="2">
-            <ScrollViewer MaxHeight="260" Padding="8">
-              <ItemsControl ItemsSource="{Binding IspFields}">
+            <ScrollViewer MaxHeight="260">
+              <!-- Inset on the content, not ScrollViewer.Padding, which deflates the
+                   viewport without shrinking the content and clips the right edge. -->
+              <ItemsControl ItemsSource="{Binding IspFields}" Margin="8">
                 <ItemsControl.ItemTemplate>
                   <DataTemplate>
                     <Grid ColumnDefinitions="160,*,Auto" Margin="0,1">
@@ -550,8 +552,8 @@
             <TextBox Text="{Binding FieldFilter, Mode=TwoWay}"
                      PlaceholderText="{Binding [CameraPage.Majestic.Search], Source={x:Static svc:Localizer.Instance}}"
                      Margin="8,6,8,0" FontSize="11" />
-            <ScrollViewer MaxHeight="320" Padding="8">
-              <ItemsControl ItemsSource="{Binding ConfigSections}">
+            <ScrollViewer MaxHeight="320">
+              <ItemsControl ItemsSource="{Binding ConfigSections}" Margin="8">
                 <ItemsControl.ItemTemplate>
                   <DataTemplate>
                     <StackPanel Spacing="3" Margin="0,0,0,8"
@@ -646,8 +648,8 @@
                       Background="Transparent" BorderBrush="{StaticResource BorderMediumBrush}" BorderThickness="1"
                       CornerRadius="4" Foreground="{StaticResource TextPrimaryBrush}" />
             </Grid>
-            <ScrollViewer MaxHeight="280" Padding="8,0,8,8">
-              <ItemsControl ItemsSource="{Binding Metrics}">
+            <ScrollViewer MaxHeight="280">
+              <ItemsControl ItemsSource="{Binding Metrics}" Margin="8,0,8,8">
                 <ItemsControl.ItemTemplate>
                   <DataTemplate>
                     <Grid ColumnDefinitions="*,Auto" Margin="0,1">