feat(installer): add SystemCheckPage with blocking-error gating

Adds a new wizard page (positioned right after Welcome, FreshInstall only)
that auto-runs EnvironmentCheckService on entry and shows one row per check
with status icon, localized title/message, and hint+help-link on
failure/unknown. A "Recheck" button re-runs it, guarded against re-entrancy.

IInstallerPage gets a BlocksNavigation default member; WizardViewModel's
Next button now binds to CanGoNext, which the current page can veto (used
here while a check run is in flight or a blocking Error+Failed result is
present — Warnings and Unknown results never block). The summary line names
the blocking checks so a disabled Next is self-explanatory.

Wires up DI for the check pipeline (IProcessRunner, IPortOwnerResolver,
per-run ClaudeCliLookup) and adds the checks.* / installer.systemCheck.*
locale keys in en.json + de.json.

Visual appearance is NOT verified — needs a manual pass in the running
installer.

src/ClaudeDo.Installer/App.xaml.cs

@@ -4,13 +4,17 @@ using System.Linq;
 using System.Net.Http;
 using System.Reflection;
 using System.Windows;
+using ClaudeDo.Installer.Checks;
+using ClaudeDo.Installer.Checks.Interfaces;
 using ClaudeDo.Installer.Core;
+using ClaudeDo.Installer.Core.Interfaces;
 using ClaudeDo.Installer.Localization;
 using ClaudeDo.Localization;
 using ClaudeDo.Releases;
 using ClaudeDo.Installer.Pages.InstallPage;
 using ClaudeDo.Installer.Pages.PathsPage;
 using ClaudeDo.Installer.Pages.ServicePage;
+using ClaudeDo.Installer.Pages.SystemCheckPage;
 using ClaudeDo.Installer.Pages.UiSettingsPage;
 using ClaudeDo.Installer.Pages.WelcomePage;
 using ClaudeDo.Installer.Steps;
@@ -121,8 +125,30 @@ public partial class App : Application
         sc.AddSingleton<IReleaseClient>(sp => new ReleaseClient(sp.GetRequiredService<HttpClient>()));
         sc.AddSingleton<InstallModeDetector>();
 
+        // Environment checks — stateless, so their infrastructure is shared; ClaudeCliLookup is
+        // rebuilt per EnvironmentCheckService instance so a re-check doesn't reuse a stale result.
+        sc.AddSingleton<IProcessRunner, ProcessRunnerAdapter>();
+        sc.AddSingleton<IPortOwnerResolver, NetstatPortOwnerResolver>();
+        sc.AddTransient<Func<EnvironmentCheckService>>(sp => () =>
+        {
+            var processRunner = sp.GetRequiredService<IProcessRunner>();
+            var claudeLookup = new ClaudeCliLookup(processRunner);
+            return new EnvironmentCheckService(new IEnvironmentCheck[]
+            {
+                new GitCheck(processRunner),
+                new GitIdentityCheck(processRunner),
+                new PortCheck(sp.GetRequiredService<IPortOwnerResolver>()),
+                new WriteAccessCheck(),
+                new ClaudeCliCheck(claudeLookup),
+                new ClaudeVersionCheck(claudeLookup),
+                new ClaudeAuthCheck(claudeLookup),
+                new PermissionModeAutoCheck(claudeLookup),
+            });
+        });
+
         // Pages
         sc.AddSingleton<IInstallerPage, WelcomePageViewModel>();
+        sc.AddSingleton<IInstallerPage, SystemCheckPageViewModel>();
         sc.AddSingleton<IInstallerPage, PathsPageViewModel>();
         sc.AddSingleton<IInstallerPage, ServicePageViewModel>();
         sc.AddSingleton<IInstallerPage, UiSettingsPageViewModel>();

src/ClaudeDo.Installer/Core/Interfaces/IInstallerPage.cs

@@ -13,4 +13,7 @@ public interface IInstallerPage
     Task LoadAsync();
     Task ApplyAsync();
     bool Validate();
+
+    /// <summary>True while this page wants "Next" disabled (e.g. a check run in progress or a blocking error).</summary>
+    bool BlocksNavigation => false;
 }

src/ClaudeDo.Installer/Pages/PathsPage/PathsPageViewModel.cs

@@ -12,7 +12,7 @@ public partial class PathsPageViewModel : ObservableObject, IInstallerPage
 
     public string Title => TrExtension.Localizer?["installer.paths.title"] ?? "Paths";
     public string Icon => "\uE8B7";
-    public int Order => 1;
+    public int Order => 2;
     public bool ShowInWizard => true;
     public bool ShowInSettings => true;
     public UserControl View => _view ??= new PathsPageView { DataContext = this };

src/ClaudeDo.Installer/Pages/ServicePage/ServicePageViewModel.cs

@@ -14,7 +14,7 @@ public partial class ServicePageViewModel : ObservableObject, IInstallerPage
 
     public string Title => TrExtension.Localizer?["installer.service.title"] ?? "Service";
     public string Icon => "\uE912";
-    public int Order => 2;
+    public int Order => 3;
     public bool ShowInWizard => true;
     public bool ShowInSettings => true;
     public UserControl View => _view ??= new ServicePageView { DataContext = this };

src/ClaudeDo.Installer/Pages/SystemCheckPage/SystemCheckPageView.xaml

@@ -0,0 +1,99 @@
+<UserControl x:Class="ClaudeDo.Installer.Pages.SystemCheckPage.SystemCheckPageView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:ClaudeDo.Installer.Pages.SystemCheckPage"
+             xmlns:loc="clr-namespace:ClaudeDo.Installer.Localization"
+             d:DataContext="{d:DesignInstance local:SystemCheckPageViewModel}"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d">
+
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition Height="Auto"/>
+            <RowDefinition Height="*"/>
+            <RowDefinition Height="Auto"/>
+            <RowDefinition Height="Auto"/>
+        </Grid.RowDefinitions>
+
+        <!-- Header -->
+        <StackPanel Grid.Row="0" Margin="0,0,0,16">
+            <TextBlock Text="{loc:Tr installer.systemCheck.title}" FontSize="18" FontWeight="SemiBold" Margin="0,0,0,4"/>
+            <TextBlock Text="{loc:Tr installer.systemCheck.subtitle}"
+                       Foreground="{StaticResource TextSecondaryBrush}" TextWrapping="Wrap"/>
+        </StackPanel>
+
+        <!-- Check list -->
+        <ScrollViewer Grid.Row="1" VerticalScrollBarVisibility="Auto">
+            <ItemsControl ItemsSource="{Binding Rows}">
+                <ItemsControl.ItemTemplate>
+                    <DataTemplate DataType="{x:Type local:CheckRowViewModel}">
+                        <Border Margin="0,0,0,6" Padding="10,8"
+                                Background="{StaticResource IslandBgBrush}"
+                                BorderBrush="{StaticResource BorderSubtleBrush}"
+                                BorderThickness="1" CornerRadius="4">
+                            <StackPanel>
+                                <Grid>
+                                    <Grid.ColumnDefinitions>
+                                        <ColumnDefinition Width="Auto"/>
+                                        <ColumnDefinition Width="*"/>
+                                    </Grid.ColumnDefinitions>
+
+                                    <Ellipse Grid.Column="0" Width="10" Height="10" Margin="0,0,10,0"
+                                             VerticalAlignment="Top"
+                                             Fill="{Binding StatusBrush}"/>
+
+                                    <StackPanel Grid.Column="1">
+                                        <TextBlock Text="{Binding Title}" FontSize="13" FontWeight="SemiBold"/>
+                                        <TextBlock Text="{Binding Message}" FontSize="12"
+                                                   Foreground="{StaticResource TextSecondaryBrush}"
+                                                   TextWrapping="Wrap" Margin="0,2,0,0"/>
+
+                                        <TextBlock Text="{Binding Hint}" FontSize="11"
+                                                   Foreground="{StaticResource TextMutedBrush}"
+                                                   TextWrapping="Wrap" Margin="0,4,0,0"
+                                                   Visibility="{Binding Hint, Converter={StaticResource NullToCollapsedConverter}}"/>
+
+                                        <Button Content="{Binding HelpUrl}"
+                                                HorizontalAlignment="Left" Margin="-16,4,0,0"
+                                                Background="Transparent" BorderThickness="0"
+                                                Foreground="{StaticResource AccentLightBrush}"
+                                                Cursor="Hand"
+                                                Command="{Binding DataContext.OpenHelpUrlCommand, RelativeSource={RelativeSource AncestorType=ItemsControl}}"
+                                                CommandParameter="{Binding HelpUrl}"
+                                                Visibility="{Binding HelpUrl, Converter={StaticResource NullToCollapsedConverter}}"/>
+                                    </StackPanel>
+                                </Grid>
+                            </StackPanel>
+                        </Border>
+                    </DataTemplate>
+                </ItemsControl.ItemTemplate>
+            </ItemsControl>
+        </ScrollViewer>
+
+        <!-- Progress + summary -->
+        <StackPanel Grid.Row="2" Margin="0,8,0,0">
+            <ProgressBar IsIndeterminate="True" Margin="0,0,0,8"
+                         Visibility="{Binding IsRunning, Converter={StaticResource BoolToVisConverter}}"/>
+            <TextBlock Text="{Binding Summary}" FontSize="12" TextWrapping="Wrap"
+                       Foreground="{StaticResource TextSecondaryBrush}">
+                <TextBlock.Style>
+                    <Style TargetType="TextBlock">
+                        <Style.Triggers>
+                            <DataTrigger Binding="{Binding HasBlockingError}" Value="True">
+                                <Setter Property="Foreground" Value="{StaticResource ErrorBrush}"/>
+                            </DataTrigger>
+                        </Style.Triggers>
+                    </Style>
+                </TextBlock.Style>
+            </TextBlock>
+        </StackPanel>
+
+        <!-- Footer -->
+        <StackPanel Grid.Row="3" Orientation="Horizontal" HorizontalAlignment="Right" Margin="0,12,0,0">
+            <!-- Reserved space: a "Claude Help Me" button lands here in a follow-up task. -->
+            <Button Content="{loc:Tr installer.systemCheck.recheck}"
+                    Command="{Binding RunChecksCommand}"/>
+        </StackPanel>
+    </Grid>
+</UserControl>

src/ClaudeDo.Installer/Pages/SystemCheckPage/SystemCheckPageView.xaml.cs

@@ -0,0 +1,8 @@
+using System.Windows.Controls;
+
+namespace ClaudeDo.Installer.Pages.SystemCheckPage;
+
+public partial class SystemCheckPageView : UserControl
+{
+    public SystemCheckPageView() => InitializeComponent();
+}

src/ClaudeDo.Installer/Pages/SystemCheckPage/SystemCheckPageViewModel.cs

@@ -0,0 +1,160 @@
+using System.Collections.ObjectModel;
+using System.Diagnostics;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Media;
+using ClaudeDo.Installer.Checks;
+using ClaudeDo.Installer.Core;
+using ClaudeDo.Installer.Localization;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace ClaudeDo.Installer.Pages.SystemCheckPage;
+
+public sealed class CheckRowViewModel
+{
+    public CheckRowViewModel(CheckResult result)
+    {
+        var loc = TrExtension.Localizer;
+        Status = result.Status;
+        Severity = result.Severity;
+        Title = loc?[result.TitleKey] ?? result.TitleKey;
+        Message = result.Message;
+        Hint = result.HintKey is not null ? loc?[result.HintKey] ?? result.HintKey : null;
+        HelpUrl = result.HelpUrl;
+        StatusBrush = ResolveBrush(Status, Severity);
+    }
+
+    public CheckStatus Status { get; }
+    public CheckSeverity Severity { get; }
+    public string Title { get; }
+    public string Message { get; }
+    public string? Hint { get; }
+    public string? HelpUrl { get; }
+    public Brush StatusBrush { get; }
+
+    private static Brush ResolveBrush(CheckStatus status, CheckSeverity severity)
+    {
+        var key = status switch
+        {
+            CheckStatus.Ok => "StatusGreenBrush",
+            CheckStatus.Unknown => "StatusGrayBrush",
+            CheckStatus.Failed when severity == CheckSeverity.Error => "StatusRedBrush",
+            CheckStatus.Failed => "StatusOrangeBrush",
+            _ => "StatusGrayBrush",
+        };
+        return Application.Current?.Resources[key] as Brush ?? Brushes.Gray;
+    }
+}
+
+public partial class SystemCheckPageViewModel : ObservableObject, IInstallerPage
+{
+    private readonly InstallContext _context;
+    private readonly Func<EnvironmentCheckService> _checkServiceFactory;
+    private SystemCheckPageView? _view;
+    private bool _hasStarted;
+
+    public string Title => TrExtension.Localizer?["installer.systemCheck.title"] ?? "System Check";
+    public string Icon => "";
+    public int Order => 1;
+    public bool ShowInWizard => true;
+    public bool ShowInSettings => false;
+    public UserControl View => _view ??= new SystemCheckPageView { DataContext = this };
+
+    public ObservableCollection<CheckRowViewModel> Rows { get; } = [];
+
+    [ObservableProperty] private bool _isRunning;
+    [ObservableProperty] private bool _hasRun;
+    [ObservableProperty] private bool _hasBlockingError;
+    [ObservableProperty] private string _summary = string.Empty;
+
+    public bool BlocksNavigation => IsRunning || HasBlockingError;
+
+    public SystemCheckPageViewModel(InstallContext context, Func<EnvironmentCheckService> checkServiceFactory)
+    {
+        _context = context;
+        _checkServiceFactory = checkServiceFactory;
+    }
+
+    partial void OnIsRunningChanged(bool value)
+    {
+        OnPropertyChanged(nameof(BlocksNavigation));
+        RunChecksCommand.NotifyCanExecuteChanged();
+    }
+
+    partial void OnHasBlockingErrorChanged(bool value) => OnPropertyChanged(nameof(BlocksNavigation));
+
+    public Task LoadAsync()
+    {
+        if (!_hasStarted)
+        {
+            _hasStarted = true;
+            _ = RunChecksAsync();
+        }
+        return Task.CompletedTask;
+    }
+
+    public Task ApplyAsync() => Task.CompletedTask;
+
+    public bool Validate() => !HasBlockingError;
+
+    [RelayCommand(CanExecute = nameof(CanRunChecks))]
+    private async Task RunChecksAsync()
+    {
+        if (IsRunning) return;
+
+        IsRunning = true;
+        Summary = TrExtension.Localizer?["installer.systemCheck.summary.running"] ?? "Checking your system…";
+
+        try
+        {
+            var service = _checkServiceFactory();
+            var report = await service.RunAllAsync(_context, CancellationToken.None);
+
+            Rows.Clear();
+            foreach (var result in report.Results)
+                Rows.Add(new CheckRowViewModel(result));
+
+            HasBlockingError = report.HasBlockingError;
+            Summary = BuildSummary(report);
+            HasRun = true;
+        }
+        finally
+        {
+            IsRunning = false;
+        }
+    }
+
+    private bool CanRunChecks() => !IsRunning;
+
+    private static string BuildSummary(EnvironmentCheckReport report)
+    {
+        var loc = TrExtension.Localizer;
+
+        var blocking = report.Results
+            .Where(r => r.Severity == CheckSeverity.Error && r.Status == CheckStatus.Failed)
+            .ToList();
+        if (blocking.Count > 0)
+        {
+            var names = string.Join(", ", blocking.Select(r => loc?[r.TitleKey] ?? r.TitleKey));
+            return loc?.Get("installer.systemCheck.summary.blocking", blocking.Count, names)
+                   ?? $"{blocking.Count} problem(s) must be fixed: {names}";
+        }
+
+        var warnings = report.Results.Count(r => r.Severity == CheckSeverity.Warning && r.Status == CheckStatus.Failed);
+        if (warnings > 0)
+        {
+            return loc?.Get("installer.systemCheck.summary.warnings", warnings)
+                   ?? $"{warnings} warning(s) found.";
+        }
+
+        return loc?["installer.systemCheck.summary.ok"] ?? "Everything looks good.";
+    }
+
+    [RelayCommand]
+    private static void OpenHelpUrl(string? url)
+    {
+        if (string.IsNullOrEmpty(url)) return;
+        Process.Start(new ProcessStartInfo(url) { UseShellExecute = true });
+    }
+}

src/ClaudeDo.Installer/Pages/UiSettingsPage/UiSettingsPageViewModel.cs

@@ -12,7 +12,7 @@ public partial class UiSettingsPageViewModel : ObservableObject, IInstallerPage
 
     public string Title => TrExtension.Localizer?["installer.uiSettings.title"] ?? "UI Settings";
     public string Icon => "\uE771";
-    public int Order => 3;
+    public int Order => 4;
     public bool ShowInWizard => true;
     public bool ShowInSettings => true;
     public UserControl View => _view ??= new UiSettingsPageView { DataContext = this };

src/ClaudeDo.Installer/Views/WizardViewModel.cs

@@ -1,3 +1,4 @@
+using System.ComponentModel;
 using System.Linq;
 using System.Windows;
 using ClaudeDo.Installer.Core;
@@ -32,10 +33,12 @@ public partial class WizardViewModel : ObservableObject
     [NotifyPropertyChangedFor(nameof(IsLastPage))]
     [NotifyPropertyChangedFor(nameof(NextButtonText))]
     [NotifyPropertyChangedFor(nameof(CurrentPage))]
+    [NotifyPropertyChangedFor(nameof(CanGoNext))]
     private int _currentPageIndex;
 
     public IInstallerPage CurrentPage => Pages[CurrentPageIndex];
     public bool CanGoBack => CurrentPageIndex > 0;
+    public bool CanGoNext => !CurrentPage.BlocksNavigation;
     public bool IsLastPage => CurrentPageIndex == Pages.Count - 1;
     public string NextButtonText => IsLastPage
         ? (_localizer["installer.nav.install"])
@@ -58,6 +61,14 @@ public partial class WizardViewModel : ObservableObject
                           || p is InstallPageViewModel).ToList()
             : all;
 
+        // A page's blocking state (e.g. a running/failed system check) can change while it's
+        // displayed; re-evaluate CanGoNext whenever any page raises a property change.
+        foreach (var page in Pages)
+        {
+            if (page is INotifyPropertyChanged notifying)
+                notifying.PropertyChanged += (_, _) => OnPropertyChanged(nameof(CanGoNext));
+        }
+
         if (Pages.Count > 0)
             _ = InitAsync();
     }

src/ClaudeDo.Installer/Views/WizardWindow.xaml

@@ -100,6 +100,7 @@
 
                 <Button Grid.Column="2" Content="{Binding NextButtonText}"
                         Command="{Binding GoNextCommand}"
+                        IsEnabled="{Binding CanGoNext}"
                         Style="{StaticResource AccentButton}"
                         MinWidth="100"/>
             </Grid>