fix(files): report success cancellation and errors with safe next actions (U02)

docs/usability-umsetzung.md

@@ -19,3 +19,7 @@ Die Sicherung enthält Konten, Anfangsbestände, Buchungen einschließlich gelö
 Wiederherstellen akzeptiert nur vollständige Datenbanken derselben Schemaversion. Vorher wird die ausgewählte Datei als konsistenter SQLite-Snapshot zwischengespeichert und auf Integrität, Fremdschlüssel, Migrationen und alle Modellspalten geprüft. Die bestehende Datenbank erhält eine eindeutige `.before-restore-…bak` daneben. Diese Rückfallsicherungen werden nicht automatisch gelöscht; nach geprüfter Wiederherstellung bewusst archivieren. Anwendungsschreibzugriffe warten während der Wiederherstellung, SQLite koordiniert offene Leser. Der Austausch erfolgt mit der SQLite-Backup-API im bestehenden Datenbankhandle. Keine automatische Sicherung beim Beenden.
 
 Prüfung U01: 16/16 Debug-Tests bestanden, darunter WAL-Rundlauf mit exaktem Buchungsstand und Rückfallsicherung, beschädigte/fremde SQLite-Datei und fehlende Quelle. Kein echter Vereinsdatenbestand wurde zurückgespielt.
+
+## U02 – Dateiaktionen
+
+Strukturierte Ergebnisse und gemeinsame Statusanzeige mit optionalen technischen Details, Speicherpfad und „Ordner öffnen“. Abbruch ist neutral. Dateiaktionen sperren erneutes Auslösen; Fehler beim Erzeugen oder Öffnen einer PDF bleiben in der aktuellen Ansicht sichtbar. Native Dateidialoge melden Start-/Prozessfehler und erhalten Unicode-Pfade. Gespeichert wird über eine temporäre Datei, damit Schreibfehler eine bestehende Datei nicht verstümmeln. Prüfung: 18/18 Debug-Tests bestanden.

src/Duempelkas.App/Components/OperationNotice.razor

@@ -0,0 +1,40 @@
+@inject IFileSaveService FileSaveService
+
+@if (Result != null)
+{
+    <div class="alert @(Result.Status == FileOperationStatus.Error ? "alert-danger" : Result.Status == FileOperationStatus.Success ? "alert-success" : "alert-info")" role="status" aria-live="polite" aria-atomic="true">
+        <p>@Result.Message</p>
+        @if (Result.Path != null)
+        {
+            <p class="text-break">@Result.Path</p>
+            <button class="btn btn-outline-secondary" disabled="@busy" @onclick="OpenFolder">Ordner öffnen</button>
+        }
+        @if (Result.Details != null)
+        {
+            <details><summary>Technische Details</summary><p class="text-break">@Result.Details</p></details>
+        }
+        @if (openResult != null)
+        {
+            <p role="alert">@openResult.Message</p>
+            @if (openResult.Details != null) { <details><summary>Technische Details</summary>@openResult.Details</details> }
+        }
+    </div>
+}
+
+@code {
+    [Parameter] public FileOperationResult? Result { get; set; }
+    private FileOperationResult? openResult;
+    private FileOperationResult? previous;
+    private bool busy;
+    protected override void OnParametersSet()
+    {
+        if (previous != Result) { openResult = null; previous = Result; }
+    }
+    private async Task OpenFolder()
+    {
+        if (busy || Result?.Path == null) return;
+        busy = true;
+        try { openResult = await FileSaveService.OpenFolderAsync(Result.Path); }
+        finally { busy = false; }
+    }
+}

src/Duempelkas.App/Pages/Accounts/AccountDetail.razor

@@ -7,6 +7,9 @@
 @inject NavigationManager Navigation
 
 <div class="container-fluid">
+    <OperationNotice Result="fileResult" />
+    @if (fileBusy) { <p role="status" aria-live="polite">Dateiaktion läuft … Bitte warten.</p> }
+
     @if (account == null)
     {
         <div class="text-center py-5">
@@ -35,7 +38,7 @@
             <button class="btn btn-info btn-nav" @onclick="() => showAddTransfer = true">
                 <i class="bi bi-arrow-left-right"></i> Umbuchung
             </button>
-            <button class="btn btn-dark btn-nav" @onclick="HandleExport">
+            <button class="btn btn-dark btn-nav" @onclick="HandleExport" disabled="@fileBusy">
                 <i class="bi bi-file-earmark-pdf"></i> PDF
             </button>
             |

src/Duempelkas.App/Pages/Accounts/AccountDetail.razor.cs

@@ -32,6 +32,8 @@ public partial class AccountDetail
     private string? confirmRestoreEntryTitle;
 
     private string? savedPdfPath;
+    private FileOperationResult? fileResult;
+    private bool fileBusy;
 
     private EntryDto? editingEntry;
     private EntryDto? editingTransferEntry;
@@ -177,20 +179,40 @@ public partial class AccountDetail
     }
 
     private async Task HandleExport()
+    {
+        if (fileBusy) return;
+        fileBusy = true;
+        fileResult = null;
+        try
         {
         var pdf = await PdfStatementService.GenerateStatementAsync(AccountId, selectedYear);
         var suffix = selectedYear.HasValue ? $"_{selectedYear.Value}" : "_Gesamt";
-        savedPdfPath = await FileSaveService.SaveFileAsync(pdf, $"{account?.Name}{suffix}.pdf");
+        fileResult = await FileSaveService.SaveFileAsync(pdf, $"{account?.Name}{suffix}.pdf");
+
+            savedPdfPath = fileResult.Status == FileOperationStatus.Success ? fileResult.Path : null;
+
+        }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private async Task HandleOpenSavedPdf()
+    {
+        if (fileBusy) return;
+        fileBusy = true;
+        fileResult = null;
+        try
         {
         if (!string.IsNullOrWhiteSpace(savedPdfPath))
         {
-            await FileSaveService.OpenFileAsync(savedPdfPath);
+            fileResult = await FileSaveService.OpenFileAsync(savedPdfPath);
         }
 
         savedPdfPath = null;
+
+        }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private void CancelOpenSavedPdf()

src/Duempelkas.App/Pages/Dashboard.razor

@@ -8,6 +8,9 @@
 @inject NavigationManager NavigationManager
 
 <div class="container-fluid">
+    <OperationNotice Result="fileResult" />
+    @if (fileBusy) { <p role="status" aria-live="polite">Dateiaktion läuft … Bitte warten.</p> }
+
 
     <div class="d-flex justify-content-between align-items-center">
         <div class="d-flex align-items-center flex-grow-1" style="min-width: 0;">
@@ -25,14 +28,14 @@
             <i class="bi bi-plus-lg"></i> Neues Konto
         </button>
         |
-        <button class="btn-nav btn-success" @onclick="HandleBackupAsync">
+        <button class="btn-nav btn-success" @onclick="HandleBackupAsync" disabled="@fileBusy">
             <i class="bi bi-save"></i> Backup
         </button>
-        <button class="btn-nav btn-warning" @onclick="HandleRestoreAsync">
+        <button class="btn-nav btn-warning" @onclick="HandleRestoreAsync" disabled="@fileBusy">
             <i class="bi bi-arrow-counterclockwise"></i> Restore
         </button>
         |
-        <button class="btn-nav btn-dark" @onclick="HandleDashboardExportAsync">
+        <button class="btn-nav btn-dark" @onclick="HandleDashboardExportAsync" disabled="@fileBusy">
             <i class="bi bi-file-earmark-pdf"></i> PDF
         </button>
         |
@@ -54,12 +57,6 @@
         </div>
     }
 
-    @if (!string.IsNullOrWhiteSpace(operationMessage))
-    {
-        <div class="alert @operationMessageClass mb-3" role="alert">
-            @operationMessage
-        </div>
-    }
 
     @if (accounts == null)
     {

src/Duempelkas.App/Pages/Dashboard.razor.cs

@@ -17,9 +17,9 @@ public partial class Dashboard
     private int? selectedYear = DateTime.Now.Year;
     private List<int> availableYears = [];
     private string clubName = string.Empty;
-    private string? operationMessage;
-    private string operationMessageClass = "alert-info";
     private string? savedPdfPath;
+    private FileOperationResult? fileResult;
+    private bool fileBusy;
     private string currentTheme = "light";
 
     #endregion
@@ -100,11 +100,16 @@ public partial class Dashboard
 
     private async Task HandleBackupAsync()
     {
-        var message = await BackupService.CreateBackupAsync();
+        if (fileBusy) return;
-        if (message.Contains("fehlgeschlagen", StringComparison.OrdinalIgnoreCase))
+        fileBusy = true;
+        fileResult = null;
+        try
         {
-            SetOperationMessage(message, false);
+            fileResult = await BackupService.CreateBackupAsync();
+
         }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private Task HandleRestoreAsync()
@@ -119,26 +124,37 @@ public partial class Dashboard
     }
 
     private async Task HandleConfirmRestore()
+    {
+        if (fileBusy) return;
+        fileBusy = true;
+        fileResult = null;
+        try
         {
             showRestoreConfirm = false;
-        var message = await BackupService.RestoreBackupAsync();
+            fileResult = await BackupService.RestoreBackupAsync();
-        var isSuccess = message.StartsWith("Wiederherstellung erfolgreich", StringComparison.OrdinalIgnoreCase);
+            if (fileResult.Status == FileOperationStatus.Success) await LoadAll();
 
-        if (isSuccess)
-        {
-            NavigationManager.NavigateTo("/", forceLoad: true);
-        }
-        else
-        {
-            SetOperationMessage(message, isSuccess);
         }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private async Task HandleDashboardExportAsync()
+    {
+        if (fileBusy) return;
+        fileBusy = true;
+        fileResult = null;
+        try
         {
         var pdf = await PdfStatementService.GenerateDashboardStatementAsync(selectedYear);
         var suffix = selectedYear.HasValue ? $"_{selectedYear.Value}" : "_Gesamt";
-        savedPdfPath = await FileSaveService.SaveFileAsync(pdf, $"{DisplayClubName}_Übersicht{suffix}.pdf");
+        fileResult = await FileSaveService.SaveFileAsync(pdf, $"{DisplayClubName}_Übersicht{suffix}.pdf");
+
+            savedPdfPath = fileResult.Status == FileOperationStatus.Success ? fileResult.Path : null;
+
+        }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private void OpenYearFilterDialog()
@@ -159,13 +175,22 @@ public partial class Dashboard
     }
 
     private async Task HandleOpenSavedPdf()
+    {
+        if (fileBusy) return;
+        fileBusy = true;
+        fileResult = null;
+        try
         {
         if (!string.IsNullOrWhiteSpace(savedPdfPath))
         {
-            await FileSaveService.OpenFileAsync(savedPdfPath);
+            fileResult = await FileSaveService.OpenFileAsync(savedPdfPath);
         }
 
         savedPdfPath = null;
+
+        }
+        catch (Exception ex) { fileResult = FileOperationResult.Error(ex); }
+        finally { fileBusy = false; }
     }
 
     private void CancelOpenSavedPdf()
@@ -177,12 +202,6 @@ public partial class Dashboard
 
     #region Helpers
 
-    private void SetOperationMessage(string message, bool success)
-    {
-        operationMessage = message;
-        operationMessageClass = success ? "alert-success" : "alert-danger";
-    }
-
     private static string FormatCurrency(decimal amount)
     {
         return amount.ToString("N2", CultureInfo.GetCultureInfo("de-DE")) + " €";

src/Duempelkas.App/Services/IBackupService.cs

@@ -1,7 +1,9 @@
+using Duempelkas.App.Services.Models;
+
 namespace Duempelkas.App.Services;
 
 public interface IBackupService
 {
-    Task<string> CreateBackupAsync();
+    Task<FileOperationResult> CreateBackupAsync();
-    Task<string> RestoreBackupAsync();
+    Task<FileOperationResult> RestoreBackupAsync();
 }

src/Duempelkas.App/Services/IFileDialogService.cs

@@ -0,0 +1,7 @@
+namespace Duempelkas.App.Services;
+
+public interface IFileDialogService
+{
+    Task<string?> SaveAsync(string suggestedFileName);
+    Task<string?> OpenBackupAsync();
+}

src/Duempelkas.App/Services/IFileSaveService.cs

@@ -1,7 +1,10 @@
+using Duempelkas.App.Services.Models;
+
 namespace Duempelkas.App.Services;
 
 public interface IFileSaveService
 {
-    Task<string?> SaveFileAsync(byte[] content, string suggestedFileName);
+    Task<FileOperationResult> SaveFileAsync(byte[] content, string suggestedFileName);
-    Task OpenFileAsync(string filePath);
+    Task<FileOperationResult> OpenFileAsync(string filePath);
+    Task<FileOperationResult> OpenFolderAsync(string filePath);
 }

src/Duempelkas.App/Services/Models/FileOperationResult.cs

@@ -0,0 +1,10 @@
+namespace Duempelkas.App.Services.Models;
+
+public enum FileOperationStatus { Success, Cancelled, Error }
+
+public sealed record FileOperationResult(FileOperationStatus Status, string Message, string? Path = null, string? Details = null)
+{
+    public static FileOperationResult Cancelled() => new(FileOperationStatus.Cancelled, "Vorgang abgebrochen. Es wurde nichts geändert.");
+    public static FileOperationResult Error(Exception error) => new(FileOperationStatus.Error,
+        "Die Dateiaktion konnte nicht abgeschlossen werden. Bitte den Speicherort und die Zugriffsrechte prüfen oder einen anderen Speicherort wählen.", Details: error.Message);
+}

src/Duempelkas.Infrastructure/DependencyInjection.cs

@@ -20,6 +20,7 @@ public static class DependencyInjection
         services.AddScoped<IEntryService, EntryService>();
         services.AddScoped<IBalanceQueryService, BalanceQueryService>();
         services.AddScoped<IPdfStatementService, PdfStatementService>();
+        services.AddSingleton<IFileDialogService, FileDialogService>();
         services.AddScoped<IFileSaveService, FileSaveService>();
         services.AddSingleton<IBackupService, BackupService>();
         services.AddSingleton<ISettingsService, SettingsService>();

src/Duempelkas.Infrastructure/Services/BackupService.cs

@@ -1,3 +1,4 @@
+using Duempelkas.App.Services.Models;
 using System.Diagnostics;
 using System.Runtime.InteropServices;
 using Duempelkas.App.Services;
@@ -9,30 +10,35 @@ public class BackupService : IBackupService
 {
     private readonly DatabaseLocation location;
 
-    public BackupService(DatabaseLocation location) => this.location = location;
+    private readonly IFileDialogService dialogs;
+    public BackupService(DatabaseLocation location, IFileDialogService? dialogs = null)
+    {
+        this.location = location;
+        this.dialogs = dialogs ?? new FileDialogService();
+    }
 
-    public async Task<string> CreateBackupAsync()
+    public async Task<FileOperationResult> CreateBackupAsync()
     {
         try
         {
-            var path = await ShowSaveDialogAsync($"duempelkas-backup-{DateTime.Now:yyyyMMdd-HHmmss}.bak");
+            var path = await dialogs.SaveAsync($"duempelkas-backup-{DateTime.Now:yyyyMMdd-HHmmss}.bak");
-            if (string.IsNullOrWhiteSpace(path)) return "Sicherung wurde abgebrochen.";
+            if (string.IsNullOrWhiteSpace(path)) return FileOperationResult.Cancelled();
             await CreateBackupToAsync(path);
-            return $"Sicherung gespeichert: {path}";
+            return new(FileOperationStatus.Success, "Sicherung gespeichert.", path);
         }
-        catch (Exception ex) { return $"Sicherung fehlgeschlagen: {ex.Message}"; }
+        catch (Exception ex) { return FileOperationResult.Error(ex); }
     }
 
-    public async Task<string> RestoreBackupAsync()
+    public async Task<FileOperationResult> RestoreBackupAsync()
     {
         try
         {
-            var path = await ShowOpenDialogAsync();
+            var path = await dialogs.OpenBackupAsync();
-            if (string.IsNullOrWhiteSpace(path)) return "Wiederherstellung wurde abgebrochen.";
+            if (string.IsNullOrWhiteSpace(path)) return FileOperationResult.Cancelled();
             var fallback = await RestoreFromAsync(path);
-            return $"Wiederherstellung erfolgreich. Rückfallsicherung: {fallback}";
+            return new(FileOperationStatus.Success, "Sicherung zurückgespielt. Die bisherigen Daten liegen in der Rückfallsicherung:", fallback);
         }
-        catch (Exception ex) { return $"Wiederherstellung fehlgeschlagen: {ex.Message}"; }
+        catch (Exception ex) { return FileOperationResult.Error(ex); }
     }
 
     public async Task CreateBackupToAsync(string path)
@@ -124,74 +130,4 @@ public class BackupService : IBackupService
         _ = db.TransferLinks.ToArray();
     }
 
-    private static Task<string?> ShowSaveDialogAsync(string suggestedFileName)
-    {
-        return Task.Run(() =>
-        {
-            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
-                return Path.Combine(documentsPath, suggestedFileName);
-            }
-
-            var script = $@"
-Add-Type -AssemblyName System.Windows.Forms
-$dialog = New-Object System.Windows.Forms.SaveFileDialog
-$dialog.Filter = 'Backup-Dateien (*.bak)|*.bak'
-$dialog.DefaultExt = 'bak'
-$dialog.AddExtension = $true
-$dialog.OverwritePrompt = $true
-$dialog.FileName = '{suggestedFileName.Replace("'", "''")}'
-$dialog.Title = 'Backup speichern'
-if ($dialog.ShowDialog() -eq 'OK') {{ $dialog.FileName }} else {{ '' }}
-";
-
-            return RunPowerShellDialog(script);
-        });
-    }
-
-    private static Task<string?> ShowOpenDialogAsync()
-    {
-        return Task.Run(() =>
-        {
-            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                return null;
-            }
-
-            var script = @"
-Add-Type -AssemblyName System.Windows.Forms
-$dialog = New-Object System.Windows.Forms.OpenFileDialog
-$dialog.Filter = 'Backup-Dateien (*.bak)|*.bak'
-$dialog.Multiselect = $false
-$dialog.Title = 'Backup auswählen'
-if ($dialog.ShowDialog() -eq 'OK') { $dialog.FileName } else { '' }
-";
-
-            return RunPowerShellDialog(script);
-        });
-    }
-
-    private static string? RunPowerShellDialog(string script)
-    {
-        var psi = new ProcessStartInfo
-        {
-            FileName = "powershell",
-            Arguments = $"-NoProfile -Command \"{script.Replace("\"", "\\\"") }\"",
-            RedirectStandardOutput = true,
-            UseShellExecute = false,
-            CreateNoWindow = true
-        };
-
-        using var process = Process.Start(psi);
-        if (process == null)
-        {
-            return null;
-        }
-
-        var result = process.StandardOutput.ReadToEnd().Trim();
-        process.WaitForExit();
-
-        return string.IsNullOrWhiteSpace(result) ? null : result;
-    }
 }

src/Duempelkas.Infrastructure/Services/FileDialogService.cs

@@ -0,0 +1,44 @@
+using System.Diagnostics;
+using System.Text;
+using Duempelkas.App.Services;
+
+namespace Duempelkas.Infrastructure.Services;
+
+public sealed class FileDialogService : IFileDialogService
+{
+    public Task<string?> SaveAsync(string suggestedFileName) => ShowAsync(suggestedFileName);
+    public Task<string?> OpenBackupAsync() => ShowAsync(null);
+
+    private static Task<string?> ShowAsync(string? suggestedFileName) => Task.Run(() =>
+    {
+        if (!OperatingSystem.IsWindows())
+            throw new PlatformNotSupportedException("Der Dateidialog ist auf diesem System nicht verfügbar.");
+        var save = suggestedFileName != null;
+        var extension = save ? (Path.GetExtension(suggestedFileName) ?? "") : ".bak";
+        var script = $$"""
+            $ErrorActionPreference = 'Stop'
+            [Console]::OutputEncoding = [System.Text.UTF8Encoding]::new($false)
+            Add-Type -AssemblyName System.Windows.Forms
+            $dialog = New-Object System.Windows.Forms.{{(save ? "SaveFileDialog" : "OpenFileDialog")}}
+            $dialog.Filter = 'Dateien (*{{extension.Replace("'", "''")}})|*{{extension.Replace("'", "''")}}'
+            $dialog.Title = '{{(save ? "Datei speichern" : "Sicherung auswählen")}}'
+            {{(save ? "$dialog.OverwritePrompt = $true\n$dialog.AddExtension = $true\n$dialog.DefaultExt = '" + extension.TrimStart('.').Replace("'", "''") + "'\n$dialog.FileName = '" + suggestedFileName!.Replace("'", "''") + "'" : "$dialog.Multiselect = $false")}}
+            try { if ($dialog.ShowDialog() -eq 'OK') { [Console]::Write($dialog.FileName) } } finally { $dialog.Dispose() }
+            """;
+        var start = new ProcessStartInfo("powershell.exe")
+        {
+            RedirectStandardOutput = true, RedirectStandardError = true,
+            StandardOutputEncoding = Encoding.UTF8, UseShellExecute = false, CreateNoWindow = true
+        };
+        start.ArgumentList.Add("-NoProfile");
+        start.ArgumentList.Add("-STA");
+        start.ArgumentList.Add("-EncodedCommand");
+        start.ArgumentList.Add(Convert.ToBase64String(Encoding.Unicode.GetBytes(script)));
+        using var process = Process.Start(start) ?? throw new IOException("Der Dateidialog konnte nicht gestartet werden.");
+        var output = process.StandardOutput.ReadToEnd();
+        var error = process.StandardError.ReadToEnd();
+        process.WaitForExit();
+        if (process.ExitCode != 0) throw new IOException("Der Dateidialog konnte nicht geöffnet werden. " + error);
+        return string.IsNullOrWhiteSpace(output) ? null : output;
+    });
+}

src/Duempelkas.Infrastructure/Services/FileSaveService.cs

@@ -1,90 +1,49 @@
+using Duempelkas.App.Services.Models;
 using System.Diagnostics;
 using System.Runtime.InteropServices;
 using Duempelkas.App.Services;
 
 namespace Duempelkas.Infrastructure.Services;
 
-public class FileSaveService : IFileSaveService
+public class FileSaveService(IFileDialogService dialogs) : IFileSaveService
 {
-    public async Task<string?> SaveFileAsync(byte[] content, string suggestedFileName)
+    public async Task<FileOperationResult> SaveFileAsync(byte[] content, string suggestedFileName)
     {
-        var filePath = await ShowSaveDialogAsync(suggestedFileName);
+        string? staged = null;
-        if (filePath == null) return null;
+        try
-
+        {
-        await File.WriteAllBytesAsync(filePath, content);
+            var path = await dialogs.SaveAsync(suggestedFileName);
-        return filePath;
+            if (string.IsNullOrWhiteSpace(path)) return FileOperationResult.Cancelled();
+            staged = path + $".{Guid.NewGuid():N}.tmp";
+            await File.WriteAllBytesAsync(staged, content);
+            File.Move(staged, path, overwrite: true);
+            return new(FileOperationStatus.Success, "Datei gespeichert.", path);
+        }
+        catch (Exception ex) { return FileOperationResult.Error(ex); }
+        finally { try { if (staged != null && File.Exists(staged)) File.Delete(staged); } catch { } }
     }
 
-    public Task OpenFileAsync(string filePath)
+    public Task<FileOperationResult> OpenFileAsync(string filePath) => OpenAsync(filePath, false);
-    {
+    public Task<FileOperationResult> OpenFolderAsync(string filePath) => OpenAsync(filePath, true);
-        if (string.IsNullOrWhiteSpace(filePath) || !File.Exists(filePath))
-        {
-            return Task.CompletedTask;
-        }
 
-        return Task.Run(() =>
+    private static Task<FileOperationResult> OpenAsync(string filePath, bool folder) => Task.Run(() =>
     {
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+        try
         {
-                Process.Start(new ProcessStartInfo
+            var path = folder ? Path.GetDirectoryName(Path.GetFullPath(filePath))! : filePath;
+            if (folder ? !Directory.Exists(path) : !File.Exists(path))
+                throw new FileNotFoundException("Der gespeicherte Pfad ist nicht mehr vorhanden.");
+            var start = new ProcessStartInfo { UseShellExecute = true };
+            if (OperatingSystem.IsWindows()) start.FileName = path;
+            else { start.FileName = OperatingSystem.IsMacOS() ? "open" : "xdg-open"; start.ArgumentList.Add(path); }
+            using var process = Process.Start(start) ?? throw new IOException("Kein Programm zum Öffnen gefunden.");
+            return new FileOperationResult(FileOperationStatus.Success, folder ? "Ordner geöffnet." : "Datei geöffnet.");
+        }
+        catch (Exception ex)
         {
-                    FileName = filePath,
+            return new FileOperationResult(FileOperationStatus.Error,
-                    UseShellExecute = true
+                "Der Pfad konnte nicht geöffnet werden. Die gespeicherte Datei bleibt erhalten; bitte den Speicherort im Datei-Explorer öffnen.", filePath, ex.Message);
+        }
     });
 
-                return;
-            }
-
-            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
-            {
-                Process.Start("open", filePath);
-                return;
-            }
-
-            Process.Start("xdg-open", filePath);
-        });
-    }
-
-    private static Task<string?> ShowSaveDialogAsync(string suggestedFileName)
-    {
-        return Task.Run(() =>
-        {
-            if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
-            {
-                // Fallback: save to Documents folder
-                var documentsPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
-                return Path.Combine(documentsPath, suggestedFileName);
-            }
-
-            var extension = Path.GetExtension(suggestedFileName);
-            var filterName = extension == ".pdf" ? "PDF-Dateien" : "Dateien";
-            var filter = $"{filterName} (*{extension})|*{extension}|Alle Dateien (*.*)|*.*";
-
-            var script = $@"
-Add-Type -AssemblyName System.Windows.Forms
-$dialog = New-Object System.Windows.Forms.SaveFileDialog
-$dialog.Filter = '{filter}'
-$dialog.FileName = '{suggestedFileName.Replace("'", "''")}'
-$dialog.Title = 'Datei speichern'
-if ($dialog.ShowDialog() -eq 'OK') {{ $dialog.FileName }} else {{ '' }}
-";
-
-            var psi = new ProcessStartInfo
-            {
-                FileName = "powershell",
-                Arguments = $"-NoProfile -Command \"{script.Replace("\"", "\\\"\"")}\"",
-                RedirectStandardOutput = true,
-                UseShellExecute = false,
-                CreateNoWindow = true
-            };
-
-            using var process = Process.Start(psi);
-            if (process == null) return null;
-
-            var result = process.StandardOutput.ReadToEnd().Trim();
-            process.WaitForExit();
-
-            return string.IsNullOrWhiteSpace(result) ? null : result;
-        });
-    }
 }

tests/Duempelkas.Tests/FileOperationTests.cs

@@ -0,0 +1,41 @@
+using Duempelkas.App.Services;
+using Duempelkas.App.Services.Models;
+using Duempelkas.Infrastructure.Services;
+using Xunit;
+
+namespace Duempelkas.Tests;
+
+public class FileOperationTests
+{
+    [Fact]
+    public async Task Cancel_IsNeutral()
+    {
+        var service = new FileSaveService(new Dialog(null));
+        Assert.Equal(FileOperationStatus.Cancelled, (await service.SaveFileAsync([1], "test.pdf")).Status);
+    }
+
+    [Fact]
+    public async Task SaveAndFailure_AreDistinct_AndOpeningMissingFileIsError()
+    {
+        var folder = Path.Combine(Path.GetTempPath(), "duempelkas-files-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(folder);
+        try
+        {
+            var path = Path.Combine(folder, "Prüfung.pdf");
+            var service = new FileSaveService(new Dialog(path));
+            Assert.Equal(FileOperationStatus.Success, (await service.SaveFileAsync([1, 2, 3], "test.pdf")).Status);
+            Assert.Equal(new byte[] { 1, 2, 3 }, await File.ReadAllBytesAsync(path));
+            // A directory cannot be overwritten as a file; the existing file is preserved.
+            Assert.Equal(FileOperationStatus.Error, (await new FileSaveService(new Dialog(folder)).SaveFileAsync([4], "test.pdf")).Status);
+            Assert.Equal(FileOperationStatus.Error, (await service.OpenFileAsync(Path.Combine(folder, "missing.pdf"))).Status);
+            Assert.Equal(new byte[] { 1, 2, 3 }, await File.ReadAllBytesAsync(path));
+        }
+        finally { Directory.Delete(folder, true); }
+    }
+
+    private sealed class Dialog(string? path) : IFileDialogService
+    {
+        public Task<string?> SaveAsync(string suggestedFileName) => Task.FromResult(path);
+        public Task<string?> OpenBackupAsync() => Task.FromResult(path);
+    }
+}