feat(sender-editor): consume bootstrap payload and auto-save draft

Accept bootstrapToken query parameter and consume one-time payload from sessionStorage-backed service.

Hydrate editor state with title, message, envelope type, receivers, and PDF document from bootstrap data.

Refactor draft save into reusable core flow and trigger non-navigating auto-save after bootstrap is applied.

Prevent stale token replay by clearing query token from URL and handling invalid tokens gracefully.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/SenderEditorPage.razor

@@ -21,6 +21,7 @@
 @inject ReceiverService ReceiverService
 @inject EnvelopeService EnvelopeService
 @inject EnvelopeTypeService EnvelopeTypeService
+@inject CreateEnvelopeBootstrapStorageService CreateEnvelopeBootstrapStorageService
 @inject AuthService AuthService
 @inject IStringLocalizer<Resource> UiLocalizer
 @inject IStringLocalizer<Model> ModelLocalizer
@@ -589,6 +590,9 @@
     [SupplyParameterFromQuery(Name = "envelopeId")]
     public int? EnvelopeId { get; set; }
 
+    [SupplyParameterFromQuery(Name = "bootstrapToken")]
+    public string? BootstrapToken { get; set; }
+
     // ── Constants ──
     // Signature field size in PDF points (fixed): 1.77" × 1.96"
     const double SigWidthPt = 1.77 * 72;   // 127.44 pt
@@ -609,6 +613,8 @@
     int? _loadedEnvelopeId;
     int? _editingEnvelopeId;
     bool _isLoadingEnvelopeForEdit;
+    bool _bootstrapApplied;
+    string? _pendingBootstrapToken;
 
     List<SignatureFieldDraft> _signatureFields = [];
     ReceiverDraft? _pendingReceiverForPlacement; // Set when user clicks "Signatur hinzufügen"
@@ -629,6 +635,7 @@
     string _saveSuccessTitle = "Vorgang erfolgreich abgeschlossen.";
     string _saveSuccessBody = string.Empty;
     bool _saveNavigateToDashboard = false;
+    bool _saveDraftAfterBootstrap;
 
     // ── Envelope metadata ──
     string _envelopeTitle = string.Empty;
@@ -697,6 +704,9 @@
         if (EnvelopeId.HasValue && EnvelopeId.Value > 0)
             _editingEnvelopeId = EnvelopeId.Value;
 
+        if (!IsEditMode && !_bootstrapApplied && !string.IsNullOrWhiteSpace(BootstrapToken))
+            _pendingBootstrapToken = BootstrapToken;
+
         if (IsEditMode && _loadedEnvelopeId != EnvelopeId)
         {
             await LoadEnvelopeForEditAsync(EnvelopeId!.Value);
@@ -707,15 +717,91 @@
             return;
     }
 
-    protected override Task OnAfterRenderAsync(bool firstRender)
+    async Task TryApplyBootstrapAsync(string token)
+    {
+        var payload = await CreateEnvelopeBootstrapStorageService.ConsumeAsync(token);
+        _bootstrapApplied = true;
+
+        if (payload is null)
+        {
+            NavigationManager.NavigateTo("/sender/editor", replace: true);
+            return;
+        }
+
+        _envelopeTitle = payload.Title ?? string.Empty;
+        _envelopeMessage = payload.Message ?? string.Empty;
+        _selectedEnvelopeTypeId = payload.EnvelopeTypeId;
+        _language = string.IsNullOrWhiteSpace(payload.Language) ? "de-DE" : payload.Language;
+
+        _receivers = payload.Receivers
+            .Select((receiver, index) => new ReceiverDraft(
+                Guid.NewGuid(),
+                receiver.FullName,
+                receiver.EmailAddress,
+                string.Empty,
+                ReceiverPalette[index % ReceiverPalette.Length]))
+            .ToList();
+
+        _originalPdfBytes = payload.DocumentBytes;
+        _fileName = string.IsNullOrWhiteSpace(payload.DocumentFileName) ? "document.pdf" : payload.DocumentFileName;
+        _pdfLoaded = _originalPdfBytes is { Length: > 0 };
+
+        _signatureFields.Clear();
+        _pendingReceiverForPlacement = null;
+
+        _saveDraftAfterBootstrap = true;
+
+        if (_pdfLoaded && _originalPdfBytes is not null)
+        {
+            try
+            {
+                _pagePreviews = (await PdfRenderService.RenderPagesAsync(_originalPdfBytes))
+                    .OrderBy(p => p.PageNumber)
+                    .ToList();
+            }
+            catch (Exception ex)
+            {
+                Logger.LogWarning(ex, "Failed to render bootstrap PDF previews.");
+                _pagePreviews = [];
+            }
+
+            _pageCount = _pagePreviews.Count > 0
+                ? _pagePreviews.Count
+                : EstimatePdfPageCount(_originalPdfBytes) ?? 1;
+        }
+        else
+        {
+            _pagePreviews = [];
+            _pageCount = 0;
+        }
+
+        NavigationManager.NavigateTo("/sender/editor", replace: true);
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
     {
         if (firstRender)
         {
             _isPageReady = true;
-            StateHasChanged();
+            await InvokeAsync(StateHasChanged);
         }
 
-        return Task.CompletedTask;
+        if (!OperatingSystem.IsBrowser())
+            return;
+
+        if (_saveDraftAfterBootstrap && !_isSaving)
+        {
+            _saveDraftAfterBootstrap = false;
+            await SaveDraftAndStayOnEditorAsync();
+            return;
+        }
+
+        if (!IsEditMode && !_bootstrapApplied && !string.IsNullOrWhiteSpace(_pendingBootstrapToken))
+        {
+            var token = _pendingBootstrapToken;
+            _pendingBootstrapToken = null;
+            await TryApplyBootstrapAsync(token);
+        }
     }
 
     async Task LoadEnvelopeForEditAsync(int envelopeId)
@@ -1108,12 +1194,17 @@
     }
 
     async Task SaveDraftAsync()
+    {
+        await SaveDraftCoreAsync(navigateToDashboard: true);
+    }
+
+    async Task<int?> SaveDraftCoreAsync(bool navigateToDashboard)
     {
         if (!ValidateSettings(out var settingsError))
         {
             _saveErrorMessage = settingsError;
             _savePopupVisible = true;
-            return;
+            return null;
         }
 
         _isSaving = true;
@@ -1134,25 +1225,37 @@
             _loadedEnvelopeId = result.Id;
             _editingEnvelopeId = result.Id;
 
-            if (previousEnvelopeId != result.Id)
+            if (navigateToDashboard)
+            {
+                NavigationManager.NavigateTo("/sender", forceLoad: false);
+            }
+            else if (previousEnvelopeId != result.Id)
             {
                 NavigationManager.NavigateTo($"/sender/editor?envelopeId={result.Id}", forceLoad: false);
             }
 
-            NavigationManager.NavigateTo("/sender", forceLoad: false);
+            return result.Id;
         }
         catch (Exception ex)
         {
             Logger.LogError(ex, "[SenderEditor] Failed to save draft");
             _saveErrorMessage = ex.Message;
             _savePopupVisible = true;
+            return null;
         }
         finally
         {
             _isSaving = false;
+            await InvokeAsync(StateHasChanged);
         }
     }
 
+    async Task SaveDraftAndStayOnEditorAsync()
+    {
+        Logger.LogInformation("[SenderEditor] Trigger bootstrap draft save.");
+        await SaveDraftCoreAsync(navigateToDashboard: false);
+    }
+
     // ── Send envelope ──
     async Task SendAsync()
     {