Improve error handling and logging for envelope receiver

Added a null check in `EnvelopeReceiverPage.razor` to log a warning when `_envelopeReceiver` is null. Updated `ReportViewer.razor` to wrap `EnvelopeReceiverService.GetAsync` in a `try-catch` block, logging `HttpRequestException` errors and allowing the UI to handle null values gracefully.

Enhanced `EnvelopeReceiverService.GetAsync` to throw detailed `HttpRequestException` on API failures, including status code and reason phrase. Added `using System.Net;` to support HTTP-related classes. Updated method documentation to reflect the new behavior.

These changes improve error diagnostics, logging, and maintainability across the codebase.

EnvelopeGenerator.ReceiverUI/Pages/EnvelopeReceiverPage.razor

@@ -576,6 +576,10 @@ const int MaxThumbnailWidth = 400;
             _signatures = signatures.Convert(UnitOfLength.Point);
 
             _envelopeReceiver = await EnvelopeReceiverService.GetAsync(EnvelopeKey);
+            if (_envelopeReceiver is null)
+            {
+                logger.LogWarning("Envelope receiver data is null for envelope {EnvelopeKey}", EnvelopeKey);
+            }
 
             await JSRuntime.InvokeVoidAsync("console.log", "Loaded signatures:", _signatures);
 

EnvelopeGenerator.ReceiverUI/Pages/Example/ReportViewer.razor

@@ -343,7 +343,13 @@ Shown="OnPopupShownAsync">
         }
 
         _annotations = await AnnotationService.GetAnnotationsAsync(EnvelopeKey);
-        _envelopeReceiver = await EnvelopeReceiverService.GetAsync(EnvelopeKey);
+        
+        try {
+            _envelopeReceiver = await EnvelopeReceiverService.GetAsync(EnvelopeKey);
+        } catch (HttpRequestException ex) {
+            // Log error but continue - UI will handle null envelope receiver gracefully
+            Console.WriteLine($"Failed to load envelope receiver: {ex.Message}");
+        }
 
         if (!AppOptions.Value.UsePredefinedReports && !string.IsNullOrWhiteSpace(EnvelopeKey)) {
             try {

EnvelopeGenerator.ReceiverUI/Services/EnvelopeReceiverService.cs

@@ -1,3 +1,4 @@
+using System.Net;
 using System.Net.Http.Json;
 using System.Text.Json;
 using EnvelopeGenerator.ReceiverUI.Models;
@@ -14,13 +15,25 @@ public class EnvelopeReceiverService(HttpClient http, IOptions<ApiOptions> apiOp
 {
     private static readonly JsonSerializerOptions _jsonOptions = new(JsonSerializerDefaults.Web);
 
+    /// <summary>
+    /// Fetches the envelope receiver data for the given envelope key from the API.
+    /// Throws HttpRequestException on failure with appropriate status code.
+    /// </summary>
+    /// <exception cref="HttpRequestException">Thrown when the API request fails.</exception>
     public async Task<EnvelopeReceiverDto?> GetAsync(string envelopeKey, CancellationToken cancel = default)
     {
         var url = $"{apiOptions.Value.BaseUrl}/api/EnvelopeReceiver/{Uri.EscapeDataString(envelopeKey)}";
         var response = await http.GetAsync(url, cancel);
 
         if (!response.IsSuccessStatusCode)
-            return null;
+        {
+            var statusCode = (int)response.StatusCode;
+            var reasonPhrase = response.ReasonPhrase ?? "Unknown error";
+            throw new HttpRequestException(
+                $"Failed to load envelope receiver data. Status: {statusCode} ({reasonPhrase})",
+                null,
+                response.StatusCode);
+        }
 
         return await response.Content.ReadFromJsonAsync<EnvelopeReceiverDto>(_jsonOptions, cancel);
     }