Expand test coverage to match specs

Endpoints/EndpointHelpers.cs

@@ -91,7 +91,7 @@ internal static class EndpointHelpers
                || path.EndsWith(".gif") || path.EndsWith(".webp") || path.EndsWith(".avif");
     }
 
-    public static async Task<bool> IsReachableImageAsync(string? url, IHttpClientFactory httpFactory, CancellationToken ct = default)
+    public static async Task<bool> IsReachableImageAsync(string? url, IHttpClientFactory httpFactory, HttpMessageHandler? handler = null, CancellationToken ct = default)
     {
         if (string.IsNullOrWhiteSpace(url)) return true;
         if (!Uri.TryCreate(url, UriKind.Absolute, out var uri)) return false;
@@ -101,11 +101,9 @@ internal static class EndpointHelpers
         using var cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
         cts.CancelAfter(TimeSpan.FromSeconds(3));
 
-        var handler = new HttpClientHandler
-        {
-            AllowAutoRedirect = false
-        };
-        var client = new HttpClient(handler);
+        var client = handler is null
+            ? httpFactory.CreateClient("imageValidation")
+            : new HttpClient(handler, disposeHandler: false);
 
         try
         {
@@ -113,10 +111,10 @@ internal static class EndpointHelpers
             var headResp = await client.SendAsync(head, HttpCompletionOption.ResponseHeadersRead, cts.Token);
             if (headResp.IsSuccessStatusCode && headResp.StatusCode is not System.Net.HttpStatusCode.Redirect)
             {
+                if (headResp.Content.Headers.ContentLength is long headLen && headLen > MaxImageBytes) return false;
                 var ctHeader = headResp.Content.Headers.ContentType?.MediaType;
                 if (!string.IsNullOrWhiteSpace(ctHeader) && ctHeader.StartsWith("image/", StringComparison.OrdinalIgnoreCase))
                     return true;
-                if (headResp.Content.Headers.ContentLength is long len && len > MaxImageBytes) return false;
             }
         }
         catch { /* fallback */ }