test(aspnetcore): add DI resolution assertions to extension tests

Verify IExceptionHandler actually resolves from the container, not just
that descriptors are registered. Covers all 3 WebApplicationBuilder
overloads and idempotency with manual AddExceptionlessExceptionHandler.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: niemyjski

test/Exceptionless.Tests/Platforms/AspNetCoreExtensionsTests.cs

@@ -1,10 +1,12 @@
 #if NET10_0_OR_GREATER
+using System;
 using Exceptionless;
 using Exceptionless.AspNetCore;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Diagnostics;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 using Xunit;
 
 namespace Exceptionless.Tests.Platforms {
@@ -53,6 +55,63 @@ public void AddExceptionless_WhenCalledWithoutArguments_RegistersClientConfigura
                 descriptor.ServiceType == typeof(IExceptionHandler) &&
                 descriptor.ImplementationType == typeof(ExceptionlessExceptionHandler));
         }
+
+        [Fact]
+        public void WebApplicationBuilder_AddExceptionless_RegistersExceptionHandlerAndResolvesFromDI() {
+            // Arrange
+            var builder = WebApplication.CreateBuilder();
+
+            // Act
+            builder.AddExceptionless();
+
+            // Assert — descriptors registered
+            Assert.Contains(builder.Services, descriptor => descriptor.ServiceType == typeof(ExceptionlessClient));
+            Assert.Contains(builder.Services, descriptor =>
+                descriptor.ServiceType == typeof(IExceptionHandler) &&
+                descriptor.ImplementationType == typeof(ExceptionlessExceptionHandler));
+
+            // Assert — actually resolves from the container
+            using var provider = builder.Services.BuildServiceProvider();
+            var handlers = provider.GetServices<IExceptionHandler>();
+            Assert.Contains(handlers, h => h is ExceptionlessExceptionHandler);
+        }
+
+        [Fact]
+        public void WebApplicationBuilder_AddExceptionless_WithApiKey_RegistersAndResolves() {
+            var builder = WebApplication.CreateBuilder();
+            builder.AddExceptionless("test-api-key");
+
+            using var provider = builder.Services.BuildServiceProvider();
+            var client = provider.GetRequiredService<ExceptionlessClient>();
+            Assert.NotNull(client);
+
+            var handlers = provider.GetServices<IExceptionHandler>();
+            Assert.Contains(handlers, h => h is ExceptionlessExceptionHandler);
+        }
+
+        [Fact]
+        public void WebApplicationBuilder_AddExceptionless_WithConfigure_RegistersAndResolves() {
+            var builder = WebApplication.CreateBuilder();
+            builder.AddExceptionless(c => c.DefaultData["test"] = "value");
+
+            using var provider = builder.Services.BuildServiceProvider();
+            var client = provider.GetRequiredService<ExceptionlessClient>();
+            Assert.NotNull(client);
+
+            var handlers = provider.GetServices<IExceptionHandler>();
+            Assert.Contains(handlers, h => h is ExceptionlessExceptionHandler);
+        }
+
+        [Fact]
+        public void WebApplicationBuilder_AddExceptionless_ThenManualCall_DoesNotDuplicate() {
+            var builder = WebApplication.CreateBuilder();
+            builder.AddExceptionless();
+            builder.Services.AddExceptionlessExceptionHandler();
+
+            Assert.Single(builder.Services, descriptor =>
+                descriptor.ServiceType == typeof(IExceptionHandler) &&
+                descriptor.ImplementationType == typeof(ExceptionlessExceptionHandler));
+        }
     }
 }
 #endif