Log tool invocation errors (#447)

* Log tool errors
* add test and implement source generated logging

tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs

@@ -1,7 +1,9 @@
 using Microsoft.Extensions.AI;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
+using ModelContextProtocol.Tests.Utils;
 using Moq;
 using System.Reflection;
 using System.Text.Json;
@@ -381,6 +383,45 @@ public partial class McpServerToolTests
         );
     }
 
+    [Fact]
+    public async Task ToolCallError_LogsErrorMessage()
+    {
+        // Arrange
+        var mockLoggerProvider = new MockLoggerProvider();
+        var loggerFactory = new LoggerFactory(new[] { mockLoggerProvider });
+        var services = new ServiceCollection();
+        services.AddSingleton<ILoggerFactory>(loggerFactory);
+        var serviceProvider = services.BuildServiceProvider();
+
+        var toolName = "tool-that-throws";
+        var exceptionMessage = "Test exception message";
+
+        McpServerTool tool = McpServerTool.Create(() =>
+        {
+            throw new InvalidOperationException(exceptionMessage);
+        }, new() { Name = toolName, Services = serviceProvider });
+
+        var mockServer = new Mock<IMcpServer>();
+        var request = new RequestContext<CallToolRequestParams>(mockServer.Object)
+        {
+            Params = new CallToolRequestParams() { Name = toolName },
+            Services = serviceProvider
+        };
+
+        // Act
+        var result = await tool.InvokeAsync(request, TestContext.Current.CancellationToken);
+
+        // Assert
+        Assert.True(result.IsError);
+        Assert.Single(result.Content);
+        Assert.Equal($"An error occurred invoking '{toolName}'.", result.Content[0].Text);
+
+        var errorLog = Assert.Single(mockLoggerProvider.LogMessages, m => m.LogLevel == LogLevel.Error);
+        Assert.Equal($"\"{toolName}\" threw an unhandled exception.", errorLog.Message);
+        Assert.IsType<InvalidOperationException>(errorLog.Exception);
+        Assert.Equal(exceptionMessage, errorLog.Exception.Message);
+    }
+
     private sealed class MyService;
 
     private class DisposableToolType : IDisposable