Add ModelContextProtocol.Core package (#428)

src/ModelContextProtocol/DefaultMcpServerBuilder.cs

@@ -0,0 +1,28 @@
+using ModelContextProtocol;
+
+namespace Microsoft.Extensions.DependencyInjection;
+
+/// <summary>
+/// Default implementation of <see cref="IMcpServerBuilder"/> that enables fluent configuration
+/// of the Model Context Protocol (MCP) server. This builder is returned by the
+/// <see cref="McpServerServiceCollectionExtensions.AddMcpServer"/> extension method and
+/// provides access to the service collection for registering additional MCP components.
+/// </summary>
+internal sealed class DefaultMcpServerBuilder : IMcpServerBuilder
+{
+    /// <inheritdoc/>
+    public IServiceCollection Services { get; }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="DefaultMcpServerBuilder"/> class.
+    /// </summary>
+    /// <param name="services">The service collection to which MCP server services will be added. This collection
+    /// is exposed through the <see cref="Services"/> property to allow additional configuration.</param>
+    /// <exception cref="ArgumentNullException">Thrown when <paramref name="services"/> is null.</exception>
+    public DefaultMcpServerBuilder(IServiceCollection services)
+    {
+        Throw.IfNull(services);
+
+        Services = services;
+    }
+}