Restructure IMcpEndpoint, IMcpClient, and IMcpServer (#723)

* Remove `McpEndpoint` & `IMcpClient`

* Revise naming, add abstract classes

* Fix missing renames

* Move extension methods to instance methods

* Add back old API, but obsoleted

* Add back obsoleted factory classes

* Move deprecation attributes

* `SseClientTransport` -> `HttpClientTransport`

* Update src/ModelContextProtocol.Core/Server/AugmentedServiceProvider.cs

Co-authored-by: Stephen Halter <halter73@gmail.com>

* PR feedback

* PR feedback

* Add back dispose lock

* Fix docs projects

* PR feedback

* Undo `docs/*.md` changes

---------

Co-authored-by: Stephen Halter <halter73@gmail.com>

src/ModelContextProtocol.Core/Protocol/ClientCapabilities.cs

@@ -44,7 +44,7 @@ public sealed class ClientCapabilities
     /// server requests for listing root URIs. Root URIs serve as entry points for resource navigation in the protocol.
     /// </para>
     /// <para>
-    /// The server can use <see cref="McpServerExtensions.RequestRootsAsync"/> to request the list of
+    /// The server can use <see cref="McpServer.RequestRootsAsync"/> to request the list of
     /// available roots from the client, which will trigger the client's <see cref="RootsCapability.RootsHandler"/>.
     /// </para>
     /// </remarks>
@@ -78,7 +78,7 @@ public sealed class ClientCapabilities
     /// </para>
     /// <para>
     /// Handlers provided via <see cref="NotificationHandlers"/> will be registered with the client for the lifetime of the client.
-    /// For transient handlers, <see cref="IMcpEndpoint.RegisterNotificationHandler"/> may be used to register a handler that can
+    /// For transient handlers, <see cref="McpSession.RegisterNotificationHandler"/> may be used to register a handler that can
     /// then be unregistered by disposing of the <see cref="IAsyncDisposable"/> returned from the method.
     /// </para>
     /// </remarks>

src/ModelContextProtocol.Core/Protocol/ITransport.cs

@@ -62,8 +62,8 @@ public interface ITransport : IAsyncDisposable
     /// </para>
     /// <para>
     /// This is a core method used by higher-level abstractions in the MCP protocol implementation.
-    /// Most client code should use the higher-level methods provided by <see cref="IMcpEndpoint"/>,
-    /// <see cref="McpEndpointExtensions"/>, <see cref="McpClientExtensions"/>, or <see cref="McpServerExtensions"/>,
+    /// Most client code should use the higher-level methods provided by <see cref="McpSession"/>,
+    /// <see cref="McpClient"/>, or <see cref="McpServer"/>,
     /// rather than accessing this method directly.
     /// </para>
     /// </remarks>

src/ModelContextProtocol.Core/Protocol/JsonRpcMessageContext.cs

@@ -29,7 +29,7 @@ public class JsonRpcMessageContext
     /// </summary>
     /// <remarks>
     /// This is used to support the Streamable HTTP transport in its default stateful mode. In this mode,
-    /// the <see cref="IMcpServer"/> outlives the initial HTTP request context it was created on, and new
+    /// the <see cref="McpServer"/> outlives the initial HTTP request context it was created on, and new
     /// JSON-RPC messages can originate from future HTTP requests. This allows the transport to flow the
     /// context with the JSON-RPC message. This is particularly useful for enabling IHttpContextAccessor
     /// in tool calls.

src/ModelContextProtocol.Core/Protocol/Reference.cs

@@ -12,7 +12,7 @@ namespace ModelContextProtocol.Protocol;
 /// </summary>
 /// <remarks>
 /// <para>
-/// References are commonly used with <see cref="McpClientExtensions.CompleteAsync"/> to request completion suggestions for arguments,
+/// References are commonly used with <see cref="McpClient.CompleteAsync"/> to request completion suggestions for arguments,
 /// and with other methods that need to reference resources or prompts.
 /// </para>
 /// <para>

src/ModelContextProtocol.Core/Protocol/SamplingCapability.cs

@@ -34,7 +34,7 @@ public sealed class SamplingCapability
     /// generated content.
     /// </para>
     /// <para>
-    /// You can create a handler using the <see cref="McpClientExtensions.CreateSamplingHandler"/> extension
+    /// You can create a handler using the <see cref="McpClient.CreateSamplingHandler"/> extension
     /// method with any implementation of <see cref="IChatClient"/>.
     /// </para>
     /// </remarks>

src/ModelContextProtocol.Core/Protocol/ServerCapabilities.cs

@@ -77,7 +77,7 @@ public sealed class ServerCapabilities
     /// </para>
     /// <para>
     /// Handlers provided via <see cref="NotificationHandlers"/> will be registered with the server for the lifetime of the server.
-    /// For transient handlers, <see cref="IMcpEndpoint.RegisterNotificationHandler"/> may be used to register a handler that can
+    /// For transient handlers, <see cref="McpSession.RegisterNotificationHandler"/> may be used to register a handler that can
     /// then be unregistered by disposing of the <see cref="IAsyncDisposable"/> returned from the method.
     /// </para>
     /// </remarks>