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/Client/HttpClientTransport.cs

@@ -0,0 +1,106 @@
+using Microsoft.Extensions.Logging;
+using ModelContextProtocol.Authentication;
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Client;
+
+/// <summary>
+/// Provides an <see cref="IClientTransport"/> over HTTP using the Server-Sent Events (SSE) or Streamable HTTP protocol.
+/// </summary>
+/// <remarks>
+/// This transport connects to an MCP server over HTTP using SSE or Streamable HTTP,
+/// allowing for real-time server-to-client communication with a standard HTTP requests.
+/// Unlike the <see cref="StdioClientTransport"/>, this transport connects to an existing server
+/// rather than launching a new process.
+/// </remarks>
+public sealed class HttpClientTransport : IClientTransport, IAsyncDisposable
+{
+    private readonly HttpClientTransportOptions _options;
+    private readonly McpHttpClient _mcpHttpClient;
+    private readonly ILoggerFactory? _loggerFactory;
+
+    private readonly HttpClient? _ownedHttpClient;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HttpClientTransport"/> class.
+    /// </summary>
+    /// <param name="transportOptions">Configuration options for the transport.</param>
+    /// <param name="loggerFactory">Logger factory for creating loggers used for diagnostic output during transport operations.</param>
+    public HttpClientTransport(HttpClientTransportOptions transportOptions, ILoggerFactory? loggerFactory = null)
+        : this(transportOptions, new HttpClient(), loggerFactory, ownsHttpClient: true)
+    {
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="HttpClientTransport"/> class with a provided HTTP client.
+    /// </summary>
+    /// <param name="transportOptions">Configuration options for the transport.</param>
+    /// <param name="httpClient">The HTTP client instance used for requests.</param>
+    /// <param name="loggerFactory">Logger factory for creating loggers used for diagnostic output during transport operations.</param>
+    /// <param name="ownsHttpClient">
+    /// <see langword="true"/> to dispose of <paramref name="httpClient"/> when the transport is disposed;
+    /// <see langword="false"/> if the caller is retaining ownership of the <paramref name="httpClient"/>'s lifetime.
+    /// </param>
+    public HttpClientTransport(HttpClientTransportOptions transportOptions, HttpClient httpClient, ILoggerFactory? loggerFactory = null, bool ownsHttpClient = false)
+    {
+        Throw.IfNull(transportOptions);
+        Throw.IfNull(httpClient);
+
+        _options = transportOptions;
+        _loggerFactory = loggerFactory;
+        Name = transportOptions.Name ?? transportOptions.Endpoint.ToString();
+
+        if (transportOptions.OAuth is { } clientOAuthOptions)
+        {
+            var oAuthProvider = new ClientOAuthProvider(_options.Endpoint, clientOAuthOptions, httpClient, loggerFactory);
+            _mcpHttpClient = new AuthenticatingMcpHttpClient(httpClient, oAuthProvider);
+        }
+        else
+        {
+            _mcpHttpClient = new(httpClient);
+        }
+
+        if (ownsHttpClient)
+        {
+            _ownedHttpClient = httpClient;
+        }
+    }
+
+    /// <inheritdoc />
+    public string Name { get; }
+
+    /// <inheritdoc />
+    public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken = default)
+    {
+        return _options.TransportMode switch
+        {
+            HttpTransportMode.AutoDetect => new AutoDetectingClientSessionTransport(Name, _options, _mcpHttpClient, _loggerFactory),
+            HttpTransportMode.StreamableHttp => new StreamableHttpClientSessionTransport(Name, _options, _mcpHttpClient, messageChannel: null, _loggerFactory),
+            HttpTransportMode.Sse => await ConnectSseTransportAsync(cancellationToken).ConfigureAwait(false),
+            _ => throw new InvalidOperationException($"Unsupported transport mode: {_options.TransportMode}"),
+        };
+    }
+
+    private async Task<ITransport> ConnectSseTransportAsync(CancellationToken cancellationToken)
+    {
+        var sessionTransport = new SseClientSessionTransport(Name, _options, _mcpHttpClient, messageChannel: null, _loggerFactory);
+
+        try
+        {
+            await sessionTransport.ConnectAsync(cancellationToken).ConfigureAwait(false);
+            return sessionTransport;
+        }
+        catch
+        {
+            await sessionTransport.DisposeAsync().ConfigureAwait(false);
+            throw;
+        }
+    }
+
+    /// <inheritdoc />
+    public ValueTask DisposeAsync()
+    {
+        _ownedHttpClient?.Dispose();
+        return default;
+    }
+}