Update signature and make test explicit

Author: localden

src/ModelContextProtocol/Protocol/Transport/SseClientTransport.cs

@@ -58,7 +58,10 @@ public SseClientTransport(SseClientTransportOptions transportOptions, HttpClient
     /// <param name="transportOptions">Configuration options for the transport.</param>
     /// <param name="authorizationProvider">The authorization provider to use for authentication.</param>
     /// <param name="loggerFactory">Logger factory for creating loggers used for diagnostic output during transport operations.</param>
-    public SseClientTransport(SseClientTransportOptions transportOptions, ITokenProvider authorizationProvider, ILoggerFactory? loggerFactory = null)
+    /// <param name="baseMessageHandler">Optional. The base message handler to use under the authorization handler. 
+    /// If null, a new <see cref="HttpClientHandler"/> will be used. This allows for custom HTTP client pipelines (e.g., from HttpClientFactory) 
+    /// to be used in conjunction with the token-based authentication provided by <paramref name="authorizationProvider"/>.</param>
+    public SseClientTransport(SseClientTransportOptions transportOptions, ITokenProvider authorizationProvider, ILoggerFactory? loggerFactory = null, HttpMessageHandler? baseMessageHandler = null)
     {
         Throw.IfNull(transportOptions);
         Throw.IfNull(authorizationProvider);
@@ -67,13 +70,11 @@ public SseClientTransport(SseClientTransportOptions transportOptions, ITokenProv
         _loggerFactory = loggerFactory;
         Name = transportOptions.Name ?? transportOptions.Endpoint.ToString();
 
-        // Create an auth handler with the authorization provider
         var authHandler = new AuthorizationDelegatingHandler(authorizationProvider)
         {
-            InnerHandler = new HttpClientHandler()
+            InnerHandler = baseMessageHandler ?? new HttpClientHandler()
         };
 
-        // Create an HttpClient with the auth handler
         _httpClient = new HttpClient(authHandler);
         _ownsHttpClient = true;
     }

tests/ModelContextProtocol.Tests/Transport/SseClientTransportTests.cs

@@ -35,7 +35,7 @@ public void Constructor_Throws_For_Null_Options()
     [Fact]
     public void Constructor_Throws_For_Null_HttpClient()
     {
-        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, null!, LoggerFactory));
+        var exception = Assert.Throws<ArgumentNullException>(() => new SseClientTransport(_transportOptions, httpClient: null!, LoggerFactory));
         Assert.Equal("httpClient", exception.ParamName);
     }