Preserve nulls required by structured output schemas

Makefile

@@ -18,6 +18,7 @@ build: restore
 test: build
 	dotnet test \
 		--no-build \
+		-p:TestTfmsInParallel=false \
 		--configuration $(CONFIGURATION) \
 		--filter '(Execution!=Manual)' \
 		--blame \

src/ModelContextProtocol.Core/Client/StreamClientSessionTransport.cs

@@ -36,11 +36,12 @@ internal class StreamClientSessionTransport : TransportBase
     /// <param name="loggerFactory">
     /// Optional factory for creating loggers. If null, a NullLogger is used.
     /// </param>
+    /// <param name="startReading">Whether to start reading immediately rather than after derived initialization.</param>
     /// <remarks>
-    /// This constructor starts a background task to read messages from the server output stream.
+    /// By default, this constructor starts a background task to read messages from the server output stream.
     /// The transport will be marked as connected once initialized.
     /// </remarks>
-    public StreamClientSessionTransport(Stream serverInput, Stream serverOutput, Encoding? encoding, string endpointName, ILoggerFactory? loggerFactory)
+    public StreamClientSessionTransport(Stream serverInput, Stream serverOutput, Encoding? encoding, string endpointName, ILoggerFactory? loggerFactory, bool startReading = true)
         : base(endpointName, loggerFactory)
     {
         Throw.IfNull(serverInput);
@@ -55,6 +56,15 @@ public StreamClientSessionTransport(Stream serverInput, Stream serverOutput, Enc
 
         SetConnected();
 
+        if (startReading)
+        {
+            StartReading();
+        }
+    }
+
+    /// <summary>Starts reading after state used by overridden cleanup methods has been initialized.</summary>
+    protected void StartReading()
+    {
         // Start reading messages in the background. We use the rarer pattern of new Task + Start
         // in order to ensure that the body of the task will always see _readTask initialized.
         // It is then able to reliably null it out on completion.

src/ModelContextProtocol.Core/ModelContextProtocol.Core.csproj

@@ -63,6 +63,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.AI.Abstractions" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" />
+    <PackageReference Include="JsonSchema.Net" />
   </ItemGroup>
 
   <!-- Reference analyzers -->