Set UseStructuredContent=true when OutputSchemaType is set, remove DynamicallyAccessedMembers

- In DeriveOptions, force UseStructuredContent=true when OutputSchemaType is set
- Simplify GetToolDescription to only check UseStructuredContent (no longer needs OutputSchema check)
- Remove unnecessary [DynamicallyAccessedMembers] from OutputSchemaType property

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs

@@ -208,6 +208,7 @@ private static McpServerToolCreateOptions DeriveOptions(MethodInfo method, McpSe
 
             if (toolAttr.OutputSchemaType is { } outputSchemaType)
             {
+                newOptions.UseStructuredContent = true;
                 newOptions.OutputSchema ??= AIJsonUtilities.CreateJsonSchema(outputSchemaType,
                     serializerOptions: newOptions.SerializerOptions ?? McpJsonUtilities.DefaultOptions,
                     inferenceOptions: newOptions.SchemaCreateOptions);
@@ -448,7 +449,7 @@ private static void ValidateToolName(string name)
         string? description = options?.Description ?? function.Description;
 
         // If structured content is enabled, the return description will be in the output schema
-        if (options?.UseStructuredContent is true || options?.OutputSchema is not null)
+        if (options?.UseStructuredContent is true)
         {
             return description;
         }
@@ -490,7 +491,7 @@ schema.ValueKind is not JsonValueKind.Object ||
     {
         structuredOutputRequiresWrapping = false;
 
-        // If an explicit OutputSchema is provided, use it directly and force UseStructuredContent.
+        // If an explicit OutputSchema is provided, use it directly.
         if (toolCreateOptions?.OutputSchema is JsonElement explicitSchema)
         {
             return explicitSchema;

src/ModelContextProtocol.Core/Server/McpServerToolAttribute.cs

@@ -265,7 +265,6 @@ public bool ReadOnly
     /// Setting this property automatically enables <see cref="UseStructuredContent"/>.
     /// </para>
     /// </remarks>
-    [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties)]
     public Type? OutputSchemaType { get; set; }
 
     /// <summary>