Address PR review comments

Author: mikekistler

src/ModelContextProtocol.Core/Client/McpClientPrompt.cs

@@ -30,12 +30,12 @@ public sealed class McpClientPrompt
     /// <remarks>
     /// <para>
     /// This constructor enables reusing cached prompt definitions across different <see cref="McpClient"/> instances
-    /// without needing to call <see cref="McpClient.ListPromptsAsync"/> on every reconnect. This is particularly useful 
+    /// without needing to call <see cref="McpClient.ListPromptsAsync"/> on every reconnect. This is particularly useful
     /// in scenarios where prompt definitions are stable and network round-trips should be minimized.
     /// </para>
     /// <para>
-    /// The provided <paramref name="prompt"/> must represent a prompt that is actually available on the server 
-    /// associated with the <paramref name="client"/>. Attempting to invoke a prompt that doesn't exist on the 
+    /// The provided <paramref name="prompt"/> must represent a prompt that is actually available on the server
+    /// associated with the <paramref name="client"/>. Attempting to invoke a prompt that doesn't exist on the
     /// server will result in an <see cref="McpException"/>.
     /// </para>
     /// </remarks>
@@ -98,6 +98,6 @@ public async ValueTask<GetPromptResult> GetAsync(
             arguments as IReadOnlyDictionary<string, object?> ??
             arguments?.ToDictionary();
 
-        return await _client.GetPromptAsync(ProtocolPrompt.Name, argDict, new RequestOptions(null, serializerOptions), cancellationToken).ConfigureAwait(false);
+        return await _client.GetPromptAsync(ProtocolPrompt.Name, argDict, new RequestOptions(){Meta = null, JsonSerializerOptions = serializerOptions}, cancellationToken).ConfigureAwait(false);
     }
 }

src/ModelContextProtocol.Core/Client/McpClientTool.cs

@@ -198,7 +198,7 @@ public ValueTask<CallToolResult> CallAsync(
             ProtocolTool.Name,
             arguments,
             progress,
-            new RequestOptions
+            serializerOptions is null ? null : new RequestOptions
             {
                 JsonSerializerOptions = serializerOptions
             },

src/ModelContextProtocol.Core/Protocol/RequestParams.cs

@@ -23,7 +23,24 @@ private protected RequestParams()
     /// Implementations must not make assumptions about its contents.
     /// </remarks>
     [JsonPropertyName("_meta")]
-    public JsonObject? Meta { get; set; }
+    public JsonObject? Meta {
+        get;
+        set
+        {
+            // If progressToken is already set in Meta and not present in the new value, preserve it.
+            if (field?["progressToken"] is JsonValue existingProgressToken &&
+                (value is null || !value.ContainsKey("progressToken")))
+            {
+                // Create a copy to avoid modifying the input parameter
+                field = value is null ? [] : new JsonObject(value);
+                field["progressToken"] = existingProgressToken;
+            }
+            else
+            {
+                field = value;
+            }
+        }
+    }
 
     /// <summary>
     /// Gets or sets an opaque token that will be attached to any subsequent progress notifications.

src/ModelContextProtocol.Core/RequestOptions.cs

@@ -24,37 +24,10 @@ public sealed class RequestOptions
     /// </summary>
     public ProgressToken? ProgressToken { get; set; }
 
-    /// <summary>
-    /// Gets a default instance with all properties set to null.
-    /// </summary>
-    public static RequestOptions Default { get; } = new();
-
     /// <summary>
     /// Initializes a new instance of the <see cref="RequestOptions"/> class.
     /// </summary>
     public RequestOptions()
     {
     }
-
-    /// <summary>
-    /// Initializes a new instance of the <see cref="RequestOptions"/> class with the specified metadata.
-    /// </summary>
-    /// <param name="meta">Optional metadata to include in the request.</param>
-    public RequestOptions(JsonObject? meta)
-    {
-        Meta = meta;
-    }
-
-    /// <summary>
-    /// Initializes a new instance of the <see cref="RequestOptions"/> class with the specified options.
-    /// </summary>
-    /// <param name="meta">Optional metadata to include in the request.</param>
-    /// <param name="jsonSerializerOptions">The JSON serializer options to use.</param>
-    /// <param name="progressToken">The progress token for tracking operations.</param>
-    public RequestOptions(JsonObject? meta = null, JsonSerializerOptions? jsonSerializerOptions = null, ProgressToken? progressToken = null)
-    {
-        Meta = meta;
-        JsonSerializerOptions = jsonSerializerOptions;
-        ProgressToken = progressToken;
-    }
 }

src/ModelContextProtocol.Core/Server/McpServer.Methods.cs

@@ -62,7 +62,9 @@ public ValueTask<CreateMessageResult> SampleAsync(
 
         if (options?.Meta is not null)
         {
-            request.Meta = options.Meta;
+            request.Meta = request.Meta is not null ?
+                            new JsonObject(request.Meta.Union(options.Meta))
+                            : options.Meta;
         }
 
         return SendRequestAsync(
@@ -234,7 +236,9 @@ public ValueTask<ListRootsResult> RequestRootsAsync(
 
         if (options?.Meta is not null)
         {
-            request.Meta = options.Meta;
+            request.Meta = request.Meta is not null ?
+                            new JsonObject(request.Meta.Union(options.Meta))
+                            : options.Meta;
         }
 
         return SendRequestAsync(