Add request options bag to high level requests and include Meta (#970)

Co-authored-by: Stephen Toub <stoub@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/ModelContextProtocol.Core/Protocol/PingRequestParams.cs

@@ -0,0 +1,11 @@
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Represents the parameters used with a <see cref="RequestMethods.Ping"/> request to verify
+/// server connectivity.
+/// </summary>
+/// <remarks>
+/// The server responds with a <see cref="PingResult"/>.
+/// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
+/// </remarks>
+public sealed class PingRequestParams : RequestParams;

src/ModelContextProtocol.Core/Protocol/RequestParams.cs

@@ -26,7 +26,7 @@ public abstract class RequestParams
     public JsonObject? Meta { get; set; }
 
     /// <summary>
-    /// Gets or sets an opaque token that will be attached to any subsequent progress notifications.
+    /// Gets the opaque token that will be attached to any subsequent progress notifications.
     /// </summary>
     [JsonIgnore]
     public ProgressToken? ProgressToken
@@ -48,21 +48,5 @@ public abstract class RequestParams
 
             return null;
         }
-        set
-        {
-            if (value is null)
-            {
-                Meta?.Remove("progressToken");
-            }
-            else
-            {
-                (Meta ??= [])["progressToken"] = value.Value.Token switch
-                {
-                    string s => JsonValue.Create(s),
-                    long l => JsonValue.Create(l),
-                    _ => throw new InvalidOperationException("ProgressToken must be a string or a long.")
-                };
-            }
-        }
     }
 }