Add 3-arg RequestContext constructor and obsolete 2-arg to eliminate null-forgiving operator usage (#1462)

Author: Copilot

docs/concepts/filters.md

@@ -317,7 +317,7 @@ Execution flow: `filter1 -> filter2 -> filter3 -> baseHandler -> filter3 -> filt
     {
         var logger = context.Services?.GetService<ILogger<Program>>();
 
-        logger?.LogInformation($"Processing request from {context.Params?.ProgressToken}");
+        logger?.LogInformation($"Processing request from {context.Params.ProgressToken}");
         var result = await next(context, cancellationToken);
         logger?.LogInformation($"Returning {result.Tools?.Count ?? 0} tools");
         return result;
@@ -339,7 +339,7 @@ Execution flow: `filter1 -> filter2 -> filter3 -> baseHandler -> filter3 -> filt
         catch (Exception ex)
         {
             var logger = context.Services?.GetService<ILogger<Program>>();
-            logger?.LogError(ex, "Error while processing CallTool request for {ProgressToken}", context.Params?.ProgressToken);
+            logger?.LogError(ex, "Error while processing CallTool request for {ProgressToken}", context.Params.ProgressToken);
 
             return new CallToolResult
             {

docs/concepts/logging/samples/server/Tools/LoggingTools.cs

@@ -13,7 +13,7 @@ public static async Task<string> LoggingTool(
         int duration = 10,
         int steps = 10)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         // <snippet_LoggingConfiguration >

docs/concepts/pagination/pagination.md

@@ -77,7 +77,7 @@ builder.Services.AddMcpServer()
         int startIndex = 0;
 
         // Parse cursor to determine starting position
-        if (ctx.Params?.Cursor is { } cursor)
+        if (ctx.Params.Cursor is { } cursor)
         {
             startIndex = int.Parse(cursor);
         }

docs/concepts/progress/samples/server/Tools/LongRunningTools.cs

@@ -15,7 +15,7 @@ public static async Task<string> LongRunningTool(
         int duration = 10,
         int steps = 5)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         for (int i = 1; i <= steps; i++)

docs/concepts/resources/resources.md

@@ -212,7 +212,7 @@ builder.Services.AddMcpServer()
     .WithResources<MyResources>()
     .WithSubscribeToResourcesHandler(async (ctx, ct) =>
     {
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             // Track the subscription (e.g., in a concurrent dictionary)
             subscriptions[ctx.Server.SessionId].TryAdd(uri, 0);
@@ -221,7 +221,7 @@ builder.Services.AddMcpServer()
     })
     .WithUnsubscribeFromResourcesHandler(async (ctx, ct) =>
     {
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
         }

docs/list-of-diagnostics.md

@@ -36,3 +36,4 @@ When APIs are marked as obsolete, a diagnostic is emitted to warn users that the
 | :------------ | :----- | :---------- |
 | `MCP9001` | In place | The `EnumSchema` and `LegacyTitledEnumSchema` APIs are deprecated as of specification version 2025-11-25. Use the current schema APIs instead. |
 | `MCP9002` | Removed | The `AddXxxFilter` extension methods on `IMcpServerBuilder` (e.g., `AddListToolsFilter`, `AddCallToolFilter`, `AddIncomingMessageFilter`) were superseded by `WithRequestFilters()` and `WithMessageFilters()`. |
+| `MCP9003` | In place | The `RequestContext<TParams>(McpServer, JsonRpcRequest)` constructor is obsolete. Use the overload that accepts a `parameters` argument: `RequestContext<TParams>(McpServer, JsonRpcRequest, TParams)`. |

samples/EverythingServer/Program.cs

@@ -130,7 +130,7 @@
         {
             throw new McpException("Cannot add subscription for server with null SessionId");
         }
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryAdd(uri, 0);
 
@@ -154,7 +154,7 @@ await ctx.Server.SampleAsync([
         {
             throw new McpException("Cannot remove subscription for server with null SessionId");
         }
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
         }
@@ -212,11 +212,6 @@ await ctx.Server.SampleAsync([
     })
     .WithSetLoggingLevelHandler(async (ctx, ct) =>
     {
-        if (ctx.Params?.Level is null)
-        {
-            throw new McpProtocolException("Missing required argument 'level'", McpErrorCode.InvalidParams);
-        }
-
         // The SDK updates the LoggingLevel field of the IMcpServer
 
         await ctx.Server.SendNotificationAsync("notifications/message", new

samples/EverythingServer/Resources/SimpleResourceType.cs

@@ -19,7 +19,7 @@ public static ResourceContents TemplateResource(RequestContext<ReadResourceReque
         int index = id - 1;
         if ((uint)index >= ResourceGenerator.Resources.Count)
         {
-            throw new NotSupportedException($"Unknown resource: {requestContext.Params?.Uri}");
+            throw new NotSupportedException($"Unknown resource: {requestContext.Params.Uri}");
         }
 
         var resource = ResourceGenerator.Resources[index];

samples/EverythingServer/Tools/LongRunningTool.cs

@@ -15,7 +15,7 @@ public static async Task<string> LongRunningOperation(
         int duration = 10,
         int steps = 5)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         for (int i = 1; i <= steps + 1; i++)

src/Common/Obsoletions.cs

@@ -25,4 +25,8 @@ internal static class Obsoletions
 
     // MCP9002 was used for the AddXxxFilter extension methods on IMcpServerBuilder that were superseded by
     // WithMessageFilters() and WithRequestFilters(). The APIs were removed; do not reuse this diagnostic ID.
+
+    public const string RequestContextParamsConstructor_DiagnosticId = "MCP9003";
+    public const string RequestContextParamsConstructor_Message = "Use the constructor overload that accepts a parameters argument.";
+    public const string RequestContextParamsConstructor_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcp9003";
 }