Implement SEP-2663 Tasks Extension

Directory.Packages.props

@@ -25,6 +25,7 @@
   <!-- Product dependencies .NET Standard -->
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageVersion Include="Microsoft.Bcl.Memory" Version="$(System10Version)" />
+    <PackageVersion Include="System.Collections.Immutable" Version="$(System10Version)" />
     <PackageVersion Include="System.Diagnostics.DiagnosticSource" Version="$(System10Version)" />
     <PackageVersion Include="System.IO.Pipelines" Version="$(System10Version)" />
     <PackageVersion Include="System.Text.Json" Version="$(System10Version)" />

ModelContextProtocol.slnx

@@ -45,7 +45,6 @@
     <Project Path="samples/ChatWithTools/ChatWithTools.csproj" />
     <Project Path="samples/EverythingServer/EverythingServer.csproj" />
     <Project Path="samples/InMemoryTransport/InMemoryTransport.csproj" />
-    <Project Path="samples/LongRunningTasks/LongRunningTasks.csproj" />
     <Project Path="samples/ProtectedMcpClient/ProtectedMcpClient.csproj" />
     <Project Path="samples/ProtectedMcpServer/ProtectedMcpServer.csproj" />
     <Project Path="samples/QuickstartClient/QuickstartClient.csproj" />

docs/experimental.md

@@ -26,8 +26,8 @@ Add the diagnostic ID to `<NoWarn>` in your project file:
 Use `#pragma warning disable` around specific call sites:
 
 ```csharp
-#pragma warning disable MCPEXP001 // The Tasks feature is experimental per the MCP specification and is subject to change.
-tool.Execution = new ToolExecution { ... };
+#pragma warning disable MCPEXP001 // The Extensions feature is part of a future MCP specification version that has not yet been ratified and is subject to change.
+capabilities.Extensions = new Dictionary<string, object> { ... };
 #pragma warning restore MCPEXP001
 ```
 
@@ -67,4 +67,3 @@ By placing the SDK's resolver first, MCP types are serialized using the SDK's co
 
 - [Versioning](versioning.md)
 - [List of diagnostics](list-of-diagnostics.md#experimental-apis)
-- [Tasks](concepts/tasks/tasks.md) (an experimental feature)

docs/list-of-diagnostics.md

@@ -23,7 +23,7 @@ If you use experimental APIs, you will get one of the diagnostics shown below. T
 
 | Diagnostic ID | Description |
 | :------------ | :---------- |
-| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [MCP Tasks specification](https://modelcontextprotocol.io/seps/1686-tasks)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
+| `MCPEXP001` | Experimental APIs for features in the MCP specification itself, including Tasks and Extensions. Tasks provide a mechanism for asynchronous long-running operations that can be polled for status and results (see [SEP-2663](https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/seps/2663-tasks-extension.md)). Extensions provide a framework for extending the Model Context Protocol while maintaining interoperability (see [SEP-2133](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2133)). |
 | `MCPEXP002` | Experimental SDK APIs unrelated to the MCP specification itself, including subclassing `McpClient`/`McpServer` (see [#1363](https://github.com/modelcontextprotocol/csharp-sdk/pull/1363)) and `RunSessionHandler`, which may be removed or change signatures in a future release (consider using `ConfigureSessionOptions` instead). |
 
 ## Obsolete APIs

docs/roadmap.md

@@ -12,7 +12,7 @@ The C# SDK tracks implementation of MCP spec components using the [modelcontextp
 
 ### Next Spec Revision
 
-The next MCP specification revision is being developed in the [protocol repository](https://github.com/modelcontextprotocol/modelcontextprotocol). The C# SDK already has experimental support for [Tasks](concepts/tasks/tasks.md) (experimental in the specification), which will be updated as the specification is revised.
+The next MCP specification revision is being developed in the [protocol repository](https://github.com/modelcontextprotocol/modelcontextprotocol).
 
 ### Feedback and End-to-End Scenarios