Merge origin/main into halter73/remove-session-id-draft

Brings in PR #1579 SEP-2663 Tasks (squash dbb7a20), SEP-990 Enterprise
Managed Authorization (8202bcc), SEP-2243 alignment (ed19286), ttlMs
renames in McpSessionHandler (711e5bb), and several quality-of-life
fixes that landed between the previous merge and today.

Conflict resolutions:
- src/ModelContextProtocol.Core/McpJsonUtilities.cs: keep both sides'
  JsonSerializable additions. Our draft additions (JsonElement,
  Implementation, ClientCapabilities, ServerCapabilities, LoggingLevel)
  coexist with origin/main's IDictionary<string,object> addition.
- src/ModelContextProtocol.Core/Protocol/NotificationMethods.cs: take
  origin/main's renamed TaskStatusNotification value ('notifications/tasks',
  formerly 'notifications/tasks/status') and the updated XML docs from
  PR #1579. Keep all our draft additions (RelatedTaskMetaKey,
  SubscriptionsAcknowledgedNotification, ProtocolVersionMetaKey,
  ClientInfoMetaKey, ClientCapabilitiesMetaKey, LogLevelMetaKey,
  SubscriptionIdMetaKey).
- tests/ModelContextProtocol.AspNetCore.Tests/HttpTaskIntegrationTests.cs:
  removed. Our pre-rebase tweak to the old SEP-1686 file is moot now
  that PR #1579's reimplementation deleted it; the new task tests live
  elsewhere.

PR #1579 author addressed the reconciliation items predicted in the
preview-merge analysis: '17f95f79 Fix _meta' nests tasks opt-in inside
the SEP-2575 capabilities envelope (preview commit 89295fb3 no longer
needed); '8b47086d Address PR feedback' fixes Failed task payload shape +
JsonDocument lifetime (preview commit 8817c9fc no longer needed);
'0b8944f9 Address PR feedback: docs' adds the IMcpTaskStore lifetime/
stateless docs (preview commit 072222db no longer needed). The only
preview reconciliation that may still be required is gating per-request
capability merge to stateful sessions only (preview commit 8b95d2ca),
which is evaluated separately after this merge by re-running
StatelessServerTests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: halter73

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

@@ -45,11 +45,11 @@
     <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" />
     <Project Path="samples/QuickstartWeatherServer/QuickstartWeatherServer.csproj" />
+    <Project Path="samples/TasksExtension/TasksExtension.csproj" />
     <Project Path="samples/TestServerWithHosting/TestServerWithHosting.csproj" />
   </Folder>
   <Folder Name="/Solution Items/">

docs/concepts/stateless/stateless.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/concepts/tasks/tasks.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/experimental.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