feat(mcp): migrate to ModelContextProtocol 2.0 line (2.0.0-preview.3)

docs/for-coding-agents.md

@@ -142,7 +142,7 @@ Use these annotations to help agents make safer decisions:
 | `.Destructive()` | May delete or mutate important state; ask for confirmation. |
 | `.Idempotent()` | Safe to retry. |
 | `.OpenWorld()` | Talks to external systems; expect latency and failures. |
-| `.LongRunning()` | May take time; use call-now / poll-later patterns. |
+| `.LongRunning()` | May take time. Documentation hint for now — no protocol-level task advertisement until Repl integrates the SDK Tasks extension. |
 | `.AutomationHidden()` | Do not expose this command to MCP automation. |
 
 Unannotated tools force agents to assume the worst. Annotate every command that will be visible through MCP.

docs/mcp-advanced.md

@@ -20,6 +20,13 @@ If your tool list is static, stay with the default setup from [mcp-overview.md](
 
 ## Client roots
 
+> **⚠️ Deprecation notice (SEP-2577):** the MCP specification (2026-07-28) deprecates the
+> Roots feature, and the SDK may remove it in a future version. Repl keeps supporting it
+> **for existing hosts and applications only** — new applications should not build on
+> native MCP roots and can use [soft roots](#soft-roots-fallback) or explicit command
+> parameters instead. See
+> [mcp-reference.md](mcp-reference.md#sdk-and-protocol-versions) for the version posture.
+
 A **root** is a URI the client declares as being in scope for the session — typically an opened project folder, a working directory, or a boundary for what the agent should inspect or modify.
 
 Roots give the server session-specific workspace context without inventing a custom protocol. When the client supports native MCP roots, `Repl.Mcp` exposes them through `IMcpClientRoots`.

docs/mcp-agent-capabilities.md

@@ -8,6 +8,14 @@
 
 See also: [sample 08-mcp-server](../samples/08-mcp-server/) for a working example that uses all three in a CSV import and feedback workflow.
 
+> **⚠️ Deprecation notice (SEP-2577):** the MCP specification (2026-07-28) deprecates the
+> Sampling and Logging features that `IMcpSampling` and `IMcpFeedback` build on, and the
+> SDK may remove them in a future version. Repl keeps supporting them **for existing hosts
+> and applications only** — new applications should not adopt these interfaces directly and
+> should prefer the portable `IReplInteractionChannel`, which degrades gracefully across
+> CLI, REPL, hosted sessions, and MCP. See
+> [mcp-reference.md](mcp-reference.md#sdk-and-protocol-versions) for the version posture.
+
 ## Overview
 
 Repl provides three MCP-oriented injectable interfaces:

docs/mcp-overview.md

@@ -63,7 +63,7 @@ app.Map("deploy", handler).Destructive().LongRunning().OpenWorld();
 | `.Destructive()` | Ask user for confirmation, sequential |
 | `.Idempotent()` | Safe to retry, can parallelize |
 | `.OpenWorld()` | Reaches external systems — expect latency and transient failures |
-| `.LongRunning()` | Enables call-now/poll-later pattern |
+| `.LongRunning()` | Slow-operation hint (protocol-level task advertisement returns once Repl integrates the SDK Tasks extension — see [mcp-reference.md](mcp-reference.md#sdk-and-protocol-versions)) |
 | `.AutomationHidden()` | Not visible to agents |
 
 **Annotate every command exposed to agents.** Unannotated tools force agents to assume the worst: confirm everything, no parallelism, no retries.

docs/mcp-reference.md

@@ -510,6 +510,12 @@ side-channel command output and are not included in `resources/read` bodies.
 
 Feature support varies across agents. Check [mcp-availability.com](https://mcp-availability.com/) for current data.
 
+### SDK and protocol versions
+
+- Repl.Mcp builds on the official C# SDK (`ModelContextProtocol`), currently on the **2.0 line** (`2.0.0-preview.3`). The SDK negotiates the protocol version with each client, including fallback to the legacy `initialize` handshake for older hosts.
+- **Roots, Sampling, and Logging** are deprecated by MCP specification 2026-07-28 (SEP-2577). Repl.Mcp keeps supporting them **for existing hosts and applications only** — new applications should not adopt these features (the SDK may remove them) and should prefer Repl's portable abstractions such as `IReplInteractionChannel`. The designated successor for server-initiated flows (SEP-2322, multi-round-trip requests) ships experimentally in the SDK 2.0 line; Repl has not adopted it yet.
+- **MCP Tasks**: the SDK reorganized Tasks into `ModelContextProtocol.Extensions.Tasks` and dropped the per-tool execution augmentation (`Tool.Execution`) from the protocol surface, so `.LongRunning()` commands no longer advertise task support at the protocol level. The annotation stays in Repl's own model (help/docs); protocol-level task support can return once Repl integrates the Tasks extension, store, and get/update/cancel lifecycle (tracked in issue #72).
+
 | Feature | Claude Desktop | Claude Code | Codex | VS Code Copilot | Cursor | Continue |
 |---|---|---|---|---|---|---|
 | Tools | Yes | Yes | Yes | Yes | Yes | Yes |

src/Directory.Packages.props

@@ -14,7 +14,7 @@
 		<PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.5"/>
 		<PackageVersion Include="Microsoft.Extensions.Hosting" Version="10.0.5"/>
 		<PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.5"/>
-		<PackageVersion Include="ModelContextProtocol" Version="1.4.1"/>
+		<PackageVersion Include="ModelContextProtocol" Version="2.0.0-preview.3"/>
 		<PackageVersion Include="Spectre.Console" Version="0.55.0"/>
 	</ItemGroup>
 

src/Repl.Core/CommandAnnotations.cs

@@ -31,8 +31,9 @@ public sealed record CommandAnnotations
 	public bool OpenWorld { get; init; }
 
 	/// <summary>
-	/// Indicates the command may take a long time to complete.
-	/// Enables task-based execution in programmatic clients.
+	/// Indicates the command may take a long time to complete, so programmatic clients
+	/// should expect a slow call. Protocol-level task-based execution (MCP Tasks) is not
+	/// advertised until Repl integrates the SDK's Tasks extension.
 	/// </summary>
 	public bool LongRunning { get; init; }
 

src/Repl.Mcp/IMcpFeedback.cs

@@ -1,6 +1,13 @@
 using ModelContextProtocol.Protocol;
 using Repl.Interaction;
 
+// Roots, Sampling, and Logging are deprecated by MCP spec 2026-07-28 (SEP-2577, SDK
+// diagnostic MCP9005); the designated successor for server-initiated flows (SEP-2322,
+// multi-round-trip requests, shipped experimentally in SDK 2.0 as MrtrContext/MrtrExchange)
+// is not adopted by Repl yet, and hosts still rely on these features, so Repl keeps
+// supporting them until the SDK removes the surface (#51).
+#pragma warning disable MCP9005
+
 namespace Repl.Mcp;
 
 /// <summary>

src/Repl.Mcp/McpClientRootsService.cs

@@ -1,24 +1,38 @@
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
 
+// Roots, Sampling, and Logging are deprecated by MCP spec 2026-07-28 (SEP-2577, SDK
+// diagnostic MCP9005); the designated successor for server-initiated flows (SEP-2322,
+// multi-round-trip requests, shipped experimentally in SDK 2.0 as MrtrContext/MrtrExchange)
+// is not adopted by Repl yet, and hosts still rely on these features, so Repl keeps
+// supporting them until the SDK removes the surface (#51).
+#pragma warning disable MCP9005
+
 namespace Repl.Mcp;
 
+// One instance PER SESSION (owned by McpSessionContext): hard roots, soft roots, and
+// their cache/version state are session state — one handler can serve several sessions,
+// and serving session A's roots to session B would expose A's workspace URIs and build
+// B's root-dependent snapshot from the wrong workspace. Outbound transport still goes
+// through the request-bound accessor (the destination is per request, finer than the
+// session).
 internal sealed class McpClientRootsService : IMcpClientRoots
 {
 	private readonly ICoreReplApp _app;
+	private readonly McpRequestServerAccessor _servers;
 	private readonly Lock _syncRoot = new();
-	private McpServer? _server;
 	private McpClientRoot[] _hardRoots = [];
 	private McpClientRoot[] _softRoots = [];
 	private bool _hardRootsLoaded;
 	private long _hardRootsVersion;
 
-	public McpClientRootsService(ICoreReplApp app)
+	public McpClientRootsService(ICoreReplApp app, McpRequestServerAccessor servers)
 	{
 		_app = app;
+		_servers = servers;
 	}
 
-	public bool IsSupported => _server?.ClientCapabilities?.Roots is not null;
+	public bool IsSupported => _servers.Effective?.ClientCapabilities?.Roots is not null;
 
 	public bool HasSoftRoots
 	{
@@ -42,15 +56,11 @@ public IReadOnlyList<McpClientRoot> Current
 		}
 	}
 
-	public void AttachServer(McpServer server)
-	{
-		ArgumentNullException.ThrowIfNull(server);
-		_server = server;
-	}
-
 	public async ValueTask<IReadOnlyList<McpClientRoot>> GetAsync(CancellationToken cancellationToken = default)
 	{
-		var server = _server;
+		// Single read: the effective server must not change between the support check and
+		// the roots request (a concurrent request re-binding the accessor must not be observed).
+		var server = _servers.Effective;
 		if (server?.ClientCapabilities?.Roots is null)
 		{
 			return Current;

src/Repl.Mcp/McpElicitationService.cs

@@ -15,13 +15,11 @@ namespace Repl.Mcp;
 /// a multi-field variant would build the <see cref="ElicitRequestParams.RequestSchema"/> with
 /// multiple properties instead of one.
 /// </remarks>
-internal sealed class McpElicitationService : IMcpElicitation
+internal sealed class McpElicitationService(McpRequestServerAccessor servers) : IMcpElicitation
 {
 	private const string FieldName = "value";
 
-	private McpServer? _server;
-
-	public bool IsSupported => _server?.ClientCapabilities?.Elicitation is not null;
+	public bool IsSupported => servers.Effective?.ClientCapabilities?.Elicitation is not null;
 
 	public async ValueTask<string?> ElicitTextAsync(
 		string message,
@@ -99,19 +97,19 @@ internal sealed class McpElicitationService : IMcpElicitation
 			: null;
 	}
 
-	internal void AttachServer(McpServer server) => _server = server;
-
 	private async ValueTask<ElicitResult?> ElicitSingleFieldAsync(
 		string message,
 		ElicitRequestParams.PrimitiveSchemaDefinition schema,
 		CancellationToken cancellationToken)
 	{
-		if (!IsSupported)
+		// Single read: the effective server must not change between the support check and
+		// the call (a concurrent request re-binding the accessor must not be observed).
+		if (servers.Effective is not { ClientCapabilities.Elicitation: not null } server)
 		{
 			return null;
 		}
 
-		var result = await _server!.ElicitAsync(
+		var result = await server.ElicitAsync(
 			new ElicitRequestParams
 			{
 				Message = message,

src/Repl.Mcp/McpFeedbackService.cs

@@ -5,38 +5,45 @@
 using ModelContextProtocol.Server;
 using Repl.Interaction;
 
+// Roots, Sampling, and Logging are deprecated by MCP spec 2026-07-28 (SEP-2577, SDK
+// diagnostic MCP9005); the designated successor for server-initiated flows (SEP-2322,
+// multi-round-trip requests, shipped experimentally in SDK 2.0 as MrtrContext/MrtrExchange)
+// is not adopted by Repl yet, and hosts still rely on these features, so Repl keeps
+// supporting them until the SDK removes the surface (#51).
+#pragma warning disable MCP9005
+
 namespace Repl.Mcp;
 
 /// <summary>
 /// Internal implementation of <see cref="IMcpFeedback"/> backed by a live <see cref="McpServer"/> session.
 /// </summary>
-internal sealed class McpFeedbackService : IMcpFeedback
+internal sealed class McpFeedbackService(McpRequestServerAccessor servers) : IMcpFeedback
 {
 	private const string LoggerName = "repl.interaction";
 
 	private readonly AsyncLocal<ProgressToken?> _progressToken = new();
-	// This service is created per McpServerHandler/session and overlaid into the
-	// per-connection service provider, so the attached server reference is not shared
-	// across concurrent MCP connections.
-	private McpServer? _server;
 
-	public bool IsProgressSupported => _server is not null && _progressToken.Value is not null;
+	public bool IsProgressSupported => servers.Effective is not null && _progressToken.Value is not null;
 
-	public bool IsLoggingSupported => _server is not null;
+	public bool IsLoggingSupported => servers.Effective is not null;
 
 	public async ValueTask ReportProgressAsync(
 		ReplProgressEvent progress,
 		CancellationToken cancellationToken = default)
 	{
 		ArgumentNullException.ThrowIfNull(progress);
 
-		if (!IsProgressSupported || progress.State == ReplProgressState.Clear || _progressToken.Value is not { } progressToken)
+		// Single read: the effective server must not change between the support check and
+		// the send (a concurrent request re-binding the accessor must not be observed).
+		if (servers.Effective is not { } server
+			|| progress.State == ReplProgressState.Clear
+			|| _progressToken.Value is not { } progressToken)
 		{
 			return;
 		}
 
 		var percent = progress.ResolvePercent();
-		await _server!.NotifyProgressAsync(
+		await server.NotifyProgressAsync(
 			progressToken,
 			new ProgressNotificationValue
 			{
@@ -52,12 +59,12 @@ public async ValueTask SendMessageAsync(
 		object? data,
 		CancellationToken cancellationToken = default)
 	{
-		if (!IsLoggingSupported)
+		if (servers.Effective is not { } server)
 		{
 			return;
 		}
 
-		await _server!.SendNotificationAsync(
+		await server.SendNotificationAsync(
 			NotificationMethods.LoggingMessageNotification,
 			new LoggingMessageNotificationParams
 			{
@@ -68,7 +75,6 @@ public async ValueTask SendMessageAsync(
 			cancellationToken: cancellationToken).ConfigureAwait(false);
 	}
 
-	internal void AttachServer(McpServer server) => _server = server;
 
 	internal IDisposable PushProgressToken(ProgressToken? progressToken) =>
 		new ProgressTokenScope(_progressToken, progressToken);

src/Repl.Mcp/McpInteractionChannel.cs

@@ -5,6 +5,13 @@
 using ModelContextProtocol.Server;
 using Repl.Interaction;
 
+// Roots, Sampling, and Logging are deprecated by MCP spec 2026-07-28 (SEP-2577, SDK
+// diagnostic MCP9005); the designated successor for server-initiated flows (SEP-2322,
+// multi-round-trip requests, shipped experimentally in SDK 2.0 as MrtrContext/MrtrExchange)
+// is not adopted by Repl yet, and hosts still rely on these features, so Repl keeps
+// these features, so Repl keeps supporting them until the SDK removes the surface (#51).
+#pragma warning disable MCP9005
+
 namespace Repl.Mcp;
 
 /// <summary>

src/Repl.Mcp/McpRequestServerAccessor.cs

@@ -0,0 +1,31 @@
+using ModelContextProtocol.Server;
+
+namespace Repl.Mcp;
+
+/// <summary>
+/// Resolves the <see cref="McpServer"/> a capability call must target.
+/// </summary>
+/// <remarks>
+/// SDK 2.0's <c>2026-07-28</c> protocol path hands each request a destination-bound
+/// <see cref="McpServer"/>, and one handler can serve several sessions. The capability
+/// services are singletons (exposed through DI to command handlers), so the effective
+/// server must be the one bound to the FLOWING request — a shared mutable field would be
+/// overwritten by whichever request attached last, cross-wiring capabilities between
+/// concurrent calls. <see cref="AsyncLocal{T}"/> flows with the invocation and cannot
+/// leak across requests; the session-level server remains the fallback for code running
+/// outside a request (e.g. routing-change notifications).
+/// </remarks>
+internal sealed class McpRequestServerAccessor
+{
+	private readonly AsyncLocal<McpServer?> _current = new();
+	private McpServer? _session;
+
+	/// <summary>Server for the flowing request, falling back to the session server.</summary>
+	public McpServer? Effective => _current.Value ?? _session;
+
+	/// <summary>Binds the flowing async context to the request's destination server.</summary>
+	public void BindRequest(McpServer server) => _current.Value = server;
+
+	/// <summary>Records the session-level server used outside request flows (null when the last session ends).</summary>
+	public void AttachSession(McpServer? server) => _session = server;
+}

src/Repl.Mcp/McpSamplingService.cs

@@ -1,28 +1,35 @@
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
 
+// Roots, Sampling, and Logging are deprecated by MCP spec 2026-07-28 (SEP-2577, SDK
+// diagnostic MCP9005); the designated successor for server-initiated flows (SEP-2322,
+// multi-round-trip requests, shipped experimentally in SDK 2.0 as MrtrContext/MrtrExchange)
+// is not adopted by Repl yet, and hosts still rely on these features, so Repl keeps
+// these features, so Repl keeps supporting them until the SDK removes the surface (#51).
+#pragma warning disable MCP9005
+
 namespace Repl.Mcp;
 
 /// <summary>
 /// Internal implementation of <see cref="IMcpSampling"/> backed by a live <see cref="McpServer"/> session.
 /// </summary>
-internal sealed class McpSamplingService : IMcpSampling
+internal sealed class McpSamplingService(McpRequestServerAccessor servers) : IMcpSampling
 {
-	private McpServer? _server;
-
-	public bool IsSupported => _server?.ClientCapabilities?.Sampling is not null;
+	public bool IsSupported => servers.Effective?.ClientCapabilities?.Sampling is not null;
 
 	public async ValueTask<string?> SampleAsync(
 		string prompt,
 		int maxTokens = 1024,
 		CancellationToken cancellationToken = default)
 	{
-		if (!IsSupported)
+		// Single read: the effective server must not change between the support check and
+		// the call (a concurrent request re-binding the accessor must not be observed).
+		if (servers.Effective is not { ClientCapabilities.Sampling: not null } server)
 		{
 			return null;
 		}
 
-		var result = await _server!.SampleAsync(
+		var result = await server.SampleAsync(
 			new CreateMessageRequestParams
 			{
 				Messages =
@@ -40,5 +47,4 @@ internal sealed class McpSamplingService : IMcpSampling
 		return result.Content?.OfType<TextContentBlock>().FirstOrDefault()?.Text;
 	}
 
-	internal void AttachServer(McpServer server) => _server = server;
 }