Fix HTTP task filter composition (#1722)

docs/concepts/filters.md

@@ -32,6 +32,22 @@ The following request filter methods are available on `IMcpRequestFilterBuilder`
 | `AddUnsubscribeFromResourcesFilter` | Resource unsubscription handlers |
 | `AddSetLoggingLevelFilter`          | Logging level handlers           |
 
+The Tasks extension and ASP.NET Core tool authorization use alternate-result `tools/call` filters.
+Alternate-result filters run in registration order outside the ordinary `AddCallToolFilter`
+pipeline. The Tasks filter creates a task at its position in that order and runs its remaining
+pipeline in the background. Consequently, alternate-result filters registered before Tasks run
+before task creation, while those registered after Tasks run in the background before the
+ordinary filters and tool. ASP.NET Core authorization is registered before Tasks, so an
+unauthorized call is rejected without creating a task.
+
+Ordinary call-tool filters run exactly once after all alternate-result filters and before the tool.
+For task-backed calls, ordinary filters execute in the background after task creation. An explicit
+`CallToolWithAlternateHandler` remains a full replacement and cannot be combined with ordinary
+call-tool filters.
+
+Configure `WithTasks` before adding ordinary call-tool filters. Tasks validates this ordering when
+its filter is installed because it must execute outside the ordinary call-tool pipeline.
+
 ## Message Filters
 
 In addition to the request-specific filters above, there are low-level message filters that intercept all JSON-RPC messages before they are routed to specific handlers.

docs/concepts/tasks/tasks.md

@@ -79,6 +79,17 @@ When tasks are enabled with `WithTasks` the SDK automatically:
 - Plumbs a `CancellationToken` through to the tool that fires when the client invokes
   `tasks/cancel`, so cancellation propagates cooperatively.
 
+Alternate-result `tools/call` filters run in registration order, with the Tasks filter creating a
+task at its position in that order. Filters before Tasks run before task creation. Filters after
+Tasks run in the background before the ordinary filter pipeline. ASP.NET Core tool authorization
+uses an alternate-result filter registered before Tasks, so an unauthorized call does not create
+a task.
+
+Ordinary `tools/call` filters still run exactly once for task-backed calls. They execute in the
+background after the task record is created and before the tool body, so validation and telemetry
+continue to apply. Each background invocation gets an independent DI scope that remains alive
+until the tool pipeline completes.
+
 For production scenarios that need durability, session isolation, multi-process routing, or
 TTL-based cleanup, implement <xref:ModelContextProtocol.Extensions.Tasks.IMcpTaskStore> yourself
 (see the [Implementing a custom task store](#implementing-a-custom-task-store) section).
@@ -126,28 +137,6 @@ options.Handlers.CallToolWithAlternateHandler = async (context, ct) =>
 > are mutually exclusive. Setting one while the other is already non-null throws
 > `InvalidOperationException` at the property setter.
 
-#### Task scope for server-initiated requests
-
-When you start background work from a custom <xref:ModelContextProtocol.Server.McpServerHandlers.CallToolWithAlternateHandler?displayProperty=nameWithType>
-(rather than the SDK's auto-wrapping), use <xref:ModelContextProtocol.Extensions.Tasks.McpTasksServerExtensions.CreateMcpTaskScope*>
-to route elicitation, sampling, and `roots/list` calls through the task store as input requests
-instead of direct JSON-RPC messages:
-
-```csharp
-using ModelContextProtocol.Extensions.Tasks;
-
-using (server.CreateMcpTaskScope(taskId, taskStore))
-{
-    // ElicitAsync/SampleAsync/RequestRootsAsync calls in here are surfaced as
-    // entries in the task's inputRequests, then await client responses via tasks/update.
-    var elicit = await server.ElicitAsync(elicitParams, ct);
-}
-```
-
-`CreateMcpTaskScope` returns an `IDisposable` that restores the prior ambient context on
-`Dispose`. The scope is established automatically for `[McpServerTool]` methods that run via
-`WithTasks`, so this API is only needed for custom handlers.
-
 ### Client usage
 
 #### Automatic polling

src/Directory.Build.targets

@@ -0,0 +1,13 @@
+<Project>
+  <Target Name="PinMcpProjectReferencePackageVersions"
+          AfterTargets="_GetProjectReferenceVersions"
+          Condition="'$(MSBuildProjectName)' == 'ModelContextProtocol'
+                  Or '$(MSBuildProjectName)' == 'ModelContextProtocol.AspNetCore'
+                  Or '$(MSBuildProjectName)' == 'ModelContextProtocol.Extensions.Tasks'">
+    <ItemGroup>
+      <_ProjectReferencesWithVersions Update="@(_ProjectReferencesWithVersions)">
+        <ProjectVersion>[%(_ProjectReferencesWithVersions.ProjectVersion)]</ProjectVersion>
+      </_ProjectReferencesWithVersions>
+    </ItemGroup>
+  </Target>
+</Project>

src/ModelContextProtocol.AspNetCore/AuthorizationCallToolFilterGuardSetup.cs

@@ -0,0 +1,32 @@
+using Microsoft.Extensions.Options;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+
+namespace ModelContextProtocol.AspNetCore;
+
+internal sealed class AuthorizationFiltersMarker;
+
+internal sealed class AuthorizationCallToolFilterGuardSetup(AuthorizationFiltersMarker? marker = null) : IPostConfigureOptions<McpServerOptions>
+{
+    public void PostConfigure(string? name, McpServerOptions options)
+    {
+        if (marker is not null)
+        {
+            return;
+        }
+
+#pragma warning disable MCPEXP002 // The guard must run before Tasks can dispatch the request.
+        options.Filters.Request.CallToolWithAlternateFilters.Insert(0, static async (context, next, cancellationToken) =>
+        {
+            if (AuthorizationFilterSetup.HasAuthorizationMetadata(context.MatchedPrimitive))
+            {
+                throw new InvalidOperationException(
+                    "Authorization filter was not invoked for tools/call operation, but authorization metadata was found on the tool. " +
+                    "Ensure that AddAuthorizationFilters() is called on the IMcpServerBuilder to configure authorization filters.");
+            }
+
+            return await next(context, cancellationToken);
+        });
+#pragma warning restore MCPEXP002
+    }
+}

src/ModelContextProtocol.AspNetCore/AuthorizationFilterSetup.cs

@@ -11,14 +11,15 @@ namespace ModelContextProtocol.AspNetCore;
 /// <summary>
 /// Evaluates authorization policies from endpoint metadata.
 /// </summary>
-internal sealed class AuthorizationFilterSetup(IAuthorizationPolicyProvider? policyProvider = null) : IConfigureOptions<McpServerOptions>, IPostConfigureOptions<McpServerOptions>
+internal sealed class AuthorizationFilterSetup(
+    IAuthorizationPolicyProvider? policyProvider = null,
+    AuthorizationFiltersMarker? marker = null) : IConfigureOptions<McpServerOptions>, IPostConfigureOptions<McpServerOptions>
 {
     private static readonly string AuthorizationFilterInvokedKey = "ModelContextProtocol.AspNetCore.AuthorizationFilter.Invoked";
 
     public void Configure(McpServerOptions options)
     {
         ConfigureListToolsFilter(options);
-        ConfigureCallToolFilter(options);
 
         ConfigureListResourcesFilter(options);
         ConfigureListResourceTemplatesFilter(options);
@@ -30,8 +31,13 @@ internal sealed class AuthorizationFilterSetup(IAuthorizationPolicyProvider? pol
 
     public void PostConfigure(string? name, McpServerOptions options)
     {
+        // Add tool authorization after all regular configuration so it always wraps Tasks.
+        if (marker is not null)
+        {
+            ConfigureCallToolFilter(options);
+        }
+
         CheckListToolsFilter(options);
-        CheckCallToolFilter(options);
 
         CheckListResourcesFilter(options);
         CheckListResourceTemplatesFilter(options);
@@ -81,7 +87,8 @@ internal sealed class AuthorizationFilterSetup(IAuthorizationPolicyProvider? pol
 
     private void ConfigureCallToolFilter(McpServerOptions options)
     {
-        options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
+#pragma warning disable MCPEXP002 // Authorization must run in the alternate-result pipeline before task dispatch.
+        options.Filters.Request.CallToolWithAlternateFilters.Insert(0, async (context, next, cancellationToken) =>
         {
             var authResult = await GetAuthorizationResultAsync(context.User, context.MatchedPrimitive, context.Services, context);
             if (!authResult.Succeeded)
@@ -93,20 +100,7 @@ internal sealed class AuthorizationFilterSetup(IAuthorizationPolicyProvider? pol
 
             return await next(context, cancellationToken);
         });
-    }
-
-    private static void CheckCallToolFilter(McpServerOptions options)
-    {
-        options.Filters.Request.CallToolFilters.Add(next => async (context, cancellationToken) =>
-        {
-            if (HasAuthorizationMetadata(context.MatchedPrimitive)
-                && !context.Items.ContainsKey(AuthorizationFilterInvokedKey))
-            {
-                throw new InvalidOperationException("Authorization filter was not invoked for tools/call operation, but authorization metadata was found on the tool. Ensure that AddAuthorizationFilters() is called on the IMcpServerBuilder to configure authorization filters.");
-            }
-
-            return await next(context, cancellationToken);
-        });
+#pragma warning restore MCPEXP002
     }
 
     private void ConfigureListResourcesFilter(McpServerOptions options)
@@ -374,7 +368,7 @@ internal sealed class AuthorizationFilterSetup(IAuthorizationPolicyProvider? pol
             : AuthorizationPolicy.Combine(policy, reqPolicyBuilder.Build());
     }
 
-    private static bool HasAuthorizationMetadata([NotNullWhen(true)] IMcpServerPrimitive? primitive)
+    internal static bool HasAuthorizationMetadata([NotNullWhen(true)] IMcpServerPrimitive? primitive)
     {
         // If no primitive was found for this request or there is IAllowAnonymous metadata anywhere on the class or method,
         // the request should go through as normal.

src/ModelContextProtocol.AspNetCore/HttpMcpServerBuilderExtensions.cs

@@ -34,6 +34,7 @@ public static class HttpMcpServerBuilderExtensions
         builder.Services.AddHostedService<IdleTrackingBackgroundService>();
 
         builder.Services.TryAddEnumerable(ServiceDescriptor.Transient<IPostConfigureOptions<McpServerOptions>, AuthorizationFilterSetup>());
+        builder.Services.TryAddEnumerable(ServiceDescriptor.Transient<IPostConfigureOptions<McpServerOptions>, AuthorizationCallToolFilterGuardSetup>());
         builder.Services.TryAddEnumerable(ServiceDescriptor.Transient<IConfigureOptions<HttpServerTransportOptions>, HttpServerTransportOptionsSetup>());
 
         if (configureOptions is not null)
@@ -55,14 +56,17 @@ public static class HttpMcpServerBuilderExtensions
     /// <remarks>
     /// This method automatically configures authorization filters for all MCP server handlers. These filters respect
     /// authorization attributes such as <see cref="AuthorizeAttribute"/>
-    /// and <see cref="AllowAnonymousAttribute"/>.
+    /// and <see cref="AllowAnonymousAttribute"/>. Tool authorization runs in the alternate-result pipeline before
+    /// the Tasks extension dispatches background execution, so an unauthorized tool call does not create a task.
     /// </remarks>
     public static IMcpServerBuilder AddAuthorizationFilters(this IMcpServerBuilder builder)
     {
         ArgumentNullException.ThrowIfNull(builder);
 
         // Allow the authorization filters to get added multiple times in case other middleware changes the matched primitive.
+        builder.Services.TryAddSingleton<AuthorizationFiltersMarker>();
         builder.Services.AddTransient<IConfigureOptions<McpServerOptions>, AuthorizationFilterSetup>();
+        builder.Services.TryAddEnumerable(ServiceDescriptor.Transient<IPostConfigureOptions<McpServerOptions>, AuthorizationFilterSetup>());
 
         return builder;
     }

src/ModelContextProtocol.Core/Server/ComposedCallToolInvocationState.cs

@@ -0,0 +1,84 @@
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Server;
+
+#pragma warning disable MCPEXP002
+internal sealed class ComposedCallToolInvocationState
+{
+    private readonly object _sync = new();
+    private readonly List<ToolCallLifecycle> _pendingOrdinaryLifecycles = [];
+    private bool _outerCompleted;
+    private bool _outerReturnedAlternate;
+
+    public IReadOnlyList<ToolCallLifecycle> RecordOrdinaryResult(CallToolResult result) =>
+        RecordOrdinaryLifecycle(new(result, null, false));
+
+    public IReadOnlyList<ToolCallLifecycle> RecordOrdinaryException(
+        Exception exception,
+        bool cancellationRequested) =>
+        RecordOrdinaryLifecycle(new(null, exception, cancellationRequested));
+
+    public IReadOnlyList<ToolCallLifecycle> CompleteOuter(ResultOrAlternate<CallToolResult> result)
+    {
+        lock (_sync)
+        {
+            if (result.IsAlternate)
+            {
+                _outerReturnedAlternate = true;
+                return DrainPendingLifecycles();
+            }
+
+            _outerCompleted = true;
+            var exceptions = _pendingOrdinaryLifecycles
+                .Where(lifecycle => lifecycle.Exception is not null)
+                .ToArray();
+            _pendingOrdinaryLifecycles.Clear();
+            return exceptions.Length > 0 ?
+                exceptions :
+                [new(result.Result!, null, false)];
+        }
+    }
+
+    public IReadOnlyList<ToolCallLifecycle> CompleteOuterException(
+        Exception exception,
+        bool cancellationRequested)
+    {
+        lock (_sync)
+        {
+            _outerCompleted = true;
+            _pendingOrdinaryLifecycles.Clear();
+            return [new(null, exception, cancellationRequested)];
+        }
+    }
+
+    private IReadOnlyList<ToolCallLifecycle> RecordOrdinaryLifecycle(ToolCallLifecycle lifecycle)
+    {
+        lock (_sync)
+        {
+            if (_outerReturnedAlternate)
+            {
+                return [lifecycle];
+            }
+
+            if (!_outerCompleted)
+            {
+                _pendingOrdinaryLifecycles.Add(lifecycle);
+            }
+
+            return [];
+        }
+    }
+
+    private IReadOnlyList<ToolCallLifecycle> DrainPendingLifecycles()
+    {
+        if (_pendingOrdinaryLifecycles.Count == 0)
+        {
+            return [];
+        }
+
+        var lifecycles = _pendingOrdinaryLifecycles.ToArray();
+        _pendingOrdinaryLifecycles.Clear();
+        return lifecycles;
+    }
+}
+#pragma warning restore MCPEXP002

src/ModelContextProtocol.Core/Server/McpRequestFilters.cs

@@ -8,6 +8,9 @@ namespace ModelContextProtocol.Server;
 /// </summary>
 public sealed class McpRequestFilters
 {
+#pragma warning disable MCPEXP002 // CallToolWithAlternateFilters references the experimental ResultOrAlternate seam
+    private IList<McpRequestFilter<CallToolRequestParams, CallToolResult>>? _callToolFilters;
+
     /// <summary>
     /// Gets or sets the filters for the list-tools handler pipeline.
     /// </summary>
@@ -43,23 +46,26 @@ public sealed class McpRequestFilters
     /// <see cref="RequestMethods.ToolsCall"/> requests. The handler should implement logic to execute the requested tool and return appropriate results.
     /// </para>
     /// <para>
-    /// Cannot be used together with <see cref="CallToolWithAlternateFilters"/>. If both are non-empty at configuration time,
-    /// an <see cref="InvalidOperationException"/> will be thrown. This can happen indirectly when combining features that
-    /// register different tool-call filter styles, such as authorization filters (which use this collection) and the
-    /// tasks extension (which uses <see cref="CallToolWithAlternateFilters"/>).
+    /// These filters run inside <see cref="CallToolWithAlternateFilters"/>. Each ordinary filter runs exactly once
+    /// when an alternate-result filter invokes the ordinary tool pipeline. For task-backed calls, that invocation
+    /// occurs in the background after the task record is created and before the matched tool is executed. Filters
+    /// that must run before task creation should use the alternate-result pipeline instead.
+    /// </para>
+    /// <para>
+    /// These filters cannot be used with an explicit <see cref="McpServerHandlers.CallToolWithAlternateHandler"/>,
+    /// which replaces the ordinary tool-call pipeline rather than augmenting it.
     /// </para>
     /// </remarks>
     public IList<McpRequestFilter<CallToolRequestParams, CallToolResult>> CallToolFilters
     {
-        get => field ??= [];
+        get => _callToolFilters ??= [];
         set
         {
             Throw.IfNull(value);
-            field = value;
+            _callToolFilters = value;
         }
     }
 
-#pragma warning disable MCPEXP002 // CallToolWithAlternateFilters references the experimental ResultOrAlternate seam
     /// <summary>
     /// Gets or sets the filters for the call-tool handler pipeline with alternate result support.
     /// </summary>
@@ -71,14 +77,15 @@ public sealed class McpRequestFilters
     /// subtype for asynchronous execution.
     /// </para>
     /// <para>
-    /// Cannot be used together with <see cref="CallToolFilters"/>. If both are non-empty at configuration time,
-    /// an <see cref="InvalidOperationException"/> will be thrown. This can happen indirectly when combining features that
-    /// register different tool-call filter styles, such as the tasks extension (which uses this collection) and
-    /// authorization filters (which use <see cref="CallToolFilters"/>).
+    /// When no explicit <see cref="McpServerHandlers.CallToolWithAlternateHandler"/> is configured, these filters
+    /// compose outside <see cref="CallToolFilters"/>. Primitive matching occurs before either filter family runs, then
+    /// the ordinary pipeline is adapted to <see cref="ResultOrAlternate{TResult}"/> before these filters are applied.
+    /// Alternate-result filters run in registration order. If one filter dispatches the remainder of the pipeline
+    /// asynchronously, filters registered after it execute as part of that asynchronous operation.
     /// </para>
     /// </remarks>
     [Experimental(Experimentals.Subclassing_DiagnosticId, UrlFormat = Experimentals.Subclassing_Url)]
-    public IList<McpRequestFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>>> CallToolWithAlternateFilters
+    public IList<McpRequestInvocationFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>>> CallToolWithAlternateFilters
     {
         get => field ??= [];
         set

src/ModelContextProtocol.Core/Server/McpRequestInvocationFilter.cs

@@ -0,0 +1,18 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace ModelContextProtocol.Server;
+
+/// <summary>
+/// Delegate type for filtering a single incoming MCP request invocation.
+/// </summary>
+/// <typeparam name="TParams">The type of the parameters sent with the request.</typeparam>
+/// <typeparam name="TResult">The type of the response returned by the handler.</typeparam>
+/// <param name="context">The context for the current request.</param>
+/// <param name="next">The next request handler in the pipeline for this invocation.</param>
+/// <param name="cancellationToken">The cancellation token for the current request.</param>
+/// <returns>The result of the filtered request invocation.</returns>
+[Experimental(Experimentals.Subclassing_DiagnosticId, UrlFormat = Experimentals.Subclassing_Url)]
+public delegate ValueTask<TResult> McpRequestInvocationFilter<TParams, TResult>(
+    RequestContext<TParams> context,
+    McpRequestHandler<TParams, TResult> next,
+    CancellationToken cancellationToken);

src/ModelContextProtocol.Core/Server/McpServer.Methods.cs

@@ -23,50 +23,27 @@ public abstract partial class McpServer : McpSession
 
     private static Dictionary<string, HashSet<string>>? s_elicitAllowedProperties = null;
 
-    /// <summary>
-    /// Ambient interceptor that, when installed, redirects server-initiated requests
-    /// (<see cref="SampleAsync(CreateMessageRequestParams, CancellationToken)"/>,
-    /// <see cref="ElicitAsync(ElicitRequestParams, CancellationToken)"/>, and
-    /// <see cref="RequestRootsAsync(ListRootsRequestParams, CancellationToken)"/>) away from the
-    /// transport. The interceptor receives the request method and pre-serialized parameters and
-    /// returns the serialized result. Used by extensions (such as the Tasks extension) to surface
-    /// these requests through an alternate channel during background execution.
-    /// </summary>
-    private static readonly AsyncLocal<Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>>?> s_outgoingRequestInterceptor = new();
+    internal virtual Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>>? OutgoingRequestInterceptor => null;
 
     /// <summary>
-    /// Gets the currently installed outgoing-request interceptor for the ambient execution context, if any.
-    /// </summary>
-    internal static Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>>? CurrentOutgoingRequestInterceptor => s_outgoingRequestInterceptor.Value;
-
-    /// <summary>
-    /// Installs an interceptor that redirects server-initiated requests for the duration of the
-    /// returned scope on the current asynchronous execution context.
+    /// Creates a non-mutating server facade that redirects server-initiated requests through an interceptor.
     /// </summary>
     /// <param name="interceptor">
     /// The interceptor invoked for each outgoing request. It receives the request method, the
     /// pre-serialized request parameters (or <see langword="null"/>), and a cancellation token, and
     /// returns the serialized result (or <see langword="null"/> to indicate no result).
     /// </param>
-    /// <returns>An <see cref="IDisposable"/> that restores the previous interceptor when disposed.</returns>
+    /// <returns>A server facade that uses <paramref name="interceptor"/> for outgoing requests.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="interceptor"/> is <see langword="null"/>.</exception>
     /// <remarks>
-    /// While an interceptor is installed, the redirected methods skip their client-capability checks,
+    /// On the returned facade, redirected methods skip their client-capability checks,
     /// because the alternate channel is responsible for delivering the request to the client.
     /// </remarks>
     [Experimental(Experimentals.Subclassing_DiagnosticId, UrlFormat = Experimentals.Subclassing_Url)]
-    public IDisposable InterceptOutgoingRequests(Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>> interceptor)
+    public McpServer WithOutgoingRequestInterceptor(Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>> interceptor)
     {
         Throw.IfNull(interceptor);
-
-        var previous = s_outgoingRequestInterceptor.Value;
-        s_outgoingRequestInterceptor.Value = interceptor;
-        return new OutgoingRequestInterceptorScope(previous);
-    }
-
-    private sealed class OutgoingRequestInterceptorScope(Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>>? previous) : IDisposable
-    {
-        public void Dispose() => s_outgoingRequestInterceptor.Value = previous;
+        return new OutgoingRequestInterceptingMcpServer(this, interceptor);
     }
 
     /// <summary>
@@ -119,7 +96,7 @@ public abstract partial class McpServer : McpSession
         // redirect sampling through it. Capability checks (ThrowIfSamplingUnsupported) are
         // intentionally skipped because the interceptor's alternate channel is responsible for
         // delivering the request to the client. See SendRequestViaInterceptorAsync remarks.
-        if (CurrentOutgoingRequestInterceptor is { } interceptor)
+        if (OutgoingRequestInterceptor is { } interceptor)
         {
             return SendRequestViaInterceptorAsync(interceptor, RequestMethods.SamplingCreateMessage, requestParams,
                 McpJsonUtilities.JsonContext.Default.CreateMessageRequestParams,
@@ -326,7 +303,7 @@ public abstract partial class McpServer : McpSession
         // redirect through it. Capability checks (ThrowIfRootsUnsupported) are intentionally skipped
         // because the interceptor's alternate channel is responsible for delivering the request to
         // the client. See SendRequestViaInterceptorAsync remarks.
-        if (CurrentOutgoingRequestInterceptor is { } interceptor)
+        if (OutgoingRequestInterceptor is { } interceptor)
         {
             return SendRequestViaInterceptorAsync(interceptor, RequestMethods.RootsList, requestParams,
                 McpJsonUtilities.JsonContext.Default.ListRootsRequestParams,
@@ -372,7 +349,7 @@ public abstract partial class McpServer : McpSession
         // redirect elicitation through it. Capability checks (ThrowIfElicitationUnsupported) are
         // intentionally skipped because the interceptor's alternate channel is responsible for
         // delivering the request to the client. See SendRequestViaInterceptorAsync remarks.
-        if (CurrentOutgoingRequestInterceptor is { } interceptor)
+        if (OutgoingRequestInterceptor is { } interceptor)
         {
             var paramsNode = JsonSerializer.SerializeToNode(requestParams, McpJsonUtilities.JsonContext.Default.ElicitRequestParams);
             var resultNode = await interceptor(RequestMethods.ElicitationCreate, paramsNode, cancellationToken).ConfigureAwait(false);

src/ModelContextProtocol.Core/Server/McpServerHandlers.cs

@@ -72,7 +72,9 @@ public sealed class McpServerHandlers
     /// a <see cref="CallToolResult"/> for immediate results or an alternate <see cref="Result"/> subtype.
     /// </para>
     /// <para>
-    /// Cannot be set if <see cref="CallToolHandler"/> is already set.
+    /// This is a low-level full replacement for the ordinary tool-call pipeline. It cannot be set if
+    /// <see cref="CallToolHandler"/> is already set, and it cannot be composed with ordinary
+    /// <see cref="McpRequestFilters.CallToolFilters"/>.
     /// </para>
     /// </remarks>
     /// <exception cref="InvalidOperationException"><see cref="CallToolHandler"/> is already set.</exception>

src/ModelContextProtocol.Core/Server/McpServerImpl.cs

@@ -33,7 +33,6 @@ internal sealed partial class McpServerImpl : McpServer
     private readonly SemaphoreSlim _disposeLock = new(1, 1);
     private readonly ConcurrentDictionary<string, MrtrContinuation> _mrtrContinuations = new();
     private readonly ConcurrentDictionary<RequestId, MrtrContext> _mrtrContextsByRequestId = new();
-
     private static readonly string[] s_perRequestMetadataKeys =
     [
         MetaKeys.ProtocolVersion,
@@ -1321,20 +1320,13 @@ internal sealed partial class McpServerImpl : McpServer
         var callToolFilters = options.Filters.Request.CallToolFilters;
         var callToolWithAlternateFilters = options.Filters.Request.CallToolWithAlternateFilters;
 
-        // Validate: cannot mix non-alternate filters/handler with alternate filters/handler.
-        bool hasNonAlternatePath = callToolHandler is not null || callToolFilters.Count > 0;
-        bool hasAlternatePath = callToolWithAlternateHandler is not null || callToolWithAlternateFilters.Count > 0;
-
-        if (hasNonAlternatePath && hasAlternatePath)
+        if (callToolWithAlternateHandler is not null && callToolFilters.Count > 0)
         {
             throw new InvalidOperationException(
-                $"Cannot mix non-alternate ({nameof(McpServerHandlers.CallToolHandler)}/{nameof(McpRequestFilters.CallToolFilters)}) " +
-                $"with alternate-based ({nameof(McpServerHandlers.CallToolWithAlternateHandler)}/{nameof(McpRequestFilters.CallToolWithAlternateFilters)}) tool-call filters or handlers. " +
-                $"These two styles cannot currently be composed on the same server. " +
-                $"This most commonly happens when combining features that register different tool-call filter styles, " +
-                $"for example AddAuthorizationFilters() (which registers a {nameof(McpRequestFilters.CallToolFilters)} filter) together with " +
-                $"WithTasks() (which registers a {nameof(McpRequestFilters.CallToolWithAlternateFilters)} filter). " +
-                $"Configure only one style, or avoid combining features that require different styles.");
+                $"Cannot apply {nameof(McpRequestFilters.CallToolFilters)} when an explicit " +
+                $"{nameof(McpServerHandlers.CallToolWithAlternateHandler)} is configured. The alternate handler " +
+                $"replaces the ordinary tool-call pipeline. Move the behavior to " +
+                $"{nameof(McpRequestFilters.CallToolWithAlternateFilters)} or remove the explicit alternate handler.");
         }
 
         // Handle tools provided via DI by augmenting the list handler.
@@ -1376,18 +1368,16 @@ internal sealed partial class McpServerImpl : McpServer
 
         listToolsHandler = BuildFilterPipeline(listToolsHandler, options.Filters.Request.ListToolsFilters);
 
-        // Build the unified alternate-result handler from one of the two paths.
-        if (hasAlternatePath)
+        // An explicit alternate handler replaces the ordinary tool-call pipeline.
+        if (callToolWithAlternateHandler is not null)
         {
-            // Case 2: alternate filter + alternate handler
-            callToolWithAlternateHandler ??= (static async (request, _) => throw new McpProtocolException($"Unknown tool: '{request.Params?.Name}'", McpErrorCode.InvalidParams));
-
             // Augment with DI tools.
             if (tools is not null)
             {
                 var originalHandler = callToolWithAlternateHandler;
                 callToolWithAlternateHandler = (request, cancellationToken) =>
                 {
+                    MatchTool(request, tools);
                     if (request.MatchedPrimitive is McpServerTool tool)
                     {
                         return InvokeToolWithAlternate(tool, request, cancellationToken);
@@ -1397,11 +1387,13 @@ internal sealed partial class McpServerImpl : McpServer
                 };
             }
 
-            callToolWithAlternateHandler = BuildFilterPipeline(callToolWithAlternateHandler, callToolWithAlternateFilters, BuildInitialAlternateToolFilter(tools));
+            callToolWithAlternateHandler = BuildInvocationFilterPipeline(
+                callToolWithAlternateHandler,
+                callToolWithAlternateFilters,
+                BuildInitialAlternateToolFilter(tools));
         }
         else
         {
-            // Case 1: non-alternate filter + non-alternate handler -> apply filters, then convert to alternate-based
             callToolHandler ??= (static async (request, _) => throw new McpProtocolException($"Unknown tool: '{request.Params?.Name}'", McpErrorCode.InvalidParams));
 
             // Augment with DI tools.
@@ -1419,12 +1411,12 @@ internal sealed partial class McpServerImpl : McpServer
                 };
             }
 
-            callToolHandler = BuildFilterPipeline(callToolHandler, callToolFilters, BuildInitialCallToolFilter(tools));
+            callToolHandler = BuildFilterPipeline(callToolHandler, callToolFilters);
 
-            // Convert to alternate-based.
-            var finalCallToolHandler = callToolHandler;
-            callToolWithAlternateHandler = async (request, cancellationToken) =>
-                await finalCallToolHandler(request, cancellationToken).ConfigureAwait(false);
+            callToolWithAlternateHandler = BuildComposedCallToolHandler(
+                callToolHandler,
+                callToolWithAlternateFilters,
+                tools);
         }
         ServerCapabilities.Tools.ListChanged = listChanged;
 
@@ -1448,58 +1440,79 @@ internal sealed partial class McpServerImpl : McpServer
         return await tool.InvokeAsync(request, cancellationToken).ConfigureAwait(false);
     }
 
-    private McpRequestFilter<CallToolRequestParams, CallToolResult> BuildInitialCallToolFilter(
-        McpServerPrimitiveCollection<McpServerTool>? tools) => handler =>
-        async (request, cancellationToken) =>
+    private McpRequestHandler<CallToolRequestParams, ResultOrAlternate<CallToolResult>> BuildComposedCallToolHandler(
+        McpRequestHandler<CallToolRequestParams, CallToolResult> callToolHandler,
+        IList<McpRequestInvocationFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>>> callToolWithAlternateFilters,
+        McpServerPrimitiveCollection<McpServerTool>? tools)
+    {
+        return async (request, cancellationToken) =>
         {
-            if (request.Params?.Name is { } toolName && tools is not null &&
-                tools.TryGetPrimitive(toolName, out var tool))
-            {
-                request.MatchedPrimitive = tool;
-            }
+            MatchTool(request, tools);
+
+            var invocation = new ComposedCallToolInvocationState();
+            var composedHandler = BuildInvocationFilterPipeline(
+                InvokeOrdinaryPipelineAsync,
+                callToolWithAlternateFilters);
 
             try
             {
-                var result = await handler(request, cancellationToken).ConfigureAwait(false);
-                ToolCallCompleted(request.Params?.Name ?? string.Empty, result.IsError is true);
+                var result = await composedHandler(request, cancellationToken).ConfigureAwait(false);
+                LogToolCallLifecycles(request, invocation.CompleteOuter(result));
                 return result;
             }
             catch (Exception e)
             {
-                // Skip logging for InputRequiredException - it's normal MRTR control flow,
-                // not an error (tools throw it to signal an InputRequiredResult).
-                if (!(e is OperationCanceledException && cancellationToken.IsCancellationRequested) && e is not InputRequiredException)
-                {
-                    ToolCallError(request.Params?.Name ?? string.Empty, e);
-                }
+                LogToolCallLifecycles(
+                    request,
+                    invocation.CompleteOuterException(
+                        e,
+                        cancellationToken.IsCancellationRequested));
 
                 if ((e is OperationCanceledException && cancellationToken.IsCancellationRequested) || e is McpProtocolException || e is InputRequiredException)
                 {
                     throw;
                 }
 
-                return new()
+                return CreateToolCallErrorResult(request, e);
+            }
+
+            async ValueTask<ResultOrAlternate<CallToolResult>> InvokeOrdinaryPipelineAsync(
+                RequestContext<CallToolRequestParams> ordinaryRequest,
+                CancellationToken ordinaryCancellationToken)
+            {
+                try
                 {
-                    IsError = true,
-                    Content = [new TextContentBlock
+                    MatchTool(ordinaryRequest, tools);
+                    var result = await callToolHandler(ordinaryRequest, ordinaryCancellationToken).ConfigureAwait(false);
+                    LogToolCallLifecycles(ordinaryRequest, invocation.RecordOrdinaryResult(result));
+                    return result;
+                }
+                catch (Exception exception)
+                {
+                    LogToolCallLifecycles(
+                        ordinaryRequest,
+                        invocation.RecordOrdinaryException(
+                            exception,
+                            ordinaryCancellationToken.IsCancellationRequested));
+
+                    if ((exception is OperationCanceledException && ordinaryCancellationToken.IsCancellationRequested) ||
+                        exception is McpProtocolException ||
+                        exception is InputRequiredException)
                     {
-                        Text = e is McpException ?
-                            $"An error occurred invoking '{request.Params?.Name}': {e.Message}" :
-                            $"An error occurred invoking '{request.Params?.Name}'.",
-                    }],
-                };
+                        throw;
+                    }
+
+                    return CreateToolCallErrorResult(ordinaryRequest, exception);
+                }
             }
         };
+    }
 
-    private McpRequestFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>> BuildInitialAlternateToolFilter(
-        McpServerPrimitiveCollection<McpServerTool>? tools) => handler =>
-        async (request, cancellationToken) =>
+    private McpRequestInvocationFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>> BuildInitialAlternateToolFilter(
+        McpServerPrimitiveCollection<McpServerTool>? tools) =>
+        async (request, handler, cancellationToken) =>
         {
-            if (request.Params?.Name is { } toolName && tools is not null &&
-                tools.TryGetPrimitive(toolName, out var tool))
-            {
-                request.MatchedPrimitive = tool;
-            }
+            MatchTool(request, tools);
 
             try
             {
@@ -1525,18 +1538,54 @@ internal sealed partial class McpServerImpl : McpServer
                     throw;
                 }
 
-                return new CallToolResult
-                {
-                    IsError = true,
-                    Content = [new TextContentBlock
-                    {
-                        Text = e is McpException ?
-                            $"An error occurred invoking '{request.Params?.Name}': {e.Message}" :
-                            $"An error occurred invoking '{request.Params?.Name}'.",
-                    }],
-                };
+                return CreateToolCallErrorResult(request, e);
             }
         };
+
+    private static void MatchTool(
+        RequestContext<CallToolRequestParams> request,
+        McpServerPrimitiveCollection<McpServerTool>? tools)
+    {
+        if (request.Params?.Name is { } toolName && tools is not null &&
+            tools.TryGetPrimitive(toolName, out var tool))
+        {
+            request.MatchedPrimitive = tool;
+        }
+    }
+
+    private static CallToolResult CreateToolCallErrorResult(
+        RequestContext<CallToolRequestParams> request,
+        Exception exception) =>
+        new()
+        {
+            IsError = true,
+            Content = [new TextContentBlock
+            {
+                Text = exception is McpException ?
+                    $"An error occurred invoking '{request.Params?.Name}': {exception.Message}" :
+                    $"An error occurred invoking '{request.Params?.Name}'.",
+            }],
+        };
+
+    private void LogToolCallLifecycles(
+        RequestContext<CallToolRequestParams> request,
+        IReadOnlyList<ToolCallLifecycle> lifecycles)
+    {
+        string toolName = request.Params?.Name ?? string.Empty;
+        foreach (var lifecycle in lifecycles)
+        {
+            if (lifecycle.Result is { } result)
+            {
+                ToolCallCompleted(toolName, result.IsError is true);
+            }
+            else if (!(lifecycle.Exception is OperationCanceledException && lifecycle.CancellationRequested) &&
+                lifecycle.Exception is not InputRequiredException)
+            {
+                ToolCallError(toolName, lifecycle.Exception!);
+            }
+        }
+    }
+
 #pragma warning restore MCPEXP002
 
     private void ConfigureLogging(McpServerOptions options)
@@ -1730,6 +1779,31 @@ internal sealed partial class McpServerImpl : McpServer
         return current;
     }
 
+#pragma warning disable MCPEXP002
+    private static McpRequestHandler<TParams, TResult> BuildInvocationFilterPipeline<TParams, TResult>(
+        McpRequestHandler<TParams, TResult> baseHandler,
+        IList<McpRequestInvocationFilter<TParams, TResult>> filters,
+        McpRequestInvocationFilter<TParams, TResult>? initialHandler = null)
+    {
+        var current = baseHandler;
+
+        for (int i = filters.Count - 1; i >= 0; i--)
+        {
+            var next = current;
+            var filter = filters[i];
+            current = (request, cancellationToken) => filter(request, next, cancellationToken);
+        }
+
+        if (initialHandler is not null)
+        {
+            var next = current;
+            current = (request, cancellationToken) => initialHandler(request, next, cancellationToken);
+        }
+
+        return current;
+    }
+#pragma warning restore MCPEXP002
+
     private JsonRpcMessageFilter BuildMessageFilterPipeline(IList<McpMessageFilter> filters)
     {
         if (filters.Count == 0)

src/ModelContextProtocol.Core/Server/OutgoingRequestInterceptingMcpServer.cs

@@ -0,0 +1,56 @@
+using ModelContextProtocol.Protocol;
+using System.Text.Json.Nodes;
+
+namespace ModelContextProtocol.Server;
+
+#pragma warning disable MCPEXP002
+internal sealed class OutgoingRequestInterceptingMcpServer(
+    McpServer server,
+    Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>> interceptor) : McpServer
+#pragma warning restore MCPEXP002
+{
+    internal override Func<string, JsonNode?, CancellationToken, ValueTask<JsonNode?>>? OutgoingRequestInterceptor => interceptor;
+
+    public override string? SessionId => server.SessionId;
+
+    public override string? NegotiatedProtocolVersion => server.NegotiatedProtocolVersion;
+
+    public override ClientCapabilities? ClientCapabilities => server.ClientCapabilities;
+
+    public override Implementation? ClientInfo => server.ClientInfo;
+
+    public override McpServerOptions ServerOptions => server.ServerOptions;
+
+    public override IServiceProvider? Services => server.Services;
+
+    [Obsolete(Obsoletions.DeprecatedLogging_Message, DiagnosticId = Obsoletions.Deprecated_DiagnosticId, UrlFormat = Obsoletions.Deprecated_Url)]
+    public override LoggingLevel? LoggingLevel => server.LoggingLevel;
+
+    public override bool IsMrtrSupported => server.IsMrtrSupported;
+
+    public override ValueTask DisposeAsync() => server.DisposeAsync();
+
+    public override IAsyncDisposable RegisterNotificationHandler(
+        string method,
+        Func<JsonRpcNotification, CancellationToken, ValueTask> handler) =>
+        server.RegisterNotificationHandler(method, handler);
+
+    public override Task RunAsync(CancellationToken cancellationToken = default) =>
+        server.RunAsync(cancellationToken);
+
+    public override Task SendMessageAsync(JsonRpcMessage message, CancellationToken cancellationToken = default) =>
+        server.SendMessageAsync(message, cancellationToken);
+
+    public override async Task<JsonRpcResponse> SendRequestAsync(
+        JsonRpcRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        Throw.IfNull(request);
+
+        return new JsonRpcResponse
+        {
+            Id = request.Id,
+            Result = await interceptor(request.Method, request.Params, cancellationToken).ConfigureAwait(false),
+        };
+    }
+}

src/ModelContextProtocol.Core/Server/ToolCallLifecycle.cs

@@ -0,0 +1,8 @@
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Server;
+
+internal sealed record ToolCallLifecycle(
+    CallToolResult? Result,
+    Exception? Exception,
+    bool CancellationRequested);

src/ModelContextProtocol.Extensions.Tasks/Server/McpTasksBuilderExtensions.cs

@@ -19,6 +19,12 @@ public static class McpTasksBuilderExtensions
     /// <summary>
     /// Enables MCP Tasks support backed by the specified task store.
     /// </summary>
+    /// <remarks>
+    /// Tasks are implemented as an alternate-result call-tool filter. Alternate-result filters registered before
+    /// the Tasks filter run before task creation. Filters registered after it, along with all ordinary call-tool
+    /// filters, run in the background before the tool.
+    /// Register Tasks before configuring ordinary call-tool filters.
+    /// </remarks>
     /// <param name="builder">The server builder.</param>
     /// <param name="store">The task store.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>
@@ -35,18 +41,25 @@ public static class McpTasksBuilderExtensions
         // Resolve ILoggerFactory from the provider (rather than requiring the caller to pass one) so the
         // background task body has somewhere to report failures. It is optional: if no logging is
         // registered, the options fall back to NullLoggerFactory.
-        builder.Services.AddSingleton<IPostConfigureOptions<McpServerOptions>>(
-            sp => new McpTasksPostConfigureOptions(store, sp.GetService<ILoggerFactory>()));
+        builder.Services.AddSingleton<IConfigureOptions<McpServerOptions>>(
+            sp => new McpTasksConfigureOptions(
+                store,
+                sp.GetRequiredService<IServiceScopeFactory>(),
+                sp.GetService<ILoggerFactory>()));
         return builder;
     }
 
-    private sealed class McpTasksPostConfigureOptions(IMcpTaskStore store, ILoggerFactory? loggerFactory) : IPostConfigureOptions<McpServerOptions>
+    private sealed class McpTasksConfigureOptions(
+        IMcpTaskStore store,
+        IServiceScopeFactory serviceScopeFactory,
+        ILoggerFactory? loggerFactory) : IConfigureOptions<McpServerOptions>
     {
         private readonly IMcpTaskStore _store = store;
-        private readonly ILogger _logger = (loggerFactory ?? NullLoggerFactory.Instance).CreateLogger<McpTasksPostConfigureOptions>();
+        private readonly IServiceScopeFactory _serviceScopeFactory = serviceScopeFactory;
+        private readonly ILogger _logger = (loggerFactory ?? NullLoggerFactory.Instance).CreateLogger<McpTasksConfigureOptions>();
         private readonly ConcurrentDictionary<string, CancellationTokenSource> _cancellationSources = new(StringComparer.Ordinal);
 
-        public void PostConfigure(string? name, McpServerOptions options)
+        public void Configure(McpServerOptions options)
         {
 #if NET
             ArgumentNullException.ThrowIfNull(options);
@@ -66,124 +79,179 @@ public static class McpTasksBuilderExtensions
             options.RequestHandlers.Add(new McpServerRequestHandler { Method = TasksProtocol.MethodTasksUpdate, Handler = HandleUpdateTask });
             options.RequestHandlers.Add(new McpServerRequestHandler { Method = TasksProtocol.MethodTasksCancel, Handler = HandleCancelTask });
 
+            if (options.Filters.Request.CallToolFilters.Count > 0)
+            {
+                throw new InvalidOperationException(
+                    $"{nameof(WithTasks)} must be configured before ordinary call-tool filters because " +
+                    "the Tasks filter must execute outside the ordinary call-tool pipeline.");
+            }
+
             // Use a filter rather than a handler so it wraps around Core's tool dispatch.
             // This ensures it intercepts tool calls BEFORE the tool is invoked, allowing
             // it to spawn background execution and return the task alternate immediately.
-            options.Filters.Request.CallToolWithAlternateFilters.Add(next => async (request, cancellationToken) =>
-            {
-                if (IsJuly2026OrLaterProtocolRequest(request.JsonRpcRequest) && HasTaskExtensionOptIn(request.Params?.Meta))
+            options.Filters.Request.CallToolWithAlternateFilters.Insert(
+                options.Filters.Request.CallToolWithAlternateFilters.Count,
+                async (request, next, cancellationToken) =>
                 {
-                    var taskInfo = await _store.CreateTaskAsync(cancellationToken).ConfigureAwait(false);
-                    var taskId = taskInfo.TaskId;
-                    var cts = new CancellationTokenSource();
-                    _cancellationSources[taskId] = cts;
-                    var taskCancellationToken = cts.Token;
-
-                    _ = Task.Run(async () =>
+                    if (!IsJuly2026OrLaterProtocolRequest(request.JsonRpcRequest) || !HasTaskExtensionOptIn(request.Params?.Meta))
                     {
-                        try
-                        {
-                            using (McpTasksServerExtensions.CreateMcpTaskScope(request.Server, taskId, _store))
-                            {
-                                try
-                                {
-                                    var augmented = await next(request, taskCancellationToken).ConfigureAwait(false);
+                        return await next(request, cancellationToken).ConfigureAwait(false);
+                    }
 
-                                    if (augmented.IsAlternate)
-                                    {
-                                        var error = new JsonRpcErrorDetail
-                                        {
-                                            Code = (int)McpErrorCode.InternalError,
-                                            Message = $"{nameof(IMcpTaskStore)} is configured and the {nameof(McpServerHandlers.CallToolWithAlternateHandler)} returned IsAlternate = true. Use only one mechanism.",
-                                        };
-                                        var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
-                                        await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
-                                        return;
-                                    }
+                    return await RunAsTaskAsync(next, request, cancellationToken).ConfigureAwait(false);
+                });
+        }
 
-                                    var resultJson = JsonSerializer.SerializeToElement(augmented.Result!, McpJsonUtilities.DefaultOptions.GetTypeInfo<CallToolResult>());
-                                    await _store.SetCompletedAsync(taskId, resultJson).ConfigureAwait(false);
-                                }
-                                catch (OperationCanceledException) when (taskCancellationToken.IsCancellationRequested)
-                                {
-                                    await _store.SetCancelledAsync(taskId, CancellationToken.None).ConfigureAwait(false);
-                                }
-                                catch (InputRequiredException)
-                                {
-                                    var error = new JsonRpcErrorDetail
-                                    {
-                                        Code = (int)McpErrorCode.InvalidRequest,
-                                        Message = "MRTR and tasks cannot be composed via [McpServerTool] yet.",
-                                    };
-                                    var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
-                                    await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
-                                }
-                                catch (McpProtocolException mcpEx)
-                                {
-                                    // SEP-2663 §186: protocol exceptions store as failed with JSON-RPC error shape.
-                                    var error = new JsonRpcErrorDetail { Code = (int)mcpEx.ErrorCode, Message = mcpEx.Message };
-                                    var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
-                                    await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
-                                }
-                                catch (Exception ex)
-                                {
-                                    // Non-protocol exceptions are wrapped as CallToolResult { IsError = true },
-                                    // matching Core's BuildInitialAlternateToolFilter behavior.
-                                    var errorResult = new CallToolResult
-                                    {
-                                        IsError = true,
-                                        Content = [new TextContentBlock
-                                        {
-                                            Text = ex is McpException
-                                                ? $"An error occurred invoking '{request.Params?.Name}': {ex.Message}"
-                                                : $"An error occurred invoking '{request.Params?.Name}'.",
-                                        }],
-                                    };
-                                    var resultJson = JsonSerializer.SerializeToElement(errorResult, McpJsonUtilities.DefaultOptions.GetTypeInfo<CallToolResult>());
-                                    await _store.SetCompletedAsync(taskId, resultJson).ConfigureAwait(false);
-                                }
-                                finally
-                                {
-                                    if (_cancellationSources.TryRemove(taskId, out var registeredCts))
-                                    {
-                                        registeredCts.Dispose();
-                                    }
-                                }
-                            }
-                        }
-                        catch (Exception outer)
-                        {
-                            // The inner handlers above record every expected outcome. Reaching here means a
-                            // store operation inside one of those handlers (or the task scope) threw, most
-                            // likely from a custom IMcpTaskStore. Record the failure best-effort and never let
-                            // it surface as an unobserved task exception.
-                            _logger.LogError(outer, "Background execution of task '{TaskId}' terminated unexpectedly while recording its result.", taskId);
+        private async ValueTask<ResultOrAlternate<CallToolResult>> RunAsTaskAsync(
+            McpRequestHandler<CallToolRequestParams, ResultOrAlternate<CallToolResult>> next,
+            RequestContext<CallToolRequestParams> request,
+            CancellationToken cancellationToken)
+        {
+            var executionScope = _serviceScopeFactory.CreateAsyncScope();
+            var executionRequest = new RequestContext<CallToolRequestParams>(
+                request.Server,
+                request.JsonRpcRequest,
+                request.Params)
+            {
+                MatchedPrimitive = request.MatchedPrimitive,
+                Services = executionScope.ServiceProvider,
+            };
 
-                            try
-                            {
-                                var error = new JsonRpcErrorDetail { Code = (int)McpErrorCode.InternalError, Message = outer.Message };
-                                var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
-                                await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
-                            }
-                            catch (Exception storeEx)
-                            {
-                                _logger.LogError(storeEx, "Failed to record the failure of background task '{TaskId}'.", taskId);
-                            }
+            McpTaskInfo taskInfo;
+            try
+            {
+                taskInfo = await _store.CreateTaskAsync(cancellationToken).ConfigureAwait(false);
+            }
+            catch
+            {
+                await executionScope.DisposeAsync().ConfigureAwait(false);
+                throw;
+            }
 
-                            if (_cancellationSources.TryRemove(taskId, out var leftoverCts))
-                            {
-                                leftoverCts.Dispose();
-                            }
-                        }
-                    }, CancellationToken.None);
+            var taskId = taskInfo.TaskId;
+            executionRequest.Server = request.Server.WithMcpTaskOutgoingRequestInterceptor(taskId, _store);
+            var cts = new CancellationTokenSource();
+            _cancellationSources[taskId] = cts;
 
-                    return ResultOrAlternate<CallToolResult>.FromAlternate(
-                        ToCreateTaskResult(taskInfo),
-                        McpTasksJsonContext.Default.CreateTaskResult);
+            // Capture the token before dispatching. Cancellation can remove and dispose the source
+            // before the background delegate starts.
+            var taskCancellationToken = cts.Token;
+            _ = Task.Run(
+                () => ExecuteTaskAsync(next, executionRequest, taskId, taskCancellationToken, executionScope),
+                CancellationToken.None);
+
+            return ResultOrAlternate<CallToolResult>.FromAlternate(
+                ToCreateTaskResult(taskInfo),
+                McpTasksJsonContext.Default.CreateTaskResult);
+        }
+
+        private async Task ExecuteTaskAsync(
+            McpRequestHandler<CallToolRequestParams, ResultOrAlternate<CallToolResult>> next,
+            RequestContext<CallToolRequestParams> request,
+            string taskId,
+            CancellationToken taskCancellationToken,
+            AsyncServiceScope executionScope)
+        {
+            try
+            {
+                try
+                {
+                    await ExecuteToolPipelineAsync(next, request, taskId, taskCancellationToken).ConfigureAwait(false);
+                }
+                finally
+                {
+                    await executionScope.DisposeAsync().ConfigureAwait(false);
+                }
+            }
+            catch (Exception outer)
+            {
+                // Expected outcomes are recorded by ExecuteToolPipelineAsync. Reaching here means a
+                // store operation, task scope, or service scope failed. Record it best-effort.
+                _logger.LogError(outer, "Background execution of task '{TaskId}' terminated unexpectedly while recording its result.", taskId);
+
+                try
+                {
+                    var error = new JsonRpcErrorDetail { Code = (int)McpErrorCode.InternalError, Message = outer.Message };
+                    var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
+                    await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
+                }
+                catch (Exception storeEx)
+                {
+                    _logger.LogError(storeEx, "Failed to record the failure of background task '{TaskId}'.", taskId);
+                }
+            }
+            finally
+            {
+                if (_cancellationSources.TryRemove(taskId, out var registeredCts))
+                {
+                    registeredCts.Dispose();
+                }
+            }
+        }
+
+        private async Task ExecuteToolPipelineAsync(
+            McpRequestHandler<CallToolRequestParams, ResultOrAlternate<CallToolResult>> next,
+            RequestContext<CallToolRequestParams> request,
+            string taskId,
+            CancellationToken taskCancellationToken)
+        {
+            try
+            {
+                var augmented = await next(request, taskCancellationToken).ConfigureAwait(false);
+
+                if (augmented.IsAlternate)
+                {
+                    var error = new JsonRpcErrorDetail
+                    {
+                        Code = (int)McpErrorCode.InternalError,
+                        Message = $"{nameof(IMcpTaskStore)} is configured and the {nameof(McpServerHandlers.CallToolWithAlternateHandler)} returned IsAlternate = true. Use only one mechanism.",
+                    };
+                    var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
+                    await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
+                    return;
                 }
 
-                return await next(request, cancellationToken).ConfigureAwait(false);
-            });
+                var resultJson = JsonSerializer.SerializeToElement(augmented.Result!, McpJsonUtilities.DefaultOptions.GetTypeInfo<CallToolResult>());
+                await _store.SetCompletedAsync(taskId, resultJson).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (taskCancellationToken.IsCancellationRequested)
+            {
+                await _store.SetCancelledAsync(taskId, CancellationToken.None).ConfigureAwait(false);
+            }
+            catch (InputRequiredException)
+            {
+                var error = new JsonRpcErrorDetail
+                {
+                    Code = (int)McpErrorCode.InvalidRequest,
+                    Message = "MRTR and tasks cannot be composed via [McpServerTool] yet.",
+                };
+                var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
+                await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
+            }
+            catch (McpProtocolException mcpEx)
+            {
+                // SEP-2663 §186: protocol exceptions store as failed with JSON-RPC error shape.
+                var error = new JsonRpcErrorDetail { Code = (int)mcpEx.ErrorCode, Message = mcpEx.Message };
+                var errorJson = JsonSerializer.SerializeToElement(error, McpJsonUtilities.DefaultOptions.GetTypeInfo<JsonRpcErrorDetail>());
+                await _store.SetFailedAsync(taskId, errorJson).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                // Non-protocol exceptions are wrapped as CallToolResult { IsError = true },
+                // matching Core's BuildInitialCallToolFilter behavior.
+                var errorResult = new CallToolResult
+                {
+                    IsError = true,
+                    Content = [new TextContentBlock
+                    {
+                        Text = ex is McpException
+                            ? $"An error occurred invoking '{request.Params?.Name}': {ex.Message}"
+                            : $"An error occurred invoking '{request.Params?.Name}'.",
+                    }],
+                };
+                var resultJson = JsonSerializer.SerializeToElement(errorResult, McpJsonUtilities.DefaultOptions.GetTypeInfo<CallToolResult>());
+                await _store.SetCompletedAsync(taskId, resultJson).ConfigureAwait(false);
+            }
         }
 
         private async ValueTask<JsonNode?> HandleGetTask(JsonRpcRequest request, CancellationToken cancellationToken)

src/ModelContextProtocol.Extensions.Tasks/Server/McpTasksServerExtensions.cs

@@ -37,14 +37,10 @@ public static class McpTasksServerExtensions
             cancellationToken);
     }
 
-    /// <summary>
-    /// Creates a scope that routes server-initiated requests through the specified task store.
-    /// </summary>
-    /// <param name="server">The server whose outgoing requests should be redirected.</param>
-    /// <param name="taskId">The related task identifier.</param>
-    /// <param name="store">The task store used to surface input requests.</param>
-    /// <returns>An <see cref="IDisposable"/> that restores the previous outgoing-request behavior.</returns>
-    public static IDisposable CreateMcpTaskScope(this McpServer server, string taskId, IMcpTaskStore store)
+    internal static McpServer WithMcpTaskOutgoingRequestInterceptor(
+        this McpServer server,
+        string taskId,
+        IMcpTaskStore store)
     {
 #if NET
         ArgumentNullException.ThrowIfNull(server);
@@ -56,7 +52,7 @@ public static class McpTasksServerExtensions
         if (store is null) throw new ArgumentNullException(nameof(store));
 #endif
 
-        return server.InterceptOutgoingRequests(async (method, paramsNode, cancellationToken) =>
+        return server.WithOutgoingRequestInterceptor(async (method, paramsNode, cancellationToken) =>
         {
             var requestId = Guid.NewGuid().ToString("N");
 

src/ModelContextProtocol/McpRequestFilterBuilderExtensions.cs

@@ -42,6 +42,10 @@ public static class McpRequestFilterBuilderExtensions
     /// <summary>
     /// Adds a filter to the call tool handler pipeline.
     /// </summary>
+    /// <remarks>
+    /// This ordinary call-tool filter runs inside all alternate-result call-tool filters. For a task-backed call,
+    /// it executes in the background after task creation and before the tool.
+    /// </remarks>
     /// <param name="builder">The request filter builder instance.</param>
     /// <param name="filter">The filter function that wraps the handler.</param>
     /// <returns>The builder provided in <paramref name="builder"/>.</returns>

tests/ModelContextProtocol.AspNetCore.Tests/HttpTaskIntegrationTests.cs

@@ -0,0 +1,178 @@
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using ModelContextProtocol.AspNetCore.Tests.Utils;
+using ModelContextProtocol.Client;
+using ModelContextProtocol.Extensions.Tasks;
+using ModelContextProtocol.Protocol;
+using ModelContextProtocol.Server;
+using Moq;
+using System.Security.Claims;
+
+namespace ModelContextProtocol.AspNetCore.Tests;
+
+public class HttpTaskIntegrationTests(ITestOutputHelper testOutputHelper) : KestrelInMemoryTest(testOutputHelper)
+{
+    [Fact]
+    public async Task WithTasks_CanCallToolOverHttp()
+    {
+        Builder.Services
+            .AddMcpServer()
+            .WithHttpTransport()
+            .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 })
+            .WithTools<TestTools>();
+
+        await using var app = Builder.Build();
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new HttpClientTransport(
+            new HttpClientTransportOptions { Endpoint = new("http://localhost:5000") },
+            HttpClient,
+            LoggerFactory);
+        await using var client = await McpClient.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        var result = await client.CallToolWithPollingAsync(
+            new CallToolRequestParams { Name = "test" },
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        Assert.Equal("Hello World!", Assert.IsType<TextContentBlock>(Assert.Single(result.Content)).Text);
+    }
+
+    [Fact]
+    public async Task WithTasks_AfterOrdinaryFilter_ThrowsActionableError()
+    {
+        Builder.Services
+            .AddMcpServer(options =>
+            {
+                options.Filters.Request.CallToolFilters.Add(next => next);
+            })
+            .WithHttpTransport()
+            .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 })
+            .WithTools<TestTools>();
+
+        await using var app = Builder.Build();
+
+        var exception = Assert.Throws<InvalidOperationException>(
+            () => app.Services.GetRequiredService<IOptions<McpServerOptions>>().Value);
+        Assert.Contains(nameof(McpTasksBuilderExtensions.WithTasks), exception.Message);
+        Assert.Contains("before ordinary call-tool filters", exception.Message);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task WithTasks_AuthorizedTool_Completes(bool registerTasksBeforeAuthorization)
+    {
+        var serverBuilder = Builder.Services
+            .AddMcpServer()
+            .WithHttpTransport();
+
+        if (registerTasksBeforeAuthorization)
+        {
+            serverBuilder
+                .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 })
+                .AddAuthorizationFilters();
+        }
+        else
+        {
+            serverBuilder
+                .AddAuthorizationFilters()
+                .WithTasks(new InMemoryMcpTaskStore { DefaultPollIntervalMs = 10 });
+        }
+
+        serverBuilder.WithTools<TestTools>();
+        Builder.Services.AddAuthorization();
+
+        await using var app = Builder.Build();
+        app.Use(next => async context =>
+        {
+            context.User = new ClaimsPrincipal(new ClaimsIdentity(
+                [new Claim(ClaimTypes.NameIdentifier, "test-user")],
+                "TestAuthType"));
+            await next(context);
+        });
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new HttpClientTransport(
+            new HttpClientTransportOptions { Endpoint = new("http://localhost:5000") },
+            HttpClient,
+            LoggerFactory);
+        await using var client = await McpClient.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        var result = await client.CallToolWithPollingAsync(
+            new CallToolRequestParams { Name = "authorized-test" },
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        Assert.Equal("Authorized", Assert.IsType<TextContentBlock>(Assert.Single(result.Content)).Text);
+    }
+
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task WithTasks_UnauthorizedTool_DoesNotCreateTask(bool registerTasksBeforeAuthorization)
+    {
+        var taskStore = new Mock<IMcpTaskStore>(MockBehavior.Strict);
+        var serverBuilder = Builder.Services
+            .AddMcpServer()
+            .WithHttpTransport();
+
+        if (registerTasksBeforeAuthorization)
+        {
+            serverBuilder
+                .WithTasks(taskStore.Object)
+                .AddAuthorizationFilters();
+        }
+        else
+        {
+            serverBuilder
+                .AddAuthorizationFilters()
+                .WithTasks(taskStore.Object);
+        }
+
+        serverBuilder.WithTools<TestTools>();
+        Builder.Services.AddAuthorization();
+
+        await using var app = Builder.Build();
+        app.MapMcp();
+        await app.StartAsync(TestContext.Current.CancellationToken);
+
+        await using var transport = new HttpClientTransport(
+            new HttpClientTransportOptions { Endpoint = new("http://localhost:5000") },
+            HttpClient,
+            LoggerFactory);
+        await using var client = await McpClient.CreateAsync(
+            transport,
+            loggerFactory: LoggerFactory,
+            cancellationToken: TestContext.Current.CancellationToken);
+
+        var exception = await Assert.ThrowsAsync<McpProtocolException>(() =>
+            client.CallToolAsTaskAsync(
+                new CallToolRequestParams { Name = "authorized-test" },
+                TestContext.Current.CancellationToken).AsTask());
+
+        Assert.Equal(McpErrorCode.InvalidRequest, exception.ErrorCode);
+        taskStore.Verify(
+            store => store.CreateTaskAsync(It.IsAny<CancellationToken>()),
+            Times.Never);
+    }
+
+    [McpServerToolType]
+    private sealed class TestTools
+    {
+        [McpServerTool(Name = "test")]
+        public static string Test() => "Hello World!";
+
+        [McpServerTool(Name = "authorized-test")]
+        [Authorize]
+        public static string AuthorizedTest() => "Authorized";
+    }
+}

tests/ModelContextProtocol.AspNetCore.Tests/ModelContextProtocol.AspNetCore.Tests.csproj

@@ -60,6 +60,7 @@
     <ProjectReference Include="..\..\samples\TestServerWithHosting\TestServerWithHosting.csproj" />
     <ProjectReference Include="..\..\src\ModelContextProtocol.Core\ModelContextProtocol.Core.csproj" />
     <ProjectReference Include="..\..\src\ModelContextProtocol.AspNetCore\ModelContextProtocol.AspNetCore.csproj" />
+    <ProjectReference Include="..\..\src\ModelContextProtocol.Extensions.Tasks\ModelContextProtocol.Extensions.Tasks.csproj" />
     <ProjectReference Include="..\ModelContextProtocol.TestSseServer\ModelContextProtocol.TestSseServer.csproj" />
     <ProjectReference Include="..\ModelContextProtocol.TestOAuthServer\ModelContextProtocol.TestOAuthServer.csproj" />
     <ProjectReference Include="..\ModelContextProtocol.ConformanceClient\ModelContextProtocol.ConformanceClient.csproj" />

tests/ModelContextProtocol.Tests/Server/CallToolFilterMixingTests.cs

@@ -5,9 +5,8 @@ using ModelContextProtocol.Tests.Utils;
 namespace ModelContextProtocol.Tests.Server;
 
 /// <summary>
-/// Verifies that combining the non-alternate <see cref="McpRequestFilters.CallToolFilters"/> with the
-/// alternate <see cref="McpRequestFilters.CallToolWithAlternateFilters"/> fails at configuration time
-/// with an actionable message.
+/// Verifies composition for the non-alternate <see cref="McpRequestFilters.CallToolFilters"/>
+/// and alternate <see cref="McpRequestFilters.CallToolWithAlternateFilters"/> pipelines.
 /// </summary>
 public class CallToolFilterMixingTests(ITestOutputHelper testOutputHelper) : LoggedTest(testOutputHelper)
 {
@@ -15,24 +14,50 @@ public class CallToolFilterMixingTests(ITestOutputHelper testOutputHelper) : Log
     private static McpRequestFilter<CallToolRequestParams, CallToolResult> PassThroughCallToolFilter =>
         next => next;
 
-    private static McpRequestFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>> PassThroughAlternateFilter =>
-        next => next;
+    private static McpRequestInvocationFilter<CallToolRequestParams, ResultOrAlternate<CallToolResult>> PassThroughAlternateFilter =>
+        static (context, next, cancellationToken) => next(context, cancellationToken);
 
     [Fact]
-    public async Task MixingCallToolFilters_WithAlternateFilters_ThrowsActionableError()
+    public async Task MixingCallToolFilters_WithAlternateFilters_Succeeds()
+    {
+        await using var transport = new StreamServerTransport(Stream.Null, Stream.Null);
+        var options = new McpServerOptions { Capabilities = new() { Tools = new() } };
+        options.Filters.Request.CallToolWithAlternateFilters.Add(PassThroughAlternateFilter);
+        options.Filters.Request.CallToolFilters.Add(PassThroughCallToolFilter);
+
+        await using var server = McpServer.Create(transport, options, LoggerFactory);
+
+        Assert.NotNull(server);
+    }
+
+    [Fact]
+    public async Task AlternateFilters_AddedAfterOrdinaryFilters_Succeeds()
     {
         await using var transport = new StreamServerTransport(Stream.Null, Stream.Null);
         var options = new McpServerOptions { Capabilities = new() { Tools = new() } };
         options.Filters.Request.CallToolFilters.Add(PassThroughCallToolFilter);
         options.Filters.Request.CallToolWithAlternateFilters.Add(PassThroughAlternateFilter);
 
+        await using var server = McpServer.Create(transport, options, LoggerFactory);
+
+        Assert.NotNull(server);
+    }
+
+    [Fact]
+    public async Task CallToolFilters_WithExplicitAlternateHandler_ThrowsActionableError()
+    {
+        await using var transport = new StreamServerTransport(Stream.Null, Stream.Null);
+        var options = new McpServerOptions { Capabilities = new() { Tools = new() } };
+        options.Handlers.CallToolWithAlternateHandler = static (_, _) =>
+            new(new ResultOrAlternate<CallToolResult>(new CallToolResult()));
+        options.Filters.Request.CallToolFilters.Add(PassThroughCallToolFilter);
+
         var ex = Assert.Throws<InvalidOperationException>(
             () => McpServer.Create(transport, options, LoggerFactory));
 
         Assert.Contains(nameof(McpRequestFilters.CallToolFilters), ex.Message);
-        Assert.Contains(nameof(McpRequestFilters.CallToolWithAlternateFilters), ex.Message);
-        Assert.Contains("AddAuthorizationFilters", ex.Message);
-        Assert.Contains("WithTasks", ex.Message);
+        Assert.Contains(nameof(McpServerHandlers.CallToolWithAlternateHandler), ex.Message);
+        Assert.Contains("replaces the ordinary tool-call pipeline", ex.Message);
     }
 
     [Fact]