diff --git a/test/Autofac.Extras.DynamicProxy.Test/ClassInterceptorsWithAttributeFilteringFixture.cs b/test/Autofac.Extras.DynamicProxy.Test/ClassInterceptorsWithAttributeFilteringFixture.cs
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+// Copyright (c) Autofac Project. All rights reserved.
+// Licensed under the MIT License. See LICENSE in the project root for license information.
+
+using Autofac.Features.AttributeFilters;
+using Castle.DynamicProxy;
+
+namespace Autofac.Extras.DynamicProxy.Test;
+
+/// <summary>
+/// Documents the interaction between <c>WithAttributeFiltering</c> and class
+/// interception, including a known limitation tracked by
+/// <see href="https://github.com/autofac/Autofac.Extras.DynamicProxy/issues/56">issue #56</see>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <c>EnableClassInterceptors</c> rewrites the implementation type to a Castle
+/// DynamicProxy subclass, replicating the original constructor parameter
+/// attributes onto the proxy constructor. Castle reproduces an <b>enum</b>
+/// argument passed to an attribute parameter that is typed <see cref="object"/>
+/// (as <c>KeyFilterAttribute(object key)</c> is) using the enum's <b>underlying
+/// integer</b> type rather than the original enum type. As a result the key on
+/// the replicated <see cref="KeyFilterAttribute"/> no longer matches the
+/// registered keyed service, and filtering silently fails.
+/// </para>
+/// <para>
+/// This is an upstream Castle DynamicProxy bug tracked at
+/// <see href="https://github.com/castleproject/Core/issues/748">castleproject/Core#748</see>.
+/// It only affects non-string keys under class interception; string keys and
+/// interface interception are unaffected. The tests below pin the current
+/// behavior so we get a signal if/when the upstream behavior changes.
+/// </para>
+/// </remarks>
+public class ClassInterceptorsWithAttributeFilteringFixture
+{
+    public enum LoggerKey
+    {
+        First,
+        Second,
+    }
+
+    [Fact]
+    public void EnumKeyFilteringWorksWithoutInterception()
+    {
+        // Baseline: WithAttributeFiltering honors an enum [KeyFilter] when
+        // interception is NOT enabled.
+        var builder = new ContainerBuilder();
+        builder.Register(c => "first").Keyed<string>(LoggerKey.First);
+        builder.Register(c => "second").Keyed<string>(LoggerKey.Second);
+        builder.RegisterType<HasEnumKeyedParameter>().WithAttributeFiltering();
+        var container = builder.Build();
+
+        var resolved = container.Resolve<HasEnumKeyedParameter>();
+
+        Assert.Equal("first", resolved.Value);
+    }
+
+    [Fact]
+    public void EnumKeyFilteringIsNotHonoredWithClassInterception()
+    {
+        // KNOWN LIMITATION (issue #56 / castleproject/Core#748): with class
+        // interception the replicated [KeyFilter] loses its enum key type, so the
+        // filter no longer matches the keyed registration and the unkeyed
+        // fallback is injected instead of the "First" keyed value.
+        //
+        // This test documents the *current, incorrect* behavior. If it starts
+        // failing because "first" is resolved, Castle has likely fixed the
+        // underlying bug and this limitation (and the docs/comments) can be
+        // removed.
+        var builder = new ContainerBuilder();
+        builder.RegisterType<NullInterceptor>();
+        builder.Register(c => "first").Keyed<string>(LoggerKey.First);
+        builder.Register(c => "fallback");
+        builder
+            .RegisterType<HasEnumKeyedParameter>()
+            .WithAttributeFiltering()
+            .EnableClassInterceptors()
+            .InterceptedBy(typeof(NullInterceptor));
+        var container = builder.Build();
+
+        var resolved = container.Resolve<HasEnumKeyedParameter>();
+
+        Assert.Equal("fallback", resolved.Value);
+    }
+
+    [Fact]
+    public void StringKeyFilteringWorksWithClassInterception()
+    {
+        // WORKAROUND: a string key round-trips through the object-typed attribute
+        // parameter losslessly, so filtering works with class interception.
+        var builder = new ContainerBuilder();
+        builder.RegisterType<NullInterceptor>();
+        builder.Register(c => "first").Keyed<string>("first-key");
+        builder.Register(c => "fallback");
+        builder
+            .RegisterType<HasStringKeyedParameter>()
+            .WithAttributeFiltering()
+            .EnableClassInterceptors()
+            .InterceptedBy(typeof(NullInterceptor));
+        var container = builder.Build();
+
+        var resolved = container.Resolve<HasStringKeyedParameter>();
+
+        Assert.Equal("first", resolved.Value);
+    }
+
+    [Fact]
+    public void EnumKeyFilteringWorksWithInterfaceInterception()
+    {
+        // WORKAROUND: interface interception does not rewrite the constructor, so
+        // the original [KeyFilter] is read intact and the enum key matches.
+        var builder = new ContainerBuilder();
+        builder.RegisterType<NullInterceptor>();
+        builder.Register(c => "first").Keyed<string>(LoggerKey.First);
+        builder.Register(c => "fallback");
+        builder
+            .RegisterType<HasEnumKeyedParameter>()
+            .WithAttributeFiltering()
+            .As<IHaveValue>()
+            .EnableInterfaceInterceptors()
+            .InterceptedBy(typeof(NullInterceptor));
+        var container = builder.Build();
+
+        var resolved = container.Resolve<IHaveValue>();
+
+        Assert.Equal("first", resolved.Value);
+    }
+
+    public interface IHaveValue
+    {
+        string Value
+        {
+            get;
+        }
+    }
+
+    public class HasEnumKeyedParameter : IHaveValue
+    {
+        public HasEnumKeyedParameter([KeyFilter(LoggerKey.First)] string value)
+        {
+            Value = value;
+        }
+
+        public virtual string Value
+        {
+            get;
+        }
+    }
+
+    public class HasStringKeyedParameter
+    {
+        public HasStringKeyedParameter([KeyFilter("first-key")] string value)
+        {
+            Value = value;
+        }
+
+        public virtual string Value
+        {
+            get;
+        }
+    }
+
+    private class NullInterceptor : IInterceptor
+    {
+        public void Intercept(IInvocation invocation)
+        {
+            invocation.Proceed();
+        }
+    }
+}