From b35dfbdab38e2767158d859901d6ab9cb26b745c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 18:58:39 +0000
Subject: [PATCH 01/19] Add workflow builder edge tests

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/3c3d5324-cdcd-4a38-8c67-94e4e78e29c5

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderSmokeTests.cs              | 179 ++++++++++++++++++
 1 file changed, 179 insertions(+)

diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 2b370de99e..feb59b35dd 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -157,4 +157,183 @@ public void Test_Workflow_NameAndDescription()
         workflow3.Name.Should().Be("Named Only");
         workflow3.Description.Should().BeNull();
     }
+
+    [Fact]
+    public void ForwardMessage_WithSingleTarget_CreatesDirectEdge()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor target = new("target");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .ForwardMessage<string>(source, target)
+            .Build();
+
+        // Assert
+        Edge edge = GetSingleEdge(workflow, source.Id);
+        edge.Kind.Should().Be(EdgeKind.Direct);
+        edge.DirectEdgeData.Should().NotBeNull();
+        edge.DirectEdgeData!.SinkId.Should().Be(target.Id);
+        edge.DirectEdgeData.Condition.Should().NotBeNull();
+        edge.DirectEdgeData.Condition!("message").Should().BeTrue();
+        edge.DirectEdgeData.Condition!(42).Should().BeFalse();
+        edge.DirectEdgeData.Condition!(null).Should().BeFalse();
+    }
+
+    [Fact]
+    public void ForwardMessage_WithMultipleTargets_CreatesFanOutEdge()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor target1 = new("target1");
+        NoOpExecutor target2 = new("target2");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .ForwardMessage<string>(source, [target1, target2], message => message == "match")
+            .Build();
+
+        // Assert
+        Edge edge = GetSingleEdge(workflow, source.Id);
+        edge.Kind.Should().Be(EdgeKind.FanOut);
+        edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SinkIds.Should().Equal([target1.Id, target2.Id]);
+        edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
+        edge.FanOutEdgeData.EdgeAssigner!("match", 2).Should().Equal([0, 1]);
+        edge.FanOutEdgeData.EdgeAssigner!("other", 2).Should().BeEmpty();
+        edge.FanOutEdgeData.EdgeAssigner!(42, 2).Should().BeEmpty();
+    }
+
+    [Fact]
+    public void ForwardExcept_WithSingleTarget_CreatesDirectEdge()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor target = new("target");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .ForwardExcept<string>(source, target)
+            .Build();
+
+        // Assert
+        Edge edge = GetSingleEdge(workflow, source.Id);
+        edge.Kind.Should().Be(EdgeKind.Direct);
+        edge.DirectEdgeData.Should().NotBeNull();
+        edge.DirectEdgeData!.SinkId.Should().Be(target.Id);
+        edge.DirectEdgeData.Condition.Should().NotBeNull();
+        edge.DirectEdgeData.Condition!("message").Should().BeFalse();
+        edge.DirectEdgeData.Condition!(42).Should().BeTrue();
+        edge.DirectEdgeData.Condition!(null).Should().BeTrue();
+    }
+
+    [Fact]
+    public void ForwardExcept_WithMultipleTargets_CreatesFanOutEdge()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor target1 = new("target1");
+        NoOpExecutor target2 = new("target2");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .ForwardExcept<string>(source, [target1, target2])
+            .Build();
+
+        // Assert
+        Edge edge = GetSingleEdge(workflow, source.Id);
+        edge.Kind.Should().Be(EdgeKind.FanOut);
+        edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SinkIds.Should().Equal([target1.Id, target2.Id]);
+        edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
+        edge.FanOutEdgeData.EdgeAssigner!(42, 2).Should().Equal([0, 1]);
+        edge.FanOutEdgeData.EdgeAssigner!("message", 2).Should().BeEmpty();
+    }
+
+    [Fact]
+    public void AddChain_CreatesSequentialDirectEdges()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor middle = new("middle");
+        NoOpExecutor end = new("end");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .AddChain(source, [middle, end])
+            .Build();
+
+        // Assert
+        GetSingleEdge(workflow, source.Id).DirectEdgeData!.SinkId.Should().Be(middle.Id);
+        GetSingleEdge(workflow, middle.Id).DirectEdgeData!.SinkId.Should().Be(end.Id);
+    }
+
+    [Fact]
+    public void AddChain_WhenExecutorRepeats_Throws()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor middle = new("middle");
+
+        // Act
+        Action act = () => new WorkflowBuilder(source.Id)
+            .AddChain(source, [middle, source]);
+
+        // Assert
+        act.Should().Throw<ArgumentException>()
+            .WithParameterName("executors");
+    }
+
+    [Fact]
+    public void AddExternalCall_CreatesRequestPortAndRoundTripEdges()
+    {
+        // Arrange
+        const string PortId = "port1";
+        NoOpExecutor source = new("start");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .AddExternalCall<string, int>(source, PortId)
+            .Build();
+
+        // Assert
+        workflow.Ports.Should().ContainKey(PortId);
+        workflow.Ports[PortId].Request.Should().Be(typeof(string));
+        workflow.Ports[PortId].Response.Should().Be(typeof(int));
+        workflow.ExecutorBindings.Should().ContainKey(PortId);
+        GetSingleEdge(workflow, source.Id).DirectEdgeData!.SinkId.Should().Be(PortId);
+        GetSingleEdge(workflow, PortId).DirectEdgeData!.SinkId.Should().Be(source.Id);
+    }
+
+    [Fact]
+    public void AddSwitch_CreatesFanOutEdgeWithCasesAndDefault()
+    {
+        // Arrange
+        NoOpExecutor source = new("start");
+        NoOpExecutor stringTarget = new("string-target");
+        NoOpExecutor intTarget = new("int-target");
+        NoOpExecutor defaultTarget = new("default-target");
+
+        // Act
+        Workflow workflow = new WorkflowBuilder(source.Id)
+            .AddSwitch(source, switchBuilder => switchBuilder
+                .AddCase<string>(message => message == "match", [stringTarget])
+                .AddCase<int>(message => message > 0, [intTarget])
+                .WithDefault([defaultTarget]))
+            .Build();
+
+        // Assert
+        Edge edge = GetSingleEdge(workflow, source.Id);
+        edge.Kind.Should().Be(EdgeKind.FanOut);
+        edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SinkIds.Should().Equal([stringTarget.Id, intTarget.Id, defaultTarget.Id]);
+        edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
+        edge.FanOutEdgeData.EdgeAssigner!("match", 3).Should().Equal([0]);
+        edge.FanOutEdgeData.EdgeAssigner!(2, 3).Should().Equal([1]);
+        edge.FanOutEdgeData.EdgeAssigner!("other", 3).Should().Equal([2]);
+    }
+
+    private static Edge GetSingleEdge(Workflow workflow, string sourceId)
+        => workflow.Edges[sourceId].Should().ContainSingle().Subject;
 }

From d12579ec6690c297b47fb2778845130433aa189b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:06:14 +0000
Subject: [PATCH 02/19] Strengthen workflow edge helper tests

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../SwitchBuilder.cs                          |   4 +
 .../WorkflowBuilderExtensions.cs              |   5 +
 .../WorkflowBuilderSmokeTests.cs              | 121 +++++++++++++++++-
 3 files changed, 126 insertions(+), 4 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 14e6ed4f7c..286329b6ec 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -39,6 +39,8 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         foreach (ExecutorBinding executor in executors)
         {
+            Throw.IfNull(executor, nameof(executors));
+
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
                 index = this._executors.Count;
@@ -66,6 +68,8 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
 
         foreach (ExecutorBinding executor in executors)
         {
+            Throw.IfNull(executor, nameof(executors));
+
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
                 index = this._executors.Count;
diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index c702cf9ece..f9c3e2056a 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -52,6 +52,8 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance.</returns>
     public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, IEnumerable<ExecutorBinding> targets, Func<TMessage, bool>? condition = null)
     {
+        Throw.IfNull(builder);
+        Throw.IfNull(source);
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
@@ -93,6 +95,8 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance with the added edges.</returns>
     public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, IEnumerable<ExecutorBinding> targets)
     {
+        Throw.IfNull(builder);
+        Throw.IfNull(source);
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
@@ -129,6 +133,7 @@ public static WorkflowBuilder AddChain(this WorkflowBuilder builder, ExecutorBin
     {
         Throw.IfNull(builder);
         Throw.IfNull(source);
+        Throw.IfNull(executors);
 
         HashSet<string> seenExecutors = [source.Id];
 
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index feb59b35dd..1ca2027446 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using FluentAssertions;
 
 namespace Microsoft.Agents.AI.Workflows.UnitTests;
@@ -174,6 +175,7 @@ public void ForwardMessage_WithSingleTarget_CreatesDirectEdge()
         Edge edge = GetSingleEdge(workflow, source.Id);
         edge.Kind.Should().Be(EdgeKind.Direct);
         edge.DirectEdgeData.Should().NotBeNull();
+        edge.DirectEdgeData!.SourceId.Should().Be(source.Id);
         edge.DirectEdgeData!.SinkId.Should().Be(target.Id);
         edge.DirectEdgeData.Condition.Should().NotBeNull();
         edge.DirectEdgeData.Condition!("message").Should().BeTrue();
@@ -198,6 +200,7 @@ public void ForwardMessage_WithMultipleTargets_CreatesFanOutEdge()
         Edge edge = GetSingleEdge(workflow, source.Id);
         edge.Kind.Should().Be(EdgeKind.FanOut);
         edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SourceId.Should().Be(source.Id);
         edge.FanOutEdgeData!.SinkIds.Should().Equal([target1.Id, target2.Id]);
         edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
         edge.FanOutEdgeData.EdgeAssigner!("match", 2).Should().Equal([0, 1]);
@@ -221,6 +224,7 @@ public void ForwardExcept_WithSingleTarget_CreatesDirectEdge()
         Edge edge = GetSingleEdge(workflow, source.Id);
         edge.Kind.Should().Be(EdgeKind.Direct);
         edge.DirectEdgeData.Should().NotBeNull();
+        edge.DirectEdgeData!.SourceId.Should().Be(source.Id);
         edge.DirectEdgeData!.SinkId.Should().Be(target.Id);
         edge.DirectEdgeData.Condition.Should().NotBeNull();
         edge.DirectEdgeData.Condition!("message").Should().BeFalse();
@@ -245,6 +249,7 @@ public void ForwardExcept_WithMultipleTargets_CreatesFanOutEdge()
         Edge edge = GetSingleEdge(workflow, source.Id);
         edge.Kind.Should().Be(EdgeKind.FanOut);
         edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SourceId.Should().Be(source.Id);
         edge.FanOutEdgeData!.SinkIds.Should().Equal([target1.Id, target2.Id]);
         edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
         edge.FanOutEdgeData.EdgeAssigner!(42, 2).Should().Equal([0, 1]);
@@ -265,8 +270,15 @@ public void AddChain_CreatesSequentialDirectEdges()
             .Build();
 
         // Assert
-        GetSingleEdge(workflow, source.Id).DirectEdgeData!.SinkId.Should().Be(middle.Id);
-        GetSingleEdge(workflow, middle.Id).DirectEdgeData!.SinkId.Should().Be(end.Id);
+        Edge firstEdge = GetSingleEdge(workflow, source.Id);
+        firstEdge.Kind.Should().Be(EdgeKind.Direct);
+        firstEdge.DirectEdgeData!.SourceId.Should().Be(source.Id);
+        firstEdge.DirectEdgeData.SinkId.Should().Be(middle.Id);
+
+        Edge secondEdge = GetSingleEdge(workflow, middle.Id);
+        secondEdge.Kind.Should().Be(EdgeKind.Direct);
+        secondEdge.DirectEdgeData!.SourceId.Should().Be(middle.Id);
+        secondEdge.DirectEdgeData.SinkId.Should().Be(end.Id);
     }
 
     [Fact]
@@ -302,8 +314,16 @@ public void AddExternalCall_CreatesRequestPortAndRoundTripEdges()
         workflow.Ports[PortId].Request.Should().Be(typeof(string));
         workflow.Ports[PortId].Response.Should().Be(typeof(int));
         workflow.ExecutorBindings.Should().ContainKey(PortId);
-        GetSingleEdge(workflow, source.Id).DirectEdgeData!.SinkId.Should().Be(PortId);
-        GetSingleEdge(workflow, PortId).DirectEdgeData!.SinkId.Should().Be(source.Id);
+
+        Edge requestEdge = GetSingleEdge(workflow, source.Id);
+        requestEdge.Kind.Should().Be(EdgeKind.Direct);
+        requestEdge.DirectEdgeData!.SourceId.Should().Be(source.Id);
+        requestEdge.DirectEdgeData.SinkId.Should().Be(PortId);
+
+        Edge responseEdge = GetSingleEdge(workflow, PortId);
+        responseEdge.Kind.Should().Be(EdgeKind.Direct);
+        responseEdge.DirectEdgeData!.SourceId.Should().Be(PortId);
+        responseEdge.DirectEdgeData.SinkId.Should().Be(source.Id);
     }
 
     [Fact]
@@ -327,6 +347,7 @@ public void AddSwitch_CreatesFanOutEdgeWithCasesAndDefault()
         Edge edge = GetSingleEdge(workflow, source.Id);
         edge.Kind.Should().Be(EdgeKind.FanOut);
         edge.FanOutEdgeData.Should().NotBeNull();
+        edge.FanOutEdgeData!.SourceId.Should().Be(source.Id);
         edge.FanOutEdgeData!.SinkIds.Should().Equal([stringTarget.Id, intTarget.Id, defaultTarget.Id]);
         edge.FanOutEdgeData.EdgeAssigner.Should().NotBeNull();
         edge.FanOutEdgeData.EdgeAssigner!("match", 3).Should().Equal([0]);
@@ -334,6 +355,98 @@ public void AddSwitch_CreatesFanOutEdgeWithCasesAndDefault()
         edge.FanOutEdgeData.EdgeAssigner!("other", 3).Should().Equal([2]);
     }
 
+    [Fact]
+    public void ForwardMessage_InvalidArguments_Throw()
+    {
+        // Arrange
+        WorkflowBuilder builder = new("start");
+        NoOpExecutor source = new("start");
+        NoOpExecutor target = new("target");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).ForwardMessage<string>(source, target));
+        Assert.Throws<ArgumentNullException>("source", () => builder.ForwardMessage<string>(null!, target));
+        Assert.Throws<ArgumentNullException>("target", () => builder.ForwardMessage<string>(source, (ExecutorBinding)null!));
+        Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardMessage<string>(source, (IEnumerable<ExecutorBinding>)null!));
+        Assert.Throws<ArgumentNullException>("executors", () => builder.ForwardMessage<string>(source, [target, null!]));
+        Assert.Throws<ArgumentException>("targets", () => builder.ForwardMessage<string>(source, []));
+    }
+
+    [Fact]
+    public void ForwardExcept_InvalidArguments_Throw()
+    {
+        // Arrange
+        WorkflowBuilder builder = new("start");
+        NoOpExecutor source = new("start");
+        NoOpExecutor target = new("target");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).ForwardExcept<string>(source, target));
+        Assert.Throws<ArgumentNullException>("source", () => builder.ForwardExcept<string>(null!, target));
+        Assert.Throws<ArgumentNullException>("target", () => builder.ForwardExcept<string>(source, (ExecutorBinding)null!));
+        Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardExcept<string>(source, (IEnumerable<ExecutorBinding>)null!));
+        Assert.Throws<ArgumentNullException>("executors", () => builder.ForwardExcept<string>(source, [target, null!]));
+        Assert.Throws<ArgumentException>("targets", () => builder.ForwardExcept<string>(source, []));
+    }
+
+    [Fact]
+    public void AddChain_InvalidArguments_Throw()
+    {
+        // Arrange
+        WorkflowBuilder builder = new("start");
+        NoOpExecutor source = new("start");
+        NoOpExecutor target = new("target");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddChain(source, [target]));
+        Assert.Throws<ArgumentNullException>("source", () => builder.AddChain(null!, [target]));
+        Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, null!));
+        Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, [target, null!]));
+        Assert.Throws<ArgumentException>("executors", () => builder.AddChain(source, [target, source]));
+    }
+
+    [Fact]
+    public void AddExternalCall_InvalidArguments_Throw()
+    {
+        // Arrange
+        WorkflowBuilder builder = new("start");
+        NoOpExecutor source = new("start");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddExternalCall<string, int>(source, "port"));
+        Assert.Throws<ArgumentNullException>("source", () => builder.AddExternalCall<string, int>(null!, "port"));
+        Assert.Throws<ArgumentNullException>("portId", () => builder.AddExternalCall<string, int>(source, null!));
+    }
+
+    [Fact]
+    public void AddSwitch_InvalidArguments_Throw()
+    {
+        // Arrange
+        WorkflowBuilder builder = new("start");
+        NoOpExecutor source = new("start");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddSwitch(source, _ => { }));
+        Assert.Throws<ArgumentNullException>("source", () => builder.AddSwitch(null!, _ => { }));
+        Assert.Throws<ArgumentNullException>("configureSwitch", () => builder.AddSwitch(source, null!));
+        Assert.Throws<ArgumentException>("targets", () => builder.AddSwitch(source, _ => { }));
+    }
+
+    [Fact]
+    public void SwitchBuilder_InvalidArguments_Throw()
+    {
+        // Arrange
+        SwitchBuilder switchBuilder = new();
+        NoOpExecutor target = new("target");
+
+        // Act/Assert
+        Assert.Throws<ArgumentNullException>("predicate", () => switchBuilder.AddCase<string>(null!, [target]));
+        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.AddCase<string>(_ => true, null!));
+        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.AddCase<string>(_ => true, [target, null!]));
+        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault(null!));
+        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault([target, null!]));
+    }
+
     private static Edge GetSingleEdge(Workflow workflow, string sourceId)
         => workflow.Edges[sourceId].Should().ContainSingle().Subject;
 }

From 096381d1c345a0fdc498ad44a964b196dca644fa Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:08:19 +0000
Subject: [PATCH 03/19] Normalize edge helper bad input validation

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs              | 34 ++++++++++---------
 .../WorkflowBuilderSmokeTests.cs              |  4 +--
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index f9c3e2056a..b09dec91f4 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -25,7 +25,11 @@ public static class WorkflowBuilderExtensions
     /// <param name="target">The target executor to which messages will be forwarded.</param>
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance.</returns>
     public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, ExecutorBinding target)
-        => builder.ForwardMessage<TMessage>(source, [target], condition: null);
+    {
+        Throw.IfNull(target);
+
+        return builder.ForwardMessage<TMessage>(source, [target], condition: null);
+    }
 
     /// <summary>
     /// Adds edges to the workflow that forward messages of the specified type from the source executor to
@@ -57,17 +61,14 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
+        List<ExecutorBinding> targetList = targets.Select(target => Throw.IfNull(target, nameof(targets))).ToList();
 
-#if NET
-        if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
-#else
-        if (targets is ICollection<ExecutorBinding> { Count: 1 })
-#endif
+        if (targetList.Count == 1)
         {
-            return builder.AddEdge(source, targets.First(), predicate);
+            return builder.AddEdge(source, targetList[0], predicate);
         }
 
-        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targets));
+        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targetList));
 
         // The reason we can check for "not null" here is that CreateConditionFunc<T> will do the correct unwrapping
         // logic for PortableValues.
@@ -83,7 +84,11 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
     /// <param name="target">The target executor to which messages, except those of type <typeparamref name="TMessage"/>, will be forwarded.</param>
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance with the added edges.</returns>
     public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, ExecutorBinding target)
-        => builder.ForwardExcept<TMessage>(source, [target]);
+    {
+        Throw.IfNull(target);
+
+        return builder.ForwardExcept<TMessage>(source, [target]);
+    }
 
     /// <summary>
     /// Adds edges from the specified source to the provided executors, excluding messages of a specified type.
@@ -100,17 +105,14 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
+        List<ExecutorBinding> targetList = targets.Select(target => Throw.IfNull(target, nameof(targets))).ToList();
 
-#if NET
-        if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
-#else
-        if (targets is ICollection<ExecutorBinding> { Count: 1 })
-#endif
+        if (targetList.Count == 1)
         {
-            return builder.AddEdge(source, targets.First(), predicate);
+            return builder.AddEdge(source, targetList[0], predicate);
         }
 
-        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targets));
+        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targetList));
 
         // The reason we can check for "null" here is that CreateConditionFunc<T> will do the correct unwrapping
         // logic for PortableValues.
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 1ca2027446..a44bd9ad8b 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -368,7 +368,7 @@ public void ForwardMessage_InvalidArguments_Throw()
         Assert.Throws<ArgumentNullException>("source", () => builder.ForwardMessage<string>(null!, target));
         Assert.Throws<ArgumentNullException>("target", () => builder.ForwardMessage<string>(source, (ExecutorBinding)null!));
         Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardMessage<string>(source, (IEnumerable<ExecutorBinding>)null!));
-        Assert.Throws<ArgumentNullException>("executors", () => builder.ForwardMessage<string>(source, [target, null!]));
+        Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardMessage<string>(source, [target, null!]));
         Assert.Throws<ArgumentException>("targets", () => builder.ForwardMessage<string>(source, []));
     }
 
@@ -385,7 +385,7 @@ public void ForwardExcept_InvalidArguments_Throw()
         Assert.Throws<ArgumentNullException>("source", () => builder.ForwardExcept<string>(null!, target));
         Assert.Throws<ArgumentNullException>("target", () => builder.ForwardExcept<string>(source, (ExecutorBinding)null!));
         Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardExcept<string>(source, (IEnumerable<ExecutorBinding>)null!));
-        Assert.Throws<ArgumentNullException>("executors", () => builder.ForwardExcept<string>(source, [target, null!]));
+        Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardExcept<string>(source, [target, null!]));
         Assert.Throws<ArgumentException>("targets", () => builder.ForwardExcept<string>(source, []));
     }
 

From 24d1effb52e618773d820ea9e3e7c6dfec2dcf72 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:10:13 +0000
Subject: [PATCH 04/19] Clarify edge helper target validation

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs              | 26 +++++++++++++++----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index b09dec91f4..03131daf8c 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -2,7 +2,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using Microsoft.Shared.Diagnostics;
 
 namespace Microsoft.Agents.AI.Workflows;
@@ -58,10 +57,9 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
     {
         Throw.IfNull(builder);
         Throw.IfNull(source);
-        Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
-        List<ExecutorBinding> targetList = targets.Select(target => Throw.IfNull(target, nameof(targets))).ToList();
+        List<ExecutorBinding> targetList = ValidateTargets(targets);
 
         if (targetList.Count == 1)
         {
@@ -102,10 +100,9 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
     {
         Throw.IfNull(builder);
         Throw.IfNull(source);
-        Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
-        List<ExecutorBinding> targetList = targets.Select(target => Throw.IfNull(target, nameof(targets))).ToList();
+        List<ExecutorBinding> targetList = ValidateTargets(targets);
 
         if (targetList.Count == 1)
         {
@@ -119,6 +116,25 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
         static bool IsAllowedType(object? message) => message is null;
     }
 
+    private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding> targets)
+    {
+        Throw.IfNull(targets);
+
+        List<ExecutorBinding> targetList = [];
+        foreach (ExecutorBinding? target in targets)
+        {
+            if (target is null)
+            {
+                throw new ArgumentNullException(nameof(targets), "Targets collection cannot contain null elements.");
+            }
+
+            targetList.Add(target);
+        }
+
+        Throw.IfNullOrEmpty(targetList, nameof(targets));
+        return targetList;
+    }
+
     /// <summary>
     /// Adds a sequential chain of executors to the workflow, connecting each executor in order so that each is
     /// executed after the previous one.

From 73d19469284da6fcb183866bc14e8da5557b4d64 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:11:36 +0000
Subject: [PATCH 05/19] Use explicit target parameter names

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs                              | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 03131daf8c..37b6f26388 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -25,7 +25,7 @@ public static class WorkflowBuilderExtensions
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance.</returns>
     public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, ExecutorBinding target)
     {
-        Throw.IfNull(target);
+        Throw.IfNull(target, nameof(target));
 
         return builder.ForwardMessage<TMessage>(source, [target], condition: null);
     }
@@ -83,7 +83,7 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
     /// <returns>The updated <see cref="WorkflowBuilder"/> instance with the added edges.</returns>
     public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder builder, ExecutorBinding source, ExecutorBinding target)
     {
-        Throw.IfNull(target);
+        Throw.IfNull(target, nameof(target));
 
         return builder.ForwardExcept<TMessage>(source, [target]);
     }

From 9c839ea6eb9e89508c849cc07d398914f83039a0 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:13:09 +0000
Subject: [PATCH 06/19] Document workflow edge test helpers

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs                           | 7 +++++++
 .../WorkflowBuilderSmokeTests.cs                           | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 37b6f26388..179dc78c88 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -116,6 +116,13 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
         static bool IsAllowedType(object? message) => message is null;
     }
 
+    /// <summary>
+    /// Validates a target collection and returns it as a list.
+    /// </summary>
+    /// <param name="targets">The target executor bindings to validate.</param>
+    /// <returns>A validated list of target executor bindings.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when <paramref name="targets"/> is null or contains a null element.</exception>
+    /// <exception cref="ArgumentException">Thrown when <paramref name="targets"/> is empty.</exception>
     private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding> targets)
     {
         Throw.IfNull(targets);
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index a44bd9ad8b..27bbb1092c 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -447,6 +447,9 @@ public void SwitchBuilder_InvalidArguments_Throw()
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault([target, null!]));
     }
 
+    /// <summary>
+    /// Gets the only edge emitted by the specified workflow source.
+    /// </summary>
     private static Edge GetSingleEdge(Workflow workflow, string sourceId)
         => workflow.Edges[sourceId].Should().ContainSingle().Subject;
 }

From 9a02dafbc36a06786cdb007d401c530eee13d00a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:14:55 +0000
Subject: [PATCH 07/19] Clarify null element validation messages

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../SwitchBuilder.cs                           | 18 ++++++++++++++----
 .../WorkflowBuilderExtensions.cs               |  4 +++-
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 286329b6ec..c347ca84f3 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -37,9 +37,13 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         HashSet<int> indicies = [];
 
-        foreach (ExecutorBinding executor in executors)
+        int executorIndex = 0;
+        foreach (ExecutorBinding? executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            if (executor is null)
+            {
+                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
+            }
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -49,6 +53,7 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
             }
 
             indicies.Add(index);
+            executorIndex++;
         }
 
         Func<object?, bool> casePredicate = WorkflowBuilder.CreateConditionFunc(predicate)!;
@@ -66,9 +71,13 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
     {
         Throw.IfNull(executors);
 
-        foreach (ExecutorBinding executor in executors)
+        int executorIndex = 0;
+        foreach (ExecutorBinding? executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            if (executor is null)
+            {
+                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
+            }
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -78,6 +87,7 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
             }
 
             this._defaultIndicies.Add(index);
+            executorIndex++;
         }
 
         return this;
diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 179dc78c88..c261036c6b 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -128,14 +128,16 @@ private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding
         Throw.IfNull(targets);
 
         List<ExecutorBinding> targetList = [];
+        int targetIndex = 0;
         foreach (ExecutorBinding? target in targets)
         {
             if (target is null)
             {
-                throw new ArgumentNullException(nameof(targets), "Targets collection cannot contain null elements.");
+                throw new ArgumentNullException(nameof(targets), $"Targets collection contains a null element at index {targetIndex}.");
             }
 
             targetList.Add(target);
+            targetIndex++;
         }
 
         Throw.IfNullOrEmpty(targetList, nameof(targets));

From 5ce002d3fd82549868bcf08f41e440c43de7ec7f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:16:28 +0000
Subject: [PATCH 08/19] Add repeated chain executor coverage

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs                      | 11 +++++++++--
 .../WorkflowBuilderSmokeTests.cs                      |  2 ++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index c261036c6b..e7f68e4f69 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -128,9 +128,16 @@ private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding
         Throw.IfNull(targets);
 
         List<ExecutorBinding> targetList = [];
+        using IEnumerator<ExecutorBinding> targetEnumerator = targets.GetEnumerator();
+        if (!targetEnumerator.MoveNext())
+        {
+            throw new ArgumentException("Targets collection cannot be empty.", nameof(targets));
+        }
+
         int targetIndex = 0;
-        foreach (ExecutorBinding? target in targets)
+        do
         {
+            ExecutorBinding? target = targetEnumerator.Current;
             if (target is null)
             {
                 throw new ArgumentNullException(nameof(targets), $"Targets collection contains a null element at index {targetIndex}.");
@@ -139,8 +146,8 @@ private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding
             targetList.Add(target);
             targetIndex++;
         }
+        while (targetEnumerator.MoveNext());
 
-        Throw.IfNullOrEmpty(targetList, nameof(targets));
         return targetList;
     }
 
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 27bbb1092c..4e9cb19ee3 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -396,6 +396,7 @@ public void AddChain_InvalidArguments_Throw()
         WorkflowBuilder builder = new("start");
         NoOpExecutor source = new("start");
         NoOpExecutor target = new("target");
+        NoOpExecutor otherTarget = new("other-target");
 
         // Act/Assert
         Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddChain(source, [target]));
@@ -403,6 +404,7 @@ public void AddChain_InvalidArguments_Throw()
         Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, null!));
         Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, [target, null!]));
         Assert.Throws<ArgumentException>("executors", () => builder.AddChain(source, [target, source]));
+        Assert.Throws<ArgumentException>("executors", () => builder.AddChain(source, [target, otherTarget, target]));
     }
 
     [Fact]

From 824ee2111bc8c8ae3fdc0c208f5a8460303a2dce Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:18:22 +0000
Subject: [PATCH 09/19] Preserve Throw helper validation style

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../SwitchBuilder.cs                          | 18 ++++-------------
 .../WorkflowBuilderExtensions.cs              | 20 ++++---------------
 2 files changed, 8 insertions(+), 30 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index c347ca84f3..286329b6ec 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -37,13 +37,9 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         HashSet<int> indicies = [];
 
-        int executorIndex = 0;
-        foreach (ExecutorBinding? executor in executors)
+        foreach (ExecutorBinding executor in executors)
         {
-            if (executor is null)
-            {
-                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
-            }
+            Throw.IfNull(executor, nameof(executors));
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -53,7 +49,6 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
             }
 
             indicies.Add(index);
-            executorIndex++;
         }
 
         Func<object?, bool> casePredicate = WorkflowBuilder.CreateConditionFunc(predicate)!;
@@ -71,13 +66,9 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
     {
         Throw.IfNull(executors);
 
-        int executorIndex = 0;
-        foreach (ExecutorBinding? executor in executors)
+        foreach (ExecutorBinding executor in executors)
         {
-            if (executor is null)
-            {
-                throw new ArgumentNullException(nameof(executors), $"Executors collection contains a null element at index {executorIndex}.");
-            }
+            Throw.IfNull(executor, nameof(executors));
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -87,7 +78,6 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
             }
 
             this._defaultIndicies.Add(index);
-            executorIndex++;
         }
 
         return this;
diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index e7f68e4f69..86699f4683 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -127,27 +127,15 @@ private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding
     {
         Throw.IfNull(targets);
 
-        List<ExecutorBinding> targetList = [];
-        using IEnumerator<ExecutorBinding> targetEnumerator = targets.GetEnumerator();
-        if (!targetEnumerator.MoveNext())
+        List<ExecutorBinding> targetList = new();
+        foreach (ExecutorBinding target in targets)
         {
-            throw new ArgumentException("Targets collection cannot be empty.", nameof(targets));
-        }
-
-        int targetIndex = 0;
-        do
-        {
-            ExecutorBinding? target = targetEnumerator.Current;
-            if (target is null)
-            {
-                throw new ArgumentNullException(nameof(targets), $"Targets collection contains a null element at index {targetIndex}.");
-            }
+            Throw.IfNull(target, nameof(targets));
 
             targetList.Add(target);
-            targetIndex++;
         }
-        while (targetEnumerator.MoveNext());
 
+        Throw.IfNullOrEmpty(targetList, nameof(targets));
         return targetList;
     }
 

From e3c0ab021ef1f1018392160c23fa5a20e31915f6 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:20:09 +0000
Subject: [PATCH 10/19] Cover empty switch case targets

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderSmokeTests.cs                                 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 4e9cb19ee3..74e911eefe 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -432,6 +432,7 @@ public void AddSwitch_InvalidArguments_Throw()
         Assert.Throws<ArgumentNullException>("source", () => builder.AddSwitch(null!, _ => { }));
         Assert.Throws<ArgumentNullException>("configureSwitch", () => builder.AddSwitch(source, null!));
         Assert.Throws<ArgumentException>("targets", () => builder.AddSwitch(source, _ => { }));
+        Assert.Throws<ArgumentException>("targets", () => builder.AddSwitch(source, switchBuilder => switchBuilder.AddCase<string>(_ => true, [])));
     }
 
     [Fact]

From e6f194bce5e4dd5611cc5d5c37623e6539501ca4 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:21:42 +0000
Subject: [PATCH 11/19] Relax builder null assertion parameter checks

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/af831ee2-0a99-4427-9ffd-a3b5022c1b3b

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderSmokeTests.cs                       | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 74e911eefe..08f14ea541 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -364,7 +364,7 @@ public void ForwardMessage_InvalidArguments_Throw()
         NoOpExecutor target = new("target");
 
         // Act/Assert
-        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).ForwardMessage<string>(source, target));
+        Assert.Throws<ArgumentNullException>(() => ((WorkflowBuilder)null!).ForwardMessage<string>(source, target));
         Assert.Throws<ArgumentNullException>("source", () => builder.ForwardMessage<string>(null!, target));
         Assert.Throws<ArgumentNullException>("target", () => builder.ForwardMessage<string>(source, (ExecutorBinding)null!));
         Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardMessage<string>(source, (IEnumerable<ExecutorBinding>)null!));
@@ -381,7 +381,7 @@ public void ForwardExcept_InvalidArguments_Throw()
         NoOpExecutor target = new("target");
 
         // Act/Assert
-        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).ForwardExcept<string>(source, target));
+        Assert.Throws<ArgumentNullException>(() => ((WorkflowBuilder)null!).ForwardExcept<string>(source, target));
         Assert.Throws<ArgumentNullException>("source", () => builder.ForwardExcept<string>(null!, target));
         Assert.Throws<ArgumentNullException>("target", () => builder.ForwardExcept<string>(source, (ExecutorBinding)null!));
         Assert.Throws<ArgumentNullException>("targets", () => builder.ForwardExcept<string>(source, (IEnumerable<ExecutorBinding>)null!));
@@ -399,7 +399,7 @@ public void AddChain_InvalidArguments_Throw()
         NoOpExecutor otherTarget = new("other-target");
 
         // Act/Assert
-        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddChain(source, [target]));
+        Assert.Throws<ArgumentNullException>(() => ((WorkflowBuilder)null!).AddChain(source, [target]));
         Assert.Throws<ArgumentNullException>("source", () => builder.AddChain(null!, [target]));
         Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, null!));
         Assert.Throws<ArgumentNullException>("executors", () => builder.AddChain(source, [target, null!]));
@@ -415,7 +415,7 @@ public void AddExternalCall_InvalidArguments_Throw()
         NoOpExecutor source = new("start");
 
         // Act/Assert
-        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddExternalCall<string, int>(source, "port"));
+        Assert.Throws<ArgumentNullException>(() => ((WorkflowBuilder)null!).AddExternalCall<string, int>(source, "port"));
         Assert.Throws<ArgumentNullException>("source", () => builder.AddExternalCall<string, int>(null!, "port"));
         Assert.Throws<ArgumentNullException>("portId", () => builder.AddExternalCall<string, int>(source, null!));
     }
@@ -428,7 +428,7 @@ public void AddSwitch_InvalidArguments_Throw()
         NoOpExecutor source = new("start");
 
         // Act/Assert
-        Assert.Throws<ArgumentNullException>("builder", () => ((WorkflowBuilder)null!).AddSwitch(source, _ => { }));
+        Assert.Throws<ArgumentNullException>(() => ((WorkflowBuilder)null!).AddSwitch(source, _ => { }));
         Assert.Throws<ArgumentNullException>("source", () => builder.AddSwitch(null!, _ => { }));
         Assert.Throws<ArgumentNullException>("configureSwitch", () => builder.AddSwitch(source, null!));
         Assert.Throws<ArgumentException>("targets", () => builder.AddSwitch(source, _ => { }));

From 2af97e5a7fdee8c0452e78eb9b3bb59bada2e866 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:28:59 +0000
Subject: [PATCH 12/19] Inline ValidateTargets into call sites

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/cb9a6a6a-02c7-41a8-a4b4-da16ad62ef86

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs              | 45 +++++++++----------
 1 file changed, 20 insertions(+), 25 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 86699f4683..ae5625edcb 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -57,9 +57,18 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
     {
         Throw.IfNull(builder);
         Throw.IfNull(source);
+        Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
-        List<ExecutorBinding> targetList = ValidateTargets(targets);
+        List<ExecutorBinding> targetList = new();
+        foreach (ExecutorBinding target in targets)
+        {
+            Throw.IfNull(target, nameof(targets));
+
+            targetList.Add(target);
+        }
+
+        Throw.IfNullOrEmpty(targetList, nameof(targets));
 
         if (targetList.Count == 1)
         {
@@ -100,9 +109,18 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
     {
         Throw.IfNull(builder);
         Throw.IfNull(source);
+        Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
-        List<ExecutorBinding> targetList = ValidateTargets(targets);
+        List<ExecutorBinding> targetList = new();
+        foreach (ExecutorBinding target in targets)
+        {
+            Throw.IfNull(target, nameof(targets));
+
+            targetList.Add(target);
+        }
+
+        Throw.IfNullOrEmpty(targetList, nameof(targets));
 
         if (targetList.Count == 1)
         {
@@ -116,29 +134,6 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
         static bool IsAllowedType(object? message) => message is null;
     }
 
-    /// <summary>
-    /// Validates a target collection and returns it as a list.
-    /// </summary>
-    /// <param name="targets">The target executor bindings to validate.</param>
-    /// <returns>A validated list of target executor bindings.</returns>
-    /// <exception cref="ArgumentNullException">Thrown when <paramref name="targets"/> is null or contains a null element.</exception>
-    /// <exception cref="ArgumentException">Thrown when <paramref name="targets"/> is empty.</exception>
-    private static List<ExecutorBinding> ValidateTargets(IEnumerable<ExecutorBinding> targets)
-    {
-        Throw.IfNull(targets);
-
-        List<ExecutorBinding> targetList = new();
-        foreach (ExecutorBinding target in targets)
-        {
-            Throw.IfNull(target, nameof(targets));
-
-            targetList.Add(target);
-        }
-
-        Throw.IfNullOrEmpty(targetList, nameof(targets));
-        return targetList;
-    }
-
     /// <summary>
     /// Adds a sequential chain of executors to the workflow, connecting each executor in order so that each is
     /// executed after the previous one.

From 80ca30b448efb01e7375fe04cff3dc4574b1b994 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:37:08 +0000
Subject: [PATCH 13/19] Refactor ForwardExcept with TFM-specialized
 TryGetNonEnumeratedCount

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/b081f61f-93ce-45dc-abbd-82c465395470

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs               | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index ae5625edcb..eeeaf63bc8 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.Shared.Diagnostics;
 
 namespace Microsoft.Agents.AI.Workflows;
@@ -112,26 +113,19 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
-        List<ExecutorBinding> targetList = new();
-        foreach (ExecutorBinding target in targets)
-        {
-            Throw.IfNull(target, nameof(targets));
-
-            targetList.Add(target);
-        }
 
-        Throw.IfNullOrEmpty(targetList, nameof(targets));
-
-        if (targetList.Count == 1)
+        if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
         {
-            return builder.AddEdge(source, targetList[0], predicate);
+            return builder.AddEdge(source, Throw.IfNull(targets.First(), nameof(targets)), predicate);
         }
 
-        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targetList));
+        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targets.Select(ValidateTarget)));
 
         // The reason we can check for "null" here is that CreateConditionFunc<T> will do the correct unwrapping
         // logic for PortableValues.
         static bool IsAllowedType(object? message) => message is null;
+
+        ExecutorBinding ValidateTarget(ExecutorBinding target) => Throw.IfNull(target, nameof(targets));
     }
 
     /// <summary>

From 27018d615d3a9e16a78e0cfbcd1cc81344164a51 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:43:17 +0000
Subject: [PATCH 14/19] Use TFM-specialized count check:
 TryGetNonEnumeratedCount for NET6+, ICollection pattern for NETFX

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/8ec28a43-e7b7-456e-8d8e-921511b4accc

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs                              | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index eeeaf63bc8..a771f89878 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -114,7 +114,11 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
 
+#if NET6_0_OR_GREATER
         if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
+#else
+        if (targets is ICollection<ExecutorBinding> { Count: 1 })
+#endif
         {
             return builder.AddEdge(source, Throw.IfNull(targets.First(), nameof(targets)), predicate);
         }

From c8a46d6219e4fcb8fd43cf53dd5c88a03ff4efb2 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 13 May 2026 19:52:22 +0000
Subject: [PATCH 15/19] Apply TFM-specialized count check to ForwardMessage as
 well

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/9238ea32-a3e8-4b83-9683-484ad400071f

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../WorkflowBuilderExtensions.cs              | 21 ++++++++-----------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index a771f89878..41cceb25a3 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -61,26 +61,23 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
         Throw.IfNull(targets);
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
-        List<ExecutorBinding> targetList = new();
-        foreach (ExecutorBinding target in targets)
-        {
-            Throw.IfNull(target, nameof(targets));
-
-            targetList.Add(target);
-        }
-
-        Throw.IfNullOrEmpty(targetList, nameof(targets));
 
-        if (targetList.Count == 1)
+#if NET6_0_OR_GREATER
+        if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
+#else
+        if (targets is ICollection<ExecutorBinding> { Count: 1 })
+#endif
         {
-            return builder.AddEdge(source, targetList[0], predicate);
+            return builder.AddEdge(source, Throw.IfNull(targets.First(), nameof(targets)), predicate);
         }
 
-        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targetList));
+        return builder.AddSwitch(source, (switch_) => switch_.AddCase(predicate, targets.Select(ValidateTarget)));
 
         // The reason we can check for "not null" here is that CreateConditionFunc<T> will do the correct unwrapping
         // logic for PortableValues.
         bool IsAllowedTypeAndMatchingCondition(TMessage? message) => message != null && (condition == null || condition(message));
+
+        ExecutorBinding ValidateTarget(ExecutorBinding target) => Throw.IfNull(target, nameof(targets));
     }
 
     /// <summary>

From 14b9c02c5259be08c603745798333cce75b6155a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 14 May 2026 12:50:37 +0000
Subject: [PATCH 16/19] Address review feedback: simplify Throw.IfNull in
 SwitchBuilder per westey-m suggestion

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/299950fd-4457-47f3-a373-f65d601b7ea5

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs     | 4 ++--
 .../WorkflowBuilderSmokeTests.cs                              | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 286329b6ec..0a6b9218f7 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -39,7 +39,7 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            Throw.IfNull(executor);
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -68,7 +68,7 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
 
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor, nameof(executors));
+            Throw.IfNull(executor);
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 08f14ea541..4997197445 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -445,9 +445,9 @@ public void SwitchBuilder_InvalidArguments_Throw()
         // Act/Assert
         Assert.Throws<ArgumentNullException>("predicate", () => switchBuilder.AddCase<string>(null!, [target]));
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.AddCase<string>(_ => true, null!));
-        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.AddCase<string>(_ => true, [target, null!]));
+        Assert.Throws<ArgumentNullException>("executor", () => switchBuilder.AddCase<string>(_ => true, [target, null!]));
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault(null!));
-        Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault([target, null!]));
+        Assert.Throws<ArgumentNullException>("executor", () => switchBuilder.WithDefault([target, null!]));
     }
 
     /// <summary>

From f94ed16bc83ab79d43dd499078371e0cd77462b6 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 14 May 2026 12:56:02 +0000
Subject: [PATCH 17/19] Use indexed parameter name in SwitchBuilder
 Throw.IfNull: executors[index]

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/c5655707-5b0b-44f3-98a9-5f3961e32cfe

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 .../src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs   | 9 +++++++--
 .../WorkflowBuilderSmokeTests.cs                         | 4 ++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 0a6b9218f7..8141be1075 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -36,10 +36,12 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
         Throw.IfNull(executors);
 
         HashSet<int> indicies = [];
+        int executorIndex = 0;
 
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor);
+            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex}]");
+            executorIndex++;
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -66,9 +68,12 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
     {
         Throw.IfNull(executors);
 
+        int executorIndex = 0;
+
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor);
+            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex}]");
+            executorIndex++;
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
index 4997197445..c2b855b8bf 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowBuilderSmokeTests.cs
@@ -445,9 +445,9 @@ public void SwitchBuilder_InvalidArguments_Throw()
         // Act/Assert
         Assert.Throws<ArgumentNullException>("predicate", () => switchBuilder.AddCase<string>(null!, [target]));
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.AddCase<string>(_ => true, null!));
-        Assert.Throws<ArgumentNullException>("executor", () => switchBuilder.AddCase<string>(_ => true, [target, null!]));
+        Assert.Throws<ArgumentNullException>("executors[1]", () => switchBuilder.AddCase<string>(_ => true, [target, null!]));
         Assert.Throws<ArgumentNullException>("executors", () => switchBuilder.WithDefault(null!));
-        Assert.Throws<ArgumentNullException>("executor", () => switchBuilder.WithDefault([target, null!]));
+        Assert.Throws<ArgumentNullException>("executors[1]", () => switchBuilder.WithDefault([target, null!]));
     }
 
     /// <summary>

From a43e6d993e22cf21496dcdc740d6a81680989e95 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 14 May 2026 12:58:08 +0000
Subject: [PATCH 18/19] Revert #if NET6_0_OR_GREATER back to #if NET; inline
 executorIndex++

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/c5655707-5b0b-44f3-98a9-5f3961e32cfe

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs   | 6 ++----
 .../WorkflowBuilderExtensions.cs                            | 4 ++--
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index 8141be1075..bee9947a6b 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -40,8 +40,7 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex}]");
-            executorIndex++;
+            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex++}]");
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
@@ -72,8 +71,7 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
 
         foreach (ExecutorBinding executor in executors)
         {
-            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex}]");
-            executorIndex++;
+            Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex++}]");
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
             {
diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
index 41cceb25a3..a22aa8e722 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilderExtensions.cs
@@ -62,7 +62,7 @@ public static WorkflowBuilder ForwardMessage<TMessage>(this WorkflowBuilder buil
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>(IsAllowedTypeAndMatchingCondition)!;
 
-#if NET6_0_OR_GREATER
+#if NET
         if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
 #else
         if (targets is ICollection<ExecutorBinding> { Count: 1 })
@@ -111,7 +111,7 @@ public static WorkflowBuilder ForwardExcept<TMessage>(this WorkflowBuilder build
 
         Func<object?, bool> predicate = WorkflowBuilder.CreateConditionFunc<TMessage>((Func<object?, bool>)IsAllowedType)!;
 
-#if NET6_0_OR_GREATER
+#if NET
         if (targets.TryGetNonEnumeratedCount(out int count) && count == 1)
 #else
         if (targets is ICollection<ExecutorBinding> { Count: 1 })

From 2392255f9f3c173a0a17a69cbbf9fc836f767a83 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 14 May 2026 12:58:35 +0000
Subject: [PATCH 19/19] Add comment explaining unusual Throw.IfNull use for
 null elements inside collection

Agent-Logs-Url: https://github.com/microsoft/agent-framework/sessions/c5655707-5b0b-44f3-98a9-5f3961e32cfe

Co-authored-by: lokitoth <6936551+lokitoth@users.noreply.github.com>
---
 dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
index bee9947a6b..66ac3e6908 100644
--- a/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Workflows/SwitchBuilder.cs
@@ -40,6 +40,7 @@ public SwitchBuilder AddCase<T>(Func<T?, bool> predicate, params IEnumerable<Exe
 
         foreach (ExecutorBinding executor in executors)
         {
+            // Explicit name: null element inside the collection argument.
             Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex++}]");
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))
@@ -71,6 +72,7 @@ public SwitchBuilder WithDefault(params IEnumerable<ExecutorBinding> executors)
 
         foreach (ExecutorBinding executor in executors)
         {
+            // Explicit name: null element inside the collection argument.
             Throw.IfNull(executor, $"{nameof(executors)}[{executorIndex++}]");
 
             if (!this._executorIndicies.TryGetValue(executor.Id, out int index))