.Net: Validate step types

dotnet/src/Experimental/Process.Core/ProcessStepBuilder.cs

@@ -278,6 +278,10 @@ internal ProcessStepBuilderTyped(Type stepType, string id, ProcessBuilder? proce
         : base(id, processBuilder)
     {
         Verify.NotNull(stepType);
+        if (!typeof(KernelProcessStep).IsAssignableFrom(stepType))
+        {
+            throw new ArgumentException($"Type '{stepType.FullName}' must be a subclass of KernelProcessStep.", nameof(stepType));
+        }
 
         this._stepType = stepType;
         this.FunctionsDict = this.GetFunctionMetadataMap();

dotnet/src/Experimental/Process.Runtime.Dapr.UnitTests/DaprStepInfoTests.cs

@@ -0,0 +1,86 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Collections.Generic;
+using Microsoft.SemanticKernel;
+using Xunit;
+
+namespace SemanticKernel.Process.Dapr.Runtime.UnitTests;
+
+/// <summary>
+/// Unit tests for the <see cref="DaprStepInfo"/> class.
+/// </summary>
+public class DaprStepInfoTests
+{
+    /// <summary>
+    /// Tests that ToKernelProcessStepInfo throws when InnerStepDotnetType is not a KernelProcessStep subclass.
+    /// </summary>
+    [Fact]
+    public void ToKernelProcessStepInfoThrowsForInvalidStepType()
+    {
+        // Arrange
+        var stepInfo = new DaprStepInfo
+        {
+            InnerStepDotnetType = typeof(string).AssemblyQualifiedName!,
+            State = new KernelProcessStepState("TestStep", version: "v1"),
+            Edges = new Dictionary<string, List<KernelProcessEdge>>()
+        };
+
+        // Act & Assert
+        var ex = Assert.Throws<KernelException>(() => stepInfo.ToKernelProcessStepInfo());
+        Assert.Contains("is not a valid KernelProcessStep type", ex.Message);
+    }
+
+    /// <summary>
+    /// Tests that ToKernelProcessStepInfo throws when InnerStepDotnetType cannot be resolved.
+    /// </summary>
+    [Fact]
+    public void ToKernelProcessStepInfoThrowsForUnresolvableType()
+    {
+        // Arrange
+        var stepInfo = new DaprStepInfo
+        {
+            InnerStepDotnetType = "NonExistent.Type, NonExistent.Assembly",
+            State = new KernelProcessStepState("TestStep", version: "v1"),
+            Edges = new Dictionary<string, List<KernelProcessEdge>>()
+        };
+
+        // Act & Assert
+        Assert.Throws<KernelException>(() => stepInfo.ToKernelProcessStepInfo());
+    }
+
+    /// <summary>
+    /// Tests that ToKernelProcessStepInfo succeeds for a valid KernelProcessStep subclass.
+    /// </summary>
+    [Fact]
+    public void ToKernelProcessStepInfoSucceedsForValidStepType()
+    {
+        // Arrange
+        var stepInfo = new DaprStepInfo
+        {
+            InnerStepDotnetType = typeof(ValidTestStep).AssemblyQualifiedName!,
+            State = new KernelProcessStepState("TestStep", version: "v1"),
+            Edges = new Dictionary<string, List<KernelProcessEdge>>()
+        };
+
+        // Act
+        var result = stepInfo.ToKernelProcessStepInfo();
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Equal(typeof(ValidTestStep), result.InnerStepType);
+    }
+
+    /// <summary>
+    /// A valid test step for type validation testing.
+    /// </summary>
+    public sealed class ValidTestStep : KernelProcessStep
+    {
+        /// <summary>
+        /// A test function.
+        /// </summary>
+        [KernelFunction]
+        public void TestFunction()
+        {
+        }
+    }
+}

dotnet/src/Experimental/Process.Runtime.Dapr.UnitTests/TypeInfoTests.cs

@@ -0,0 +1,74 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.Text.Json;
+using Microsoft.SemanticKernel;
+using Microsoft.SemanticKernel.Process.Serialization;
+using Xunit;
+
+namespace SemanticKernel.Process.Dapr.Runtime.UnitTests;
+
+/// <summary>
+/// Unit tests for the <see cref="TypeInfo"/> class.
+/// </summary>
+public class TypeInfoTests
+{
+    /// <summary>
+    /// Tests that ConvertValue deserializes a JsonElement to the correct type.
+    /// </summary>
+    [Fact]
+    public void ConvertValueDeserializesJsonElement()
+    {
+        // Arrange
+        var json = JsonSerializer.SerializeToElement(42);
+        var typeName = typeof(int).AssemblyQualifiedName;
+
+        // Act
+        var result = TypeInfo.ConvertValue(typeName, json);
+
+        // Assert
+        Assert.Equal(42, result);
+    }
+
+    /// <summary>
+    /// Tests that ConvertValue throws when the type name cannot be resolved.
+    /// </summary>
+    [Fact]
+    public void ConvertValueThrowsForUnresolvableType()
+    {
+        // Arrange
+        var json = JsonSerializer.SerializeToElement(42);
+
+        // Act & Assert
+        Assert.Throws<KernelException>(() =>
+            TypeInfo.ConvertValue("NonExistent.Type, NonExistent.Assembly", json));
+    }
+
+    /// <summary>
+    /// Tests that ConvertValue returns non-JsonElement values unchanged.
+    /// </summary>
+    [Fact]
+    public void ConvertValueReturnsNonJsonElementUnchanged()
+    {
+        // Arrange
+        var value = "plain string";
+
+        // Act
+        var result = TypeInfo.ConvertValue(typeof(string).AssemblyQualifiedName, value);
+
+        // Assert
+        Assert.Equal("plain string", result);
+    }
+
+    /// <summary>
+    /// Tests that ConvertValue returns null when value is null.
+    /// </summary>
+    [Fact]
+    public void ConvertValueReturnsNullWhenValueIsNull()
+    {
+        // Act
+        var result = TypeInfo.ConvertValue(typeof(string).AssemblyQualifiedName, null);
+
+        // Assert
+        Assert.Null(result);
+    }
+}

dotnet/src/Experimental/Process.Runtime.Dapr/Actors/StepActor.cs

@@ -102,6 +102,11 @@ private void InitializeStep(DaprStepInfo stepInfo, string? parentProcessId, stri
             throw new KernelException($"Could not load the inner step type '{stepInfo.InnerStepDotnetType}'.").Log(this._logger);
         }
 
+        if (!typeof(KernelProcessStep).IsAssignableFrom(this._innerStepType))
+        {
+            throw new KernelException($"Type '{stepInfo.InnerStepDotnetType}' is not a valid KernelProcessStep type.").Log(this._logger);
+        }
+
         this.ParentProcessId = parentProcessId;
         this._stepInfo = stepInfo;
         this._stepState = this._stepInfo.State;
@@ -373,8 +378,18 @@ protected virtual async ValueTask ActivateStepAsync()
         if (stepStateType.HasValue)
         {
             stateType = Type.GetType(stepStateType.Value);
+            if (stateType is null)
+            {
+                throw new KernelException($"Type '{stepStateType.Value}' could not be resolved to a valid KernelProcessStepState type.").Log(this._logger);
+            }
+
+            if (!typeof(KernelProcessStepState).IsAssignableFrom(stateType))
+            {
+                throw new KernelException($"Type '{stepStateType.Value}' is not a valid KernelProcessStepState type.").Log(this._logger);
+            }
+
             var stateObjectJson = await this.StateManager.GetStateAsync<string>(ActorStateKeys.StepStateJson).ConfigureAwait(false);
-            stateObject = JsonSerializer.Deserialize(stateObjectJson, stateType!) as KernelProcessStepState;
+            stateObject = JsonSerializer.Deserialize(stateObjectJson, stateType) as KernelProcessStepState;
         }
         else
         {

dotnet/src/Experimental/Process.Runtime.Dapr/DaprStepInfo.cs

@@ -50,6 +50,11 @@ public KernelProcessStepInfo ToKernelProcessStepInfo()
             throw new KernelException($"Unable to create inner step type from assembly qualified name `{this.InnerStepDotnetType}`");
         }
 
+        if (!typeof(KernelProcessStep).IsAssignableFrom(innerStepType))
+        {
+            throw new KernelException($"Type '{this.InnerStepDotnetType}' is not a valid KernelProcessStep type.");
+        }
+
         return new KernelProcessStepInfo(innerStepType, this.State, this.Edges);
     }
 

dotnet/src/Experimental/Process.Runtime.Dapr/Serialization/TypeInfo.cs

@@ -39,6 +39,11 @@ internal static class TypeInfo
         }
 
         Type? valueType = Type.GetType(assemblyQualifiedTypeName);
-        return ((JsonElement)value).Deserialize(valueType!);
+        if (valueType is null)
+        {
+            throw new KernelException($"Could not load type '{assemblyQualifiedTypeName}'.");
+        }
+
+        return ((JsonElement)value).Deserialize(valueType);
     }
 }

dotnet/src/Experimental/Process.UnitTests/Core/ProcessBuilderTests.cs

@@ -167,6 +167,37 @@ public void OnFunctionErrorCreatesEdgeBuilder()
         Assert.EndsWith("Global.OnError", edgeBuilder.EventData.EventId);
     }
 
+    /// <summary>
+    /// Tests that AddStepFromType(Type) throws ArgumentException for non-KernelProcessStep types.
+    /// </summary>
+    [Fact]
+    public void AddStepFromTypeWithInvalidTypeThrowsArgumentException()
+    {
+        // Arrange
+        var processBuilder = new ProcessBuilder(ProcessName);
+
+        // Act & Assert
+        var ex = Assert.Throws<ArgumentException>(() => processBuilder.AddStepFromType(typeof(string)));
+        Assert.Contains("must be a subclass of KernelProcessStep", ex.Message);
+    }
+
+    /// <summary>
+    /// Tests that AddStepFromType(Type) succeeds for valid KernelProcessStep types.
+    /// </summary>
+    [Fact]
+    public void AddStepFromTypeWithValidTypeAddsStep()
+    {
+        // Arrange
+        var processBuilder = new ProcessBuilder(ProcessName);
+
+        // Act
+        var stepBuilder = processBuilder.AddStepFromType(typeof(TestStep), StepName);
+
+        // Assert
+        Assert.Single(processBuilder.Steps);
+        Assert.Equal(StepName, stepBuilder.Name);
+    }
+
     /// <summary>
     /// A class that represents a step for testing.
     /// </summary>