Add Cancel alteration type and handler for workflow cancellation

Introduced a new `Cancel` alteration type with its corresponding handler to allow workflow instance cancellations in alteration plans. Updated related services, serialization configurations, and activity metadata to support the new type. Improved JSON polymorphism handling to include the `Cancel` type.

src/clients/Elsa.Api.Client/Helpers/RefitSettingsHelper.cs

@@ -1,6 +1,9 @@
 using System.Text.Json;
 using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
 using Elsa.Api.Client.Converters;
+using Elsa.Api.Client.Resources.Alterations.Contracts;
+using Elsa.Api.Client.Resources.Alterations.Models;
 using Refit;
 
 namespace Elsa.Api.Client;
@@ -34,6 +37,27 @@ public static class RefitSettingsHelper
         options.Converters.Add(new VersionOptionsJsonConverter());
         options.Converters.Add(new TypeJsonConverter());
 
+        var alterationTypes = new[] { typeof(Cancel) };
+
+        options.TypeInfoResolver = new DefaultJsonTypeInfoResolver()
+            .WithAddedModifier(typeInfo =>
+            {
+                if (typeInfo.Type != typeof(IAlteration))
+                    return;
+
+                if (typeInfo.Kind != JsonTypeInfoKind.Object)
+                    return;
+
+                var polymorphismOptions = new JsonPolymorphismOptions { TypeDiscriminatorPropertyName = "type" };
+
+                foreach (var alterationType in alterationTypes.ToList())
+                {
+                    polymorphismOptions.DerivedTypes.Add(new(alterationType, alterationType.Name));
+                }
+
+                typeInfo.PolymorphismOptions = polymorphismOptions;
+            });
+
         configureJsonSerializerOptions?.Invoke(serviceProvider, options);
 
         return options;

src/clients/Elsa.Api.Client/Resources/Alterations/Models/Cancel.cs

@@ -0,0 +1,6 @@
+namespace Elsa.Api.Client.Resources.Alterations.Models;
+
+/// <summary>
+/// Cancels the workflow instances in an alteration plan.
+/// </summary>
+public class Cancel : AlterationBase;

src/modules/Elsa.Alterations.Core/Serialization/AlterationSerializationOptionConfigurator.cs

@@ -1,4 +1,3 @@
-using System.Text.Json;
 using System.Text.Json.Serialization;
 using System.Text.Json.Serialization.Metadata;
 using Elsa.Alterations.Core.Contracts;
@@ -35,7 +34,7 @@ public class AlterationSerializationOptionConfigurator(IOptions<AlterationOption
 
             foreach (var alterationType in alterationTypes.ToList())
             {
-                polymorphismOptions.DerivedTypes.Add(new JsonDerivedType(alterationType, alterationType.Name));
+                polymorphismOptions.DerivedTypes.Add(new(alterationType, alterationType.Name));
             }
 
             typeInfo.PolymorphismOptions = polymorphismOptions;

src/modules/Elsa.Alterations/Activities/CompleteAlterationPlan.cs

@@ -13,7 +13,7 @@ namespace Elsa.Alterations.Activities;
 /// Marks an alteration plan as completed.
 /// </summary>
 [Browsable(false)]
-[Activity("Elsa", "Alterations", "Dispatches jobs for the specified Alteration Plan", Kind = ActivityKind.Job)]
+[Activity("Elsa", "Alterations", "Dispatches jobs for the specified Alteration Plan", Kind = ActivityKind.Task)]
 public class CompleteAlterationPlan : CodeActivity
 {
     /// <inheritdoc />

src/modules/Elsa.Alterations/Activities/DispatchAlterationJobs.cs

@@ -15,7 +15,7 @@ namespace Elsa.Alterations.Activities;
 /// Submits an alteration plan for execution.
 /// </summary>
 [Browsable(false)]
-[Activity("Elsa", "Alterations", "Dispatches jobs for the specified Alteration Plan", Kind = ActivityKind.Job)]
+[Activity("Elsa", "Alterations", "Dispatches jobs for the specified Alteration Plan", Kind = ActivityKind.Task)]
 public class DispatchAlterationJobs : CodeActivity
 {
     /// <inheritdoc />

src/modules/Elsa.Alterations/Activities/GenerateAlterationJobs.cs

@@ -20,7 +20,7 @@ namespace Elsa.Alterations.Activities;
 /// Submits an alteration plan for execution.
 /// </summary>
 [Browsable(false)]
-[Activity("Elsa", "Alterations", "Generates jobs for the specified Alteration Plan", Kind = ActivityKind.Job)]
+[Activity("Elsa", "Alterations", "Generates jobs for the specified Alteration Plan", Kind = ActivityKind.Task)]
 public class GenerateAlterationJobs : CodeActivity<int>
 {
     /// <inheritdoc />

src/modules/Elsa.Alterations/AlterationHandlers/CancelHandler.cs

@@ -0,0 +1,22 @@
+using Elsa.Alterations.AlterationTypes;
+using Elsa.Alterations.Core.Abstractions;
+using Elsa.Alterations.Core.Contexts;
+using JetBrains.Annotations;
+
+namespace Elsa.Alterations.AlterationHandlers;
+
+/// <summary>
+/// Upgrades the version of the workflow instance.
+/// </summary>
+[UsedImplicitly]
+public class CancelHandler : AlterationHandlerBase<Cancel>
+{
+    /// <inheritdoc />
+    protected override ValueTask HandleAsync(AlterationContext context, Cancel alteration)
+    {
+        context.WorkflowExecutionContext.Cancel();
+        
+        context.Succeed();
+        return ValueTask.CompletedTask;
+    }
+}

src/modules/Elsa.Alterations/AlterationTypes/Cancel.cs

@@ -0,0 +1,10 @@
+using Elsa.Alterations.Core.Abstractions;
+using JetBrains.Annotations;
+
+namespace Elsa.Alterations.AlterationTypes;
+
+/// <summary>
+/// Cancels the workflow instances in an alteration plan.
+/// </summary>
+[UsedImplicitly]
+public class Cancel : AlterationBase;

src/modules/Elsa.Alterations/Extensions/ServiceCollectionExtensions.cs

@@ -20,6 +20,7 @@ public static class ServiceCollectionExtensions
         services.AddAlteration<ModifyVariable, ModifyVariableHandler>();
         services.AddAlteration<ScheduleActivity, ScheduleActivityHandler>();
         services.AddAlteration<CancelActivity, CancelActivityHandler>();
+        services.AddAlteration<Cancel, CancelHandler>();
         services.AddNotificationHandlersFrom<AlterationsFeature>();
         return services;
     }