Provide extension methods to get Aggregate Id Variable in HTTP Chain Policy

src/Http/Wolverine.Http.Marten/HttpChainExtensions.cs

@@ -0,0 +1,19 @@
+using System.Diagnostics.CodeAnalysis;
+using JasperFx.CodeGeneration.Model;
+using Wolverine.Marten;
+
+namespace Wolverine.Http.Marten;
+
+public static class HttpChainExtensions
+{
+    public static Variable? GetAggregateIdVariable(this HttpChain chain)
+        => chain.Tags.TryGetValue(nameof(AggregateHandling), out var obj) && obj is AggregateHandling aggregateHandling
+            ? aggregateHandling.AggregateId
+            : null;
+
+    public static bool TryGetAggregateIdVariable(this HttpChain chain, [MaybeNullWhen(false)] out Variable variable)
+    {
+        variable = chain.GetAggregateIdVariable();
+        return variable != null;
+    }
+}

src/Http/Wolverine.Http.Tests/Marten/using_aggregate_handler_workflow.cs

@@ -2,6 +2,7 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.DependencyInjection;
 using Shouldly;
+using Wolverine.Http.Marten;
 using Wolverine.Marten;
 using WolverineWebApi.Marten;
 
@@ -351,5 +352,31 @@ public async Task return_updated_aggregate_in_tuple()
         stream.Select(x => x.Data).OfType<UpdatedAggregate>().Any().ShouldBeFalse();
 
     }
+
+    [Fact]
+    public async Task aggregate_id_variable_is_fetchable_from_http_chain_for_handler_marked_with_AggregateHandler()
+    {
+        // Guaranteeing that it's warmed up
+        var result1 = await Scenario(x =>
+        {
+            x.Post.Json(new StartOrder(["Socks", "Shoes", "Shirt"])).ToUrl("/orders/create");
+        });
+
+        var status1 = result1.ReadAsJson<OrderStatus>();
+
+        await Scenario(x =>
+        {
+            x.Post.Json(new MarkItemReady(status1.OrderId, "Socks", 1)).ToUrl("/orders/itemready");
+        });
+
+        var chain = Host.Services.GetRequiredService<WolverineHttpOptions>().Endpoints!.ChainFor("POST", "/orders/itemready");
+        chain.ShouldNotBeNull();
+
+        var aggregateIdVariable = chain.GetAggregateIdVariable();
+        aggregateIdVariable.ShouldNotBeNull();
+
+        aggregateIdVariable.VariableType.FullName.ShouldBe(typeof(Guid).FullName);
+        aggregateIdVariable.Usage.ShouldBe("order_Id");
+    }
 
 }