fix(domain): correlate withdrawal by process instance to the subscribed execution (refs #12)

verify-stack surfaced a Flowable 500: delivering messageEventReceived to the Beoordelen task's

execution is wrong — a message boundary event's subscription lives on its own execution. Correlate

instead by the registration's process instance id (recorded at submit): query the execution

subscribed to RegistratieIngetrokken and deliver the message there. Withdrawal moves from

IUserTaskClient to IWorkflowClient.WithdrawProcessAsync; the handler no longer needs a task lookup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

services/domain/Big.Tests/WithdrawRegistrationTests.cs

@@ -5,15 +5,20 @@ namespace Big.Tests;
 
 public class WithdrawRegistrationTests
 {
-    private static FakeUserTaskClient NoTasks() => new([]);
+    private static Registration Submitted(string processInstanceId = "proc-1")
+    {
+        var registration = Registration.Submit("123456782");
+        registration.RecordProcessStarted(processInstanceId);
+        return registration;
+    }
 
     [Fact]
     public async Task Withdrawing_marks_the_registration_ingetrokken_and_persists_it()
     {
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Submitted();
         store.Seed(registration);
-        var handler = new WithdrawRegistration(store, NoTasks());
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
         await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
 
@@ -23,43 +28,42 @@ public class WithdrawRegistrationTests
     }
 
     [Fact]
-    public async Task Withdrawing_cancels_the_open_beoordelen_task_via_its_execution()
+    public async Task Withdrawing_cancels_the_running_process()
     {
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Submitted("proc-42");
         store.Seed(registration);
-        var tasks = new FakeUserTaskClient([new BeoordelingTask("task-1", "exec-1", registration.Id)]);
-        var handler = new WithdrawRegistration(store, tasks);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
 
         await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
 
-        // The withdrawal message is delivered to the Beoordelen task's execution, tripping the
-        // boundary event that ends the process (ADR-0014).
-        Assert.Equal("exec-1", tasks.WithdrawnExecutionId);
+        // The process the registration recorded at submit is cancelled (ADR-0014).
+        Assert.Equal("proc-42", workflow.WithdrawnProcessInstanceId);
     }
 
     [Fact]
-    public async Task Withdrawing_with_no_open_task_still_marks_ingetrokken()
+    public async Task Withdrawing_before_a_process_was_started_still_marks_ingetrokken()
     {
-        // If the process has not parked at Beoordelen yet (or already ended), the withdrawal stands:
-        // the aggregate is INGETROKKEN and nothing is cancelled.
+        // A registration with no recorded process (e.g. start never happened) can still be withdrawn;
+        // there is simply no process to cancel.
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Registration.Submit("123456782"); // no RecordProcessStarted
         store.Seed(registration);
-        var tasks = NoTasks();
-        var handler = new WithdrawRegistration(store, tasks);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
 
         await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
 
         Assert.Equal(RegistrationStatus.Ingetrokken, (await store.GetAsync(registration.Id))!.Status);
-        Assert.Null(tasks.WithdrawnExecutionId);
+        Assert.Null(workflow.WithdrawnProcessInstanceId);
     }
 
     [Fact]
     public async Task Rejects_a_null_command_without_touching_the_store()
     {
         var store = new FakeRegistrationStore();
-        var handler = new WithdrawRegistration(store, NoTasks());
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
         await Assert.ThrowsAsync<ArgumentNullException>(() => handler.HandleAsync(null!));
         Assert.Equal(0, store.SaveCount);
@@ -69,7 +73,7 @@ public class WithdrawRegistrationTests
     public async Task Withdrawing_an_unknown_registration_throws()
     {
         var store = new FakeRegistrationStore();
-        var handler = new WithdrawRegistration(store, NoTasks());
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
         var ex = await Assert.ThrowsAsync<InvalidOperationException>(
             () => handler.HandleAsync(new WithdrawRegistrationCommand(RegistrationId.New())));
@@ -81,9 +85,10 @@ public class WithdrawRegistrationTests
     public async Task Re_withdrawing_an_already_ingetrokken_registration_is_idempotent()
     {
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Submitted();
         store.Seed(registration);
-        var handler = new WithdrawRegistration(store, NoTasks());
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
 
         await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
         await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));