services/domain/Big.Application/OpenZaakWorker.cs

@@ -20,8 +20,17 @@ public sealed class OpenZaakWorker(IRegistrationStore store, IAclClient acl)
     {
         ArgumentNullException.ThrowIfNull(job);
 
-        // STUB (red): does not load, call the ACL, or attach.
+        var registration = await store.GetAsync(job.RegistrationId, ct)
-        await Task.CompletedTask;
+            ?? throw new InvalidOperationException(
-        return new Uri("about:blank");
+                $"No registration {job.RegistrationId} for OpenZaakAanmaken job {job.JobId}.");
+
+        // A redelivered job whose zaak was already opened completes without opening a second one.
+        if (registration.ZaakUrl is not null)
+            return registration.ZaakUrl;
+
+        var zaakUrl = await acl.OpenZaakAsync(registration.Bsn, ct);
+        registration.AttachZaak(zaakUrl);
+        await store.SaveAsync(registration, ct);
+        return zaakUrl;
     }
 }

services/domain/Big.Application/SubmitRegistration.cs

@@ -18,8 +18,16 @@ public sealed class SubmitRegistration(IRegistrationStore store, IWorkflowClient
     {
         ArgumentNullException.ThrowIfNull(command);
 
-        // STUB (red): no persistence, no process start.
+        var registration = Registration.Submit(command.Bsn);
-        await Task.CompletedTask;
+
-        return RegistrationId.New();
+        // Persist before starting the process so the worker can correlate the OpenZaakAanmaken
+        // job back to an aggregate that already exists (ADR-0009).
+        await store.SaveAsync(registration, ct);
+
+        var processInstanceId = await workflow.StartRegistrationProcessAsync(registration.Id, ct);
+        registration.RecordProcessStarted(processInstanceId);
+        await store.SaveAsync(registration, ct);
+
+        return registration.Id;
     }
 }