feat(domain): the werkbak lists only registrations still open for beoordeling (refs #12)

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

services/domain/Big.Application/Werkbak.cs

@@ -1,3 +1,5 @@
+using Big.Domain;
+
 namespace Big.Application;
 
 /// <summary>One row of the behandelaar's werkbak: a registration awaiting beoordeling, with the
@@ -8,7 +10,8 @@ public sealed record WerkbakItem(string RegistrationId, string Bsn, string Statu
 /// The werkbak query (S-12c): the registrations awaiting a behandelaar's beoordeling. It reads the
 /// open <c>Beoordelen</c> tasks from the workflow engine (§8.2, via <see cref="IUserTaskClient"/>) —
 /// the authoritative set of work items — and enriches each with its aggregate (bsn + status). A task
-/// whose registration the domain doesn't know is skipped rather than invented.
+/// whose registration the domain doesn't know, or whose registration is no longer open for beoordeling
+/// (e.g. withdrawn — S-11 — while its task lingers until the workflow cancels it), is skipped.
 /// </summary>
 public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
 {
@@ -20,7 +23,7 @@ public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
         foreach (var task in open)
         {
             var registration = await store.GetAsync(task.RegistrationId, ct);
-            if (registration is null)
+            if (registration is null || !IsOpenForBeoordeling(registration.Status))
                 continue;
 
             items.Add(new WerkbakItem(
@@ -29,4 +32,9 @@ public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
 
         return items;
     }
+
+    // Only registrations still open for a decision belong in the werkbak; a terminal one (decided or
+    // withdrawn — S-11) whose Beoordelen task has not yet been cleared must not surface to a behandelaar.
+    private static bool IsOpenForBeoordeling(RegistrationStatus status)
+        => status is RegistrationStatus.Ingediend or RegistrationStatus.InBehandeling;
 }