refactor(event-subscriber): drop the hoofdObject fallback (refs #153)

For a `resource: object` notification Objecten sends the object as both hoofdObject and
resourceUrl — the object *is* the main resource — so `HoofdObject ?? ResourceUrl` was a
branch that can never take its left side and that no test could distinguish. It came across
from the zaken path, where hoofdObject genuinely differed (the zaak behind a status).

Tests unchanged and green.

services/event-subscriber/EventSubscriber.Api/Program.cs

@@ -84,11 +84,12 @@ app.MapPost("/admin/rebuild", async (NotificationProjector projector, Cancellati
 
 await app.RunAsync();
 
-/// <summary>The NRC notification body, as Open Notificaties POSTs it. Only the fields the
+/// <summary>The NRC notification body, as Open Notificaties POSTs it. Only the fields the projector
-/// projection needs are bound; <c>aanmaakdatum</c>/<c>kenmerken</c> are ignored for the minimal slice.</summary>
+/// needs are bound; <c>aanmaakdatum</c>, <c>kenmerken</c> and <c>hoofdObject</c> are ignored — for a
-public sealed record NotificationDto(string Kanaal, string Resource, string Actie, Uri ResourceUrl, Uri? HoofdObject = null)
+/// register write hoofdObject is the same object as resourceUrl (ADR-0030).</summary>
+public sealed record NotificationDto(string Kanaal, string Resource, string Actie, Uri ResourceUrl)
 {
-    public Notification ToNotification() => new(Kanaal, Resource, Actie, ResourceUrl, HoofdObject);
+    public Notification ToNotification() => new(Kanaal, Resource, Actie, ResourceUrl);
 }
 
 public partial class Program

services/event-subscriber/EventSubscriber.Application/Notification.cs

@@ -16,15 +16,15 @@ public sealed record Notification(
     string Kanaal,
     string Resource,
     string Actie,
-    Uri ResourceUrl,
+    Uri ResourceUrl)
-    Uri? HoofdObject = null)
 {
     /// <summary>A register record written to Objecten — <c>create</c> on submit, <c>update</c> on
     /// approval, since the ACL upserts the same object for a registration (§8.6).</summary>
     public bool IsRegisterRecordWritten =>
         Kanaal == "objecten" && Resource == "object" && Actie is "create" or "update";
 
-    /// <summary>The object holding the register record. Objecten sets both fields to the object;
+    /// <summary>The object holding the register record. For a <c>resource: object</c> notification
-    /// <c>hoofdObject</c> is the main resource by definition, so prefer it.</summary>
+    /// Objecten sends the object as both <c>hoofdObject</c> and <c>resourceUrl</c> — the object is
-    public Uri ObjectUrl => HoofdObject ?? ResourceUrl;
+    /// the main resource — so the notification's own <c>hoofdObject</c> is not modelled.</summary>
+    public Uri ObjectUrl => ResourceUrl;
 }

services/event-subscriber/EventSubscriber.Tests/NotificationProjectorTests.cs

@@ -22,7 +22,7 @@ public sealed class NotificationProjectorTests
     private Notification RecordWritten(string actie = "create", string url = ObjectUrl, string status = RegistrationStatus.Ingediend, string zaakId = ZaakId)
     {
         _acl.Records[url] = new RegisterRecord(zaakId, status, "REG-2026-0001");
-        return new Notification("objecten", "object", actie, new Uri(url), new Uri(url));
+        return new Notification("objecten", "object", actie, new Uri(url));
     }
 
     [Fact]

tests/acceptance/Steps/RegisterProjectieBijwerkenSteps.cs

@@ -28,7 +28,7 @@ public sealed class RegisterProjectieBijwerkenSteps
         // The ACL upserts one object per registration, so submit and approval share an object URL.
         var objectUrl = ObjectBase + id;
         _register.Records[objectUrl] = new RegisterRecord(id, status, "REG-" + id);
-        _notification = new Notification("objecten", "object", "create", new Uri(objectUrl), new Uri(objectUrl));
+        _notification = new Notification("objecten", "object", "create", new Uri(objectUrl));
     }
 
     [Given("the register notification is delivered to the event subscriber")]