test(event-subscriber): the projection is sourced from register records (refs #153)

Ports, schema and failing tests for the subscriber half of S-19b-2, ahead of the
implementation.

The subscriber now listens on the `objecten` kanaal instead of `zaken`. An Objecten
notification carries no record data — only the object URL — so the record is read back
through the ACL (§8.1), and the zaak-shaped surface goes away: IsZaakCreated /
IsZaakStatusSet / ZaakUrl / ZaakId and ToEntry's `Resource == "status"` mapping are replaced
by IsRegisterRecordWritten + ObjectUrl.

The notification log now holds the projected row itself (register id, status, reference),
so a rebuild is a replay with no mapping rules and no upstream reads. The migration drops
the old columns rather than renaming them — EF scaffolded renames that would have carried
ZGW values into columns meaning something else — and empties both tables, since a
pre-slice row is neither reprojectable nor re-derivable from the new source.

Red: HandleAsync recognises a register write but does not yet read or project it, so the
seven projection assertions fail on an empty store.

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

@@ -3,28 +3,22 @@ namespace EventSubscriber.Application;
 /// <summary>
 /// Projects inbound NRC notifications into the read projection. Tolerates duplicate and
 /// out-of-order deliveries (CLAUDE.md §8.6): the notification log dedups, and the projection
-/// upsert is idempotent on the zaak id. Rebuilds the projection by replaying the log.
+/// upsert is idempotent on the register id. Rebuilds the projection by replaying the log.
 /// </summary>
 public sealed class NotificationProjector(INotificationLog log, IProjectionStore store, IAclClient acl)
 {
-    /// <summary>Handle one inbound notification. Reacts to a zaak being created (INGEDIEND) and a
-    /// status being set (INGESCHREVEN); ignores everything else. Enriches the row with the zaak's
-    /// reference via the ACL (§8.1) and records it so a rebuild needs no ZGW access (#78).</summary>
+    /// <summary>Handle one inbound notification. Reacts to a register record being written to
+    /// Objecten (S-19b-2, ADR-0030) and ignores everything else.</summary>
     public async Task HandleAsync(Notification notification, CancellationToken ct = default)
     {
-        if (!notification.IsZaakCreated && !notification.IsZaakStatusSet)
+        ArgumentNullException.ThrowIfNull(notification);
+
+        if (!notification.IsRegisterRecordWritten)
             return;
 
-        var reference = await acl.GetZaakReferenceAsync(notification.ZaakUrl, ct);
-        var recorded = new RecordedNotification(
-            notification.IdempotencyKey, notification.Actie, notification.ZaakId, notification.Resource, reference);
-
-        // Atomic record-or-skip: a duplicate (or concurrent) delivery is recognised and dropped
-        // before it touches the projection, so the projection stays a faithful derived artefact.
-        if (!await log.TryRecordAsync(recorded, ct))
-            return;
-
-        await store.UpsertAsync(ToEntry(recorded), ct);
+        // S-19b-2: reading the record back through the ACL and projecting it lands with the
+        // implementation; today nothing reaches the store.
+        await Task.CompletedTask;
     }
 
     /// <summary>Rebuild the projection from the durable notification log (PRD §8.4).</summary>
@@ -35,11 +29,9 @@ public sealed class NotificationProjector(INotificationLog log, IProjectionStore
             await store.UpsertAsync(ToEntry(recorded), ct);
     }
 
-    /// <summary>The projection row for an accepted notification: a status-set maps to INGESCHREVEN,
-    /// a zaak-create to INGEDIEND. bsn/naam are deferred (ADR-0008).</summary>
+    /// <summary>The projection row for an accepted notification. The log already holds exactly the
+    /// row's fields, so a rebuild needs no mapping rules and no upstream reads. bsn/naam stay
+    /// deferred — the register record is public-safe by construction (ADR-0027).</summary>
     private static RegisterEntry ToEntry(RecordedNotification recorded)
-        => new(
-            recorded.ZaakId,
-            recorded.Resource == "status" ? RegistrationStatus.Ingeschreven : RegistrationStatus.Ingediend,
-            Reference: recorded.Reference);
+        => new(recorded.RegisterId, recorded.Status, recorded.Reference);
 }