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.Tests/AclHttpClientTests.cs

@@ -5,27 +5,42 @@ using EventSubscriber.Api;
 namespace EventSubscriber.Tests;
 
 /// <summary>
-/// Unit tests for the subscriber's ACL client, which reads a zaak's reference (identificatie) through
-/// the ACL — the only code allowed to talk to ZGW (§8.1, #78). Uses a scripted message handler so no
-/// real ACL is required.
+/// Unit tests for the subscriber's ACL client, which reads a register record through the ACL — the
+/// only code allowed to talk to Objecten (§8.1, ADR-0028/ADR-0030). Uses a scripted message handler
+/// so no real ACL is required.
 /// </summary>
 public class AclHttpClientTests
 {
+    private const string ObjectUrl = "http://objecten.local:8000/api/v2/objects/obj-9";
+
     private static AclHttpClient Client(StubHandler handler) =>
         new(new HttpClient(handler) { BaseAddress = new Uri("http://acl/") });
 
     [Fact]
-    public async Task Reads_a_zaak_reference_by_posting_the_zaak_url_and_returns_it()
+    public async Task Reads_a_register_record_by_posting_the_object_url()
     {
         var capture = new RequestCapture();
-        var client = Client(capture.Responds(HttpStatusCode.OK, """{"reference":"REG-42"}"""));
+        var client = Client(capture.Responds(
+            HttpStatusCode.OK, """{"id":"zaak-1","status":"INGESCHREVEN","reference":"REG-42"}"""));
 
-        var reference = await client.GetZaakReferenceAsync(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        var record = await client.GetRegisterRecordAsync(new Uri(ObjectUrl));
 
-        Assert.Equal("REG-42", reference);
+        Assert.Equal("zaak-1", record!.Id);
+        Assert.Equal("INGESCHREVEN", record.Status);
+        Assert.Equal("REG-42", record.Reference);
         Assert.Equal(HttpMethod.Post, capture.Seen!.Method);
-        Assert.Equal("http://acl/zaken/reference", capture.Seen.RequestUri!.ToString());
-        Assert.Contains("\"zaakUrl\":\"http://openzaak/zaken/api/v1/zaken/abc\"", capture.Body);
+        Assert.Equal("http://acl/register-records/read", capture.Seen.RequestUri!.ToString());
+        Assert.Contains($"\"objectUrl\":\"{ObjectUrl}\"", capture.Body);
+    }
+
+    [Fact]
+    public async Task Reads_a_missing_record_as_nothing_to_project()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.NotFound));
+
+        // The object may be gone by the time a redelivered notification is handled (§8.6).
+        Assert.Null(await client.GetRegisterRecordAsync(new Uri(ObjectUrl)));
     }
 
     [Fact]
@@ -35,7 +50,7 @@ public class AclHttpClientTests
         var client = Client(capture.Responds(HttpStatusCode.BadGateway));
 
         await Assert.ThrowsAsync<HttpRequestException>(
-            () => client.GetZaakReferenceAsync(new Uri("http://openzaak/zaken/api/v1/zaken/abc")));
+            () => client.GetRegisterRecordAsync(new Uri(ObjectUrl)));
     }
 
     [Fact]
@@ -45,17 +60,17 @@ public class AclHttpClientTests
         var client = Client(capture.Responds(HttpStatusCode.OK, "null"));
 
         var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-            () => client.GetZaakReferenceAsync(new Uri("http://openzaak/zaken/api/v1/zaken/abc")));
+            () => client.GetRegisterRecordAsync(new Uri(ObjectUrl)));
         Assert.Contains("empty", ex.Message, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]
-    public async Task Rejects_a_null_zaak_url_without_sending_a_request()
+    public async Task Rejects_a_null_object_url_without_sending_a_request()
     {
         var capture = new RequestCapture();
-        var client = Client(capture.Responds(HttpStatusCode.OK, """{"reference":"REG-1"}"""));
+        var client = Client(capture.Responds(HttpStatusCode.OK, "{}"));
 
-        await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetZaakReferenceAsync(null!));
+        await Assert.ThrowsAsync<ArgumentNullException>(() => client.GetRegisterRecordAsync(null!));
         Assert.Null(capture.Seen);
     }
 }