services/acl/Acl.Api/Program.cs

@@ -90,6 +90,16 @@ app.MapPost("/zaken/reference", async (ZaakReferenceRequest body, AclService acl
     return Results.Ok(new { reference });
 });
 
+// Read the register record an object in Objecten holds. The Event Subscriber projects a register
+// write from the notification NRC delivers, which carries only the object URL, and may not talk to
+// Objecten itself (§8.1, ADR-0028/ADR-0030). 404 when the object holds no record — the subscriber
+// treats that as "nothing to project" rather than an error (§8.6).
+app.MapPost("/register-records/read", async (RegisterRecordReadRequest body, AclService acl, CancellationToken ct) =>
+{
+    var record = await acl.GetRegisterRecordAsync(new Uri(body.ObjectUrl), ct);
+    return record is null ? Results.NotFound() : Results.Ok(record);
+});
+
 // Store an uploaded diploma against a zaak (S-10b): the domain sends the file as base64; the ACL
 // creates the ZGW enkelvoudiginformatieobject and relates it to the zaak (§8.1). Returns its URL.
 app.MapPost("/documenten", async (StoreDocumentRequest body, AclService acl, CancellationToken ct) =>
@@ -131,6 +141,9 @@ public sealed record CancelZaakRequest(string ZaakUrl);
 
 public sealed record ZaakReferenceRequest(string ZaakUrl);
 
+/// <summary>The object whose register record the Event Subscriber wants read back (S-19b-2).</summary>
+public sealed record RegisterRecordReadRequest(string ObjectUrl);
+
 public sealed record StoreDocumentRequest(string ZaakUrl, string ContentBase64, string FileName, string ContentType);
 
 public partial class Program;

services/acl/Acl.Application/AclService.cs

@@ -24,7 +24,16 @@ public sealed class AclService(
             clock.Today,
             registration.Reference);
 
-        return await gateway.OpenZaakAsync(request, ct);
+        var zaakUrl = await gateway.OpenZaakAsync(request, ct);
+
+        // The register — not ZGW — is what the read projection is sourced from (ADR-0028/ADR-0030),
+        // so the record exists from submission, not only from approval. Same two-writes-converging
+        // posture as ApproveZaakAsync: the upsert is keyed on the zaak id, so a retried submit
+        // updates the record rather than adding a second one (§8.6).
+        await register.UpsertAsync(
+            new RegisterRecord(ZaakId(zaakUrl), RegisterRecordStatus.Ingediend, registration.Reference), ct);
+
+        return zaakUrl;
     }
 
     /// <summary>

services/acl/Acl.Infrastructure/ObjectenGateway.cs

@@ -1,3 +1,4 @@
+using System.Net;
 using System.Net.Http.Headers;
 using System.Net.Http.Json;
 using System.Text.Json.Serialization;
@@ -38,8 +39,29 @@ public sealed class ObjectenGateway(HttpClient http, ObjectenOptions options, IC
                 "Updating the register record", ct);
     }
 
-    public Task<RegisterRecord?> GetAsync(Uri objectUrl, CancellationToken ct = default)
-        => throw new NotImplementedException();
+    public async Task<RegisterRecord?> GetAsync(Uri objectUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(objectUrl);
+
+        // Fetched by the URL the notification carried, so no objecttype resolution and no search —
+        // unlike a write, which has to find the object for a registration id.
+        using var message = new HttpRequestMessage(HttpMethod.Get, objectUrl);
+        message.Headers.Authorization = new AuthenticationHeaderValue("Token", options.Token);
+        message.Headers.Add("Accept-Crs", "EPSG:4326");
+
+        using var response = await http.SendAsync(message, ct);
+        // The object may be gone by the time a (possibly redelivered) notification is handled —
+        // there is simply nothing to project, which is not a failure (§8.6).
+        if (response.StatusCode == HttpStatusCode.NotFound)
+            return null;
+
+        await EnsureSuccessAsync(response, "Reading the register record", ct);
+
+        var body = await response.Content.ReadFromJsonAsync<ReadObjectDto>(ct)
+            ?? throw new InvalidOperationException("Objecten returned an empty object response");
+        var data = body.Record?.Data;
+        return data is null ? null : new RegisterRecord(data.Id, data.Status, data.Reference);
+    }
 
     private RecordDto NewRecord(int typeVersion, RecordDataDto data) =>
         new(typeVersion, data, clock.Today.ToString("yyyy-MM-dd"));
@@ -144,6 +166,12 @@ public sealed class ObjectenGateway(HttpClient http, ObjectenOptions options, IC
     private sealed record ObjectDto(
         [property: JsonPropertyName("url")] string Url);
 
+    private sealed record ReadObjectDto(
+        [property: JsonPropertyName("record")] ReadRecordDto? Record);
+
+    private sealed record ReadRecordDto(
+        [property: JsonPropertyName("data")] RecordDataDto? Data);
+
     private sealed record CreateObjectDto(
         [property: JsonPropertyName("type")] string Type,
         [property: JsonPropertyName("record")] RecordDto Record);