feat(acl): CancelZaakAsync service + POST /annuleringen endpoint (S-10c) (refs #106)

The ACL exposes zaak cancellation as a service operation the domain calls on
document-timeout expiry; it default-fills the zaaktype and dates the status
today, translating the domain intent to the ZGW cancellation status/resultaat.

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

services/acl/Acl.Api/Program.cs

@@ -32,6 +32,14 @@ app.MapPost("/statussen", async (SetStatusRequest body, AclService acl, Cancella
     return Results.NoContent();
 });
 
+// Cancel a zaak on document-timeout expiry (S-10c): set it to its zaaktype's cancellation statustype
+// + resultaat. The domain hands over only the zaak URL; the ACL owns the ZGW resolution (§8.1).
+app.MapPost("/annuleringen", async (CancelZaakRequest body, AclService acl, CancellationToken ct) =>
+{
+    await acl.CancelZaakAsync(new Uri(body.ZaakUrl), ct);
+    return Results.NoContent();
+});
+
 // Read a zaak's public-safe reference (its identificatie). The Event Subscriber calls this to enrich
 // the read projection without reading ZGW itself (§8.1, #78).
 app.MapPost("/zaken/reference", async (ZaakReferenceRequest body, AclService acl, CancellationToken ct) =>
@@ -55,6 +63,8 @@ public sealed record OpenZaakRequest(string Bsn, string Reference);
 
 public sealed record SetStatusRequest(string ZaakUrl);
 
+public sealed record CancelZaakRequest(string ZaakUrl);
+
 public sealed record ZaakReferenceRequest(string ZaakUrl);
 
 public sealed record StoreDocumentRequest(string ZaakUrl, string ContentBase64, string FileName, string ContentType);

services/acl/Acl.Application/AclService.cs

@@ -30,6 +30,18 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
         return gateway.SetZaakToEindstatusAsync(zaakUrl, defaults.ZaaktypeUrl, clock.Today, ct);
     }
 
+    /// <summary>
+    /// Cancel a zaak on document-timeout expiry (S-10c): set it to the configured BIG zaaktype's
+    /// cancellation statustype + resultaat. The domain hands over only the zaak URL; the ACL owns which
+    /// statustype/resultaat means "cancelled" (§8.1).
+    /// </summary>
+    public Task CancelZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+
+        return gateway.SetZaakToCancellationStatusAsync(zaakUrl, defaults.ZaaktypeUrl, clock.Today, ct);
+    }
+
     /// <summary>The zaak's reference (its ZGW identificatie), for the read projection (#78).</summary>
     public Task<string> GetZaakReferenceAsync(Uri zaakUrl, CancellationToken ct = default)
     {

services/acl/Acl.Tests/AclServiceTests.cs

@@ -134,6 +134,34 @@ public class AclServiceTests
         Assert.Null(gateway.Approved);
     }
 
+    [Fact]
+    public async Task Cancelling_a_zaak_sets_it_to_the_cancellation_status_dated_today()
+    {
+        var gateway = new FakeGateway();
+        var defaults = Defaults();
+        var service = new AclService(gateway, defaults, new FixedClock(new DateOnly(2026, 6, 4)));
+        var zaak = new Uri("http://openzaak/zaken/api/v1/zaken/abc");
+
+        await service.CancelZaakAsync(zaak);
+
+        Assert.NotNull(gateway.Cancelled);
+        Assert.Equal(zaak, gateway.Cancelled!.Value.Zaak);
+        Assert.Equal(defaults.ZaaktypeUrl, gateway.Cancelled.Value.Zaaktype);
+        Assert.Equal(new DateOnly(2026, 6, 4), gateway.Cancelled.Value.Datum);
+        // Cancellation must not touch the approval path.
+        Assert.Null(gateway.Approved);
+    }
+
+    [Fact]
+    public async Task Cancelling_a_null_zaak_is_rejected_without_touching_the_gateway()
+    {
+        var gateway = new FakeGateway();
+        var service = new AclService(gateway, Defaults(), new FixedClock(new DateOnly(2026, 6, 4)));
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.CancelZaakAsync(null!));
+        Assert.Null(gateway.Cancelled);
+    }
+
     [Fact]
     public async Task Storing_a_diploma_default_fills_the_document_fields_and_returns_its_url()
     {