S-09b: Approval flow — temp admin endpoint + status transition to projection (#77)

## What & why

S-09b (#75, split from #10) — the **approval flow** that completes the walking skeleton. A behandelaar can now approve a submitted registration; the entry flips from `INGEDIEND` to `INGESCHREVEN` in the public register. Flow: `POST /registrations/{id}/approve` (domain) → ACL sets the zaak eindstatus (ZGW `/statussen`) → OpenZaak → NRC → event-subscriber → projection → openbaar.

## Changes (bottom-up, each red→green TDD)

- **Domain** — `RegistrationStatus.Ingeschreven` + `Registration.Approve()` (guards: opened zaak, only from INGEDIEND); `ApproveRegistration` use case (idempotent) + temp `POST /registrations/{id}/approve` endpoint; `IAclClient.ApproveZaakAsync`.
- **ACL** — resolves the zaaktype's **eindstatus** from the catalogus (`isEindstatus` / highest volgnummer) and POSTs a ZGW status; exposed as `POST /statussen`. Unit + real-OpenZaak integration test.
- **Event-subscriber** — binds NRC `hoofdObject`, projects a `status`/`create` as `INGESCHREVEN` keyed on the zaak (updates the existing row), **without reading OpenZaak** (§8.1). Retains the ZGW `resource` in the log (new column + EF migration) so a rebuild reproduces the status.
- **e2e** — extended: submit → public INGEDIEND → approve → public INGESCHREVEN.
- **Docs** — ADR-0011 (the two non-obvious decisions + the walking-skeleton assumption) + demo note.

## Key decisions (see ADR-0011)

- **ACL discovers the eindstatus** (chosen over injecting a statustype URL): no new config/seed plumbing, domain stays ZGW-ignorant.
- **Any post-creation status-set ⇒ INGESCHREVEN**: in the walking skeleton the only status ever set after creation is the approval, and the subscriber may not read ZGW — documented to tighten when more transitions arrive (S-12+).

## Verification

- All .NET unit suites green locally (domain 47, acl 11, event-subscriber 14, bff 16, acceptance 7); Release build + `dotnet format` clean.
- No new compose config (the eindstatus-discovery approach avoided it).
- The real-OpenZaak integration test (ACL status-set) and the full submit→approve→visible e2e run in CI `verify-stack` (live NRC→projection + selectielijst egress, not reproducible locally).

closes #75

Reviewed-on: #77

services/acl/Acl.Api/Program.cs

@@ -24,8 +24,18 @@ app.MapPost("/zaken", async (OpenZaakRequest body, AclService acl, CancellationT
     return Results.Ok(new { zaakUrl = zaakUrl.ToString() });
 });
 
+// Approve a zaak: set it to its zaaktype's eindstatus (S-09b). The domain hands over only the zaak
+// URL; the ACL owns the ZGW statustype resolution (§8.1).
+app.MapPost("/statussen", async (SetStatusRequest body, AclService acl, CancellationToken ct) =>
+{
+    await acl.ApproveZaakAsync(new Uri(body.ZaakUrl), ct);
+    return Results.NoContent();
+});
+
 app.Run();
 
 public sealed record OpenZaakRequest(string Bsn);
 
+public sealed record SetStatusRequest(string ZaakUrl);
+
 public partial class Program;

services/acl/Acl.Application/AclService.cs

@@ -17,4 +17,15 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
 
         return gateway.OpenZaakAsync(request, ct);
     }
+
+    /// <summary>
+    /// Approve a zaak: set it to the eindstatus of the configured BIG zaaktype (ADR-0003 default). The
+    /// domain hands over only the zaak URL; the ACL owns which statustype means "approved" (§8.1).
+    /// </summary>
+    public Task ApproveZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+
+        return gateway.SetZaakToEindstatusAsync(zaakUrl, defaults.ZaaktypeUrl, clock.Today, ct);
+    }
 }

services/acl/Acl.Application/IZaakGateway.cs

@@ -5,4 +5,11 @@ namespace Acl.Application;
 public interface IZaakGateway
 {
     Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default);
+
+    /// <summary>
+    /// Set the given zaak to the <em>eindstatus</em> (final statustype) of the supplied zaaktype —
+    /// the ZGW translation of "approve". The gateway resolves which statustype is the eindstatus from
+    /// the catalogus and POSTs a status against the zaak, dated <paramref name="datumStatusGezet"/>.
+    /// </summary>
+    Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default);
 }

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -41,6 +41,92 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return new Uri(created.Url);
     }
 
+    public async Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+        ArgumentNullException.ThrowIfNull(zaaktypeUrl);
+
+        var eindstatus = await ResolveEindstatusAsync(zaaktypeUrl, ct);
+        var resultaattype = await ResolveResultaattypeAsync(zaaktypeUrl, ct);
+
+        // OpenZaak refuses to set a zaak's eindstatus unless the zaak has a resultaat
+        // ("resultaat-does-not-exist"), so record the resultaat first, then the status.
+        await PostAsync("/zaken/api/v1/resultaten",
+            new ResultaatDto(zaakUrl.ToString(), resultaattype.ToString()), "Setting the zaak resultaat", ct);
+
+        await PostAsync("/zaken/api/v1/statussen",
+            // datumStatusGezet is a ZGW date-time; set it at the start of the given day (UTC).
+            new StatusDto(zaakUrl.ToString(), eindstatus.ToString(),
+                datumStatusGezet.ToDateTime(TimeOnly.MinValue, DateTimeKind.Utc).ToString("yyyy-MM-ddTHH:mm:ssZ")),
+            "Setting the zaak status", ct);
+    }
+
+    // POSTs a non-geo ZGW resource (resultaat/status — no CRS headers). Buffers the body so uwsgi gets
+    // a Content-Length instead of a chunked body (as with zaak-create).
+    private async Task PostAsync(string path, object dto, string action, CancellationToken ct)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Post, new Uri(options.BaseUrl, path))
+        {
+            Content = JsonContent.Create(dto),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        await message.Content.LoadIntoBufferAsync(ct);
+
+        using var response = await http.SendAsync(message, ct);
+        await EnsureSuccessAsync(response, action, ct);
+    }
+
+    // EnsureSuccessStatusCode discards the response body; ZGW returns a JSON problem detail on 400 that
+    // is essential for diagnosing a rejected request, so surface it in the exception.
+    private static async Task EnsureSuccessAsync(HttpResponseMessage response, string action, CancellationToken ct)
+    {
+        if (response.IsSuccessStatusCode)
+            return;
+
+        var body = await response.Content.ReadAsStringAsync(ct);
+        throw new HttpRequestException($"{action} failed: {(int)response.StatusCode} {response.ReasonPhrase}. {body}");
+    }
+
+    /// <summary>Resolve the zaaktype's eindstatus (the terminal statustype) from the catalogus.</summary>
+    private async Task<Uri> ResolveEindstatusAsync(Uri zaaktypeUrl, CancellationToken ct)
+    {
+        var page = await GetCatalogusAsync<StatustypePage>("statustypen", zaaktypeUrl, "statustypen", ct);
+        var results = page.Results ?? [];
+
+        // OpenZaak flags the terminal statustype (highest volgnummer) as isEindstatus; fall back to the
+        // highest volgnummer if the flag is absent.
+        var eindstatus = results.FirstOrDefault(s => s.IsEindstatus)
+            ?? results.OrderByDescending(s => s.Volgnummer).FirstOrDefault()
+            ?? throw new InvalidOperationException($"No statustypen found for zaaktype {zaaktypeUrl}");
+        return new Uri(eindstatus.Url);
+    }
+
+    /// <summary>Resolve the zaaktype's resultaattype from the catalogus (the seed defines one).</summary>
+    private async Task<Uri> ResolveResultaattypeAsync(Uri zaaktypeUrl, CancellationToken ct)
+    {
+        var page = await GetCatalogusAsync<ResultaattypePage>("resultaattypen", zaaktypeUrl, "resultaattypen", ct);
+        var resultaattype = (page.Results ?? []).FirstOrDefault()
+            ?? throw new InvalidOperationException($"No resultaattypen found for zaaktype {zaaktypeUrl}");
+        return new Uri(resultaattype.Url);
+    }
+
+    // GETs a catalogus collection filtered by zaaktype (status=alles includes concept + published).
+    private async Task<T> GetCatalogusAsync<T>(string resource, Uri zaaktypeUrl, string label, CancellationToken ct)
+    {
+        var query = new Uri(options.BaseUrl,
+            $"/catalogi/api/v1/{resource}?status=alles&zaaktype=" + Uri.EscapeDataString(zaaktypeUrl.ToString()));
+        using var message = new HttpRequestMessage(HttpMethod.Get, query);
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+
+        using var response = await http.SendAsync(message, ct);
+        await EnsureSuccessAsync(response, $"Querying {label}", ct);
+
+        return await response.Content.ReadFromJsonAsync<T>(ct)
+            ?? throw new InvalidOperationException($"OpenZaak returned an empty {label} response");
+    }
+
     private sealed record ZaakDto(
         [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
         [property: JsonPropertyName("zaaktype")] string Zaaktype,
@@ -50,4 +136,27 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
 
     private sealed record ZaakCreatedDto(
         [property: JsonPropertyName("url")] string Url);
+
+    private sealed record StatusDto(
+        [property: JsonPropertyName("zaak")] string Zaak,
+        [property: JsonPropertyName("statustype")] string Statustype,
+        [property: JsonPropertyName("datumStatusGezet")] string DatumStatusGezet);
+
+    private sealed record StatustypePage(
+        [property: JsonPropertyName("results")] IReadOnlyList<StatustypeDto>? Results);
+
+    private sealed record StatustypeDto(
+        [property: JsonPropertyName("url")] string Url,
+        [property: JsonPropertyName("volgnummer")] int Volgnummer,
+        [property: JsonPropertyName("isEindstatus")] bool IsEindstatus);
+
+    private sealed record ResultaatDto(
+        [property: JsonPropertyName("zaak")] string Zaak,
+        [property: JsonPropertyName("resultaattype")] string Resultaattype);
+
+    private sealed record ResultaattypePage(
+        [property: JsonPropertyName("results")] IReadOnlyList<ResultaattypeDto>? Results);
+
+    private sealed record ResultaattypeDto(
+        [property: JsonPropertyName("url")] string Url);
 }

services/acl/Acl.IntegrationTests/OpenZaakFixture.cs

@@ -65,6 +65,43 @@ public sealed class OpenZaakFixture : IDisposable
         return JsonDocument.Parse(json).RootElement.Clone();
     }
 
+    /// <summary>GETs a non-geo ZGW resource (e.g. a status) by URL — no CRS headers.</summary>
+    public async Task<JsonElement> GetJsonAsync(Uri url, CancellationToken ct = default)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Get, url);
+        message.Headers.Authorization = new AuthenticationHeaderValue("Bearer", MintToken());
+
+        using var response = await Http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+        var json = await response.Content.ReadAsStringAsync(ct);
+        return JsonDocument.Parse(json).RootElement.Clone();
+    }
+
+    /// <summary>The zaaktype's eindstatus (terminal statustype) URL — the one an approval sets.</summary>
+    public async Task<Uri> FindEindstatustypeAsync(Uri zaaktypeUrl, CancellationToken ct = default)
+    {
+        var query = new Uri(BaseUrl,
+            "/catalogi/api/v1/statustypen?status=alles&zaaktype=" + Uri.EscapeDataString(zaaktypeUrl.ToString()));
+        var page = await GetJsonAsync(query, ct);
+        var results = page.GetProperty("results");
+
+        Uri? fallback = null;
+        var highest = int.MinValue;
+        foreach (var st in results.EnumerateArray())
+        {
+            if (st.TryGetProperty("isEindstatus", out var eind) && eind.GetBoolean())
+                return new Uri(st.GetProperty("url").GetString()!);
+            var volgnummer = st.GetProperty("volgnummer").GetInt32();
+            if (volgnummer > highest)
+            {
+                highest = volgnummer;
+                fallback = new Uri(st.GetProperty("url").GetString()!);
+            }
+        }
+
+        return fallback ?? throw new InvalidOperationException($"No statustypen for zaaktype {zaaktypeUrl}");
+    }
+
     // A ZGW (vng-api-common) HS256 JWT, mirroring the seed's client. Minted here
     // rather than reusing Acl.Infrastructure's internal minter to keep that internal.
     private string MintToken()

services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs

@@ -42,4 +42,32 @@ public sealed class OpenZaakGatewayIntegrationTests(OpenZaakFixture stack)
         Assert.Equal("517439943", zaak.GetProperty("bronorganisatie").GetString());
         Assert.Equal("openbaar", zaak.GetProperty("vertrouwelijkheidaanduiding").GetString());
     }
+
+    [Fact]
+    public async Task Setting_a_zaak_to_its_eindstatus_records_the_terminal_statustype()
+    {
+        var zaaktype = await stack.FindPublishedBigZaaktypeAsync();
+        Assert.True(zaaktype is not null,
+            "No published BIG-REGISTRATIE zaaktype found in OpenZaak — bring the stack up and " +
+            "seed it with OZ_PUBLISH=1 (`make integration` does this).");
+
+        var gateway = new OpenZaakGateway(stack.Http, stack.Options);
+        var zaakUrl = await gateway.OpenZaakAsync(new ZaakRequest(
+            Bronorganisatie: "517439943",
+            VerantwoordelijkeOrganisatie: "517439943",
+            Vertrouwelijkheidaanduiding: "openbaar",
+            Zaaktype: zaaktype!,
+            Startdatum: DateOnly.FromDateTime(DateTime.UtcNow)));
+
+        await gateway.SetZaakToEindstatusAsync(zaakUrl, zaaktype!, DateOnly.FromDateTime(DateTime.UtcNow));
+
+        // The zaak now carries a current status, and it is the zaaktype's eindstatus.
+        var zaak = await stack.GetZaakAsync(zaakUrl);
+        var statusUrl = zaak.GetProperty("status").GetString();
+        Assert.False(string.IsNullOrEmpty(statusUrl), "the approved zaak has no current status");
+
+        var status = await stack.GetJsonAsync(new Uri(statusUrl!));
+        var eindstatustype = await stack.FindEindstatustypeAsync(zaaktype!);
+        Assert.Equal(eindstatustype.ToString(), status.GetProperty("statustype").GetString());
+    }
 }

services/acl/Acl.Tests/AclServiceTests.cs

@@ -9,13 +9,29 @@ public class AclServiceTests
         public ZaakRequest? Captured;
         public Uri Result { get; } = new("http://openzaak/zaken/api/v1/zaken/abc");
 
+        public (Uri Zaak, Uri Zaaktype, DateOnly Datum)? Approved;
+
         public Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
         {
             Captured = request;
             return Task.FromResult(Result);
         }
+
+        public Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default)
+        {
+            Approved = (zaakUrl, zaaktypeUrl, datumStatusGezet);
+            return Task.CompletedTask;
+        }
     }
 
+    private static AclDefaults Defaults() => new()
+    {
+        Bronorganisatie = "517439943",
+        VerantwoordelijkeOrganisatie = "517439943",
+        Vertrouwelijkheidaanduiding = "openbaar",
+        ZaaktypeUrl = new("http://openzaak/catalogi/api/v1/zaaktypen/big"),
+    };
+
     private sealed class FixedClock(DateOnly today) : IClock
     {
         public DateOnly Today { get; } = today;
@@ -61,4 +77,30 @@ public class AclServiceTests
         await Assert.ThrowsAsync<ArgumentNullException>(() => service.OpenZaakAsync(null!));
         Assert.Null(gateway.Captured);
     }
+
+    [Fact]
+    public async Task Approving_a_zaak_sets_it_to_its_zaaktypes_eindstatus_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.ApproveZaakAsync(zaak);
+
+        Assert.NotNull(gateway.Approved);
+        Assert.Equal(zaak, gateway.Approved!.Value.Zaak);
+        Assert.Equal(defaults.ZaaktypeUrl, gateway.Approved.Value.Zaaktype);
+        Assert.Equal(new DateOnly(2026, 6, 4), gateway.Approved.Value.Datum);
+    }
+
+    [Fact]
+    public async Task Approving_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.ApproveZaakAsync(null!));
+        Assert.Null(gateway.Approved);
+    }
 }

services/acl/Acl.Tests/OpenZaakGatewayTests.cs

@@ -131,8 +131,9 @@ public class OpenZaakGatewayTests
                 Content = new StringContent("null", Encoding.UTF8, "application/json"),
             }));
 
-        await Assert.ThrowsAsync<InvalidOperationException>(
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
             () => Gateway(handler).OpenZaakAsync(SampleRequest()));
+        Assert.Contains("empty zaak response", ex.Message);
     }
 
     [Fact]
@@ -144,6 +145,229 @@ public class OpenZaakGatewayTests
             () => Gateway(handler).OpenZaakAsync(null!));
     }
 
+    // --- SetZaakToEindstatusAsync (approval / S-09b) ---
+
+    private const string ZaakUrl = "http://openzaak/zaken/api/v1/zaken/xyz";
+    private static readonly Uri Zaaktype = new("http://openzaak/catalogi/api/v1/zaaktypen/big");
+
+    private sealed class Recorder
+    {
+        public List<HttpRequestMessage> Requests { get; } = [];
+        public List<string?> Bodies { get; } = [];
+        public List<long?> ContentLengths { get; } = [];
+
+        public int IndexOf(string pathContains) =>
+            Requests.FindIndex(r => r.RequestUri!.ToString().Contains(pathContains));
+
+        // The (body, content-length, request) of the single request whose URL contains the segment.
+        public (string? Body, long? Length, HttpRequestMessage Request) Sent(string pathContains)
+        {
+            var i = IndexOf(pathContains);
+            return (Bodies[i], ContentLengths[i], Requests[i]);
+        }
+    }
+
+    // Per-route response config for the four calls the approval makes.
+    private sealed class OzRoutes
+    {
+        public string StatustypenJson { get; init; } = StatustypenPage(withEindstatusFlag: true);
+        public string ResultaattypenJson { get; init; } = """{"results":[{"url":"http://openzaak/catalogi/api/v1/resultaattypen/1"}]}""";
+        public HttpStatusCode StatustypenStatus { get; init; } = HttpStatusCode.OK;
+        public HttpStatusCode ResultaattypenStatus { get; init; } = HttpStatusCode.OK;
+        public HttpStatusCode ResultaatPostStatus { get; init; } = HttpStatusCode.Created;
+        public HttpStatusCode StatusPostStatus { get; init; } = HttpStatusCode.Created;
+    }
+
+    // Routes the approval's four calls by URL: GET /statustypen, GET /resultaattypen (catalogus),
+    // then POST /resultaten and POST /statussen (zaken).
+    private static StubHandler ApprovalStub(Recorder rec, OzRoutes routes) => new(async req =>
+    {
+        rec.Requests.Add(req);
+        // Capture the length BEFORE reading the body (ReadAsStringAsync buffers as a side effect).
+        rec.ContentLengths.Add(req.Content?.Headers.ContentLength);
+        rec.Bodies.Add(req.Content is null ? null : await req.Content.ReadAsStringAsync());
+
+        var url = req.RequestUri!.ToString();
+        if (req.Method == HttpMethod.Get && url.Contains("/statustypen"))
+            return Json(routes.StatustypenStatus, routes.StatustypenJson);
+        if (req.Method == HttpMethod.Get && url.Contains("/resultaattypen"))
+            return Json(routes.ResultaattypenStatus, routes.ResultaattypenJson);
+        if (url.Contains("/resultaten"))
+            return Json(routes.ResultaatPostStatus, """{"url":"http://openzaak/zaken/api/v1/resultaten/new"}""");
+        return Json(routes.StatusPostStatus, """{"url":"http://openzaak/zaken/api/v1/statussen/new"}""");
+    });
+
+    private static HttpResponseMessage Json(HttpStatusCode status, string body) =>
+        new(status) { Content = new StringContent(body, Encoding.UTF8, "application/json") };
+
+    // Two statustypen; the eindstatus is flagged on the *lower* volgnummer so the tests prove the
+    // isEindstatus flag is preferred over "highest volgnummer", not coincidentally equal to it.
+    private static string StatustypenPage(bool withEindstatusFlag) => JsonSerializer.Serialize(new
+    {
+        results = new object[]
+        {
+            new { url = "http://openzaak/catalogi/api/v1/statustypen/1", volgnummer = 1, isEindstatus = withEindstatusFlag },
+            new { url = "http://openzaak/catalogi/api/v1/statustypen/2", volgnummer = 2, isEindstatus = false },
+        },
+    });
+
+    [Fact]
+    public async Task Approving_sets_a_resultaat_then_posts_the_flagged_eindstatus_against_the_zaak()
+    {
+        var rec = new Recorder();
+
+        await Gateway(ApprovalStub(rec, new OzRoutes()))
+            .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4));
+
+        Assert.Equal(4, rec.Requests.Count);
+
+        // Both catalogus queries filter by the zaaktype and carry the bearer.
+        var statustypenGet = rec.Sent("/statustypen").Request;
+        Assert.Equal(HttpMethod.Get, statustypenGet.Method);
+        Assert.Contains(Uri.EscapeDataString(Zaaktype.ToString()), statustypenGet.RequestUri!.ToString());
+        Assert.Equal("Bearer", statustypenGet.Headers.Authorization!.Scheme);
+        Assert.Contains(Uri.EscapeDataString(Zaaktype.ToString()), rec.Sent("/resultaattypen").Request.RequestUri!.ToString());
+
+        // OpenZaak requires a resultaat before the eindstatus, so /resultaten precedes /statussen.
+        Assert.True(rec.IndexOf("/resultaten") < rec.IndexOf("/statussen"));
+
+        var resultaat = rec.Sent("/resultaten");
+        Assert.Equal("http://openzaak/zaken/api/v1/resultaten", resultaat.Request.RequestUri!.ToString());
+        Assert.Equal("Bearer", resultaat.Request.Headers.Authorization!.Scheme);
+        Assert.Contains("\"zaak\":\"" + ZaakUrl + "\"", resultaat.Body);
+        Assert.Contains("\"resultaattype\":\"http://openzaak/catalogi/api/v1/resultaattypen/1\"", resultaat.Body);
+        Assert.True(resultaat.Length > 0);
+
+        var status = rec.Sent("/statussen");
+        Assert.Equal("http://openzaak/zaken/api/v1/statussen", status.Request.RequestUri!.ToString());
+        Assert.Equal("Bearer", status.Request.Headers.Authorization!.Scheme);
+        Assert.Contains("\"zaak\":\"" + ZaakUrl + "\"", status.Body);
+        // The isEindstatus-flagged statustype (/1) is chosen — even though /2 has a higher volgnummer.
+        Assert.Contains("\"statustype\":\"http://openzaak/catalogi/api/v1/statustypen/1\"", status.Body);
+        Assert.Contains("\"datumStatusGezet\":\"2026-06-04T00:00:00Z\"", status.Body);
+        // Bodies are buffered (Content-Length set), so uwsgi doesn't get a chunked body.
+        Assert.True(status.Length > 0);
+    }
+
+    [Fact]
+    public async Task Approving_falls_back_to_the_highest_volgnummer_when_no_eindstatus_is_flagged()
+    {
+        var rec = new Recorder();
+
+        await Gateway(ApprovalStub(rec, new OzRoutes { StatustypenJson = StatustypenPage(withEindstatusFlag: false) }))
+            .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4));
+
+        // No isEindstatus flag → the highest volgnummer (/2) is chosen.
+        Assert.Contains("\"statustype\":\"http://openzaak/catalogi/api/v1/statustypen/2\"", rec.Sent("/statussen").Body);
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_the_zaaktype_has_no_statustypen()
+    {
+        var rec = new Recorder();
+
+        // A page with no `results` property (Results is null) — the eindstatus cannot be resolved.
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { StatustypenJson = "{}" }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("No statustypen found", ex.Message);
+        // It never posts anything when it cannot resolve the eindstatus.
+        Assert.Single(rec.Requests);
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_the_statustypen_response_is_empty()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { StatustypenJson = "null" }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("empty statustypen", ex.Message);
+        Assert.Single(rec.Requests);
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_the_statustypen_query_fails()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { StatustypenStatus = HttpStatusCode.InternalServerError }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("Querying statustypen", ex.Message);
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_the_resultaattypen_query_fails()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { ResultaattypenStatus = HttpStatusCode.InternalServerError }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("Querying resultaattypen", ex.Message);
+        Assert.Equal(-1, rec.IndexOf("/resultaten"));
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_the_zaaktype_has_no_resultaattype()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { ResultaattypenJson = "{}" }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("No resultaattypen found", ex.Message);
+        // Resolved the eindstatus + queried resultaattypen, but posted nothing.
+        Assert.Equal(-1, rec.IndexOf("/resultaten"));
+        Assert.Equal(-1, rec.IndexOf("/statussen"));
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_posting_the_resultaat_fails()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { ResultaatPostStatus = HttpStatusCode.BadRequest }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("Setting the zaak resultaat", ex.Message);
+        // The status is never posted if the resultaat could not be recorded.
+        Assert.Equal(-1, rec.IndexOf("/statussen"));
+    }
+
+    [Fact]
+    public async Task Approving_throws_when_posting_the_status_fails()
+    {
+        var rec = new Recorder();
+
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(() =>
+            Gateway(ApprovalStub(rec, new OzRoutes { StatusPostStatus = HttpStatusCode.BadRequest }))
+                .SetZaakToEindstatusAsync(new Uri(ZaakUrl), Zaaktype, new DateOnly(2026, 6, 4)));
+
+        Assert.Contains("Setting the zaak status", ex.Message);
+        // It got as far as the resultaat + the status POST (4 calls) before failing.
+        Assert.Equal(4, rec.Requests.Count);
+    }
+
+    [Fact]
+    public async Task Approving_rejects_a_null_zaak_or_zaaktype()
+    {
+        var handler = new StubHandler(_ => throw new InvalidOperationException("should not be sent"));
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() =>
+            Gateway(handler).SetZaakToEindstatusAsync(null!, Zaaktype, new DateOnly(2026, 6, 4)));
+        await Assert.ThrowsAsync<ArgumentNullException>(() =>
+            Gateway(handler).SetZaakToEindstatusAsync(new Uri(ZaakUrl), null!, new DateOnly(2026, 6, 4)));
+    }
+
     // ZGW tokens are base64url with padding stripped (ZgwToken.B64Url); restore it to decode.
     private static string DecodeSegment(string segment)
     {