fix(acl): set a resultaat before the eindstatus so OpenZaak accepts the status (refs #75)

The status-set integration test hit 400 "resultaat-does-not-exist: Zaak has no
resultaat" — OpenZaak refuses a zaak's eindstatus until the zaak has a resultaat.
Resolve the zaaktype's resultaattype and POST /resultaten before POST /statussen.
Also surface the ZGW response body in the failure exception (EnsureSuccessStatusCode
hid the 400 detail that pinpointed this). Reworked the gateway with shared
GetCatalogusAsync/PostAsync helpers and rewrote the stub-handler tests for the new
4-call flow incl. failure paths. Verified against real OpenZaak (integration test
green) and locally: acl mutation 100%.

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

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -47,40 +47,51 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         ArgumentNullException.ThrowIfNull(zaaktypeUrl);
 
         var eindstatus = await ResolveEindstatusAsync(zaaktypeUrl, ct);
+        var resultaattype = await ResolveResultaattypeAsync(zaaktypeUrl, ct);
 
-        using var message = new HttpRequestMessage(
-            HttpMethod.Post, new Uri(options.BaseUrl, "/zaken/api/v1/statussen"))
+        // 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(new StatusDto(
-                zaakUrl.ToString(),
-                eindstatus.ToString(),
-                // datumStatusGezet is a ZGW date-time; set it at the start of the given day (UTC).
-                datumStatusGezet.ToDateTime(TimeOnly.MinValue, DateTimeKind.Utc).ToString("yyyy-MM-ddTHH:mm:ssZ"))),
+            Content = JsonContent.Create(dto),
         };
         message.Headers.Authorization =
             new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
-        // The status resource carries no geometry, so no CRS headers. As with zaak-create, buffer the
-        // body so uwsgi gets a Content-Length instead of a chunked body.
         await message.Content.LoadIntoBufferAsync(ct);
 
         using var response = await http.SendAsync(message, ct);
-        response.EnsureSuccessStatusCode();
+        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 query = new Uri(options.BaseUrl,
-            "/catalogi/api/v1/statustypen?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);
-        response.EnsureSuccessStatusCode();
-
-        var page = await response.Content.ReadFromJsonAsync<StatustypePage>(ct)
-            ?? throw new InvalidOperationException("OpenZaak returned an empty statustypen response");
+        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
@@ -91,6 +102,31 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         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,
@@ -113,4 +149,14 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         [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);
 }