ci(acl): run the ACL integration test as a Gitea Actions job (refs #46)

New integration job: setup-dotnet + make integration (stack up, OZ_PUBLISH=1 seed,
Integration-category tests, tear down), with on-failure log dump + teardown like
compose-smoke. Documents the job and the new make target in the CI runbook.

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

.gitea/workflows/ci.yaml

@@ -63,6 +63,25 @@ jobs:
           path: services/acl/StrykerOutput/**/reports/mutation-report.html
           if-no-files-found: warn
 
+  integration:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: https://github.com/actions/checkout@v4
+      - uses: https://github.com/actions/setup-dotnet@v4
+        with:
+          dotnet-version: '10.0.x'
+      # `make integration` brings the OpenZaak stack up, seeds a PUBLISHED BIG
+      # zaaktype (OZ_PUBLISH=1) and runs the Integration-category tests, then tears
+      # down. Needs Docker + python3 (both on ubuntu-latest) and outbound access to
+      # selectielijst.openzaak.nl from the OpenZaak container (see ADR-0006).
+      - run: make integration
+      - name: dump OpenZaak logs on failure
+        if: failure()
+        run: docker compose -f infra/openzaak/docker-compose.yml logs --no-color --tail=80 oz-init openzaak 2>&1 || true
+      - name: tear down on failure
+        if: failure()
+        run: docker compose -f infra/openzaak/docker-compose.yml down --volumes 2>&1 || true
+
   compose-smoke:
     runs-on: ubuntu-latest
     steps:

Makefile

@@ -43,7 +43,7 @@ export DOCKER_HOST := unix://$(PODMAN_SOCK)
 endif
 endif
 
-.PHONY: ci lint build unit mutation smoke up down local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
+.PHONY: ci lint build unit mutation integration smoke up down local local-down changelog openzaak-up openzaak-smoke openzaak-seed openzaak-down stack-up stack-smoke stack-down keycloak-up keycloak-smoke keycloak-down flowable-up flowable-smoke flowable-down help
 
 ## ci: run the full pipeline — lint, build, unit, mutation, smoke (mirrors Gitea Actions)
 ci: lint build unit mutation smoke
@@ -56,9 +56,9 @@ lint:
 build:
 	dotnet build $(SLN) -c Release
 
-## unit: run unit tests
+## unit: run unit tests (excludes the container-backed Integration lane)
 unit:
-	dotnet test $(SLN) -c Release
+	dotnet test $(SLN) -c Release --filter "Category!=Integration"
 
 ## mutation: run the Stryker.NET ratchet on the ACL (fails below the recorded baseline)
 # Stryker is pinned as a local dotnet tool (.config/dotnet-tools.json); `tool restore`
@@ -106,6 +106,21 @@ local-down:
 changelog:
 	git-cliff --output CHANGELOG.md
 
+## integration: ACL integration tests against a real OpenZaak (S-04a, #46). Brings
+## the stack up, seeds a PUBLISHED BIG zaaktype (OZ_PUBLISH=1, so OpenZaak accepts a
+## real zaak POST), runs the Integration-category tests, then always tears down.
+## Kept out of `unit`/`mutation` because it needs the live stack. See ADR-0006.
+integration: openzaak-up
+	@bash -c 'set -e; \
+	  for i in $$(seq 1 60); do \
+	    c=$$(curl -s -o /dev/null -w "%{http_code}" $(OZ_BASE)/catalogi/api/v1/ || true); \
+	    [ "$$c" = "200" ] && break; sleep 3; done; echo "OpenZaak ready ($$c)"; \
+	  OZ_PUBLISH=1 python3 infra/openzaak/seed_catalogus.py; \
+	  rc=0; dotnet test $(SLN) -c Release --filter "Category=Integration" || rc=$$?; \
+	  docker compose -f $(OZ_COMPOSE) down --volumes >/dev/null 2>&1 || true; \
+	  docker volume rm -f rr-oz-config >/dev/null 2>&1 || true; \
+	  exit $$rc'
+
 ## openzaak-up: start the OpenZaak stack (migrations run on first start)
 openzaak-up:
 	$(SEED) oz

docs/architecture/adr-0006-integration-test-provisioning.md

@@ -0,0 +1,84 @@
+# ADR-0006: Provision the ACL integration test against the compose stack
+
+- **Status:** Accepted
+- **Date:** 2026-06-29
+- **Deciders:** Respellion engineering
+- **Relates to:** S-04a (#46); proposed in #53; builds on ADR-0001 (loose coupling), ADR-0002 (catalogus design), ADR-0003 (default-fill); supports CLAUDE.md §11 (integration tests via real containers)
+
+## Context
+
+S-04 delivered the ACL's one operation — `OpenZaakGateway.OpenZaakAsync` — with unit
+tests against a stubbed `HttpMessageHandler` and a Reqnroll scenario over an in-memory
+stand-in. The deferred S-04 acceptance criterion (S-04a) is the one a stub cannot meet:
+
+> Integration test using Testcontainers against real OpenZaak passes.
+
+The test must drive the gateway against a **real** OpenZaak — real ZGW JWT auth, the real
+`POST /zaken/api/v1/zaken` contract, real CRS handling — and assert a zaak comes back.
+
+Two ways to stand OpenZaak up were considered (the issue's open question): (a) a full
+**Testcontainers** graph started by the test, or (b) target the **running compose stack**
+the repo already defines (`infra/openzaak/docker-compose.yml`, `make openzaak-up`).
+
+Investigation reversed the initially-favoured Testcontainers option:
+
+1. **Testcontainers .NET has no docker-compose support.** OpenZaak needs PostGIS + Redis +
+   a `setup_configuration` one-shot (the JWT client) + the API. Honouring "full graph" would
+   mean re-implementing that five-service stack — init ordering, the config volume, health
+   gating — by hand in C#, duplicating the maintained compose file and rotting with it. That
+   rubs against CLAUDE.md §13 ("if a test is hard to write, the design is wrong").
+2. **The test cannot be hermetic anyway.** OpenZaak's Zaken API rejects a zaak against a
+   *concept* zaaktype (`not-published`), and a *published* zaaktype requires ≥1 resultaattype,
+   which OpenZaak validates by fetching the external **Selectielijst** reference API
+   (`selectielijst.openzaak.nl`). So a real zaak POST already depends on outbound internet
+   from the OpenZaak container — the self-containment that motivated Testcontainers is lost
+   regardless of how the containers are started.
+
+## Decision
+
+**The ACL integration test targets the running compose stack; it does not start containers
+itself. No new test dependency is added.**
+
+- A gated test project `Acl.IntegrationTests` (`[Trait("Category","Integration")]`) talks to
+  OpenZaak with a plain `HttpClient`, reusing the same endpoint + JWT-client config the seed
+  uses (`OZ_BASE` / `OZ_CLIENT_ID` / `OZ_SECRET`, defaulting to the local stack). It locates
+  the published `BIG-REGISTRATIE` zaaktype via the Catalogi API and exercises the real
+  `OpenZaakGateway` against it.
+- **The lane is kept out of the fast checks.** `make unit` runs with
+  `--filter "Category!=Integration"`; Stryker is pinned to `Acl.Tests` (`test-projects`), so
+  neither the unit nor the mutation lane needs a live stack. A new `make integration` target
+  brings the stack up, seeds, runs the lane, and always tears down — mirrored by a Gitea
+  Actions `integration` job. This matches `make` being the single source of truth (ADR-0005).
+- **Publishing is opt-in in the seed.** `infra/openzaak/seed_catalogus.py` gains an
+  `OZ_PUBLISH=1` path that adds the relations OpenZaak's publish requires — two statustypen
+  (begin/eind), a roltype, and a resultaattype whose Selectielijst procestype is matched onto
+  the zaaktype — then publishes. The default seed (S-01 / ADR-0002) still leaves the zaaktype
+  a concept; only `make integration` flips the switch.
+
+## Consequences
+
+- **Positive:** a small, honest test over the real ZGW contract with no bespoke orchestration
+  to maintain; the compose stack is exercised exactly as operators run it; no new dependency.
+- **It caught a real bug.** The gateway sent the zaak body via `JsonContent` without a
+  `Content-Length`, so .NET framed it as `Transfer-Encoding: chunked`, which OpenZaak's uwsgi
+  rejects with 400. A stubbed handler accepts either framing, so only a real OpenZaak surfaced
+  it. Fixed by buffering the body (`LoadIntoBufferAsync`); guarded in the fast lane by a unit
+  test asserting a `Content-Length` is set. This is the concrete justification for §11's
+  integration tier.
+- **External dependency:** the integration job needs the OpenZaak container to reach
+  `selectielijst.openzaak.nl`. It is a stable public reference API (the same one OpenZaak uses
+  in production) but it is a network touchpoint, and a CI environment without egress would need
+  a local Selectielijst service or a recorded fixture. `OZ_SELECTIELIJST` overrides the base URL.
+- **Cost:** the lane needs the stack up first; CI runs it as a dedicated job (Docker + dotnet +
+  python3), separate from the fast lanes.
+
+## Alternatives considered
+
+- **Full Testcontainers graph** — rejected: re-implements the compose stack in C# (brittle,
+  duplicative) for no hermeticity gain, since the Selectielijst dependency remains.
+- **Single OpenZaak container (sqlite/locmem)** — rejected: diverges from the real
+  PostGIS-backed, Redis-cached deployment; the Zaken API is a geo API and the divergence would
+  undermine the contract the test exists to verify.
+- **Mock OpenZaak / record-replay** — rejected: that is what the existing stubbed-handler unit
+  tests already do; it cannot exercise the real contract, and would not have caught the chunked
+  body bug.

docs/runbooks/ci.md

@@ -15,8 +15,9 @@ and CI cannot drift:
 |---|---|---|
 | `lint` | `make lint` → `dotnet format … --verify-no-changes` | .NET 10 SDK |
 | `build` | `make build` → `dotnet build … -c Release` | .NET 10 SDK |
-| `unit` | `make unit` → `dotnet test … -c Release` | .NET 10 SDK |
+| `unit` | `make unit` → `dotnet test … -c Release --filter "Category!=Integration"` | .NET 10 SDK |
 | `mutation` | `make mutation` → `dotnet tool restore` → `dotnet stryker` (ACL); uploads the HTML report as an artifact | .NET 10 SDK |
+| `integration` | `make integration` → `openzaak-up` → seed a **published** BIG zaaktype (`OZ_PUBLISH=1`) → `dotnet test … --filter "Category=Integration"` → tear down | .NET 10 SDK + container engine + python3 + egress to `selectielijst.openzaak.nl` |
 | `compose-smoke` | `make smoke` → seed config volumes → `up -d` (full stack) → `up --wait` durable services → `down` | container engine + compose v2 |
 
 All `uses:` references are absolute, tag-pinned URLs (`https://github.com/actions/checkout@v4`,
@@ -88,12 +89,17 @@ the containerized CI runner). Keep the two files in sync.
 Until the runner exists, run the full pipeline yourself before pushing:
 
 ```bash
-make ci          # lint + build + unit + mutation + smoke — what the pipeline runs
+make ci          # lint + build + unit + mutation + smoke — the fast pipeline lanes
 make lint        # or a single stage
 make mutation    # Stryker.NET ratchet on the ACL
 make smoke       # compose up --wait, curl /health, tear down
+make integration # ACL ↔ real OpenZaak (its own CI job; not part of `make ci`)
 ```
 
+> `make integration` is a separate, heavier lane (it stands the OpenZaak stack up and
+> seeds a published zaaktype), so it is **not** folded into `make ci`. Run it before
+> pushing changes that touch the ACL gateway or the OpenZaak seed. See ADR-0006.
+
 **Prerequisites:** .NET 10 SDK, a container engine with Compose v2, and `curl`.
 
 On a **rootless Podman** box (the default dev setup here), the `smoke` target needs

infra/openzaak/seed_catalogus.py

@@ -18,6 +18,16 @@ SECRET = os.environ.get("OZ_SECRET", "insecure-dev-secret-change-me")
 ZTC = f"{BASE}/catalogi/api/v1"
 RSIN = "517439943"  # elfproef-valid test RSIN
 
+# Opt-in: also publish the zaaktype so OpenZaak's Zaken API accepts a zaak against
+# it (a concept zaaktype is rejected with `not-published`). Off by default — the
+# S-01 compose seed keeps it a concept (ADR-0002). The ACL integration test
+# (S-04a, #46) sets OZ_PUBLISH=1. Publishing requires ≥2 statustypen, ≥1 roltype
+# and ≥1 resultaattype; the resultaattype is validated against the external
+# Selectielijst reference API, so this path needs outbound access to it. See ADR-0006.
+PUBLISH = os.environ.get("OZ_PUBLISH", "").lower() in ("1", "true", "yes")
+SELECTIELIJST = os.environ.get(
+    "OZ_SELECTIELIJST", "https://selectielijst.openzaak.nl/api/v1").rstrip("/")
+
 
 def token():
     b64 = lambda b: base64.urlsafe_b64encode(b).rstrip(b"=")
@@ -52,6 +62,68 @@ def find(path):
     return body.get("results", [])
 
 
+def selectielijst(path):
+    """GET the external Selectielijst reference API (no auth). Used only when publishing."""
+    req = urllib.request.Request(f"{SELECTIELIJST}{path}", headers={"Accept": "application/json"})
+    with urllib.request.urlopen(req, timeout=30) as r:
+        return json.loads(r.read())
+
+
+def publish_zaaktype(zt):
+    """Add the relations OpenZaak requires to publish, then publish (idempotent).
+
+    Publish validation (verified against OpenZaak 1.28.2) demands: ≥2 statustypen
+    (begin + eind), ≥1 roltype, ≥1 resultaattype. A resultaattype needs a
+    Selectielijst `selectielijstklasse` whose procestype matches the zaaktype's
+    `selectielijstProcestype`, plus a `resultaattypeomschrijving`.
+    """
+    have_st = {s.get("volgnummer") for s in find(f"/statustypen?zaaktype={zt['url']}&status=alles")}
+    for volgnummer, omschrijving in [(1, "Ontvangen"), (2, "Afgehandeld")]:
+        if volgnummer not in have_st:
+            st, body = api("POST", "/statustypen", {
+                "omschrijving": omschrijving, "zaaktype": zt["url"], "volgnummer": volgnummer})
+            if st != 201:
+                sys.exit(f"create statustype {volgnummer} -> {st}: {json.dumps(body, indent=2)}")
+            print(f"create statustype {volgnummer} ({omschrijving})")
+
+    if find(f"/roltypen?zaaktype={zt['url']}&status=alles"):
+        print("skip   roltype Aanvrager")
+    else:
+        st, body = api("POST", "/roltypen", {
+            "zaaktype": zt["url"], "omschrijving": "Aanvrager", "omschrijvingGeneriek": "initiator"})
+        if st != 201:
+            sys.exit(f"create roltype -> {st}: {json.dumps(body, indent=2)}")
+        print("create roltype Aanvrager")
+
+    if find(f"/resultaattypen?zaaktype={zt['url']}&status=alles"):
+        print("skip   resultaattype Geregistreerd")
+    else:
+        resultaat = selectielijst("/resultaten?pageSize=1")["results"][0]
+        omschrijvingen = selectielijst("/resultaattypeomschrijvingen")
+        oms = (omschrijvingen if isinstance(omschrijvingen, list) else omschrijvingen["results"])[0]["url"]
+        # The selectielijstklasse and the zaaktype must share a procestype.
+        st, body = api("PATCH", zt["url"], {"selectielijstProcestype": resultaat["procesType"]})
+        if st != 200:
+            sys.exit(f"set procestype -> {st}: {json.dumps(body, indent=2)}")
+        st, body = api("POST", "/resultaattypen", {
+            "zaaktype": zt["url"], "omschrijving": "Geregistreerd",
+            "resultaattypeomschrijving": oms, "selectielijstklasse": resultaat["url"],
+            "archiefnominatie": "blijvend_bewaren",
+            "brondatumArchiefprocedure": {"afleidingswijze": "afgehandeld"},
+        })
+        if st != 201:
+            sys.exit(f"create resultaattype -> {st}: {json.dumps(body, indent=2)}")
+        print("create resultaattype Geregistreerd")
+
+    if zt.get("concept", True):
+        st, body = api("POST", f"{zt['url']}/publish")
+        if st != 200:
+            sys.exit(f"publish zaaktype -> {st}: {json.dumps(body, indent=2)}")
+        print(f"publish zaaktype BIG-REGISTRATIE ({zt['url']})")
+    else:
+        print("skip   publish (already published)")
+
+
 def main():
     # 1. Catalogus
     existing = [c for c in find(f"/catalogussen?domein=BIG") if c.get("domein") == "BIG"]
@@ -121,16 +193,24 @@ def main():
     else:
         print("warn   zaaktype already published; cannot add bsn eigenschap")
 
-    # Intentionally NOT published. Publishing requires roltypen, resultaattypen
-    # and statustypen, which go beyond the "lean / schema-mandatory" zaaktype this
-    # slice asks for; they arrive with the workflow/zaak slices. See ADR-0002.
+    # 4. Optionally publish. By default the zaaktype stays a concept: publishing
+    # requires roltypen, resultaattypen and statustypen, beyond the "lean /
+    # schema-mandatory" zaaktype S-01 asks for (ADR-0002). Set OZ_PUBLISH=1 to add
+    # those relations and publish — needed so a real zaak POST is accepted, which
+    # the ACL integration test (S-04a, #46) exercises. See ADR-0006.
+    if PUBLISH:
+        # Re-fetch: the bsn-eigenschap branch above may hold a stale concept flag.
+        zt = next(z for z in find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
+                  if z.get("identificatie") == "BIG-REGISTRATIE")
+        publish_zaaktype(zt)
 
-    # 4. Verify the JWT client can list the zaaktype (concepts included).
+    # 5. Verify the JWT client can list the zaaktype (concepts included).
     zaaktypen = find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
     names = [z.get("identificatie") for z in zaaktypen]
     print(f"zaaktypen in BIG: {names}")
     assert "BIG-REGISTRATIE" in names, "BIG-REGISTRATIE not listed"
-    print("OK — BIG catalogus seeded (BIG-REGISTRATIE concept + bsn eigenschap)")
+    state = "published" if PUBLISH else "concept"
+    print(f"OK — BIG catalogus seeded (BIG-REGISTRATIE {state} + bsn eigenschap)")
 
 
 if __name__ == "__main__":

mkdocs.yml

@@ -27,6 +27,7 @@ nav:
       - "ADR-0003: ACL default-fill": architecture/adr-0003-default-fill.md
       - "ADR-0004: BDD framework": architecture/adr-0004-bdd-framework.md
       - "ADR-0005: Mutation testing": architecture/adr-0005-mutation-testing.md
+      - "ADR-0006: ACL integration test provisioning": architecture/adr-0006-integration-test-provisioning.md
   - Working in Gitea: gitea-workflow.md
   - Runbooks:
       - CI: runbooks/ci.md

register-referentie.slnx

@@ -4,6 +4,7 @@
     <Project Path="services/acl/Acl.Api/Acl.Api.csproj" />
     <Project Path="services/acl/Acl.Application/Acl.Application.csproj" />
     <Project Path="services/acl/Acl.Infrastructure/Acl.Infrastructure.csproj" />
+    <Project Path="services/acl/Acl.IntegrationTests/Acl.IntegrationTests.csproj" />
     <Project Path="services/acl/Acl.Tests/Acl.Tests.csproj" />
   </Folder>
   <Folder Name="/services/bff/">

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -27,6 +27,11 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         // ZRC is a geo API; it requires the CRS headers.
         message.Headers.Add("Accept-Crs", "EPSG:4326");
         message.Content.Headers.Add("Content-Crs", "EPSG:4326");
+        // OpenZaak runs behind uwsgi, which rejects a chunked request body with 400.
+        // JsonContent streams without a known length (→ Transfer-Encoding: chunked),
+        // so buffer it first to send a Content-Length instead. Only a real OpenZaak
+        // surfaces this — a stubbed HttpMessageHandler accepts either framing.
+        await message.Content.LoadIntoBufferAsync(ct);
 
         using var response = await http.SendAsync(message, ct);
         response.EnsureSuccessStatusCode();

services/acl/Acl.IntegrationTests/Acl.IntegrationTests.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!-- Integration tests: they talk to a real OpenZaak (the compose stack), so they
+       are gated behind [Trait("Category","Integration")] and excluded from the fast
+       `make unit` / mutation lanes. `make integration` brings the stack up, seeds a
+       published BIG zaaktype (OZ_PUBLISH=1) and runs this project. See ADR-0006. -->
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Acl.Application\Acl.Application.csproj" />
+    <ProjectReference Include="..\Acl.Infrastructure\Acl.Infrastructure.csproj" />
+  </ItemGroup>
+
+</Project>

services/acl/Acl.IntegrationTests/OpenZaakFixture.cs

@@ -0,0 +1,97 @@
+using System.Net.Http.Headers;
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using Acl.Infrastructure;
+
+namespace Acl.IntegrationTests;
+
+/// <summary>
+/// Shared connection to the running OpenZaak compose stack (ADR-0006). Reads the
+/// same endpoint + JWT-client config the seed uses, and locates the published
+/// BIG-REGISTRATIE zaaktype the ACL opens zaken against. Defaults match
+/// `infra/openzaak/seed_catalogus.py`; override via OZ_BASE / OZ_CLIENT_ID / OZ_SECRET.
+/// </summary>
+public sealed class OpenZaakFixture : IDisposable
+{
+    private static string Env(string key, string fallback) =>
+        Environment.GetEnvironmentVariable(key) is { Length: > 0 } v ? v : fallback;
+
+    public Uri BaseUrl { get; } = new(Env("OZ_BASE", "http://localhost:8000"));
+    public string ClientId { get; } = Env("OZ_CLIENT_ID", "big-reference-seed");
+    public string Secret { get; } = Env("OZ_SECRET", "insecure-dev-secret-change-me");
+
+    public HttpClient Http { get; } = new();
+
+    public OpenZaakOptions Options => new()
+    {
+        BaseUrl = BaseUrl,
+        ClientId = ClientId,
+        Secret = Secret,
+    };
+
+    /// <summary>
+    /// The URL of the published BIG-REGISTRATIE zaaktype, or null when none is
+    /// published yet (a concept-only stack). `status=definitief` returns published
+    /// zaaktypen only — a concept zaaktype is deliberately excluded.
+    /// </summary>
+    public async Task<Uri?> FindPublishedBigZaaktypeAsync(CancellationToken ct = default)
+    {
+        var query = new Uri(BaseUrl,
+            "/catalogi/api/v1/zaaktypen?identificatie=BIG-REGISTRATIE&status=definitief");
+        using var message = new HttpRequestMessage(HttpMethod.Get, query);
+        message.Headers.Authorization = new AuthenticationHeaderValue("Bearer", MintToken());
+
+        using var response = await Http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+
+        using var document = JsonDocument.Parse(await response.Content.ReadAsStringAsync(ct));
+        var results = document.RootElement.GetProperty("results");
+        return results.GetArrayLength() == 0
+            ? null
+            : new Uri(results[0].GetProperty("url").GetString()!);
+    }
+
+    /// <summary>GETs a previously-created zaak to prove it was really persisted.</summary>
+    public async Task<JsonElement> GetZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Get, zaakUrl);
+        message.Headers.Authorization = new AuthenticationHeaderValue("Bearer", MintToken());
+        message.Headers.Add("Accept-Crs", "EPSG:4326");
+
+        using var response = await Http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+        var json = await response.Content.ReadAsStringAsync(ct);
+        return JsonDocument.Parse(json).RootElement.Clone();
+    }
+
+    // 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()
+    {
+        static string B64(byte[] b) =>
+            Convert.ToBase64String(b).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+
+        var header = B64(JsonSerializer.SerializeToUtf8Bytes(new { alg = "HS256", typ = "JWT" }));
+        var payload = B64(JsonSerializer.SerializeToUtf8Bytes(new
+        {
+            iss = ClientId,
+            iat = DateTimeOffset.UtcNow.ToUnixTimeSeconds(),
+            client_id = ClientId,
+            user_id = "acl-integration-test",
+            user_representation = "acl-integration-test",
+        }));
+        var signingInput = $"{header}.{payload}";
+        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(Secret));
+        var signature = B64(hmac.ComputeHash(Encoding.UTF8.GetBytes(signingInput)));
+        return $"{signingInput}.{signature}";
+    }
+
+    public void Dispose() => Http.Dispose();
+}
+
+[CollectionDefinition(Name)]
+public sealed class OpenZaakCollection : ICollectionFixture<OpenZaakFixture>
+{
+    public const string Name = "OpenZaak";
+}

services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs

@@ -0,0 +1,45 @@
+using Acl.Application;
+using Acl.Infrastructure;
+
+namespace Acl.IntegrationTests;
+
+/// <summary>
+/// S-04a (#46): the deferred S-04 acceptance criterion — the ACL's OpenZaakGateway
+/// opening a zaak against a *real* OpenZaak, exercising real ZGW JWT auth and the
+/// real POST /zaken/api/v1/zaken contract (CRS headers, default-fill, the created
+/// zaak URL) that the stubbed-HttpMessageHandler unit tests cannot. See ADR-0006.
+/// </summary>
+[Trait("Category", "Integration")]
+[Collection(OpenZaakCollection.Name)]
+public sealed class OpenZaakGatewayIntegrationTests(OpenZaakFixture stack)
+{
+    [Fact]
+    public async Task Opens_a_real_zaak_against_the_published_big_zaaktype_and_returns_its_url()
+    {
+        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 request = new ZaakRequest(
+            Bronorganisatie: "517439943",
+            VerantwoordelijkeOrganisatie: "517439943",
+            Vertrouwelijkheidaanduiding: "openbaar",
+            Zaaktype: zaaktype!,
+            Startdatum: DateOnly.FromDateTime(DateTime.UtcNow));
+
+        var zaakUrl = await gateway.OpenZaakAsync(request);
+
+        // The gateway returns the canonical zaak URL on OpenZaak's Zaken API...
+        Assert.StartsWith(
+            new Uri(stack.BaseUrl, "/zaken/api/v1/zaken/").ToString(),
+            zaakUrl.ToString());
+
+        // ...and that zaak is really persisted with the default-filled fields.
+        var zaak = await stack.GetZaakAsync(zaakUrl);
+        Assert.Equal(zaaktype.ToString(), zaak.GetProperty("zaaktype").GetString());
+        Assert.Equal("517439943", zaak.GetProperty("bronorganisatie").GetString());
+        Assert.Equal("openbaar", zaak.GetProperty("vertrouwelijkheidaanduiding").GetString());
+    }
+}

services/acl/Acl.Tests/OpenZaakGatewayTests.cs

@@ -31,6 +31,10 @@ public class OpenZaakGatewayTests
         return new StubHandler(async req =>
         {
             c.Seen = req;
+            // Capture the length BEFORE reading the body: ReadAsStringAsync buffers the
+            // content and would set ContentLength as a side effect, masking the gateway's
+            // own buffering. Read here to assert the gateway sent a length (not chunked).
+            c.ContentLength = req.Content?.Headers.ContentLength;
             c.Body = req.Content is null ? null : await req.Content.ReadAsStringAsync();
             return new HttpResponseMessage(HttpStatusCode.Created)
             {
@@ -43,6 +47,7 @@ public class OpenZaakGatewayTests
     {
         public HttpRequestMessage? Seen;
         public string? Body;
+        public long? ContentLength;
     }
 
     [Fact]
@@ -75,6 +80,20 @@ public class OpenZaakGatewayTests
         Assert.Equal("EPSG:4326", Assert.Single(capture.Seen.Content!.Headers.GetValues("Content-Crs")));
     }
 
+    [Fact]
+    public async Task Sends_the_body_with_a_content_length_so_it_is_not_chunked()
+    {
+        // OpenZaak's uwsgi rejects a chunked request body (400). The gateway buffers
+        // the body so a Content-Length is sent. JsonContent has no length until
+        // buffered, so this guards the fix the real-OpenZaak integration test found.
+        var handler = Created(out var capture);
+
+        await Gateway(handler).OpenZaakAsync(SampleRequest());
+
+        Assert.NotNull(capture.ContentLength);
+        Assert.True(capture.ContentLength > 0);
+    }
+
     [Fact]
     public async Task Mints_a_hs256_jwt_carrying_the_acl_identity_claims()
     {

services/acl/Acl.slnx

@@ -2,5 +2,6 @@
   <Project Path="Acl.Api/Acl.Api.csproj" />
   <Project Path="Acl.Application/Acl.Application.csproj" />
   <Project Path="Acl.Infrastructure/Acl.Infrastructure.csproj" />
+  <Project Path="Acl.IntegrationTests/Acl.IntegrationTests.csproj" />
   <Project Path="Acl.Tests/Acl.Tests.csproj" />
 </Solution>

services/acl/stryker-config.json

@@ -1,6 +1,7 @@
 {
   "stryker-config": {
     "solution": "Acl.slnx",
+    "test-projects": ["Acl.Tests/Acl.Tests.csproj"],
     "reporters": ["progress", "html"],
     "thresholds": {
       "high": 95,