feat(portal-beheer): ACL default-fill configuration editor (closes #131) (#138)

## What & why

S-15b, second of the S-15 (#16) split, on top of S-15a (#133). A beheerder edits the ACL's ZGW **default-fill** values from the beheer portal, and the next zaak is stamped with the new values — no restart.

Closes #131

### The vertical

portal → BFF `GET/PUT /beheer/default-fill` (medewerker realm + `beheerder` role) → ACL `GET/PUT /default-fill` → a runtime-mutable in-memory store the ACL reads **per zaak**.

- **ACL**: `IDefaultFillStore` / `InMemoryDefaultFillStore` (thread-safe, seeded from `Acl:Defaults`); `AclService` reads `fill.Current` per zaak (not cached at construction); `GET`/`PUT /default-fill` with required-field validation.
- **BFF**: `IAclClient` gains `GetDefaultFillAsync`/`UpdateDefaultFillAsync`; `GET`/`PUT /beheer/default-fill` behind the `beheerder` policy. OpenAPI + generated client regenerated.
- **Frontend**: a *Default-fill* editor page in the beheer app (load → edit → save, with saved/failure states) + nav between Catalogus and Default-fill.

### Scope decision → ADR-0026

Only the **three ZGW fill fields** (bronorganisatie, verantwoordelijke organisatie, vertrouwelijkheidaanduiding) are editable. The S-27 catalog-resolution keys stay **static config** — editing them would desync the zaaktype-URL cache (ADR-0021), and they're catalogus wiring, not "default fill". The store is **in-memory** (seeded from config): an edit reverts on restart. That's the reference-app-appropriate ceiling (no DB added to the stateless ACL); upgrade path documented. Recorded in **ADR-0026**.

## Verified locally

lint (`dotnet format`) ✓ · .NET unit — acl 60 / bff 45 / domain 152 / event-subscriber 19 / acceptance 17 ✓ · frontend lint+test (8 projects) ✓ · beheer build ✓. Clean full-solution build (caught + fixed the acceptance `AclService` ctor drift). TDD red→green per layer (ACL store, ACL endpoints, BFF, frontend).

## Definition of Done

- [x] Failing test committed before each implementation (red→green per layer).
- [x] Conventional Commits referencing #131.
- [ ] CI green — see note below.
- [x] Docs: ADR-0026 + S-15b demo note.
- [x] Demo note in `docs/demo-script.md`.

## Note on CI

The bulk validates in the fast jobs (lint/build/unit/frontend/mutation). The **verify-stack e2e** (incl. the new `default-fill.spec.ts`) can't go green until the pre-existing **verify-stack bring-up failure on the 1.27/2.0.0 runner** is resolved (that fails on plain `main` too — unrelated to this PR). Additive change; no existing e2e touched.

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #138

services/bff/Bff.Api/DownstreamClients.cs

@@ -59,12 +59,26 @@ public interface IProjectionClient
 /// internal reference, not shown in the portal.</summary>
 public sealed record BeheerZaaktype(string Identificatie, string Omschrijving);
 
-/// <summary>Port to the ACL for read-only catalogus queries (beheer portal, S-15a). The BFF reaches the
-/// ACL directly for this read: the catalogus isn't a domain concern, and the ACL is the only code
-/// allowed to read the ZGW Catalogi API (§8.1, ADR-0025).</summary>
+/// <summary>The ACL default-fill settings the beheer portal reads + edits (S-15b): the three ZGW-mandatory
+/// fields the ACL stamps on every zaak (ADR-0003).</summary>
+public sealed record BeheerDefaultFill(
+    string Bronorganisatie,
+    string VerantwoordelijkeOrganisatie,
+    string Vertrouwelijkheidaanduiding);
+
+/// <summary>Port to the ACL for beheer queries (beheer portal). The BFF reaches the ACL directly: these
+/// aren't a domain concern, and the ACL is the only code allowed to read/own the ZGW-facing config
+/// (§8.1, ADR-0025).</summary>
 public interface IAclClient
 {
+    /// <summary>The published catalogus zaaktypen, read-only (S-15a).</summary>
     Task<IReadOnlyList<BeheerZaaktype>> GetZaaktypenAsync(CancellationToken ct = default);
+
+    /// <summary>The current default-fill settings (S-15b).</summary>
+    Task<BeheerDefaultFill> GetDefaultFillAsync(CancellationToken ct = default);
+
+    /// <summary>Replace the default-fill settings (S-15b).</summary>
+    Task UpdateDefaultFillAsync(BeheerDefaultFill settings, CancellationToken ct = default);
 }
 
 /// <summary>Calls the Domain Service's <c>POST /registrations</c>.</summary>
@@ -141,4 +155,14 @@ public sealed class AclClient(HttpClient http) : IAclClient
 {
     public async Task<IReadOnlyList<BeheerZaaktype>> GetZaaktypenAsync(CancellationToken ct = default)
         => await http.GetFromJsonAsync<List<BeheerZaaktype>>("catalogi/zaaktypen", ct) ?? [];
+
+    public async Task<BeheerDefaultFill> GetDefaultFillAsync(CancellationToken ct = default)
+        => await http.GetFromJsonAsync<BeheerDefaultFill>("default-fill", ct)
+           ?? throw new InvalidOperationException("The ACL returned an empty default-fill response.");
+
+    public async Task UpdateDefaultFillAsync(BeheerDefaultFill settings, CancellationToken ct = default)
+    {
+        using var response = await http.PutAsJsonAsync("default-fill", settings, ct);
+        response.EnsureSuccessStatusCode();
+    }
 }

services/bff/Bff.Api/Program.cs

@@ -228,6 +228,25 @@ app.MapGet("/beheer/catalogi/zaaktypen", async (IAclClient acl, CancellationToke
     .Produces(StatusCodes.Status401Unauthorized)
     .Produces(StatusCodes.Status403Forbidden);
 
+// Beheer default-fill config (S-15b): read + edit the ACL's default-fill values. Behind medewerker-
+// realm + beheerder authorization; the BFF proxies the ACL (ADR-0025). The ACL validates the values.
+app.MapGet("/beheer/default-fill", async (IAclClient acl, CancellationToken ct) =>
+    Results.Ok(await acl.GetDefaultFillAsync(ct)))
+    .RequireAuthorization(BeheerAuth.Policy)
+    .Produces<BeheerDefaultFill>(StatusCodes.Status200OK)
+    .Produces(StatusCodes.Status401Unauthorized)
+    .Produces(StatusCodes.Status403Forbidden);
+
+app.MapPut("/beheer/default-fill", async (BeheerDefaultFill body, IAclClient acl, CancellationToken ct) =>
+{
+    await acl.UpdateDefaultFillAsync(body, ct);
+    return Results.NoContent();
+})
+    .RequireAuthorization(BeheerAuth.Policy)
+    .Produces(StatusCodes.Status204NoContent)
+    .Produces(StatusCodes.Status401Unauthorized)
+    .Produces(StatusCodes.Status403Forbidden);
+
 app.Run();
 
 /// <summary>The behandelaar's decision on a registration.</summary>

services/bff/Bff.Tests/BeheerDefaultFillEndpointTests.cs

@@ -0,0 +1,84 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using Bff.Api;
+
+namespace Bff.Tests;
+
+/// <summary>
+/// The beheer default-fill config endpoints (S-15b): read (GET) and edit (PUT) the ACL's default-fill,
+/// reached only with a medewerker-realm token carrying the <c>beheerder</c> role. Missing token → 401;
+/// a medewerker without the role → 403; a beheerder reads and updates via the ACL client.
+/// </summary>
+public class BeheerDefaultFillEndpointTests
+{
+    private static HttpRequestMessage Get(string? bearer)
+    {
+        var r = new HttpRequestMessage(HttpMethod.Get, "/beheer/default-fill");
+        if (bearer is not null) r.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
+        return r;
+    }
+
+    private static HttpRequestMessage Put(string? bearer, object body)
+    {
+        var r = new HttpRequestMessage(HttpMethod.Put, "/beheer/default-fill") { Content = JsonContent.Create(body) };
+        if (bearer is not null) r.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
+        return r;
+    }
+
+    [Fact]
+    public async Task Rejects_read_without_a_token()
+    {
+        using var factory = new BffFactory();
+        var response = await factory.CreateClient().SendAsync(Get(bearer: null));
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Rejects_a_medewerker_without_the_beheerder_role()
+    {
+        using var factory = new BffFactory();
+        var response = await factory.CreateClient().SendAsync(Get(TestTokens.Medewerker("behandelaar")));
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Serves_the_current_default_fill_to_a_beheerder()
+    {
+        using var factory = new BffFactory();
+        factory.Acl.DefaultFill = new BeheerDefaultFill("517439943", "517439943", "openbaar");
+
+        var response = await factory.CreateClient().SendAsync(Get(TestTokens.Medewerker("beheerder")));
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        var body = await response.Content.ReadFromJsonAsync<BeheerDefaultFill>();
+        Assert.Equal("517439943", body!.Bronorganisatie);
+        Assert.Equal("openbaar", body.Vertrouwelijkheidaanduiding);
+    }
+
+    [Fact]
+    public async Task Updates_the_default_fill_via_the_acl_for_a_beheerder()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(
+            Put(TestTokens.Medewerker("beheerder"),
+                new { bronorganisatie = "999999999", verantwoordelijkeOrganisatie = "888888888", vertrouwelijkheidaanduiding = "vertrouwelijk" }));
+
+        Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+        Assert.Equal("999999999", factory.Acl.Updated!.Bronorganisatie);
+        Assert.Equal("vertrouwelijk", factory.Acl.Updated.Vertrouwelijkheidaanduiding);
+    }
+
+    [Fact]
+    public async Task Rejects_an_update_from_a_non_beheerder()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(
+            Put(TestTokens.Medewerker("behandelaar"), new { bronorganisatie = "1", verantwoordelijkeOrganisatie = "2", vertrouwelijkheidaanduiding = "openbaar" }));
+
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+        Assert.Null(factory.Acl.Updated);
+    }
+}

services/bff/Bff.Tests/BffFactory.cs

@@ -142,11 +142,24 @@ internal sealed class FakeProjectionClient : IProjectionClient
         => Task.FromResult<IReadOnlyList<ProjectionEntry>>(Entries);
 }
 
-/// <summary>Serves a configurable set of catalogus zaaktypen (beheer viewer, S-15a).</summary>
+/// <summary>Serves catalogus zaaktypen (S-15a) and holds the default-fill settings (S-15b).</summary>
 internal sealed class FakeAclClient : IAclClient
 {
     public List<BeheerZaaktype> Zaaktypen { get; } = [];
 
     public Task<IReadOnlyList<BeheerZaaktype>> GetZaaktypenAsync(CancellationToken ct = default)
         => Task.FromResult<IReadOnlyList<BeheerZaaktype>>(Zaaktypen);
+
+    public BeheerDefaultFill DefaultFill { get; set; } = new("517439943", "517439943", "openbaar");
+    public BeheerDefaultFill? Updated { get; private set; }
+
+    public Task<BeheerDefaultFill> GetDefaultFillAsync(CancellationToken ct = default)
+        => Task.FromResult(DefaultFill);
+
+    public Task UpdateDefaultFillAsync(BeheerDefaultFill settings, CancellationToken ct = default)
+    {
+        Updated = settings;
+        DefaultFill = settings;
+        return Task.CompletedTask;
+    }
 }

services/bff/openapi.json

@@ -255,10 +255,80 @@
           }
         }
       }
+    },
+    "/beheer/default-fill": {
+      "get": {
+        "tags": [
+          "Bff.Api"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/BeheerDefaultFill"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "403": {
+            "description": "Forbidden"
+          }
+        }
+      },
+      "put": {
+        "tags": [
+          "Bff.Api"
+        ],
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/BeheerDefaultFill"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "204": {
+            "description": "No Content"
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "403": {
+            "description": "Forbidden"
+          }
+        }
+      }
     }
   },
   "components": {
     "schemas": {
+      "BeheerDefaultFill": {
+        "required": [
+          "bronorganisatie",
+          "verantwoordelijkeOrganisatie",
+          "vertrouwelijkheidaanduiding"
+        ],
+        "type": "object",
+        "properties": {
+          "bronorganisatie": {
+            "type": "string"
+          },
+          "verantwoordelijkeOrganisatie": {
+            "type": "string"
+          },
+          "vertrouwelijkheidaanduiding": {
+            "type": "string"
+          }
+        }
+      },
       "BeheerZaaktype": {
         "required": [
           "identificatie",