test(acceptance): beoordeling scenario asserts the workflow task is completed (refs #13)

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

docs/architecture/adr-0013-behandel-portal-wiring.md

@@ -0,0 +1,76 @@
+# ADR-0013: Behandel-portal wiring — multi-realm BFF auth, werkbak from Flowable tasks, decision completes the task
+
+- **Status:** Accepted
+- **Date:** 2026-07-15
+- **Deciders:** Respellion engineering
+- **Relates to:** #84 (adr-proposal), S-12 (#13); builds on ADR-0010 (BFF OIDC), ADR-0011 (approval status flow), ADR-0009 (external-task worker), ADR-0008 (read projection)
+
+## Context
+
+S-12 adds the behandel-portal: a behandelaar logs in, sees a **werkbak** of registrations awaiting
+beoordeling, and decides each (goedkeuren/afwijzen). Three questions had no obvious answer and shape
+the whole slice.
+
+1. **Which realm authenticates behandelaars, and how does the BFF accept it?** Citizens use the
+   `digid` realm (ADR-0010); staff use a separate `medewerker` realm with roles (`behandelaar`,
+   `teamlead`). Keycloak realms are distinct issuers with distinct signing keys, so the BFF's single
+   `digid`-realm JWT validation rejects a medewerker token outright.
+2. **Where does the werkbak get its data?** The registrations awaiting beoordeling could come from
+   the read projection (status-filtered rows) or from the Flowable `Beoordelen` user tasks (S-12b).
+3. **How does a decision correlate to the workflow?** The process parks at the `Beoordelen` user
+   task; the decision must advance it, and also apply the domain transition (ADR-0011).
+
+## Decision
+
+**The BFF validates a second realm for behandel endpoints; the werkbak is the set of open Flowable
+`Beoordelen` tasks (read through the domain); and a decision both applies the domain transition and
+completes the Flowable task.**
+
+- **Multi-realm BFF auth.** The BFF registers a second JWT bearer scheme (`medewerker`, authority =
+  the medewerker realm) alongside the default `digid` scheme. `/behandel/*` endpoints require an
+  authorization policy bound to the `medewerker` scheme **and** the `behandelaar` role. Keycloak puts
+  realm roles in the nested `realm_access.roles` claim, which ASP.NET does not map automatically, so
+  the scheme's `OnTokenValidated` lifts those roles onto the principal as role claims. Self-service
+  keeps the `digid` scheme. Audience validation stays off (ADR-0010's deferred hardening).
+- **Werkbak = Flowable user tasks (via the domain).** The domain's `Werkbak` query reads the open
+  `Beoordelen` tasks from the Workflow Client (§8.2, `IUserTaskClient`) and enriches each with its
+  aggregate's bsn + status; `GET /behandel/werkbak` exposes it and the BFF proxies it behind the
+  behandelaar policy. The list **is** the authoritative set of claimable/decidable work items, so a
+  decision acts on a real task with no separate correlation store. The read projection stays the
+  anonymous openbaar model — we do **not** project `IN_BEHANDELING` or populate staff-only personal
+  data (both deferred in ADR-0008) just to render a staff view.
+- **Decision completes the task (S-12c-2).** A behandelaar decision applies the domain transition
+  (aggregate + ACL for approval, per ADR-0011) **and** completes the Flowable `Beoordelen` task
+  (looked up by registrationId), so the process advances. Implemented in the next sub-slice; recorded
+  here so the boundary is decided up front.
+
+Delivery is split: **S-12c-1** (this PR) = multi-realm auth + werkbak read; **S-12c-2** = the decide
+endpoint + task completion.
+
+## Consequences
+
+**Positive**
+
+- Staff and citizens are cleanly separated by realm; the `behandelaar` role gates the behandel API.
+- The werkbak reflects exactly what a behandelaar can act on; claim/decide need no extra correlation.
+- No premature projection changes — the openbaar read model stays focused and personal-data-free.
+- Only the ACL/Workflow Client talk to their peers; the BFF still fans out only to domain/projection
+  (§8.3).
+
+**Negative / costs**
+
+- The BFF now depends on two Keycloak realms being reachable (`Keycloak:MedewerkerAuthority`).
+- Rendering the werkbak fans out to Flowable (one task query) plus a store read per task — acceptable
+  for the caseload sizes here; a denormalized staff read model is an additive follow-up if needed.
+- Realm separation (distinct issuers/keys) is validated live, not in the BFF unit tests, where issuer
+  validation is off and one test key signs both realms; the tests exercise the role-based authorization.
+
+## Alternatives considered
+
+- **Werkbak from the read projection** — rejected for now: needs new plumbing to project
+  `IN_BEHANDELING` and to populate staff-only bsn/naam (deferred, ADR-0008), plus a separate way to
+  find the Flowable task at decide-time. Revisit if a high-volume denormalized staff view is needed.
+- **One JWT scheme accepting both realms (issuer validation off)** — rejected: trusting multiple
+  issuers without validation is a security regression; two schemes keep each realm's issuer/key checked.
+- **A dedicated behandel BFF/service** — rejected as premature; one BFF with per-endpoint policies is
+  enough at this size and keeps §8.3 simple.

infra/docker-compose.yml

@@ -349,6 +349,8 @@ services:
       # Keycloak (start-dev) derives the issuer from the request host, so the BFF authority and the
       # verify token request both use keycloak:8080 to keep the issuer consistent.
       Keycloak__Authority: http://keycloak:8080/realms/digid
+      # Behandelaars authenticate against the medewerker realm; the BFF validates it for /behandel/* (S-12c).
+      Keycloak__MedewerkerAuthority: http://keycloak:8080/realms/medewerker
       Downstream__Domain__BaseUrl: http://domain:8080/
       Downstream__Projection__BaseUrl: http://projection-api:8080/
     ports:

infra/run-domain-check.sh

@@ -51,18 +51,71 @@ loc="$(docker run --rm --network "$net" curlimages/curl:latest \
 echo ">> registration accepted at $loc"
 
 echo ">> polling the domain until the worker records the opened zaak"
+zaak_ok=""
 for _ in $(seq 1 30); do
   body="$(docker run --rm --network "$net" curlimages/curl:latest \
     -fsS "http://$dom_ip:8080$loc" 2>/dev/null || true)"
   if echo "$body" | grep -q '/zaken/api/v1/zaken/'; then
     echo "OK — the domain opened a zaak and recorded it on the registration:"
     echo "$body" | cut -c1-300
-    exit 0
+    zaak_ok=1
+    break
   fi
   sleep 2
 done
-echo "FAIL — the registration never received a zaak URL" >&2
-echo "--- domain log ---" >&2; docker logs "$dom" 2>&1 | tail -15 >&2
-acl="$(docker ps -q --filter 'name=[-_]acl[-_]' | head -1)"
-[ -n "$acl" ] && { echo "--- acl log ---" >&2; docker logs "$acl" 2>&1 | tail -15 >&2; }
-exit 1
+if [ -z "$zaak_ok" ]; then
+  echo "FAIL — the registration never received a zaak URL" >&2
+  echo "--- domain log ---" >&2; docker logs "$dom" 2>&1 | tail -15 >&2
+  acl="$(docker ps -q --filter 'name=[-_]acl[-_]' | head -1)"
+  [ -n "$acl" ] && { echo "--- acl log ---" >&2; docker logs "$acl" 2>&1 | tail -15 >&2; }
+  exit 1
+fi
+
+# ── S-12b: the process now parks at the Beoordelen user task. Exercise the exact Flowable REST
+# contract the Workflow Client uses (query/claim/complete) against the live engine, reaching
+# flowable-rest by container IP (same in-network constraint as above). ──────────────────────────
+fl="$(docker ps -q --filter 'name=flowable-rest' | head -1)"
+[ -n "$fl" ] || { echo "ERROR: no running flowable-rest container" >&2; exit 1; }
+fl_base="http://$(ip "$fl"):8080/flowable-rest/service"
+reg_id="${loc##*/}"
+
+# Extracts the Beoordelen task id for our registration from a Flowable task-query response on stdin.
+# Tolerates an empty/non-JSON body (a transient failure during the poll) by printing nothing.
+task_for_reg() { REG_ID="$reg_id" python3 -c "import os,sys,json
+try:
+    d=json.load(sys.stdin)
+except Exception:
+    d={}
+rid=os.environ['REG_ID']
+# Flowable's task-query returns the included process variables under 'variables'.
+print(next((t['id'] for t in (d.get('data') or [])
+    if any(v.get('name')=='registrationId' and v.get('value')==rid for v in (t.get('variables') or []))), ''))"; }
+
+flcurl() { docker run --rm --network "$net" curlimages/curl:latest -fsS -u rest-admin:test "$@"; }
+query='{"processDefinitionKey":"registratie","taskDefinitionKey":"Beoordelen","includeProcessVariables":true}'
+
+echo ">> polling Flowable for the Beoordelen user task (werkbak)"
+task_id=""
+for _ in $(seq 1 30); do
+  resp="$(flcurl -X POST "$fl_base/query/tasks" -H 'Content-Type: application/json' -d "$query" 2>/dev/null || true)"
+  task_id="$(printf '%s' "$resp" | task_for_reg)"
+  [ -n "$task_id" ] && break
+  sleep 2
+done
+[ -n "$task_id" ] || { echo "FAIL — no Beoordelen task appeared for registration $reg_id" >&2; docker logs "$dom" 2>&1 | tail -15 >&2; exit 1; }
+echo ">> Beoordelen task $task_id is waiting"
+
+echo ">> claiming the task as merel-behandelaar"
+flcurl -X POST "$fl_base/runtime/tasks/$task_id" -H 'Content-Type: application/json' \
+  -d '{"action":"claim","assignee":"merel-behandelaar"}' >/dev/null
+
+echo ">> completing the beoordeling (goedkeuren)"
+flcurl -X POST "$fl_base/runtime/tasks/$task_id" -H 'Content-Type: application/json' \
+  -d '{"action":"complete","variables":[{"name":"besluit","type":"string","value":"goedkeuren"}]}' >/dev/null
+
+echo ">> asserting the process finished (no Beoordelen task remains for the registration)"
+resp="$(flcurl -X POST "$fl_base/query/tasks" -H 'Content-Type: application/json' -d "$query")"
+still="$(printf '%s' "$resp" | task_for_reg)"
+[ -z "$still" ] || { echo "FAIL — Beoordelen task $still still active after completion" >&2; exit 1; }
+echo "OK — behandelaar claimed and completed the Beoordelen task; the registratie process finished"
+exit 0

libs/api-client/src/lib/generated/bff-api.ts

@@ -24,6 +24,10 @@ import {
   Observable
 } from 'rxjs';
 
+export interface DecideRequest {
+  besluit: string;
+}
+
 export interface OpenbaarEntry {
   id: string;
   status: string;
@@ -36,6 +40,12 @@ export interface SubmitAccepted {
   status: string;
 }
 
+export interface WerkbakItem {
+  registrationId: string;
+  bsn: string;
+  status: string;
+}
+
 export type GetOpenbaarRegisterParams = {
 q?: string;
 };
@@ -215,4 +225,73 @@ export class BffApiV1Service {
     );
   }
 
+ getBehandelWerkbak<TData = WerkbakItem[]>( options?: HttpClientBodyOptions): Observable<TData>;
+ getBehandelWerkbak<TData = WerkbakItem[]>( options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
+ getBehandelWerkbak<TData = WerkbakItem[]>( options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;
+  getBehandelWerkbak<TData = WerkbakItem[]>(
+     options?: HttpClientObserveOptions): Observable<TData | HttpEvent<TData> | AngularHttpResponse<TData>> {
+    if (options?.observe === 'events') {
+      return this.http.get<TData>(
+      `/behandel/werkbak`,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'events',
+      }
+    );
+    }
+
+    if (options?.observe === 'response') {
+      return this.http.get<TData>(
+      `/behandel/werkbak`,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'response',
+      }
+    );
+    }
+
+    return this.http.get<TData>(
+      `/behandel/werkbak`,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'body',
+      }
+    );
+  }
+
+ postBehandelRegistrationsIdDecide<TData = void>(id: string,
+    decideRequest: DecideRequest, options?: HttpClientBodyOptions): Observable<TData>;
+ postBehandelRegistrationsIdDecide<TData = void>(id: string,
+    decideRequest: DecideRequest, options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
+ postBehandelRegistrationsIdDecide<TData = void>(id: string,
+    decideRequest: DecideRequest, options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;
+  postBehandelRegistrationsIdDecide<TData = void>(
+    id: string,
+    decideRequest: DecideRequest, options?: HttpClientObserveOptions): Observable<TData | HttpEvent<TData> | AngularHttpResponse<TData>> {
+    if (options?.observe === 'events') {
+      return this.http.post<TData>(
+      `/behandel/registrations/${id}/decide`,
+      decideRequest,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'events',
+      }
+    );
+    }
+
+    if (options?.observe === 'response') {
+      return this.http.post<TData>(
+      `/behandel/registrations/${id}/decide`,
+      decideRequest,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'response',
+      }
+    );
+    }
+
+    return this.http.post<TData>(
+      `/behandel/registrations/${id}/decide`,
+      decideRequest,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'body',
+      }
+    );
+  }
+
 };

services/bff/Bff.Api/DownstreamClients.cs

@@ -13,10 +13,20 @@ public sealed record ProjectionEntry(string Id, string Status, string? Reference
 /// <summary>A public-safe openbaar register row — only non-sensitive fields leave the BFF.</summary>
 public sealed record OpenbaarEntry(string Id, string Status, string? Reference);
 
+/// <summary>A behandelaar's werkbak row: a registration awaiting beoordeling, with the bsn + status a
+/// behandelaar sees (staff view — reached only behind medewerker/behandelaar authorization, S-12c).</summary>
+public sealed record WerkbakItem(string RegistrationId, string Bsn, string Status);
+
 /// <summary>Port to the Domain Service (§8.3: the BFF is the portals' only backend; it fans out).</summary>
 public interface IDomainClient
 {
     Task<SubmitAccepted> SubmitRegistrationAsync(string bsn, CancellationToken ct = default);
+
+    /// <summary>The behandelaar's werkbak — registrations awaiting beoordeling.</summary>
+    Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default);
+
+    /// <summary>Apply a behandelaar's decision (<c>goedkeuren</c>/<c>afwijzen</c>) to a registration.</summary>
+    Task DecideAsync(string registrationId, string besluit, CancellationToken ct = default);
 }
 
 /// <summary>Port to the read projection.</summary>
@@ -37,6 +47,16 @@ public sealed class DomainClient(HttpClient http) : IDomainClient
         return new SubmitAccepted(dto.RegistrationId, dto.Status);
     }
 
+    public async Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
+        => await http.GetFromJsonAsync<List<WerkbakItem>>("behandel/werkbak", ct) ?? [];
+
+    public async Task DecideAsync(string registrationId, string besluit, CancellationToken ct = default)
+    {
+        using var response = await http.PostAsJsonAsync(
+            $"registrations/{registrationId}/decide", new { besluit }, ct);
+        response.EnsureSuccessStatusCode();
+    }
+
     private sealed record DomainResponse(string RegistrationId, string Status, string? ZaakUrl);
 }
 

services/bff/Bff.Api/Program.cs

@@ -1,4 +1,6 @@
 using System.Security.Claims;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using Bff.Api;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 
@@ -6,6 +8,10 @@ var builder = WebApplication.CreateBuilder(args);
 
 var keycloakAuthority = builder.Configuration["Keycloak:Authority"]
     ?? throw new InvalidOperationException("Missing configuration 'Keycloak:Authority'");
+// Behandelaars authenticate against a *different* Keycloak realm (medewerker) than citizens (digid),
+// so the BFF validates a second issuer for the behandel endpoints (ADR-0013).
+var medewerkerAuthority = builder.Configuration["Keycloak:MedewerkerAuthority"]
+    ?? throw new InvalidOperationException("Missing configuration 'Keycloak:MedewerkerAuthority'");
 var domainBaseUrl = builder.Configuration["Downstream:Domain:BaseUrl"]
     ?? throw new InvalidOperationException("Missing configuration 'Downstream:Domain:BaseUrl'");
 var projectionBaseUrl = builder.Configuration["Downstream:Projection:BaseUrl"]
@@ -19,8 +25,28 @@ builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
         options.Authority = keycloakAuthority;
         options.RequireHttpsMetadata = false;
         options.TokenValidationParameters.ValidateAudience = false;
+    })
+    // The medewerker realm — behandel endpoints only. On validation we lift Keycloak's realm roles
+    // (the nested realm_access.roles claim) into role claims so authorization policies can require them.
+    .AddJwtBearer(BehandelAuth.Scheme, options =>
+    {
+        options.Authority = medewerkerAuthority;
+        options.RequireHttpsMetadata = false;
+        options.TokenValidationParameters.ValidateAudience = false;
+        options.Events = new JwtBearerEvents
+        {
+            OnTokenValidated = context =>
+            {
+                BehandelAuth.AddRealmRoles(context.Principal);
+                return Task.CompletedTask;
+            },
+        };
     });
-builder.Services.AddAuthorization();
+builder.Services.AddAuthorization(options =>
+    options.AddPolicy(BehandelAuth.Policy, policy => policy
+        .AddAuthenticationSchemes(BehandelAuth.Scheme)
+        .RequireAuthenticatedUser()
+        .RequireRole(BehandelAuth.BehandelaarRole)));
 
 // The BFF is the portals' only backend; it fans out to the domain and projection (§8.3).
 builder.Services.AddHttpClient<IDomainClient, DomainClient>(c => c.BaseAddress = new Uri(domainBaseUrl));
@@ -68,7 +94,79 @@ app.MapGet("/openbaar/register", async (string? q, IProjectionClient projection,
 })
     .Produces<IReadOnlyList<OpenbaarEntry>>(StatusCodes.Status200OK);
 
+// Behandelaar's werkbak: registrations awaiting beoordeling. Reached only with a medewerker-realm
+// token carrying the behandelaar role; the BFF proxies the domain's werkbak (staff view, ADR-0013).
+app.MapGet("/behandel/werkbak", async (IDomainClient domain, CancellationToken ct) =>
+    Results.Ok(await domain.GetWerkbakAsync(ct)))
+    .RequireAuthorization(BehandelAuth.Policy)
+    .Produces<IReadOnlyList<WerkbakItem>>(StatusCodes.Status200OK)
+    .Produces(StatusCodes.Status401Unauthorized)
+    .Produces(StatusCodes.Status403Forbidden);
+
+// A behandelaar's beoordeling on a registration (goedkeuren/afwijzen). Forwarded to the domain, which
+// applies the decision and completes the workflow task (ADR-0013). Same medewerker/behandelaar gate.
+app.MapPost("/behandel/registrations/{id}/decide",
+    async (string id, DecideRequest body, IDomainClient domain, CancellationToken ct) =>
+    {
+        if (!BehandelAuth.IsKnownBesluit(body.Besluit))
+            return Results.BadRequest(new { error = $"Unknown besluit '{body.Besluit}'. Expected 'goedkeuren' or 'afwijzen'." });
+
+        await domain.DecideAsync(id, body.Besluit, ct);
+        return Results.NoContent();
+    })
+    .RequireAuthorization(BehandelAuth.Policy)
+    .Produces(StatusCodes.Status204NoContent)
+    .Produces(StatusCodes.Status400BadRequest)
+    .Produces(StatusCodes.Status401Unauthorized)
+    .Produces(StatusCodes.Status403Forbidden);
+
 app.Run();
 
+/// <summary>The behandelaar's decision on a registration.</summary>
+public sealed record DecideRequest(string Besluit);
+
+// Behandel (medewerker-realm) authentication + authorization wiring (ADR-0013).
+internal static class BehandelAuth
+{
+    public const string Scheme = "medewerker";
+    public const string Policy = "behandelaar";
+    public const string BehandelaarRole = "behandelaar";
+
+    /// <summary>The beoordeling vocabulary the BFF accepts (case-insensitive); an unknown besluit is a
+    /// 400 without troubling the domain. Mirrors the domain's <c>BeoordelingsBesluit</c>.</summary>
+    public static bool IsKnownBesluit(string? besluit) =>
+        string.Equals(besluit, "goedkeuren", StringComparison.OrdinalIgnoreCase) ||
+        string.Equals(besluit, "afwijzen", StringComparison.OrdinalIgnoreCase);
+
+    /// <summary>Lift Keycloak's realm roles (the nested <c>realm_access.roles</c> claim) onto the
+    /// principal as role claims, so <c>RequireRole</c> can authorize on them.</summary>
+    public static void AddRealmRoles(ClaimsPrincipal? principal)
+    {
+        if (principal?.Identity is not ClaimsIdentity identity)
+            return;
+
+        var realmAccess = principal.FindFirst("realm_access")?.Value;
+        if (string.IsNullOrWhiteSpace(realmAccess))
+            return;
+
+        // A malformed realm_access claim must not fail authentication (a throw here becomes a 401);
+        // it simply yields no roles, so the authorization policy answers 403.
+        string[] roles;
+        try
+        {
+            roles = JsonSerializer.Deserialize<RealmAccess>(realmAccess)?.Roles ?? [];
+        }
+        catch (JsonException)
+        {
+            return;
+        }
+
+        foreach (var role in roles)
+            identity.AddClaim(new Claim(identity.RoleClaimType, role));
+    }
+
+    private sealed record RealmAccess([property: JsonPropertyName("roles")] string[] Roles);
+}
+
 // Exposed so the test host (WebApplicationFactory<Program>) can boot the app.
 public partial class Program;

services/bff/Bff.Api/appsettings.json

@@ -7,7 +7,8 @@
   },
   "AllowedHosts": "*",
   "Keycloak": {
-    "Authority": "http://localhost:8180/realms/digid"
+    "Authority": "http://localhost:8180/realms/digid",
+    "MedewerkerAuthority": "http://localhost:8180/realms/medewerker"
   },
   "Downstream": {
     "Domain": { "BaseUrl": "http://localhost:8130/" },

services/bff/Bff.Tests/BehandelEndpointTests.cs

@@ -0,0 +1,114 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using Bff.Api;
+
+namespace Bff.Tests;
+
+/// <summary>
+/// The behandel werkbak endpoint (S-12c): reached only with a medewerker-realm token that carries the
+/// <c>behandelaar</c> role. A missing token is 401; an authenticated medewerker without the role is
+/// 403; a behandelaar gets the werkbak (staff view, incl. bsn).
+/// </summary>
+public class BehandelEndpointTests
+{
+    private static HttpRequestMessage Werkbak(string? bearer)
+    {
+        var request = new HttpRequestMessage(HttpMethod.Get, "/behandel/werkbak");
+        if (bearer is not null)
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
+        return request;
+    }
+
+    [Fact]
+    public async Task Rejects_the_werkbak_without_a_token()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Werkbak(bearer: null));
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Rejects_a_medewerker_without_the_behandelaar_role()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Werkbak(TestTokens.Medewerker("teamlead")));
+
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+    }
+
+    [Fact]
+    public async Task Serves_the_werkbak_to_a_behandelaar()
+    {
+        using var factory = new BffFactory();
+        factory.Domain.Werkbak.Add(new WerkbakItem("reg-1", "123456782", "InBehandeling"));
+
+        var response = await factory.CreateClient().SendAsync(Werkbak(TestTokens.Medewerker("behandelaar")));
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        var items = await response.Content.ReadFromJsonAsync<List<WerkbakItem>>();
+        var item = Assert.Single(items!);
+        Assert.Equal("reg-1", item.RegistrationId);
+        Assert.Equal("123456782", item.Bsn);
+    }
+
+    private static HttpRequestMessage Decide(string? bearer, string id = "reg-1", string besluit = "goedkeuren")
+    {
+        var request = new HttpRequestMessage(HttpMethod.Post, $"/behandel/registrations/{id}/decide")
+        {
+            Content = JsonContent.Create(new { besluit }),
+        };
+        if (bearer is not null)
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
+        return request;
+    }
+
+    [Fact]
+    public async Task Rejects_a_decision_without_a_token()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Decide(bearer: null));
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+        Assert.Null(factory.Domain.Decided);
+    }
+
+    [Fact]
+    public async Task Rejects_a_decision_from_a_medewerker_without_the_behandelaar_role()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Decide(TestTokens.Medewerker("teamlead")));
+
+        Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+        Assert.Null(factory.Domain.Decided);
+    }
+
+    [Fact]
+    public async Task Forwards_a_behandelaar_decision_to_the_domain()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient()
+            .SendAsync(Decide(TestTokens.Medewerker("behandelaar"), id: "reg-42", besluit: "afwijzen"));
+
+        Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+        Assert.Equal(("reg-42", "afwijzen"), factory.Domain.Decided);
+    }
+
+    [Fact]
+    public async Task Rejects_an_unknown_besluit_without_calling_the_domain()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient()
+            .SendAsync(Decide(TestTokens.Medewerker("behandelaar"), besluit: "misschien"));
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+        Assert.Null(factory.Domain.Decided);
+    }
+}

services/bff/Bff.Tests/BffFactory.cs

@@ -5,6 +5,7 @@ using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.AspNetCore.TestHost;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.IdentityModel.Protocols;
 using Microsoft.IdentityModel.Protocols.OpenIdConnect;
 using Microsoft.IdentityModel.Tokens;
 
@@ -23,9 +24,34 @@ internal sealed class BffFactory : WebApplicationFactory<Program>
     public FakeDomainClient Domain { get; } = new();
     public FakeProjectionClient Projection { get; } = new();
 
+    private static void ValidateWithTestKey(IServiceCollection services, string scheme) =>
+        services.Configure<JwtBearerOptions>(scheme, options =>
+        {
+            // Validate locally against the test key and NEVER reach out for OIDC metadata. A static
+            // configuration manager guarantees this regardless of Configure/PostConfigure ordering —
+            // clearing Authority alone left the medewerker scheme fetching metadata under CI timing
+            // (2s hang → 401), because JwtBearer's PostConfigure could still build a ConfigurationManager.
+            options.Authority = null;
+            options.MetadataAddress = null!;
+            options.RequireHttpsMetadata = false;
+            options.Configuration = new OpenIdConnectConfiguration();
+            options.ConfigurationManager =
+                new StaticConfigurationManager<OpenIdConnectConfiguration>(new OpenIdConnectConfiguration());
+            options.TokenValidationParameters = new TokenValidationParameters
+            {
+                ValidateIssuer = false,
+                ValidateAudience = false,
+                ValidateLifetime = true,
+                ValidateIssuerSigningKey = true,
+                IssuerSigningKey = TestSigningKey,
+                ClockSkew = TimeSpan.Zero,
+            };
+        });
+
     protected override void ConfigureWebHost(IWebHostBuilder builder)
     {
         builder.UseSetting("Keycloak:Authority", "https://keycloak.invalid/realms/digid");
+        builder.UseSetting("Keycloak:MedewerkerAuthority", "https://keycloak.invalid/realms/medewerker");
         builder.UseSetting("Downstream:Domain:BaseUrl", "http://domain.invalid/");
         builder.UseSetting("Downstream:Projection:BaseUrl", "http://projection.invalid/");
 
@@ -34,23 +60,11 @@ internal sealed class BffFactory : WebApplicationFactory<Program>
             services.AddSingleton<IDomainClient>(Domain);
             services.AddSingleton<IProjectionClient>(Projection);
 
-            services.Configure<JwtBearerOptions>(JwtBearerDefaults.AuthenticationScheme, options =>
-            {
-                // Validate locally against the test key; never reach out for OIDC metadata.
-                options.Authority = null;
-                options.MetadataAddress = null!;
-                options.RequireHttpsMetadata = false;
-                options.Configuration = new OpenIdConnectConfiguration();
-                options.TokenValidationParameters = new TokenValidationParameters
-                {
-                    ValidateIssuer = false,
-                    ValidateAudience = false,
-                    ValidateLifetime = true,
-                    ValidateIssuerSigningKey = true,
-                    IssuerSigningKey = TestSigningKey,
-                    ClockSkew = TimeSpan.Zero,
-                };
-            });
+            // Both realms validate locally against the test key (no live Keycloak). The medewerker
+            // scheme keeps its OnTokenValidated role-lifting from Program.cs — only the validation
+            // parameters are swapped here.
+            ValidateWithTestKey(services, JwtBearerDefaults.AuthenticationScheme);
+            ValidateWithTestKey(services, "medewerker");
         });
     }
 }
@@ -60,12 +74,24 @@ internal sealed class FakeDomainClient : IDomainClient
 {
     public string? SubmittedBsn { get; private set; }
     public SubmitAccepted Result { get; set; } = new("reg-123", "Ingediend");
+    public List<WerkbakItem> Werkbak { get; } = [];
 
     public Task<SubmitAccepted> SubmitRegistrationAsync(string bsn, CancellationToken ct = default)
     {
         SubmittedBsn = bsn;
         return Task.FromResult(Result);
     }
+
+    public (string RegistrationId, string Besluit)? Decided { get; private set; }
+
+    public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<WerkbakItem>>(Werkbak);
+
+    public Task DecideAsync(string registrationId, string besluit, CancellationToken ct = default)
+    {
+        Decided = (registrationId, besluit);
+        return Task.CompletedTask;
+    }
 }
 
 /// <summary>Serves a configurable set of projection rows.</summary>

services/bff/Bff.Tests/TestTokens.cs

@@ -17,6 +17,22 @@ internal static class TestTokens
         new SymmetricSecurityKey(Encoding.UTF8.GetBytes("a-different-signing-key-256-bits-long-indeed-yes!")),
         expired: false);
 
+    /// <summary>A medewerker-realm token carrying the given realm roles under <c>realm_access.roles</c>
+    /// (Keycloak's shape), signed with the valid test key. Used to exercise behandel authorization.</summary>
+    public static string Medewerker(params string[] roles)
+    {
+        var handler = new JsonWebTokenHandler();
+        return handler.CreateToken(new SecurityTokenDescriptor
+        {
+            Claims = new Dictionary<string, object>
+            {
+                ["realm_access"] = new Dictionary<string, object> { ["roles"] = roles },
+            },
+            Expires = DateTime.UtcNow.AddMinutes(30),
+            SigningCredentials = new SigningCredentials(BffFactory.TestSigningKey, SecurityAlgorithms.HmacSha256),
+        });
+    }
+
     private static string Create(string bsn, SymmetricSecurityKey key, bool expired)
     {
         var handler = new JsonWebTokenHandler();

services/bff/openapi.json

@@ -60,10 +60,90 @@
           }
         }
       }
+    },
+    "/behandel/werkbak": {
+      "get": {
+        "tags": [
+          "Bff.Api"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "$ref": "#/components/schemas/WerkbakItem"
+                  }
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "403": {
+            "description": "Forbidden"
+          }
+        }
+      }
+    },
+    "/behandel/registrations/{id}/decide": {
+      "post": {
+        "tags": [
+          "Bff.Api"
+        ],
+        "parameters": [
+          {
+            "name": "id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/DecideRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "204": {
+            "description": "No Content"
+          },
+          "400": {
+            "description": "Bad Request"
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "403": {
+            "description": "Forbidden"
+          }
+        }
+      }
     }
   },
   "components": {
     "schemas": {
+      "DecideRequest": {
+        "required": [
+          "besluit"
+        ],
+        "type": "object",
+        "properties": {
+          "besluit": {
+            "type": "string"
+          }
+        }
+      },
       "OpenbaarEntry": {
         "required": [
           "id",
@@ -100,6 +180,25 @@
             "type": "string"
           }
         }
+      },
+      "WerkbakItem": {
+        "required": [
+          "registrationId",
+          "bsn",
+          "status"
+        ],
+        "type": "object",
+        "properties": {
+          "registrationId": {
+            "type": "string"
+          },
+          "bsn": {
+            "type": "string"
+          },
+          "status": {
+            "type": "string"
+          }
+        }
       }
     }
   },

services/domain/Big.Api/Program.cs

@@ -20,10 +20,13 @@ builder.Services.AddSingleton<IRegistrationStore, InMemoryRegistrationStore>();
 builder.Services.AddHttpClient<FlowableWorkflowClient>();
 builder.Services.AddTransient<IWorkflowClient>(sp => sp.GetRequiredService<FlowableWorkflowClient>());
 builder.Services.AddTransient<IExternalWorkerClient>(sp => sp.GetRequiredService<FlowableWorkflowClient>());
+builder.Services.AddTransient<IUserTaskClient>(sp => sp.GetRequiredService<FlowableWorkflowClient>());
 builder.Services.AddHttpClient<IAclClient, AclHttpClient>();
 
 builder.Services.AddScoped<SubmitRegistration>();
 builder.Services.AddScoped<ApproveRegistration>();
+builder.Services.AddScoped<BeoordeelRegistratie>();
+builder.Services.AddScoped<Werkbak>();
 builder.Services.AddScoped<OpenZaakWorker>();
 builder.Services.AddScoped<OpenZaakJobProcessor>();
 
@@ -55,6 +58,28 @@ app.MapPost("/registrations/{id}/approve", async (string id, ApproveRegistration
     return Results.NoContent();
 });
 
+// The behandelaar's beoordeling (S-12): decide a registration goedkeuren (→ INGESCHREVEN, sets the
+// zaak's final status via the ACL) or afwijzen (→ AFGEWEZEN). Idempotent. This is the domain contract
+// the behandel-portal's decision reaches through the BFF; it supersedes the temporary /approve above,
+// which is retired once the portal lands.
+app.MapPost("/registrations/{id}/decide", async (string id, DecideRequest body, BeoordeelRegistratie beoordeel, CancellationToken ct) =>
+{
+    if (!Guid.TryParse(id, out var guid))
+        return Results.NotFound();
+
+    if (!Enum.TryParse<BeoordelingsBesluit>(body.Besluit, ignoreCase: true, out var besluit))
+        return Results.BadRequest(new { error = $"Unknown besluit '{body.Besluit}'. Expected 'goedkeuren' or 'afwijzen'." });
+
+    await beoordeel.HandleAsync(new BeoordeelRegistratieCommand(new RegistrationId(guid), besluit), ct);
+    return Results.NoContent();
+});
+
+// The behandelaar's werkbak (S-12): the registrations awaiting beoordeling, read from the open
+// Beoordelen user tasks (§8.2) and enriched with bsn + status. The BFF proxies this behind
+// medewerker-realm + behandelaar-role authorization; the domain trusts its callers (§8.3).
+app.MapGet("/behandel/werkbak", async (Werkbak werkbak, CancellationToken ct) =>
+    Results.Ok(await werkbak.GetAsync(ct)));
+
 // Read a registration. Its zaak URL appears once the worker has opened the zaak (eventually).
 app.MapGet("/registrations/{id}", async (string id, IRegistrationStore store, CancellationToken ct) =>
 {
@@ -72,6 +97,8 @@ await app.RunAsync();
 
 public sealed record SubmitRegistrationRequest(string Bsn);
 
+public sealed record DecideRequest(string Besluit);
+
 public sealed record RegistrationResponse(string RegistrationId, string Status, string? ZaakUrl);
 
 public partial class Program;

services/domain/Big.Application/BeoordeelRegistratie.cs

@@ -0,0 +1,71 @@
+using Big.Domain;
+
+namespace Big.Application;
+
+/// <summary>A behandelaar's beoordeling outcome, in domain language.</summary>
+public enum BeoordelingsBesluit
+{
+    /// <summary>Approve — enter the registration in the register.</summary>
+    Goedkeuren,
+
+    /// <summary>Reject — turn the registration down.</summary>
+    Afwijzen,
+}
+
+/// <summary>A behandelaar's decision on a registration.</summary>
+public sealed record BeoordeelRegistratieCommand(RegistrationId RegistrationId, BeoordelingsBesluit Besluit);
+
+/// <summary>
+/// The beoordeling use case (S-12): apply a behandelaar's decision to a registration.
+/// <see cref="BeoordelingsBesluit.Goedkeuren"/> sets the zaak's final status via the ACL (§8.1) and
+/// advances the aggregate to INGESCHREVEN; <see cref="BeoordelingsBesluit.Afwijzen"/> advances it to
+/// AFGEWEZEN in the domain (propagating a rejection to the zaak, so the openbaar projection reflects
+/// it, is a later sub-slice of S-12). After applying the decision it completes the Flowable
+/// <c>Beoordelen</c> task (found by registrationId) so the workflow advances (ADR-0013). Both
+/// decisions are idempotent — a repeated or redelivered decision that matches the current terminal
+/// state is a no-op, so the ACL is not called and the task not completed twice.
+/// </summary>
+public sealed class BeoordeelRegistratie(IRegistrationStore store, IAclClient acl, IUserTaskClient tasks)
+{
+    public async Task HandleAsync(BeoordeelRegistratieCommand command, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(command);
+
+        var registration = await store.GetAsync(command.RegistrationId, ct)
+            ?? throw new InvalidOperationException($"No registration {command.RegistrationId} to decide.");
+
+        switch (command.Besluit)
+        {
+            case BeoordelingsBesluit.Goedkeuren:
+                // A repeated approval is a no-op: don't set the zaak status a second time.
+                if (registration.Status == RegistrationStatus.Ingeschreven)
+                    return;
+                if (registration.ZaakUrl is null)
+                    throw new InvalidOperationException(
+                        $"Registration {command.RegistrationId} has no zaak yet; it cannot be approved.");
+                await acl.ApproveZaakAsync(registration.ZaakUrl, ct);
+                registration.Approve();
+                break;
+
+            case BeoordelingsBesluit.Afwijzen:
+                if (registration.Status == RegistrationStatus.Afgewezen)
+                    return;
+                registration.Reject();
+                break;
+        }
+
+        await store.SaveAsync(registration, ct);
+        await CompleteWorkflowTaskAsync(command.RegistrationId, command.Besluit, ct);
+    }
+
+    // Advance the workflow: complete the open Beoordelen task for this registration. If none is open
+    // (already completed, or the process hasn't parked yet) the decision still stands — we complete
+    // nothing rather than fail.
+    private async Task CompleteWorkflowTaskAsync(RegistrationId registrationId, BeoordelingsBesluit besluit, CancellationToken ct)
+    {
+        var open = await tasks.GetOpenBeoordelingenAsync(ct);
+        var task = open.FirstOrDefault(t => t.RegistrationId == registrationId);
+        if (task is not null)
+            await tasks.CompleteBeoordelingAsync(task.TaskId, besluit, ct);
+    }
+}

services/domain/Big.Application/Ports.cs

@@ -36,6 +36,30 @@ public interface IAclClient
     Task ApproveZaakAsync(Uri zaakUrl, CancellationToken ct = default);
 }
 
+/// <summary>
+/// The port to the behandelaar's user tasks in the workflow engine (S-12). Implemented by the
+/// Workflow Client — the only code that talks to Flowable (§8.2). The application lists the open
+/// <c>Beoordelen</c> tasks (the werkbak), claims one for a behandelaar, and completes it with the
+/// decision; it never names Flowable's REST shapes.
+/// </summary>
+public interface IUserTaskClient
+{
+    /// <summary>The werkbak: the <c>Beoordelen</c> tasks awaiting a behandelaar, each with the
+    /// registration it belongs to.</summary>
+    Task<IReadOnlyList<BeoordelingTask>> GetOpenBeoordelingenAsync(CancellationToken ct = default);
+
+    /// <summary>Claim a beoordeling task for a behandelaar (assigns it to them).</summary>
+    Task ClaimAsync(string taskId, string behandelaar, CancellationToken ct = default);
+
+    /// <summary>Complete a beoordeling task, carrying the decision into the process as the
+    /// <c>besluit</c> variable so the workflow can continue on the chosen branch.</summary>
+    Task CompleteBeoordelingAsync(string taskId, BeoordelingsBesluit besluit, CancellationToken ct = default);
+}
+
+/// <summary>A <c>Beoordelen</c> user task in the werkbak: the Flowable task id (needed to claim and
+/// complete it) and the registration it carries as a process variable.</summary>
+public sealed record BeoordelingTask(string TaskId, RegistrationId RegistrationId);
+
 /// <summary>
 /// Persistence port for the <see cref="Registration"/> aggregate. In-memory for the minimal slice
 /// (ADR-0009); an EF-backed store is a documented follow-up, and this port keeps that change additive.

services/domain/Big.Application/Werkbak.cs

@@ -0,0 +1,32 @@
+namespace Big.Application;
+
+/// <summary>One row of the behandelaar's werkbak: a registration awaiting beoordeling, with the
+/// public-facing reference (its id) plus the bsn and status a behandelaar needs to triage it.</summary>
+public sealed record WerkbakItem(string RegistrationId, string Bsn, string Status);
+
+/// <summary>
+/// The werkbak query (S-12c): the registrations awaiting a behandelaar's beoordeling. It reads the
+/// open <c>Beoordelen</c> tasks from the workflow engine (§8.2, via <see cref="IUserTaskClient"/>) —
+/// the authoritative set of work items — and enriches each with its aggregate (bsn + status). A task
+/// whose registration the domain doesn't know is skipped rather than invented.
+/// </summary>
+public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
+{
+    public async Task<IReadOnlyList<WerkbakItem>> GetAsync(CancellationToken ct = default)
+    {
+        var open = await tasks.GetOpenBeoordelingenAsync(ct);
+
+        var items = new List<WerkbakItem>(open.Count);
+        foreach (var task in open)
+        {
+            var registration = await store.GetAsync(task.RegistrationId, ct);
+            if (registration is null)
+                continue;
+
+            items.Add(new WerkbakItem(
+                registration.Id.ToString(), registration.Bsn, registration.Status.ToString()));
+        }
+
+        return items;
+    }
+}

services/domain/Big.Domain/Registration.cs

@@ -66,10 +66,28 @@ public sealed class Registration
     }
 
     /// <summary>
-    /// Approve the registration — the behandelaar's decision to enter it in the register. Advances
-    /// <see cref="RegistrationStatus.Ingediend"/> → <see cref="RegistrationStatus.Ingeschreven"/>.
-    /// Requires an opened zaak (the approval sets that zaak's status via the ACL), and only a
-    /// submitted registration can be approved: re-approving is rejected as an invalid transition.
+    /// A behandelaar picks the registration up for beoordeling. Advances
+    /// <see cref="RegistrationStatus.Ingediend"/> → <see cref="RegistrationStatus.InBehandeling"/>.
+    /// Re-taking one already <see cref="RegistrationStatus.InBehandeling"/> is a no-op (the same or
+    /// another behandelaar re-opens it); a decided registration can no longer be taken into behandeling.
+    /// </summary>
+    public void TakeIntoBehandeling()
+    {
+        if (Status == RegistrationStatus.InBehandeling)
+            return;
+
+        if (Status != RegistrationStatus.Ingediend)
+            throw new InvalidOperationException(
+                $"Registration {Id} is {Status}; only an INGEDIEND registration can be taken into behandeling.");
+
+        Status = RegistrationStatus.InBehandeling;
+    }
+
+    /// <summary>
+    /// Approve the registration — the behandelaar's decision to enter it in the register. Advances a
+    /// submitted or in-behandeling registration to <see cref="RegistrationStatus.Ingeschreven"/>.
+    /// Requires an opened zaak (the approval sets that zaak's status via the ACL); a registration that
+    /// has already been decided cannot be approved again.
     /// </summary>
     public void Approve()
     {
@@ -77,10 +95,27 @@ public sealed class Registration
             throw new InvalidOperationException(
                 $"Registration {Id} has no zaak yet; it cannot be approved before its zaak is opened.");
 
-        if (Status != RegistrationStatus.Ingediend)
-            throw new InvalidOperationException(
-                $"Registration {Id} is {Status}; only an INGEDIEND registration can be approved.");
-
+        RequireOpenForDecision(nameof(Approve));
         Status = RegistrationStatus.Ingeschreven;
     }
+
+    /// <summary>
+    /// Reject the registration — the behandelaar's decision not to enter it in the register. Advances a
+    /// submitted or in-behandeling registration to <see cref="RegistrationStatus.Afgewezen"/>. Unlike
+    /// approval this needs no zaak: a registration can be rejected before or after its zaak is opened.
+    /// A registration that has already been decided cannot be rejected again.
+    /// </summary>
+    public void Reject()
+    {
+        RequireOpenForDecision(nameof(Reject));
+        Status = RegistrationStatus.Afgewezen;
+    }
+
+    // A decision is only valid while the registration is still open (INGEDIEND or IN_BEHANDELING).
+    private void RequireOpenForDecision(string decision)
+    {
+        if (Status is not (RegistrationStatus.Ingediend or RegistrationStatus.InBehandeling))
+            throw new InvalidOperationException(
+                $"Registration {Id} is {Status}; only an INGEDIEND or IN_BEHANDELING registration can be decided ({decision}).");
+    }
 }

services/domain/Big.Domain/RegistrationStatus.cs

@@ -1,13 +1,20 @@
 namespace Big.Domain;
 
-/// <summary>The lifecycle states a <see cref="Registration"/> moves through. The walking
-/// skeleton knows <see cref="Ingediend"/> and the terminal <see cref="Ingeschreven"/>; withdrawal,
-/// beoordeling and herregistratie states arrive in their own slices (Iteration 2+).</summary>
+/// <summary>The lifecycle states a <see cref="Registration"/> moves through. Submission starts in
+/// <see cref="Ingediend"/>; a behandelaar takes it <see cref="InBehandeling"/> and decides it into one
+/// of the terminal states <see cref="Ingeschreven"/> (approved) or <see cref="Afgewezen"/> (rejected).
+/// Withdrawal and herregistratie states arrive in their own slices (S-11+).</summary>
 public enum RegistrationStatus
 {
     /// <summary>Submitted by the zorgprofessional; the registratie process has been started.</summary>
     Ingediend,
 
-    /// <summary>Approved: entered in the register. Terminal in the walking skeleton (S-09b).</summary>
+    /// <summary>Picked up by a behandelaar for beoordeling (S-12).</summary>
+    InBehandeling,
+
+    /// <summary>Approved: entered in the register. Terminal.</summary>
     Ingeschreven,
+
+    /// <summary>Rejected by the behandelaar. Terminal.</summary>
+    Afgewezen,
 }

services/domain/Big.Infrastructure/FlowableWorkflowClient.cs

@@ -15,12 +15,14 @@ namespace Big.Infrastructure;
 /// The REST contract here is the one verified against a live flowable-rest engine (ADR-0009).
 /// </summary>
 public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions options)
-    : IWorkflowClient, IExternalWorkerClient
+    : IWorkflowClient, IExternalWorkerClient, IUserTaskClient
 {
     private const string Topic = "OpenZaakAanmaken";
     private const string ProcessDefinitionKey = "registratie";
+    private const string BeoordelenTaskKey = "Beoordelen";
     private const string RegistrationIdVariable = "registrationId";
     private const string ZaakUrlVariable = "zaakUrl";
+    private const string BesluitVariable = "besluit";
 
     public async Task<string> StartRegistrationProcessAsync(RegistrationId registrationId, CancellationToken ct = default)
     {
@@ -55,6 +57,34 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         response.EnsureSuccessStatusCode();
     }
 
+    public async Task<IReadOnlyList<BeoordelingTask>> GetOpenBeoordelingenAsync(CancellationToken ct = default)
+    {
+        var request = new TaskQueryRequest(ProcessDefinitionKey, BeoordelenTaskKey, IncludeProcessVariables: true);
+
+        var page = await PostAsync<TaskQueryRequest, TaskQueryResult>(
+            "service/query/tasks", request, ct);
+
+        var tasks = page?.Data ?? [];
+        return [.. tasks.Select(t => new BeoordelingTask(t.Id, RegistrationId.Parse(t.RegistrationId())))];
+    }
+
+    public async Task ClaimAsync(string taskId, string behandelaar, CancellationToken ct = default)
+    {
+        using var response = await SendAsync(
+            $"service/runtime/tasks/{taskId}", new ClaimTaskRequest("claim", behandelaar), ct);
+        response.EnsureSuccessStatusCode();
+    }
+
+    public async Task CompleteBeoordelingAsync(string taskId, BeoordelingsBesluit besluit, CancellationToken ct = default)
+    {
+        var request = new CompleteTaskRequest(
+            "complete",
+            [new Variable(BesluitVariable, "string", besluit.ToString().ToLowerInvariant())]);
+
+        using var response = await SendAsync($"service/runtime/tasks/{taskId}", request, ct);
+        response.EnsureSuccessStatusCode();
+    }
+
     private async Task<TResponse?> PostAsync<TRequest, TResponse>(string path, TRequest body, CancellationToken ct)
     {
         using var response = await SendAsync(path, body, ct);
@@ -89,6 +119,34 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         [property: JsonPropertyName("workerId")] string WorkerId,
         [property: JsonPropertyName("variables")] IReadOnlyList<Variable> Variables);
 
+    private sealed record TaskQueryRequest(
+        [property: JsonPropertyName("processDefinitionKey")] string ProcessDefinitionKey,
+        [property: JsonPropertyName("taskDefinitionKey")] string TaskDefinitionKey,
+        [property: JsonPropertyName("includeProcessVariables")] bool IncludeProcessVariables);
+
+    private sealed record ClaimTaskRequest(
+        [property: JsonPropertyName("action")] string Action,
+        [property: JsonPropertyName("assignee")] string Assignee);
+
+    private sealed record CompleteTaskRequest(
+        [property: JsonPropertyName("action")] string Action,
+        [property: JsonPropertyName("variables")] IReadOnlyList<Variable> Variables);
+
+    private sealed record TaskQueryResult(
+        [property: JsonPropertyName("data")] IReadOnlyList<UserTaskDto>? Data);
+
+    private sealed record UserTaskDto(
+        [property: JsonPropertyName("id")] string Id,
+        // Flowable's task-query returns the (included) process variables under "variables", not
+        // "processVariables"; the request opts in via includeProcessVariables.
+        [property: JsonPropertyName("variables")] IReadOnlyList<Variable>? Variables)
+    {
+        /// <summary>The registration id this task carries as a process variable.</summary>
+        public string RegistrationId() =>
+            Variables?.SingleOrDefault(v => v.Name == "registrationId")?.Value
+            ?? throw new InvalidOperationException($"Beoordelen task {Id} carries no registrationId variable.");
+    }
+
     private sealed record Variable(
         [property: JsonPropertyName("name")] string Name,
         [property: JsonPropertyName("type")] string Type,

services/domain/Big.Tests/BeoordeelRegistratieTests.cs

@@ -0,0 +1,168 @@
+using Big.Application;
+using Big.Domain;
+
+namespace Big.Tests;
+
+/// <summary>
+/// The beoordeling use case (S-12): a behandelaar's decision on a registration. Goedkeuren sets the
+/// zaak's final status via the ACL (§8.1) and marks the aggregate INGESCHREVEN; Afwijzen marks it
+/// AFGEWEZEN. Either way the decision also completes the Flowable Beoordelen task (found by
+/// registrationId) so the process advances. All idempotent — a repeated decision is a no-op.
+/// </summary>
+public class BeoordeelRegistratieTests
+{
+    private static Registration WithZaak(string bsn = "123456782")
+    {
+        var registration = Registration.Submit(bsn);
+        registration.AttachZaak(FakeAclClient.DefaultZaakUrl);
+        return registration;
+    }
+
+    private static FakeUserTaskClient TaskFor(Registration registration) =>
+        new([new BeoordelingTask("task-1", registration.Id)]);
+
+    [Fact]
+    public async Task Goedkeuren_sets_the_zaak_status_via_the_acl_and_marks_the_registration_ingeschreven()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        store.Seed(registration);
+        var tasks = TaskFor(registration);
+        var handler = new BeoordeelRegistratie(store, acl, tasks);
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren));
+
+        var saved = await store.GetAsync(registration.Id);
+        Assert.Equal(RegistrationStatus.Ingeschreven, saved!.Status);
+        Assert.Equal(FakeAclClient.DefaultZaakUrl, acl.ApprovedZaakUrl);
+        Assert.Equal(1, acl.ApproveCallCount);
+        Assert.Equal(1, store.SaveCount);
+        // The behandelaar's decision advances the workflow: the Beoordelen task is completed.
+        Assert.Equal(("task-1", BeoordelingsBesluit.Goedkeuren), tasks.Completed);
+    }
+
+    [Fact]
+    public async Task Afwijzen_marks_the_registration_afgewezen_without_calling_the_acl()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        store.Seed(registration);
+        var tasks = TaskFor(registration);
+        var handler = new BeoordeelRegistratie(store, acl, tasks);
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Afwijzen));
+
+        var saved = await store.GetAsync(registration.Id);
+        Assert.Equal(RegistrationStatus.Afgewezen, saved!.Status);
+        Assert.Equal(0, acl.ApproveCallCount);
+        Assert.Equal(1, store.SaveCount);
+        Assert.Equal(("task-1", BeoordelingsBesluit.Afwijzen), tasks.Completed);
+    }
+
+    [Fact]
+    public async Task Goedkeuren_an_in_behandeling_registration_marks_it_ingeschreven()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        registration.TakeIntoBehandeling();
+        store.Seed(registration);
+        var handler = new BeoordeelRegistratie(store, acl, TaskFor(registration));
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren));
+
+        Assert.Equal(RegistrationStatus.Ingeschreven, (await store.GetAsync(registration.Id))!.Status);
+    }
+
+    [Fact]
+    public async Task Rejects_a_null_command_without_touching_the_store_or_acl()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var handler = new BeoordeelRegistratie(store, acl, new FakeUserTaskClient([]));
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => handler.HandleAsync(null!));
+        Assert.Equal(0, acl.ApproveCallCount);
+        Assert.Equal(0, store.SaveCount);
+    }
+
+    [Fact]
+    public async Task Deciding_an_unknown_registration_throws_and_does_not_call_the_acl()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var handler = new BeoordeelRegistratie(store, acl, new FakeUserTaskClient([]));
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            handler.HandleAsync(new BeoordeelRegistratieCommand(RegistrationId.New(), BeoordelingsBesluit.Goedkeuren)));
+        Assert.Contains("No registration", ex.Message);
+        Assert.Equal(0, acl.ApproveCallCount);
+    }
+
+    [Fact]
+    public async Task Goedkeuren_before_the_zaak_is_opened_throws_without_calling_the_acl()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = Registration.Submit("123456782"); // no zaak yet
+        store.Seed(registration);
+        var handler = new BeoordeelRegistratie(store, acl, TaskFor(registration));
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() =>
+            handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren)));
+        Assert.Contains("no zaak", ex.Message);
+        Assert.Equal(0, acl.ApproveCallCount);
+    }
+
+    [Fact]
+    public async Task Re_goedkeuren_an_already_ingeschreven_registration_is_idempotent()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        store.Seed(registration);
+        var handler = new BeoordeelRegistratie(store, acl, TaskFor(registration));
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren));
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren));
+
+        Assert.Equal(1, acl.ApproveCallCount);
+        Assert.Equal(RegistrationStatus.Ingeschreven, (await store.GetAsync(registration.Id))!.Status);
+    }
+
+    [Fact]
+    public async Task Re_afwijzen_an_already_afgewezen_registration_is_idempotent()
+    {
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        store.Seed(registration);
+        var handler = new BeoordeelRegistratie(store, acl, TaskFor(registration));
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Afwijzen));
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Afwijzen));
+
+        Assert.Equal(1, store.SaveCount);
+        Assert.Equal(RegistrationStatus.Afgewezen, (await store.GetAsync(registration.Id))!.Status);
+    }
+
+    [Fact]
+    public async Task Deciding_completes_no_task_when_none_is_open_for_the_registration()
+    {
+        // The task may already be gone (redelivery / manual completion). The decision still applies
+        // and simply completes nothing rather than failing.
+        var store = new FakeRegistrationStore();
+        var acl = new FakeAclClient();
+        var registration = WithZaak();
+        store.Seed(registration);
+        var tasks = new FakeUserTaskClient([]); // no open task for this registration
+        var handler = new BeoordeelRegistratie(store, acl, tasks);
+
+        await handler.HandleAsync(new BeoordeelRegistratieCommand(registration.Id, BeoordelingsBesluit.Goedkeuren));
+
+        Assert.Equal(RegistrationStatus.Ingeschreven, (await store.GetAsync(registration.Id))!.Status);
+        Assert.Null(tasks.Completed);
+    }
+}

services/domain/Big.Tests/Fakes.cs

@@ -41,6 +41,29 @@ internal sealed class FakeWorkflowClient(string processInstanceId = "proc-1", Ac
     }
 }
 
+/// <summary>A fake user-task client for the werkbak/decision use cases: returns a scripted set of
+/// open beoordeling tasks and records claim/complete calls.</summary>
+internal sealed class FakeUserTaskClient(IReadOnlyList<BeoordelingTask> open) : IUserTaskClient
+{
+    public (string TaskId, string Behandelaar)? Claimed { get; private set; }
+    public (string TaskId, BeoordelingsBesluit Besluit)? Completed { get; private set; }
+
+    public Task<IReadOnlyList<BeoordelingTask>> GetOpenBeoordelingenAsync(CancellationToken ct = default)
+        => Task.FromResult(open);
+
+    public Task ClaimAsync(string taskId, string behandelaar, CancellationToken ct = default)
+    {
+        Claimed = (taskId, behandelaar);
+        return Task.CompletedTask;
+    }
+
+    public Task CompleteBeoordelingAsync(string taskId, BeoordelingsBesluit besluit, CancellationToken ct = default)
+    {
+        Completed = (taskId, besluit);
+        return Task.CompletedTask;
+    }
+}
+
 /// <summary>A fake ACL client that records the bsn it was asked to open a zaak for and returns a
 /// fixed zaak URL.</summary>
 internal sealed class FakeAclClient(Uri? zaakUrl = null) : IAclClient

services/domain/Big.Tests/FlowableWorkflowClientTests.cs

@@ -1,5 +1,6 @@
 using System.Net;
 using System.Text;
+using Big.Application;
 using Big.Domain;
 using Big.Infrastructure;
 
@@ -127,6 +128,17 @@ public class FlowableWorkflowClientTests
             () => client.StartRegistrationProcessAsync(RegistrationId.New()));
     }
 
+    [Fact]
+    public async Task Start_throws_when_flowable_returns_an_empty_body()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.Created, "null"));
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => client.StartRegistrationProcessAsync(RegistrationId.New()));
+        Assert.Contains("empty process-instance", ex.Message);
+    }
+
     [Fact]
     public async Task Complete_throws_when_flowable_rejects_the_request()
     {
@@ -136,4 +148,107 @@ public class FlowableWorkflowClientTests
         await Assert.ThrowsAsync<HttpRequestException>(
             () => client.CompleteOpenZaakJobAsync("job-1", new Uri("http://openzaak/zaken/api/v1/zaken/abc")));
     }
+
+    // ── S-12b: behandelaar user tasks (werkbak / claim / complete) ────────────────────────────────
+
+    [Fact]
+    public async Task Open_beoordelingen_queries_beoordelen_tasks_with_their_registration_id()
+    {
+        var rid = RegistrationId.New();
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK,
+            $$"""
+            {"data":[{"id":"task-1","variables":[{"name":"registrationId","type":"string","value":"{{rid}}"}]}],"total":1}
+            """));
+
+        var tasks = await client.GetOpenBeoordelingenAsync();
+
+        var task = Assert.Single(tasks);
+        Assert.Equal("task-1", task.TaskId);
+        Assert.Equal(rid, task.RegistrationId);
+        Assert.Equal(HttpMethod.Post, capture.Seen!.Method);
+        Assert.Equal("http://flowable/flowable-rest/service/query/tasks",
+            capture.Seen.RequestUri!.ToString());
+        Assert.Equal("rest-admin:test", DecodeBasic(capture.Seen));
+        Assert.Contains("\"processDefinitionKey\":\"registratie\"", capture.Body);
+        Assert.Contains("\"taskDefinitionKey\":\"Beoordelen\"", capture.Body);
+        Assert.Contains("\"includeProcessVariables\":true", capture.Body);
+    }
+
+    [Theory]
+    [InlineData("""{"data":[],"total":0}""")]
+    [InlineData("""{"data":null,"total":0}""")]
+    public async Task Open_beoordelingen_is_empty_when_no_tasks_are_waiting(string body)
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK, body));
+
+        Assert.Empty(await client.GetOpenBeoordelingenAsync());
+        Assert.NotNull(capture.Seen);
+    }
+
+    [Fact]
+    public async Task Open_beoordelingen_throws_when_a_task_carries_no_registration_id()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK,
+            """{"data":[{"id":"task-1","variables":[]}],"total":1}"""));
+
+        var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => client.GetOpenBeoordelingenAsync());
+        Assert.Contains("task-1", ex.Message);
+        Assert.Contains("registrationId", ex.Message);
+    }
+
+    [Fact]
+    public async Task Claim_assigns_the_task_to_the_behandelaar()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK));
+
+        await client.ClaimAsync("task-1", "merel-behandelaar");
+
+        Assert.Equal(HttpMethod.Post, capture.Seen!.Method);
+        Assert.Equal("http://flowable/flowable-rest/service/runtime/tasks/task-1",
+            capture.Seen.RequestUri!.ToString());
+        Assert.Contains("\"action\":\"claim\"", capture.Body);
+        Assert.Contains("\"assignee\":\"merel-behandelaar\"", capture.Body);
+    }
+
+    [Fact]
+    public async Task Claim_throws_when_flowable_rejects_the_request()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.Conflict));
+
+        await Assert.ThrowsAsync<HttpRequestException>(() => client.ClaimAsync("task-1", "merel-behandelaar"));
+    }
+
+    [Theory]
+    [InlineData(BeoordelingsBesluit.Goedkeuren, "goedkeuren")]
+    [InlineData(BeoordelingsBesluit.Afwijzen, "afwijzen")]
+    public async Task Complete_posts_the_besluit_variable_to_the_task(BeoordelingsBesluit besluit, string expected)
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.OK));
+
+        await client.CompleteBeoordelingAsync("task-1", besluit);
+
+        Assert.Equal(HttpMethod.Post, capture.Seen!.Method);
+        Assert.Equal("http://flowable/flowable-rest/service/runtime/tasks/task-1",
+            capture.Seen.RequestUri!.ToString());
+        Assert.Contains("\"action\":\"complete\"", capture.Body);
+        Assert.Contains("\"name\":\"besluit\"", capture.Body);
+        Assert.Contains("\"type\":\"string\"", capture.Body);
+        Assert.Contains($"\"value\":\"{expected}\"", capture.Body);
+    }
+
+    [Fact]
+    public async Task Complete_beoordeling_throws_when_flowable_rejects_the_request()
+    {
+        var capture = new RequestCapture();
+        var client = Client(capture.Responds(HttpStatusCode.InternalServerError));
+
+        await Assert.ThrowsAsync<HttpRequestException>(
+            () => client.CompleteBeoordelingAsync("task-1", BeoordelingsBesluit.Goedkeuren));
+    }
 }

services/domain/Big.Tests/RegistrationTests.cs

@@ -121,4 +121,100 @@ public class RegistrationTests
         Assert.Contains("only an INGEDIEND", ex.Message);
         Assert.Equal(RegistrationStatus.Ingeschreven, registration.Status);
     }
+
+    [Fact]
+    public void Taking_a_registration_into_behandeling_moves_it_to_in_behandeling()
+    {
+        var registration = Registration.Submit("123456782");
+
+        registration.TakeIntoBehandeling();
+
+        Assert.Equal(RegistrationStatus.InBehandeling, registration.Status);
+    }
+
+    [Fact]
+    public void Re_taking_an_in_behandeling_registration_is_idempotent()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.TakeIntoBehandeling();
+
+        registration.TakeIntoBehandeling();
+
+        Assert.Equal(RegistrationStatus.InBehandeling, registration.Status);
+    }
+
+    [Fact]
+    public void Taking_a_decided_registration_into_behandeling_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        registration.Approve();
+
+        var ex = Assert.Throws<InvalidOperationException>(() => registration.TakeIntoBehandeling());
+        Assert.Contains("only an INGEDIEND", ex.Message);
+        Assert.Equal(RegistrationStatus.Ingeschreven, registration.Status);
+    }
+
+    [Fact]
+    public void Approving_an_in_behandeling_registration_with_a_zaak_sets_it_ingeschreven()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+        registration.TakeIntoBehandeling();
+
+        registration.Approve();
+
+        Assert.Equal(RegistrationStatus.Ingeschreven, registration.Status);
+    }
+
+    [Fact]
+    public void Rejecting_a_registration_sets_it_afgewezen()
+    {
+        var registration = Registration.Submit("123456782");
+
+        registration.Reject();
+
+        Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
+    }
+
+    [Fact]
+    public void Rejecting_needs_no_zaak()
+    {
+        // A registration can be turned down before its zaak is ever opened, so Reject must not require one.
+        var registration = Registration.Submit("123456782");
+
+        registration.Reject();
+
+        Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
+        Assert.Null(registration.ZaakUrl);
+    }
+
+    [Fact]
+    public void Rejecting_an_in_behandeling_registration_sets_it_afgewezen()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.TakeIntoBehandeling();
+
+        registration.Reject();
+
+        Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
+    }
+
+    [Fact]
+    public void Deciding_an_already_decided_registration_is_rejected()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.Reject();
+
+        var approveEx = Assert.Throws<InvalidOperationException>(() =>
+        {
+            registration.AttachZaak(new Uri("http://openzaak/zaken/api/v1/zaken/abc"));
+            registration.Approve();
+        });
+        Assert.Contains("IN_BEHANDELING", approveEx.Message);
+
+        var rejectEx = Assert.Throws<InvalidOperationException>(() => registration.Reject());
+        Assert.Contains("Afgewezen", rejectEx.Message);
+        Assert.Equal(RegistrationStatus.Afgewezen, registration.Status);
+    }
 }

services/domain/Big.Tests/WerkbakTests.cs

@@ -0,0 +1,49 @@
+using Big.Application;
+using Big.Domain;
+
+namespace Big.Tests;
+
+/// <summary>
+/// The werkbak query (S-12c): the behandelaar's list of registrations awaiting beoordeling. It reads
+/// the open Beoordelen tasks from the workflow engine (§8.2) and enriches each with its registration
+/// (bsn + status) from the store. A task whose registration is unknown is skipped defensively.
+/// </summary>
+public class WerkbakTests
+{
+    [Fact]
+    public async Task Lists_an_item_per_open_beoordeling_enriched_from_the_registration()
+    {
+        var store = new FakeRegistrationStore();
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(FakeAclClient.DefaultZaakUrl);
+        registration.TakeIntoBehandeling();
+        store.Seed(registration);
+        var tasks = new FakeUserTaskClient([new BeoordelingTask("task-1", registration.Id)]);
+        var werkbak = new Werkbak(tasks, store);
+
+        var items = await werkbak.GetAsync();
+
+        var item = Assert.Single(items);
+        Assert.Equal(registration.Id.ToString(), item.RegistrationId);
+        Assert.Equal("123456782", item.Bsn);
+        Assert.Equal("InBehandeling", item.Status);
+    }
+
+    [Fact]
+    public async Task Is_empty_when_no_beoordelingen_are_open()
+    {
+        var werkbak = new Werkbak(new FakeUserTaskClient([]), new FakeRegistrationStore());
+
+        Assert.Empty(await werkbak.GetAsync());
+    }
+
+    [Fact]
+    public async Task Skips_a_task_whose_registration_is_unknown()
+    {
+        // Defensive: the werkbak never invents an item for a task the domain has no aggregate for.
+        var tasks = new FakeUserTaskClient([new BeoordelingTask("task-1", RegistrationId.New())]);
+        var werkbak = new Werkbak(tasks, new FakeRegistrationStore());
+
+        Assert.Empty(await werkbak.GetAsync());
+    }
+}

tests/acceptance/Features/EenRegistratieBeoordelen.feature

@@ -0,0 +1,26 @@
+# language: en
+# Drives S-12 (#13). A behandelaar picks up a submitted registration for beoordeling and decides it:
+# goedkeuren enters it in the register (INGESCHREVEN, the zaak's final status set via the ACL, §8.1),
+# afwijzen turns it down (AFGEWEZEN). This scenario exercises the use cases against in-memory
+# stand-ins for the ACL and the store; real Flowable user-task claim/complete arrives in a later
+# sub-slice and is verified live.
+Feature: Een registratie beoordelen
+  Als behandelaar wil ik een ingediende registratie beoordelen
+  zodat deze wordt ingeschreven of afgewezen.
+
+  Scenario: Goedkeuren schrijft de registratie in via de ACL
+    Given a submitted registration with an opened zaak
+    When the behandelaar takes it into behandeling
+    Then the registration has status "INBEHANDELING"
+    When the behandelaar decides "goedkeuren"
+    Then the registration has status "INGESCHREVEN"
+    And the zaak's final status is set via the ACL
+    And the beoordeling task is completed with "goedkeuren"
+
+  Scenario: Afwijzen wijst de registratie af zonder de ACL
+    Given a submitted registration with an opened zaak
+    When the behandelaar takes it into behandeling
+    And the behandelaar decides "afwijzen"
+    Then the registration has status "AFGEWEZEN"
+    And the ACL is not asked to set the zaak status
+    And the beoordeling task is completed with "afwijzen"

tests/acceptance/Steps/EenRegistratieBeoordelenSteps.cs

@@ -0,0 +1,65 @@
+using Acceptance.Support;
+using Big.Application;
+using Big.Domain;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>EenRegistratieBeoordelen.feature</c> (S-12). Drives the TakeIntoBehandeling
+/// transition and the BeoordeelRegistratie use case against in-memory ports; one instance per scenario.
+/// Scoped to this feature so its "the registration has status" step does not clash with the identically
+/// phrased (but differently-asserting) step in <see cref="RegistratieIndienenSteps"/>.</summary>
+[Binding]
+[Scope(Feature = "Een registratie beoordelen")]
+public sealed class EenRegistratieBeoordelenSteps
+{
+    private readonly InMemoryAclClient _acl = new();
+    private readonly InMemoryRegistrationStore _store = new();
+    private readonly InMemoryUserTaskClient _tasks = new();
+    private RegistrationId _id;
+
+    [Given("a submitted registration with an opened zaak")]
+    public async Task GivenASubmittedRegistrationWithAnOpenedZaak()
+    {
+        var registration = Registration.Submit("123456782");
+        registration.AttachZaak(InMemoryAclClient.OpenedZaakUrl);
+        await _store.SaveAsync(registration);
+        _id = registration.Id;
+        // The process has parked at the Beoordelen user task awaiting the behandelaar.
+        _tasks.Open(_id);
+    }
+
+    [When("the behandelaar takes it into behandeling")]
+    public async Task WhenTheBehandelaarTakesItIntoBehandeling()
+    {
+        var registration = await _store.GetAsync(_id);
+        registration!.TakeIntoBehandeling();
+        await _store.SaveAsync(registration);
+    }
+
+    [When("the behandelaar decides \"(.*)\"")]
+    public async Task WhenTheBehandelaarDecides(string besluit)
+        => await new BeoordeelRegistratie(_store, _acl, _tasks).HandleAsync(
+            new BeoordeelRegistratieCommand(_id, Enum.Parse<BeoordelingsBesluit>(besluit, ignoreCase: true)));
+
+    [Then("the registration has status \"(.*)\"")]
+    public async Task ThenTheRegistrationHasStatus(string expected)
+    {
+        var registration = await _store.GetAsync(_id);
+        Assert.NotNull(registration);
+        Assert.Equal(expected, registration.Status.ToString().ToUpperInvariant());
+    }
+
+    [Then("the zaak's final status is set via the ACL")]
+    public void ThenTheZaakFinalStatusIsSetViaTheAcl()
+        => Assert.Equal(InMemoryAclClient.OpenedZaakUrl, _acl.ApprovedZaakUrl);
+
+    [Then("the ACL is not asked to set the zaak status")]
+    public void ThenTheAclIsNotAskedToSetTheZaakStatus()
+        => Assert.Null(_acl.ApprovedZaakUrl);
+
+    [Then("the beoordeling task is completed with \"(.*)\"")]
+    public void ThenTheBeoordelingTaskIsCompletedWith(string besluit)
+        => Assert.Equal(Enum.Parse<BeoordelingsBesluit>(besluit, ignoreCase: true), _tasks.Completed?.Besluit);
+}

tests/acceptance/Support/BffAcceptanceHost.cs

@@ -68,6 +68,12 @@ public sealed class CapturingDomainClient : IDomainClient
         SubmittedBsn = bsn;
         return Task.FromResult(new SubmitAccepted("reg-acc-1", "Ingediend"));
     }
+
+    public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<WerkbakItem>>([]);
+
+    public Task DecideAsync(string registrationId, string besluit, CancellationToken ct = default)
+        => Task.CompletedTask;
 }
 
 /// <summary>Serves configurable projection rows.</summary>

tests/acceptance/Support/InMemoryDomainPorts.cs

@@ -43,6 +43,29 @@ public sealed class InMemoryAclClient : IAclClient
     }
 }
 
+/// <summary>An in-memory user-task client for the beoordeling acceptance scenario: it holds one open
+/// Beoordelen task per registration and records the besluit each is completed with.</summary>
+public sealed class InMemoryUserTaskClient : IUserTaskClient
+{
+    private readonly List<BeoordelingTask> _open = [];
+
+    public (string TaskId, BeoordelingsBesluit Besluit)? Completed { get; private set; }
+
+    public void Open(RegistrationId registrationId) => _open.Add(new BeoordelingTask($"task-{registrationId}", registrationId));
+
+    public Task<IReadOnlyList<BeoordelingTask>> GetOpenBeoordelingenAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<BeoordelingTask>>(_open);
+
+    public Task ClaimAsync(string taskId, string behandelaar, CancellationToken ct = default) => Task.CompletedTask;
+
+    public Task CompleteBeoordelingAsync(string taskId, BeoordelingsBesluit besluit, CancellationToken ct = default)
+    {
+        Completed = (taskId, besluit);
+        _open.RemoveAll(t => t.TaskId == taskId);
+        return Task.CompletedTask;
+    }
+}
+
 /// <summary>An in-memory registration store for the domain acceptance scenario.</summary>
 public sealed class InMemoryRegistrationStore : IRegistrationStore
 {

workflows/registratie.bpmn

@@ -6,9 +6,12 @@
              xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI"
              targetNamespace="http://respellion.nl/big">
 
-  <!-- S-03: minimal "Registratie ontvangen" flow.
-       start -> external-worker task (OpenZaakAanmaken) -> end.
-       The external task is handled by the Workflow Client / ACL in later slices. -->
+  <!-- Registratie ontvangen flow.
+       start -> external-worker task (OpenZaakAanmaken) -> Beoordelen (behandelaar user task) -> end.
+       S-03 added the external task (Workflow Client / ACL). S-12 adds the behandelaar's beoordeling
+       as a user task: the process parks here until a behandelaar claims and completes it with a
+       `besluit` (goedkeuren/afwijzen). The registrationId set at start rides along as a process
+       variable so the werkbak can correlate each task back to its aggregate. -->
   <process id="registratie" name="Registratie ontvangen" isExecutable="true">
 
     <startEvent id="start" name="Registratie ontvangen"/>
@@ -19,9 +22,13 @@
                  flowable:type="external-worker"
                  flowable:topic="OpenZaakAanmaken"/>
 
-    <sequenceFlow id="flow2" sourceRef="OpenZaakAanmaken" targetRef="end"/>
+    <sequenceFlow id="flow2" sourceRef="OpenZaakAanmaken" targetRef="Beoordelen"/>
 
-    <endEvent id="end" name="Zaak aangemaakt"/>
+    <userTask id="Beoordelen" name="Beoordelen" flowable:candidateGroups="behandelaar"/>
+
+    <sequenceFlow id="flow3" sourceRef="Beoordelen" targetRef="end"/>
+
+    <endEvent id="end" name="Registratie beoordeeld"/>
   </process>
 
   <bpmndi:BPMNDiagram id="diagram">
@@ -32,8 +39,11 @@
       <bpmndi:BPMNShape id="s_task" bpmnElement="OpenZaakAanmaken">
         <omgdc:Bounds x="200" y="85" width="120" height="60"/>
       </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="s_beoordelen" bpmnElement="Beoordelen">
+        <omgdc:Bounds x="390" y="85" width="120" height="60"/>
+      </bpmndi:BPMNShape>
       <bpmndi:BPMNShape id="s_end" bpmnElement="end">
-        <omgdc:Bounds x="400" y="100" width="30" height="30"/>
+        <omgdc:Bounds x="580" y="100" width="30" height="30"/>
       </bpmndi:BPMNShape>
       <bpmndi:BPMNEdge id="e_flow1" bpmnElement="flow1">
         <omgdi:waypoint x="130" y="115"/>
@@ -41,7 +51,11 @@
       </bpmndi:BPMNEdge>
       <bpmndi:BPMNEdge id="e_flow2" bpmnElement="flow2">
         <omgdi:waypoint x="320" y="115"/>
-        <omgdi:waypoint x="400" y="115"/>
+        <omgdi:waypoint x="390" y="115"/>
+      </bpmndi:BPMNEdge>
+      <bpmndi:BPMNEdge id="e_flow3" bpmnElement="flow3">
+        <omgdi:waypoint x="510" y="115"/>
+        <omgdi:waypoint x="580" y="115"/>
       </bpmndi:BPMNEdge>
     </bpmndi:BPMNPlane>
   </bpmndi:BPMNDiagram>