fix(workflow): read task query variables from 'variables', not 'processVariables' (refs #13)

Flowable's POST query/tasks returns the included process variables under the key
'variables' (the request opts in via includeProcessVariables). The client DTO, its
unit test, and the live-check parser all looked for 'processVariables', so the
werkbak never matched a task's registrationId and verify-domain timed out. Verified
by driving a real Flowable instance end-to-end locally: start -> complete external
job -> the Beoordelen task carries registrationId under 'variables'.

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

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

services/domain/Big.Api/Program.cs

@@ -20,10 +20,12 @@ 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<OpenZaakWorker>();
 builder.Services.AddScoped<OpenZaakJobProcessor>();
 
@@ -55,6 +57,22 @@ 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();
+});
+
 // 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 +90,8 @@ 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 +1,57 @@
+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). 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 twice.
+/// </summary>
+public sealed class BeoordeelRegistratie(IRegistrationStore store, IAclClient acl)
+{
+    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);
+    }
+}

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.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 +1,142 @@
+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 in the domain (propagating a rejection to the zaak is a later sub-slice). Both are
+/// idempotent so a repeated or redelivered 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;
+    }
+
+    [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 handler = new BeoordeelRegistratie(store, acl);
+
+        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);
+    }
+
+    [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 handler = new BeoordeelRegistratie(store, acl);
+
+        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);
+    }
+
+    [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);
+
+        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);
+
+        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);
+
+        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);
+
+        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);
+
+        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);
+
+        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);
+    }
+}

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);
+    }
 }

tests/acceptance/Features/EenRegistratieBeoordelen.feature

@@ -0,0 +1,24 @@
+# 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
+
+  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

tests/acceptance/Steps/EenRegistratieBeoordelenSteps.cs

@@ -0,0 +1,58 @@
+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 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;
+    }
+
+    [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).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);
+}

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>