Merge branch 'main' into fix/portal-nginx-resolver

## What & why

Closes #94. The local compose's `event-subscriber` lacked `Acl__BaseUrl` (and the `acl` dependency) that the canonical compose sets (#78) — so it threw `Missing configuration 'Acl:BaseUrl'` and exited on startup, which also knocked over podman-compose's bring-up of the rest of the stack (the frontends were left uncreated). Adds the env + dependency, matching `docker-compose.yml`.

## How verified

Recreated `event-subscriber` from the fixed compose locally — it now starts healthy, and the three portals come up (self-service :8140, openbaar :8141, behandel :8142). `docker compose config` valid.

## Note (separate, not fixed here)

On **rootless podman** the portal→BFF nginx proxy still 502s (`resolver 127.0.0.11` is Docker's embedded DNS; podman uses its own), and podman-compose orchestration of this dependency graph is flaky — both are pre-existing local-engine limitations, clean on Docker Desktop / CI. Tracking separately.

Reviewed-on: #95

apps/behandel/Dockerfile

@@ -19,5 +19,9 @@ COPY --from=build /src/dist/apps/behandel/browser /usr/share/nginx/html
 # Compose-time OIDC config: the browser (Playwright, on the compose network) reaches Keycloak by
 # service name, so the token issuer matches the BFF's medewerker authority (host-consistent, ADR-0013).
 RUN printf '{ "authority": "http://keycloak:8080/realms/medewerker" }\n' > /usr/share/nginx/html/config.json
+# Make the reverse-proxy resolver engine-portable (Docker 127.0.0.11 vs podman aardvark); runs from
+# the nginx image's /docker-entrypoint.d before nginx starts.
+COPY apps/portal-nginx-resolver.sh /docker-entrypoint.d/40-resolver.sh
+RUN chmod +x /docker-entrypoint.d/40-resolver.sh
 
 EXPOSE 80

apps/openbaar/Dockerfile

@@ -17,5 +17,9 @@ FROM nginx:1.27-alpine AS runtime
 COPY apps/openbaar/nginx.conf /etc/nginx/conf.d/default.conf
 COPY --from=build /src/dist/apps/openbaar/browser /usr/share/nginx/html
 # No runtime config: the openbaar register is anonymous (no OIDC authority to inject).
+# Make the reverse-proxy resolver engine-portable (Docker 127.0.0.11 vs podman aardvark); runs from
+# the nginx image's /docker-entrypoint.d before nginx starts.
+COPY apps/portal-nginx-resolver.sh /docker-entrypoint.d/40-resolver.sh
+RUN chmod +x /docker-entrypoint.d/40-resolver.sh
 
 EXPOSE 80

apps/portal-nginx-resolver.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+# Point nginx's reverse-proxy `resolver` at THIS container's real DNS server.
+#
+# The portal nginx configs use a variable proxy_pass, which needs a `resolver` so the BFF hostname is
+# resolved at request time (nginx can start before the BFF is up). The config hardcodes Docker's
+# embedded DNS (127.0.0.11) — correct on Docker/Docker Desktop, but rootless podman uses a
+# network-specific address (aardvark, e.g. 10.89.0.1), so proxied calls 502 there. Read the actual
+# nameserver from /etc/resolv.conf and substitute it, so the reverse proxy works on any engine.
+#
+# Runs from the nginx image's /docker-entrypoint.d/ before nginx starts. On Docker the nameserver IS
+# 127.0.0.11, so the substitution is a no-op. Guarded (no `set -e`) so it's safe whether the nginx
+# entrypoint executes or sources it.
+ns="$(awk '/^nameserver/{print $2; exit}' /etc/resolv.conf 2>/dev/null)"
+if [ -n "$ns" ] && [ "$ns" != "127.0.0.11" ]; then
+  sed -i "s/resolver 127\.0\.0\.11/resolver $ns/" /etc/nginx/conf.d/default.conf 2>/dev/null || true
+  echo "portal-nginx-resolver: set resolver to $ns"
+fi

apps/self-service/Dockerfile

@@ -19,5 +19,9 @@ COPY --from=build /src/dist/apps/self-service/browser /usr/share/nginx/html
 # Compose-time OIDC config: the browser (Playwright, on the compose network) reaches Keycloak by
 # service name, so the token issuer matches the BFF's authority (host-consistent, ADR-0010).
 RUN printf '{ "authority": "http://keycloak:8080/realms/digid" }\n' > /usr/share/nginx/html/config.json
+# Make the reverse-proxy resolver engine-portable (Docker 127.0.0.11 vs podman aardvark); runs from
+# the nginx image's /docker-entrypoint.d before nginx starts.
+COPY apps/portal-nginx-resolver.sh /docker-entrypoint.d/40-resolver.sh
+RUN chmod +x /docker-entrypoint.d/40-resolver.sh
 
 EXPOSE 80

apps/self-service/src/app/registration/registration-page.html

@@ -3,9 +3,29 @@
     <utrecht-heading-1>Zelfservice — BIG-registratie</utrecht-heading-1>
 
     @if (submitted()) {
-      <p utrecht-paragraph role="status">
-        Uw registratie is ontvangen. Referentie: {{ reference() }}.
-      </p>
+      @if (withdrawn()) {
+        <p utrecht-paragraph role="status">
+          Uw registratie met referentie {{ reference() }} is ingetrokken.
+        </p>
+      } @else {
+        <p utrecht-paragraph role="status">
+          Uw registratie is ontvangen. Referentie: {{ reference() }}.
+        </p>
+        @if (withdrawFailed()) {
+          <p utrecht-paragraph role="alert">
+            Het intrekken van uw registratie is niet gelukt. Probeer het opnieuw.
+          </p>
+        }
+        <button
+          utrecht-button
+          appearance="secondary-action-button"
+          type="button"
+          [disabled]="withdrawing()"
+          (click)="withdraw()"
+        >
+          Trek aanvraag in
+        </button>
+      }
     } @else {
       <p utrecht-paragraph>U bent ingelogd met BSN {{ bsn() }}.</p>
       @if (failed()) {

apps/self-service/src/app/registration/registration-page.spec.ts

@@ -17,12 +17,22 @@ class FakeAuth extends AuthService {
   }
 }
 
-function providers(post = vi.fn().mockReturnValue(of({ registrationId: 'reg-9', status: 'Ingediend' }))) {
+function providers(
+  post = vi.fn().mockReturnValue(of({ registrationId: 'reg-9', status: 'Ingediend' })),
+  withdraw = vi.fn().mockReturnValue(of(undefined)),
+) {
   return {
     post,
+    withdraw,
     providers: [
       { provide: AuthService, useClass: FakeAuth },
-      { provide: BffApiV1Service, useValue: { postSelfServiceRegistrations: post } },
+      {
+        provide: BffApiV1Service,
+        useValue: {
+          postSelfServiceRegistrations: post,
+          postSelfServiceRegistrationsIdWithdraw: withdraw,
+        },
+      },
     ],
   };
 }
@@ -56,6 +66,36 @@ describe('RegistrationPage', () => {
     expect(screen.getByRole('button', { name: /indienen/i })).toBeTruthy();
   });
 
+  it('offers to withdraw after submitting, and withdrawing confirms', async () => {
+    const { withdraw, providers: p } = providers();
+    await render(RegistrationPage, { providers: p });
+
+    fireEvent.click(screen.getByRole('button', { name: /indienen/i }));
+    await screen.findByText(/ontvangen/i);
+
+    fireEvent.click(await screen.findByRole('button', { name: /trek aanvraag in/i }));
+
+    // The withdrawal is keyed by the reference the submit returned, and the page confirms it.
+    expect(withdraw).toHaveBeenCalledWith('reg-9');
+    expect(await screen.findByText(/ingetrokken/i)).toBeTruthy();
+  });
+
+  it('surfaces a withdraw failure and keeps the action available', async () => {
+    const { providers: p } = providers(
+      vi.fn().mockReturnValue(of({ registrationId: 'reg-9', status: 'Ingediend' })),
+      vi.fn().mockReturnValue(throwError(() => new Error('withdraw rejected'))),
+    );
+    await render(RegistrationPage, { providers: p });
+
+    fireEvent.click(screen.getByRole('button', { name: /indienen/i }));
+    await screen.findByText(/ontvangen/i);
+    fireEvent.click(await screen.findByRole('button', { name: /trek aanvraag in/i }));
+
+    expect(await screen.findByRole('alert')).toBeTruthy();
+    expect(screen.queryByText(/is ingetrokken/i)).toBeNull();
+    expect(screen.getByRole('button', { name: /trek aanvraag in/i })).toBeTruthy();
+  });
+
   it('has no WCAG 2.1 AA violations on the submit page', async () => {
     // The portal is Dutch; the real index.html sets lang. Set it here so the document-level
     // html-has-lang rule reflects the app, not the bare jsdom document.

apps/self-service/src/app/registration/registration-page.ts

@@ -6,7 +6,8 @@ import { UtrechtComponentsModule } from 'ui';
 /**
  * The self-service submit page: a signed-in zorgprofessional confirms and submits their BIG
  * registration. The bsn comes from the DigiD token (not a form field), so this is a confirm-and-
- * submit flow that posts to the BFF and shows the returned reference (ADR-0010; S-08c).
+ * submit flow that posts to the BFF and shows the returned reference (ADR-0010; S-08c). After
+ * submitting they can withdraw it — "trek aanvraag in" — keyed by that reference (S-11c).
  */
 @Component({
   selector: 'app-registration-page',
@@ -22,6 +23,9 @@ export class RegistrationPage {
   protected readonly reference = signal<string | undefined>(undefined);
   protected readonly submitted = signal(false);
   protected readonly failed = signal(false);
+  protected readonly withdrawing = signal(false);
+  protected readonly withdrawn = signal(false);
+  protected readonly withdrawFailed = signal(false);
 
   submit(): void {
     this.submitting.set(true);
@@ -39,4 +43,24 @@ export class RegistrationPage {
       },
     });
   }
+
+  withdraw(): void {
+    const reference = this.reference();
+    if (!reference) {
+      return;
+    }
+    this.withdrawing.set(true);
+    this.withdrawFailed.set(false);
+    this.bff.postSelfServiceRegistrationsIdWithdraw(reference).subscribe({
+      next: () => {
+        this.withdrawn.set(true);
+        this.withdrawing.set(false);
+      },
+      // Surface the failure instead of swallowing it: keep the action so the user can retry.
+      error: () => {
+        this.withdrawFailed.set(true);
+        this.withdrawing.set(false);
+      },
+    });
+  }
 }

docs/architecture/adr-0014-withdrawal-cancels-the-process.md

@@ -0,0 +1,72 @@
+# ADR-0014: Withdrawal cancels the registratie process via a BPMN message event
+
+- **Status:** Accepted
+- **Date:** 2026-07-16
+- **Deciders:** Respellion engineering
+- **Relates to:** S-11 (#12); builds on ADR-0009 (external-task worker / Workflow Client), ADR-0013
+  (behandel-portal wiring, the Beoordelen user task)
+
+## Context
+
+S-11 lets a zorgprofessional withdraw a still-open registration ("trek aanvraag in"). S-11a already
+advances the aggregate to INGETROKKEN (domain state). But the registratie process is still running in
+Flowable — parked at the `Beoordelen` user task — so without a second step the withdrawn registration
+would linger as work for a behandelaar. The withdrawal must also **cancel the running process**.
+
+Two questions shape this sub-slice.
+
+1. **How does the case get cancelled — in code, or in the BPMN model?**
+2. **How does a withdrawal correlate to the right running process instance?**
+
+## Decision
+
+**The BPMN models the cancellation as an interrupting message boundary event on the `Beoordelen`
+task; the Workflow Client correlates a `RegistratieIngetrokken` message to the task's execution.**
+
+- **Modelled in BPMN, not deleted from code.** The `Beoordelen` user task carries an interrupting
+  message boundary event (`RegistratieIngetrokken`) that routes to a dedicated "Registratie
+  ingetrokken" end event. The process's own model says *how* a withdrawal ends it — the Workflow
+  Client only delivers the message; it never reaches into Flowable to delete an instance. This keeps
+  the workflow's control flow in the workflow (§8.2) and leaves an audit trail in Flowable history
+  (the process ended via the ingetrokken path, not a raw delete).
+- **Correlated by the registration's own process instance.** The aggregate records its Flowable
+  process instance id at submit, so the `WithdrawRegistration` handler correlates directly by that
+  id — no task lookup. The Workflow Client asks Flowable for the execution **subscribed to** the
+  `RegistratieIngetrokken` message in that instance and delivers `messageEventReceived` to it.
+  Targeting the subscribed execution (not the user task's execution — a message boundary event's
+  subscription lives on its own execution) is what makes the correlation land.
+- **Best-effort, mirroring the beoordeling.** If no open `Beoordelen` task is found (the process has
+  not yet parked there — the `OpenZaakAanmaken` window — or has already ended), the withdrawal still
+  stands: the aggregate is INGETROKKEN and the werkbak filters it out regardless (S-11b). We complete
+  the domain transition first and cancel the workflow best-effort, exactly as `BeoordeelRegistratie`
+  completes its task best-effort.
+
+## Consequences
+
+**Positive**
+
+- The cancellation path is visible in `registratie.bpmn`; the Workflow Client stays the only code
+  that talks to Flowable and does not delete instances behind the model's back.
+- Reuses the existing task-query correlation — no new plumbing, no correlation store.
+- A withdrawn case leaves the werkbak (its `Beoordelen` task is cancelled), and the werkbak also
+  filters non-open registrations as a belt-and-braces for the brief window before cancellation lands.
+
+**Negative / costs**
+
+- A withdrawal raced ahead of the process reaching `Beoordelen` (during `OpenZaakAanmaken`, seconds)
+  finds no task to cancel, so that process instance runs on to `Beoordelen` and parks there with no
+  one to act on it (it is hidden from the werkbak by the status filter). Acceptable for this
+  reference at these volumes; a process-level interrupting event subprocess would close the gap and
+  is an additive follow-up if it matters.
+- The Flowable message-correlation REST shape is validated live (verify-stack), not in the
+  Workflow Client's unit tests, which stub the HTTP exchange and assert only the request shape
+  (consistent with ADR-0009).
+
+## Alternatives considered
+
+- **Delete the process instance from the Workflow Client** (`DELETE /runtime/process-instances/{id}`)
+  — rejected: it cancels the case but hides the reason from the BPMN model; the "why" lives in code,
+  not the process. The message event keeps the cancellation a first-class part of the workflow.
+- **Interrupting message event subprocess at process level** — more robust (correlates anytime,
+  closing the `OpenZaakAanmaken`-race gap), but a heavier BPMN construct; deferred as an additive
+  change if the race proves to matter.

docs/demo-script.md

@@ -275,3 +275,26 @@ ACL → NRC → event-subscriber → projection → openbaar register shows INGE
 > The full round-trip — DigiD submit → public INGEDIEND → behandelaar goedkeurt in the werkbak →
 > public INGESCHREVEN — is the Playwright happy path (`tests/e2e/registration.spec.ts`), which now
 > drives the behandel portal in place of the old admin endpoint.
+
+## S-11 — Withdrawal: "trek aanvraag in" (#12, ADR-0014)
+
+A zorgprofessional can withdraw their own still-open registration from the self-service portal. The
+withdrawal is owner-scoped (the BFF forwards the DigiD token's bsn; the domain only lets the owner
+withdraw) and cancels the running workflow via a BPMN message event, so the case leaves the
+behandelaar's werkbak.
+
+```text
+# 1. Log in and submit at the self-service portal (http://localhost:8140/, jan-burger / test123),
+#    note the "Referentie" on the confirmation.
+# 2. Click "Trek aanvraag in" → the page confirms the registration is ingetrokken.
+# 3. In the behandel werkbak (http://localhost:8142/, merel-behandelaar) the registration no longer
+#    appears — its Beoordelen task was cancelled.
+```
+
+**The path:** self-service → BFF `POST /self-service/registrations/{id}/withdraw` (DigiD, owner-scoped)
+→ domain sets INGETROKKEN + correlates the `RegistratieIngetrokken` message to the process → the
+interrupting boundary event ends it → the werkbak drops the case.
+
+> DigiD submit → trek aanvraag in → ingetrokken is the Playwright happy path
+> (`tests/e2e/withdrawal.spec.ts`); the owner-scoping + workflow cancellation are covered by the
+> `Een registratie intrekken` acceptance scenarios and the domain live check.

docs/frontend-decisions.md

@@ -151,3 +151,19 @@ frontend work is the medewerker realm auth and the werkbak/decide page. Wiring r
   to assert the medewerker token attaches to `/behandel/*` (and not to the anonymous openbaar call).
   The full DigiD-submit → behandel-decide → public INGESCHREVEN round-trip is the Playwright happy
   path.
+
+## Self-service withdrawal: "trek aanvraag in" (S-11c, #12)
+
+The submit confirmation grows a **"Trek aanvraag in"** action so a zorgprofessional can withdraw the
+registration they just submitted (`apps/self-service`, on the existing `RegistrationPage`).
+
+- **Keyed by the reference, owner-scoped at the BFF.** The button calls the generated
+  `postSelfServiceRegistrationsIdWithdraw(reference)` with the reference the submit returned. The
+  DigiD token (attached by the interceptor) carries the bsn the BFF forwards; the domain only lets
+  the owner withdraw (a mismatch is 404). No extra identity is entered in the UI.
+- **Same confirm-and-surface pattern as submit.** A secondary-action button; on success the page
+  switches to an ingetrokken confirmation; a failure is surfaced (`role="alert"`) and the action
+  stays available to retry — mirroring how submit handles its failure rather than swallowing it.
+- **Testing.** Component tests (`@testing-library/angular`, mocked BFF) cover the button appearing
+  after submit, the reference being passed, the ingetrokken confirmation, and the failure path; the
+  browser round-trip is `tests/e2e/withdrawal.spec.ts`.

infra/docker-compose.local.yml

@@ -17,7 +17,12 @@
 #
 # Port map (host):
 #   8000 OpenZaak · 8001 Open Notificaties · 8080 BFF · 8090 Flowable REST
-#   8100 ACL · 8180 Keycloak   (all admin: admin / admin — dev only)
+#   8100 ACL · 8130 Domain · 8180 Keycloak   (all admin: admin / admin — dev only)
+#   8140 self-service portal · 8141 openbaar register · 8142 behandel portal
+#
+# Portal OIDC on the HOST: browse the portals at their 8140/8141/8142 ports and log in via
+# Keycloak on localhost:8180 (KC_HOSTNAME below pins the issuer there; the BFF still validates
+# in-network via keycloak:8080). Test users are in docs/synthetic-data.md.
 
 services:
 
@@ -205,6 +210,12 @@ services:
       KEYCLOAK_ADMIN_PASSWORD: admin
       KC_HEALTH_ENABLED: "true"
       KC_HTTP_ENABLED: "true"
+      # Pin the frontend/issuer URL to the host-published address so a browser on the host and the
+      # tokens it gets both use localhost:8180. KC_HOSTNAME_BACKCHANNEL_DYNAMIC lets in-network
+      # callers (the BFF via keycloak:8080) still resolve token/jwks endpoints to their request host,
+      # so the BFF validates the localhost:8180 issuer while fetching keys over the compose network.
+      KC_HOSTNAME: http://localhost:8180
+      KC_HOSTNAME_BACKCHANNEL_DYNAMIC: "true"
     ports:
       - "8180:8080"
     volumes:
@@ -295,6 +306,14 @@ services:
       context: ../services/bff
       dockerfile: Dockerfile
     image: register-referentie/bff:dev
+    environment:
+      # Reach Keycloak over the compose network for metadata/keys; the discovered issuer is the
+      # host-pinned localhost:8180 (KC_HOSTNAME above), which is what browser tokens carry — so
+      # validation matches without the BFF ever needing to resolve localhost:8180 itself.
+      Keycloak__Authority: http://keycloak:8080/realms/digid
+      Keycloak__MedewerkerAuthority: http://keycloak:8080/realms/medewerker
+      Downstream__Domain__BaseUrl: http://domain:8080/
+      Downstream__Projection__BaseUrl: http://projection-api:8080/
     ports:
       - "8080:8080"
     healthcheck:
@@ -303,6 +322,39 @@ services:
       timeout: 3s
       retries: 5
       start_period: 10s
+    depends_on:
+      domain:
+        condition: service_healthy
+      projection-api:
+        condition: service_healthy
+      keycloak:
+        condition: service_started
+    networks: [cg]
+
+  # ── BIG Domain Service (S-05) ─────────────────────────────────────────────
+  domain:
+    build:
+      context: ../services/domain
+      dockerfile: Dockerfile
+    image: register-referentie/domain:dev
+    environment:
+      Flowable__BaseUrl: http://flowable-rest:8080/flowable-rest/
+      Flowable__Username: rest-admin
+      Flowable__Password: test
+      Acl__BaseUrl: http://acl:8080/
+    ports:
+      - "8130:8080"
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://localhost:8080/health"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 10s
+    depends_on:
+      acl:
+        condition: service_healthy
+      flowable-init:
+        condition: service_completed_successfully
     networks: [cg]
 
   # ── Read projection (S-06) ────────────────────────────────────────────────
@@ -328,6 +380,10 @@ services:
     image: register-referentie/event-subscriber:dev
     environment:
       ConnectionStrings__Projection: Host=projection-db;Database=projection;Username=projection;Password=projection
+      # The subscriber enriches the projection with each zaak's reference by asking the ACL — the only
+      # code allowed to read ZGW (§8.1, #78). Required: startup throws without it (parity with the
+      # canonical compose).
+      Acl__BaseUrl: http://acl:8080/
       EventSubscriber__Webhook__AuthToken: ${NOTIFICATION_WEBHOOK_TOKEN:-Bearer big-reference-notifications}
     ports:
       - "8110:8080"
@@ -340,6 +396,8 @@ services:
     depends_on:
       projection-db:
         condition: service_healthy
+      acl:
+        condition: service_healthy
     networks: [cg]
 
   projection-api:
@@ -362,6 +420,73 @@ services:
         condition: service_healthy
     networks: [cg]
 
+  # ── Portals (S-08/S-09/S-12) ──────────────────────────────────────────────
+  # nginx serves each Angular app and reverse-proxies its endpoint group to the BFF (same-origin).
+  # The images bake config.json with the compose authority (keycloak:8080), which a HOST browser
+  # can't resolve — so here we bind-mount a config.json pointing at the host-published localhost:8180
+  # (matching KC_HOSTNAME). openbaar is anonymous and needs no config.
+  self-service:
+    build:
+      context: ..
+      dockerfile: apps/self-service/Dockerfile
+    image: register-referentie/self-service:dev
+    ports:
+      - "8140:80"
+    volumes:
+      - ./local-config/self-service.config.json:/usr/share/nginx/html/config.json:ro,z
+    healthcheck:
+      test: ["CMD-SHELL", "wget -q -O /dev/null http://127.0.0.1/ || exit 1"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 10s
+    depends_on:
+      bff:
+        condition: service_healthy
+      keycloak:
+        condition: service_started
+    networks: [cg]
+
+  openbaar:
+    build:
+      context: ..
+      dockerfile: apps/openbaar/Dockerfile
+    image: register-referentie/openbaar:dev
+    ports:
+      - "8141:80"
+    healthcheck:
+      test: ["CMD-SHELL", "wget -q -O /dev/null http://127.0.0.1/ || exit 1"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 10s
+    depends_on:
+      bff:
+        condition: service_healthy
+    networks: [cg]
+
+  behandel:
+    build:
+      context: ..
+      dockerfile: apps/behandel/Dockerfile
+    image: register-referentie/behandel:dev
+    ports:
+      - "8142:80"
+    volumes:
+      - ./local-config/behandel.config.json:/usr/share/nginx/html/config.json:ro,z
+    healthcheck:
+      test: ["CMD-SHELL", "wget -q -O /dev/null http://127.0.0.1/ || exit 1"]
+      interval: 5s
+      timeout: 3s
+      retries: 5
+      start_period: 10s
+    depends_on:
+      bff:
+        condition: service_healthy
+      keycloak:
+        condition: service_started
+    networks: [cg]
+
 volumes:
   oz-db:
   nrc-db:

infra/local-config/behandel.config.json

@@ -0,0 +1,3 @@
+{
+  "authority": "http://localhost:8180/realms/medewerker"
+}

infra/local-config/self-service.config.json

@@ -0,0 +1,3 @@
+{
+  "authority": "http://localhost:8180/realms/digid"
+}

infra/run-domain-check.sh

@@ -79,9 +79,9 @@ fl="$(docker ps -q --filter 'name=flowable-rest' | head -1)"
 fl_base="http://$(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
+# Extracts the Beoordelen task id for a given 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="$1" python3 -c "import os,sys,json
 try:
     d=json.load(sys.stdin)
 except Exception:
@@ -98,7 +98,7 @@ 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)"
+  task_id="$(printf '%s' "$resp" | task_for_reg "$reg_id")"
   [ -n "$task_id" ] && break
   sleep 2
 done
@@ -115,7 +115,46 @@ flcurl -X POST "$fl_base/runtime/tasks/$task_id" -H 'Content-Type: application/j
 
 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' "$resp" | task_for_reg)"
+still="$(printf '%s' "$resp" | task_for_reg "$reg_id")"
 [ -z "$still" ] || { echo "FAIL — Beoordelen task $still still active after completion" >&2; exit 1; }
 echo "OK — behandelaar claimed and completed the Beoordelen task; the registratie process finished"
+
+# ── S-11: withdrawal. A second registration parks at Beoordelen; the citizen withdraws it via the
+# domain, which delivers the RegistratieIngetrokken message to the task's execution, tripping the
+# BPMN boundary event so the process ends and the Beoordelen task disappears (ADR-0014). ────────────
+echo ">> submitting a second registration to withdraw"
+loc2="$(docker run --rm --network "$net" curlimages/curl:latest \
+  -fsS -D - -o /dev/null -X POST "http://$dom_ip:8080/registrations" \
+  -H 'Content-Type: application/json' -d '{"bsn":"123456782"}' \
+  | sed -n 's/\r$//; s/^[Ll]ocation: //p' | head -1)"
+[ -n "$loc2" ] || { echo "FAIL — second POST /registrations returned no Location" >&2; exit 1; }
+reg_id2="${loc2##*/}"
+echo ">> second registration $reg_id2"
+
+echo ">> polling Flowable for its Beoordelen task"
+task_id2=""
+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_id2="$(printf '%s' "$resp" | task_for_reg "$reg_id2")"
+  [ -n "$task_id2" ] && break
+  sleep 2
+done
+[ -n "$task_id2" ] || { echo "FAIL — no Beoordelen task appeared for registration $reg_id2" >&2; docker logs "$dom" 2>&1 | tail -15 >&2; exit 1; }
+echo ">> Beoordelen task $task_id2 is waiting; withdrawing the registration via the domain"
+
+# Owner-scoped: the withdraw carries the same bsn the registration was submitted with (S-11c).
+docker run --rm --network "$net" curlimages/curl:latest \
+  -fsS -X POST "http://$dom_ip:8080/registrations/$reg_id2/withdraw" \
+  -H 'Content-Type: application/json' -d '{"bsn":"123456782"}' >/dev/null
+
+echo ">> asserting the process was cancelled (no Beoordelen task remains for the registration)"
+gone=""
+for _ in $(seq 1 15); do
+  resp="$(flcurl -X POST "$fl_base/query/tasks" -H 'Content-Type: application/json' -d "$query" 2>/dev/null || true)"
+  still2="$(printf '%s' "$resp" | task_for_reg "$reg_id2")"
+  [ -z "$still2" ] && { gone=1; break; }
+  sleep 2
+done
+[ -n "$gone" ] || { echo "FAIL — Beoordelen task for $reg_id2 still active after withdrawal" >&2; docker logs "$dom" 2>&1 | tail -15 >&2; exit 1; }
+echo "OK — withdrawal cancelled the Beoordelen task; the registratie process ended (ingetrokken)"
 exit 0

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

@@ -192,6 +192,40 @@ export class BffApiV1Service {
     );
   }
 
+ postSelfServiceRegistrationsIdWithdraw<TData = void>(id: string, options?: HttpClientBodyOptions): Observable<TData>;
+ postSelfServiceRegistrationsIdWithdraw<TData = void>(id: string, options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
+ postSelfServiceRegistrationsIdWithdraw<TData = void>(id: string, options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;
+  postSelfServiceRegistrationsIdWithdraw<TData = void>(
+    id: string, options?: HttpClientObserveOptions): Observable<TData | HttpEvent<TData> | AngularHttpResponse<TData>> {
+    if (options?.observe === 'events') {
+      return this.http.post<TData>(
+      `/self-service/registrations/${id}/withdraw`,
+      undefined,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'events',
+      }
+    );
+    }
+
+    if (options?.observe === 'response') {
+      return this.http.post<TData>(
+      `/self-service/registrations/${id}/withdraw`,
+      undefined,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'response',
+      }
+    );
+    }
+
+    return this.http.post<TData>(
+      `/self-service/registrations/${id}/withdraw`,
+      undefined,{
+        ...(options as Omit<NonNullable<typeof options>, 'observe'>),
+        observe: 'body',
+      }
+    );
+  }
+
  getOpenbaarRegister<TData = OpenbaarEntry[]>(params?: GetOpenbaarRegisterParams, options?: HttpClientBodyOptions): Observable<TData>;
  getOpenbaarRegister<TData = OpenbaarEntry[]>(params?: GetOpenbaarRegisterParams, options?: HttpClientEventOptions): Observable<HttpEvent<TData>>;
  getOpenbaarRegister<TData = OpenbaarEntry[]>(params?: GetOpenbaarRegisterParams, options?: HttpClientResponseOptions): Observable<AngularHttpResponse<TData>>;

services/bff/Bff.Api/DownstreamClients.cs

@@ -22,6 +22,11 @@ public interface IDomainClient
 {
     Task<SubmitAccepted> SubmitRegistrationAsync(string bsn, CancellationToken ct = default);
 
+    /// <summary>Withdraw the caller's own registration ("trek aanvraag in"). Owner-scoped by
+    /// <paramref name="bsn"/>. Returns <c>false</c> when the domain reports the registration is
+    /// unknown or not the caller's (404), so the BFF can relay a 404 rather than a 500.</summary>
+    Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default);
+
     /// <summary>The behandelaar's werkbak — registrations awaiting beoordeling.</summary>
     Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default);
 
@@ -47,6 +52,17 @@ public sealed class DomainClient(HttpClient http) : IDomainClient
         return new SubmitAccepted(dto.RegistrationId, dto.Status);
     }
 
+    public async Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default)
+    {
+        using var response = await http.PostAsJsonAsync(
+            $"registrations/{registrationId}/withdraw", new { bsn }, ct);
+        // The domain 404s an unknown or not-owned registration; relay that rather than fail hard.
+        if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
+            return false;
+        response.EnsureSuccessStatusCode();
+        return true;
+    }
+
     public async Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
         => await http.GetFromJsonAsync<List<WerkbakItem>>("behandel/werkbak", ct) ?? [];
 

services/bff/Bff.Api/Program.cs

@@ -86,6 +86,24 @@ app.MapPost("/self-service/registrations", async (ClaimsPrincipal user, IDomainC
     .Produces(StatusCodes.Status400BadRequest)
     .Produces(StatusCodes.Status401Unauthorized);
 
+// Self-service withdrawal (S-11): the signed-in zorgprofessional withdraws their own registration.
+// The bsn comes from the DigiD token and is forwarded to the domain, which owner-scopes the action;
+// a registration that is unknown or not the caller's comes back 404 (ownership is not revealed).
+app.MapPost("/self-service/registrations/{id}/withdraw", async (string id, ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
+{
+    var bsn = user.FindFirstValue("bsn");
+    if (string.IsNullOrWhiteSpace(bsn))
+        return Results.BadRequest("The token carries no bsn claim.");
+
+    var withdrawn = await domain.WithdrawRegistrationAsync(id, bsn, ct);
+    return withdrawn ? Results.NoContent() : Results.NotFound();
+})
+    .RequireAuthorization()
+    .Produces(StatusCodes.Status204NoContent)
+    .Produces(StatusCodes.Status400BadRequest)
+    .Produces(StatusCodes.Status401Unauthorized)
+    .Produces(StatusCodes.Status404NotFound);
+
 // Openbaar register: an anonymous public lookup that exposes only public-safe fields (S-09).
 app.MapGet("/openbaar/register", async (string? q, IProjectionClient projection, CancellationToken ct) =>
 {

services/bff/Bff.Tests/BffFactory.cs

@@ -82,6 +82,18 @@ internal sealed class FakeDomainClient : IDomainClient
         return Task.FromResult(Result);
     }
 
+    public (string RegistrationId, string Bsn)? Withdrawn { get; private set; }
+
+    /// <summary>Whether the fake domain reports the withdrawal as done (true → 204) or not-found/not-owned
+    /// (false → 404). Tests set this to exercise the relay.</summary>
+    public bool WithdrawSucceeds { get; set; } = true;
+
+    public Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default)
+    {
+        Withdrawn = (registrationId, bsn);
+        return Task.FromResult(WithdrawSucceeds);
+    }
+
     public (string RegistrationId, string Besluit)? Decided { get; private set; }
 
     public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)

services/bff/Bff.Tests/SelfServiceEndpointTests.cs

@@ -71,5 +71,46 @@ public class SelfServiceEndpointTests
         Assert.Equal("reg-123", body!.RegistrationId);
     }
 
+    private static HttpRequestMessage Withdraw(string? bearer, string id = "reg-123")
+    {
+        var request = new HttpRequestMessage(HttpMethod.Post, $"/self-service/registrations/{id}/withdraw");
+        if (bearer is not null)
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
+        return request;
+    }
+
+    [Fact]
+    public async Task Rejects_a_withdrawal_without_a_token()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Withdraw(bearer: null));
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+        Assert.Null(factory.Domain.Withdrawn);
+    }
+
+    [Fact]
+    public async Task Withdraws_the_callers_registration_forwarding_the_id_and_bsn()
+    {
+        using var factory = new BffFactory();
+
+        var response = await factory.CreateClient().SendAsync(Withdraw(TestTokens.Valid("123456782"), "reg-9"));
+
+        Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+        Assert.Equal(("reg-9", "123456782"), factory.Domain.Withdrawn);
+    }
+
+    [Fact]
+    public async Task Relays_not_found_when_the_registration_is_unknown_or_not_the_callers()
+    {
+        using var factory = new BffFactory();
+        factory.Domain.WithdrawSucceeds = false;
+
+        var response = await factory.CreateClient().SendAsync(Withdraw(TestTokens.Valid("123456782")));
+
+        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
+    }
+
     private sealed record SubmitAcceptedDto(string RegistrationId, string Status);
 }

services/bff/openapi.json

@@ -30,6 +30,37 @@
         }
       }
     },
+    "/self-service/registrations/{id}/withdraw": {
+      "post": {
+        "tags": [
+          "Bff.Api"
+        ],
+        "parameters": [
+          {
+            "name": "id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "204": {
+            "description": "No Content"
+          },
+          "400": {
+            "description": "Bad Request"
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "404": {
+            "description": "Not Found"
+          }
+        }
+      }
+    },
     "/openbaar/register": {
       "get": {
         "tags": [

services/domain/Big.Api/Program.cs

@@ -76,16 +76,19 @@ app.MapPost("/registrations/{id}/decide", async (string id, DecideRequest body,
 });
 
 // Withdraw a registration (S-11): the zorgprofessional pulls their own still-open submission back,
-// advancing it to INGETROKKEN. Idempotent. The BFF reaches this behind a digid token, owner-scoped
-// to the caller's bsn (S-11c); the domain trusts its callers (§8.3). Cancelling the running Flowable
-// process is a later sub-slice (S-11b).
-app.MapPost("/registrations/{id}/withdraw", async (string id, WithdrawRegistration withdraw, CancellationToken ct) =>
+// advancing it to INGETROKKEN and cancelling its workflow. Owner-scoped by the caller's bsn (the BFF
+// forwards it from the DigiD token, S-11c); a registration that is unknown or not the caller's is
+// 404 (indistinguishable, so ownership isn't leaked). Idempotent.
+app.MapPost("/registrations/{id}/withdraw", async (string id, WithdrawRequest body, WithdrawRegistration withdraw, CancellationToken ct) =>
 {
     if (!Guid.TryParse(id, out var guid))
         return Results.NotFound();
 
-    await withdraw.HandleAsync(new WithdrawRegistrationCommand(new RegistrationId(guid)), ct);
-    return Results.NoContent();
+    if (string.IsNullOrWhiteSpace(body?.Bsn))
+        return Results.BadRequest(new { error = "A bsn is required to withdraw a registration." });
+
+    var outcome = await withdraw.HandleAsync(new WithdrawRegistrationCommand(new RegistrationId(guid), body.Bsn), ct);
+    return outcome == WithdrawOutcome.Withdrawn ? Results.NoContent() : Results.NotFound();
 });
 
 // The behandelaar's werkbak (S-12): the registrations awaiting beoordeling, read from the open
@@ -113,6 +116,8 @@ public sealed record SubmitRegistrationRequest(string Bsn);
 
 public sealed record DecideRequest(string Besluit);
 
+public sealed record WithdrawRequest(string Bsn);
+
 public sealed record RegistrationResponse(string RegistrationId, string Status, string? ZaakUrl);
 
 public partial class Program;

services/domain/Big.Application/Ports.cs

@@ -15,6 +15,14 @@ public interface IWorkflowClient
     /// aggregate. Returns the process instance id.
     /// </summary>
     Task<string> StartRegistrationProcessAsync(RegistrationId registrationId, CancellationToken ct = default);
+
+    /// <summary>
+    /// Cancel a running <c>registratie</c> process on withdrawal (S-11): correlate the
+    /// <c>RegistratieIngetrokken</c> message to the instance, tripping the interrupting message event
+    /// that ends it (ADR-0014). Best-effort — if the instance is not waiting on that message (already
+    /// ended, or not yet parked) it is a no-op; the aggregate is INGETROKKEN regardless.
+    /// </summary>
+    Task WithdrawProcessAsync(string processInstanceId, CancellationToken ct = default);
 }
 
 /// <summary>

services/domain/Big.Application/Werkbak.cs

@@ -1,3 +1,5 @@
+using Big.Domain;
+
 namespace Big.Application;
 
 /// <summary>One row of the behandelaar's werkbak: a registration awaiting beoordeling, with the
@@ -8,7 +10,8 @@ public sealed record WerkbakItem(string RegistrationId, string Bsn, string Statu
 /// 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.
+/// whose registration the domain doesn't know, or whose registration is no longer open for beoordeling
+/// (e.g. withdrawn — S-11 — while its task lingers until the workflow cancels it), is skipped.
 /// </summary>
 public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
 {
@@ -20,7 +23,7 @@ public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
         foreach (var task in open)
         {
             var registration = await store.GetAsync(task.RegistrationId, ct);
-            if (registration is null)
+            if (registration is null || !IsOpenForBeoordeling(registration.Status))
                 continue;
 
             items.Add(new WerkbakItem(
@@ -29,4 +32,9 @@ public sealed class Werkbak(IUserTaskClient tasks, IRegistrationStore store)
 
         return items;
     }
+
+    // Only registrations still open for a decision belong in the werkbak; a terminal one (decided or
+    // withdrawn — S-11) whose Beoordelen task has not yet been cleared must not surface to a behandelaar.
+    private static bool IsOpenForBeoordeling(RegistrationStatus status)
+        => status is RegistrationStatus.Ingediend or RegistrationStatus.InBehandeling;
 }

services/domain/Big.Application/WithdrawRegistration.cs

@@ -2,31 +2,54 @@ using Big.Domain;
 
 namespace Big.Application;
 
-/// <summary>A zorgprofessional's request to withdraw their own registration ("trek aanvraag in").</summary>
-public sealed record WithdrawRegistrationCommand(RegistrationId RegistrationId);
+/// <summary>A zorgprofessional's request to withdraw their own registration ("trek aanvraag in").
+/// <paramref name="Bsn"/> is the authenticated caller (from the DigiD token, forwarded by the BFF):
+/// only the registration's own bsn may withdraw it.</summary>
+public sealed record WithdrawRegistrationCommand(RegistrationId RegistrationId, string Bsn);
+
+/// <summary>The outcome of a withdrawal request.</summary>
+public enum WithdrawOutcome
+{
+    /// <summary>The registration is now (or already was) INGETROKKEN.</summary>
+    Withdrawn,
+
+    /// <summary>No registration with that id belongs to the caller — unknown, or owned by someone
+    /// else (the two are deliberately indistinguishable, so the endpoint reveals neither).</summary>
+    NotFound,
+}
 
 /// <summary>
 /// The withdrawal use case (S-11): a zorgprofessional pulls a still-open registration back. It
-/// advances the aggregate to INGETROKKEN and persists it. Idempotent — a repeated or redelivered
-/// withdrawal of an already-withdrawn registration is a no-op (the aggregate is not persisted again).
-/// Cancelling the running Flowable process (so the case leaves the behandelaar's werkbak) is a later
-/// sub-slice (S-11b, via a BPMN message event); this sub-slice owns the domain transition only —
-/// mirroring how the beoordeling's rejection deferred its zaak propagation.
+/// advances the aggregate to INGETROKKEN, persists it, then cancels the running registratie process
+/// by correlating the withdrawal message to its instance (ADR-0014), so the case leaves the
+/// behandelaar's werkbak. Idempotent — a repeated or redelivered withdrawal of an already-withdrawn
+/// registration is a no-op (not persisted or cancelled again). Cancelling is best-effort: if the
+/// registration never started a process the withdrawal still stands (the process cancel is skipped),
+/// mirroring how <see cref="BeoordeelRegistratie"/> completes its task best-effort.
 /// </summary>
-public sealed class WithdrawRegistration(IRegistrationStore store)
+public sealed class WithdrawRegistration(IRegistrationStore store, IWorkflowClient workflow)
 {
-    public async Task HandleAsync(WithdrawRegistrationCommand command, CancellationToken ct = default)
+    public async Task<WithdrawOutcome> HandleAsync(WithdrawRegistrationCommand command, CancellationToken ct = default)
     {
         ArgumentNullException.ThrowIfNull(command);
 
-        var registration = await store.GetAsync(command.RegistrationId, ct)
-            ?? throw new InvalidOperationException($"No registration {command.RegistrationId} to withdraw.");
+        var registration = await store.GetAsync(command.RegistrationId, ct);
 
-        // A repeated withdrawal is a no-op: don't persist the already-withdrawn aggregate again.
+        // Unknown, or not the caller's registration: report NotFound either way (don't reveal which).
+        if (registration is null || registration.Bsn != command.Bsn)
+            return WithdrawOutcome.NotFound;
+
+        // A repeated withdrawal is a no-op: don't persist or cancel the already-withdrawn one again.
         if (registration.Status == RegistrationStatus.Ingetrokken)
-            return;
+            return WithdrawOutcome.Withdrawn;
 
         registration.Withdraw();
         await store.SaveAsync(registration, ct);
+
+        // Cancel the running process (if one was started) so its Beoordelen task leaves the werkbak.
+        if (registration.ProcessInstanceId is not null)
+            await workflow.WithdrawProcessAsync(registration.ProcessInstanceId, ct);
+
+        return WithdrawOutcome.Withdrawn;
     }
 }

services/domain/Big.Infrastructure/FlowableWorkflowClient.cs

@@ -23,6 +23,7 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
     private const string RegistrationIdVariable = "registrationId";
     private const string ZaakUrlVariable = "zaakUrl";
     private const string BesluitVariable = "besluit";
+    private const string IngetrokkenMessage = "RegistratieIngetrokken";
 
     public async Task<string> StartRegistrationProcessAsync(RegistrationId registrationId, CancellationToken ct = default)
     {
@@ -85,6 +86,35 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         response.EnsureSuccessStatusCode();
     }
 
+    public async Task WithdrawProcessAsync(string processInstanceId, CancellationToken ct = default)
+    {
+        // Correlate the withdrawal message to the instance: find the execution subscribed to it (the
+        // interrupting message event's own execution — NOT the user task's), then deliver
+        // messageEventReceived to that execution so the process ends (ADR-0014). If nothing is
+        // subscribed (the process is not parked at Beoordelen) this is a best-effort no-op.
+        var subscribed = await GetAsync<ExecutionQueryResult>(
+            $"service/runtime/executions?messageEventSubscriptionName={IngetrokkenMessage}&processInstanceId={processInstanceId}",
+            ct);
+
+        var execution = subscribed?.Data?.FirstOrDefault();
+        if (execution is null)
+            return;
+
+        var request = new MessageEventRequest("messageEventReceived", IngetrokkenMessage);
+        using var response = await SendAsync(
+            $"service/runtime/executions/{execution.Id}", request, ct, HttpMethod.Put);
+        response.EnsureSuccessStatusCode();
+    }
+
+    private async Task<TResponse?> GetAsync<TResponse>(string path, CancellationToken ct)
+    {
+        var message = new HttpRequestMessage(HttpMethod.Get, new Uri(options.BaseUrl, path));
+        message.Headers.Authorization = new AuthenticationHeaderValue("Basic", BasicCredentials());
+        using var response = await http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+        return await response.Content.ReadFromJsonAsync<TResponse>(ct);
+    }
+
     private async Task<TResponse?> PostAsync<TRequest, TResponse>(string path, TRequest body, CancellationToken ct)
     {
         using var response = await SendAsync(path, body, ct);
@@ -92,9 +122,9 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         return await response.Content.ReadFromJsonAsync<TResponse>(ct);
     }
 
-    private Task<HttpResponseMessage> SendAsync<TRequest>(string path, TRequest body, CancellationToken ct)
+    private Task<HttpResponseMessage> SendAsync<TRequest>(string path, TRequest body, CancellationToken ct, HttpMethod? method = null)
     {
-        var message = new HttpRequestMessage(HttpMethod.Post, new Uri(options.BaseUrl, path))
+        var message = new HttpRequestMessage(method ?? HttpMethod.Post, new Uri(options.BaseUrl, path))
         {
             Content = JsonContent.Create(body),
         };
@@ -132,6 +162,10 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
         [property: JsonPropertyName("action")] string Action,
         [property: JsonPropertyName("variables")] IReadOnlyList<Variable> Variables);
 
+    private sealed record MessageEventRequest(
+        [property: JsonPropertyName("action")] string Action,
+        [property: JsonPropertyName("messageName")] string MessageName);
+
     private sealed record TaskQueryResult(
         [property: JsonPropertyName("data")] IReadOnlyList<UserTaskDto>? Data);
 
@@ -154,6 +188,11 @@ public sealed class FlowableWorkflowClient(HttpClient http, FlowableOptions opti
 
     private sealed record ProcessInstance([property: JsonPropertyName("id")] string Id);
 
+    private sealed record ExecutionQueryResult(
+        [property: JsonPropertyName("data")] IReadOnlyList<ExecutionDto>? Data);
+
+    private sealed record ExecutionDto([property: JsonPropertyName("id")] string Id);
+
     private sealed record AcquiredJob(
         [property: JsonPropertyName("id")] string Id,
         [property: JsonPropertyName("variables")] IReadOnlyList<Variable> Variables)

services/domain/Big.Tests/Fakes.cs

@@ -32,6 +32,7 @@ internal sealed class FakeWorkflowClient(string processInstanceId = "proc-1", Ac
     : IWorkflowClient
 {
     public RegistrationId? StartedFor { get; private set; }
+    public string? WithdrawnProcessInstanceId { get; private set; }
 
     public Task<string> StartRegistrationProcessAsync(RegistrationId registrationId, CancellationToken ct = default)
     {
@@ -39,6 +40,12 @@ internal sealed class FakeWorkflowClient(string processInstanceId = "proc-1", Ac
         StartedFor = registrationId;
         return Task.FromResult(processInstanceId);
     }
+
+    public Task WithdrawProcessAsync(string processInstanceId, CancellationToken ct = default)
+    {
+        WithdrawnProcessInstanceId = processInstanceId;
+        return Task.CompletedTask;
+    }
 }
 
 /// <summary>A fake user-task client for the werkbak/decision use cases: returns a scripted set of

services/domain/Big.Tests/FlowableWorkflowClientTests.cs

@@ -242,6 +242,61 @@ public class FlowableWorkflowClientTests
         Assert.Contains($"\"value\":\"{expected}\"", capture.Body);
     }
 
+    [Fact]
+    public async Task Withdraw_process_correlates_the_message_to_the_subscribed_execution()
+    {
+        HttpRequestMessage? getReq = null;
+        HttpRequestMessage? putReq = null;
+        string? putBody = null;
+        var client = Client(new StubHandler(async req =>
+        {
+            if (req.Method == HttpMethod.Get)
+            {
+                getReq = req;
+                return new HttpResponseMessage(HttpStatusCode.OK)
+                {
+                    Content = new StringContent("""{"data":[{"id":"exec-9"}]}""", Encoding.UTF8, "application/json"),
+                };
+            }
+            putReq = req;
+            putBody = await req.Content!.ReadAsStringAsync();
+            return new HttpResponseMessage(HttpStatusCode.OK);
+        }));
+
+        await client.WithdrawProcessAsync("pi-1");
+
+        // 1. Find the execution subscribed to the withdrawal message for this instance.
+        Assert.Equal(HttpMethod.Get, getReq!.Method);
+        Assert.Contains("service/runtime/executions", getReq.RequestUri!.ToString());
+        Assert.Contains("messageEventSubscriptionName=RegistratieIngetrokken", getReq.RequestUri!.Query);
+        Assert.Contains("processInstanceId=pi-1", getReq.RequestUri!.Query);
+        // 2. Deliver messageEventReceived to that execution (PUT), tripping the interrupting event.
+        Assert.Equal(HttpMethod.Put, putReq!.Method);
+        Assert.Equal("http://flowable/flowable-rest/service/runtime/executions/exec-9",
+            putReq.RequestUri!.ToString());
+        Assert.Contains("\"action\":\"messageEventReceived\"", putBody);
+        Assert.Contains("\"messageName\":\"RegistratieIngetrokken\"", putBody);
+    }
+
+    [Fact]
+    public async Task Withdraw_process_is_a_no_op_when_no_execution_is_subscribed()
+    {
+        var methods = new List<HttpMethod>();
+        var client = Client(new StubHandler(req =>
+        {
+            methods.Add(req.Method);
+            return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
+            {
+                Content = new StringContent("""{"data":[]}""", Encoding.UTF8, "application/json"),
+            });
+        }));
+
+        await client.WithdrawProcessAsync("pi-1");
+
+        // No subscribed execution → no message delivered (best-effort), no throw.
+        Assert.DoesNotContain(HttpMethod.Put, methods);
+    }
+
     [Fact]
     public async Task Complete_beoordeling_throws_when_flowable_rejects_the_request()
     {

services/domain/Big.Tests/WerkbakTests.cs

@@ -46,4 +46,19 @@ public class WerkbakTests
 
         Assert.Empty(await werkbak.GetAsync());
     }
+
+    [Fact]
+    public async Task Skips_a_task_whose_registration_is_no_longer_open()
+    {
+        // A withdrawn registration (S-11) may still have a Beoordelen task lingering until the workflow
+        // cancels it; the werkbak lists only registrations still open for beoordeling, so it drops off.
+        var store = new FakeRegistrationStore();
+        var registration = Registration.Submit("123456782");
+        registration.Withdraw();
+        store.Seed(registration);
+        var tasks = new FakeUserTaskClient([new BeoordelingTask("task-1", registration.Id)]);
+        var werkbak = new Werkbak(tasks, store);
+
+        Assert.Empty(await werkbak.GetAsync());
+    }
 }

services/domain/Big.Tests/WithdrawRegistrationTests.cs

@@ -5,40 +5,101 @@ namespace Big.Tests;
 
 public class WithdrawRegistrationTests
 {
+    private const string Bsn = "123456782";
+
+    private static Registration Submitted(string processInstanceId = "proc-1")
+    {
+        var registration = Registration.Submit(Bsn);
+        registration.RecordProcessStarted(processInstanceId);
+        return registration;
+    }
+
+    private static WithdrawRegistrationCommand Command(RegistrationId id, string bsn = Bsn) => new(id, bsn);
+
     [Fact]
     public async Task Withdrawing_marks_the_registration_ingetrokken_and_persists_it()
     {
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Submitted();
         store.Seed(registration);
-        var handler = new WithdrawRegistration(store);
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
-        await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
+        var outcome = await handler.HandleAsync(Command(registration.Id));
 
+        Assert.Equal(WithdrawOutcome.Withdrawn, outcome);
         var saved = await store.GetAsync(registration.Id);
         Assert.Equal(RegistrationStatus.Ingetrokken, saved!.Status);
         Assert.Equal(1, store.SaveCount);
     }
 
+    [Fact]
+    public async Task Withdrawing_cancels_the_running_process()
+    {
+        var store = new FakeRegistrationStore();
+        var registration = Submitted("proc-42");
+        store.Seed(registration);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
+
+        await handler.HandleAsync(Command(registration.Id));
+
+        // The process the registration recorded at submit is cancelled (ADR-0014).
+        Assert.Equal("proc-42", workflow.WithdrawnProcessInstanceId);
+    }
+
+    [Fact]
+    public async Task Withdrawing_before_a_process_was_started_still_marks_ingetrokken()
+    {
+        var store = new FakeRegistrationStore();
+        var registration = Registration.Submit(Bsn); // no RecordProcessStarted
+        store.Seed(registration);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
+
+        await handler.HandleAsync(Command(registration.Id));
+
+        Assert.Equal(RegistrationStatus.Ingetrokken, (await store.GetAsync(registration.Id))!.Status);
+        Assert.Null(workflow.WithdrawnProcessInstanceId);
+    }
+
+    [Fact]
+    public async Task A_different_bsn_cannot_withdraw_the_registration()
+    {
+        // Owner-scoping: only the zorgprofessional who submitted may withdraw. Another bsn is told
+        // NotFound (we don't reveal the registration exists) and nothing is changed.
+        var store = new FakeRegistrationStore();
+        var registration = Submitted();
+        store.Seed(registration);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
+
+        var outcome = await handler.HandleAsync(Command(registration.Id, bsn: "999999990"));
+
+        Assert.Equal(WithdrawOutcome.NotFound, outcome);
+        Assert.Equal(RegistrationStatus.Ingediend, (await store.GetAsync(registration.Id))!.Status);
+        Assert.Equal(0, store.SaveCount);
+        Assert.Null(workflow.WithdrawnProcessInstanceId);
+    }
+
     [Fact]
     public async Task Rejects_a_null_command_without_touching_the_store()
     {
         var store = new FakeRegistrationStore();
-        var handler = new WithdrawRegistration(store);
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
         await Assert.ThrowsAsync<ArgumentNullException>(() => handler.HandleAsync(null!));
         Assert.Equal(0, store.SaveCount);
     }
 
     [Fact]
-    public async Task Withdrawing_an_unknown_registration_throws()
+    public async Task Withdrawing_an_unknown_registration_is_not_found()
     {
         var store = new FakeRegistrationStore();
-        var handler = new WithdrawRegistration(store);
+        var handler = new WithdrawRegistration(store, new FakeWorkflowClient());
 
-        var ex = await Assert.ThrowsAsync<InvalidOperationException>(
-            () => handler.HandleAsync(new WithdrawRegistrationCommand(RegistrationId.New())));
-        Assert.Contains("No registration", ex.Message);
+        var outcome = await handler.HandleAsync(Command(RegistrationId.New()));
+
+        Assert.Equal(WithdrawOutcome.NotFound, outcome);
         Assert.Equal(0, store.SaveCount);
     }
 
@@ -46,14 +107,16 @@ public class WithdrawRegistrationTests
     public async Task Re_withdrawing_an_already_ingetrokken_registration_is_idempotent()
     {
         var store = new FakeRegistrationStore();
-        var registration = Registration.Submit("123456782");
+        var registration = Submitted();
         store.Seed(registration);
-        var handler = new WithdrawRegistration(store);
+        var workflow = new FakeWorkflowClient();
+        var handler = new WithdrawRegistration(store, workflow);
 
-        await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
-        await handler.HandleAsync(new WithdrawRegistrationCommand(registration.Id));
+        await handler.HandleAsync(Command(registration.Id));
+        var second = await handler.HandleAsync(Command(registration.Id));
 
-        // The second withdrawal is a no-op: the aggregate is not persisted again.
+        // The second withdrawal is a no-op: still Withdrawn, but the aggregate is not persisted again.
+        Assert.Equal(WithdrawOutcome.Withdrawn, second);
         Assert.Equal(1, store.SaveCount);
         Assert.Equal(RegistrationStatus.Ingetrokken, (await store.GetAsync(registration.Id))!.Status);
     }

tests/acceptance/Features/EenRegistratieIntrekken.feature

@@ -0,0 +1,22 @@
+# language: en
+# Drives S-11 (#12). A zorgprofessional withdraws their own submitted registration ("trek aanvraag
+# in"): it advances to INGETROKKEN and its running workflow is cancelled (ADR-0014). Only the owner
+# may withdraw — another bsn is told not-found. Exercised against in-memory stand-ins for the store
+# and the Workflow Client; the live Flowable message correlation is verified by the domain check.
+Feature: Een registratie intrekken
+  Als zorgprofessional wil ik mijn ingediende registratie kunnen intrekken
+  zodat een aanvraag die ik niet meer wil niet in behandeling blijft.
+
+  Scenario: De zorgprofessional trekt zijn eigen registratie in
+    Given a submitted registration with a running process
+    When the zorgprofessional withdraws it
+    Then the withdrawal succeeds
+    And the registration has status "INGETROKKEN"
+    And the running process is cancelled
+
+  Scenario: Een andere zorgprofessional kan de registratie niet intrekken
+    Given a submitted registration with a running process
+    When a different zorgprofessional tries to withdraw it
+    Then the withdrawal is reported not found
+    And the registration has status "INGEDIEND"
+    And the running process is not cancelled

tests/acceptance/Steps/EenRegistratieIntrekkenSteps.cs

@@ -0,0 +1,59 @@
+using Acceptance.Support;
+using Big.Application;
+using Big.Domain;
+using Reqnroll;
+using Xunit;
+
+namespace Acceptance.Steps;
+
+/// <summary>Bindings for <c>EenRegistratieIntrekken.feature</c> (S-11). Submits a registration (which
+/// records its process) and then applies the WithdrawRegistration 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 steps in the other features.</summary>
+[Binding]
+[Scope(Feature = "Een registratie intrekken")]
+public sealed class EenRegistratieIntrekkenSteps
+{
+    private const string OwnerBsn = "123456782";
+
+    private readonly InMemoryRegistrationStore _store = new();
+    private readonly InMemoryWorkflowClient _workflow = new();
+    private RegistrationId _id;
+    private WithdrawOutcome _outcome;
+
+    [Given("a submitted registration with a running process")]
+    public async Task GivenASubmittedRegistrationWithARunningProcess()
+        => _id = await new SubmitRegistration(_store, _workflow).HandleAsync(new SubmitRegistrationCommand(OwnerBsn));
+
+    [When("the zorgprofessional withdraws it")]
+    public async Task WhenTheZorgprofessionalWithdrawsIt()
+        => _outcome = await new WithdrawRegistration(_store, _workflow).HandleAsync(
+            new WithdrawRegistrationCommand(_id, OwnerBsn));
+
+    [When("a different zorgprofessional tries to withdraw it")]
+    public async Task WhenADifferentZorgprofessionalTriesToWithdrawIt()
+        => _outcome = await new WithdrawRegistration(_store, _workflow).HandleAsync(
+            new WithdrawRegistrationCommand(_id, "999999990"));
+
+    [Then("the withdrawal succeeds")]
+    public void ThenTheWithdrawalSucceeds() => Assert.Equal(WithdrawOutcome.Withdrawn, _outcome);
+
+    [Then("the withdrawal is reported not found")]
+    public void ThenTheWithdrawalIsReportedNotFound() => Assert.Equal(WithdrawOutcome.NotFound, _outcome);
+
+    [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 running process is cancelled")]
+    public void ThenTheRunningProcessIsCancelled()
+        => Assert.Equal(InMemoryWorkflowClient.StartedProcessInstanceId, _workflow.WithdrawnProcessInstanceId);
+
+    [Then("the running process is not cancelled")]
+    public void ThenTheRunningProcessIsNotCancelled()
+        => Assert.Null(_workflow.WithdrawnProcessInstanceId);
+}

tests/acceptance/Support/BffAcceptanceHost.cs

@@ -69,6 +69,9 @@ public sealed class CapturingDomainClient : IDomainClient
         return Task.FromResult(new SubmitAccepted("reg-acc-1", "Ingediend"));
     }
 
+    public Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default)
+        => Task.FromResult(true);
+
     public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
         => Task.FromResult<IReadOnlyList<WerkbakItem>>([]);
 

tests/acceptance/Support/InMemoryDomainPorts.cs

@@ -11,12 +11,19 @@ public sealed class InMemoryWorkflowClient : IWorkflowClient
     public const string StartedProcessInstanceId = "proc-acc-1";
 
     public RegistrationId? StartedFor { get; private set; }
+    public string? WithdrawnProcessInstanceId { get; private set; }
 
     public Task<string> StartRegistrationProcessAsync(RegistrationId registrationId, CancellationToken ct = default)
     {
         StartedFor = registrationId;
         return Task.FromResult(StartedProcessInstanceId);
     }
+
+    public Task WithdrawProcessAsync(string processInstanceId, CancellationToken ct = default)
+    {
+        WithdrawnProcessInstanceId = processInstanceId;
+        return Task.CompletedTask;
+    }
 }
 
 /// <summary>An in-memory ACL stand-in: records the bsn it opened a zaak for and returns a fixed URL,

tests/e2e/withdrawal.spec.ts

@@ -0,0 +1,27 @@
+import { expect, test } from '@playwright/test';
+
+// S-11 (Flow 3): a zorgprofessional logs in via mock DigiD, submits a registration, then withdraws
+// it ("trek aanvraag in") from the self-service portal. The withdrawal goes portal → BFF (owner-
+// scoped by the DigiD token's bsn) → domain, which cancels the running workflow (ADR-0014); the page
+// then confirms the registration is ingetrokken.
+test('DigiD submit → trek aanvraag in → self-service confirms ingetrokken', async ({ page }) => {
+  // Visiting the guarded page redirects to the Keycloak (mock DigiD) login.
+  await page.goto('/');
+
+  await page.locator('#username').fill('jan-burger');
+  await page.locator('#password').fill('test123');
+  await page.locator('#kc-login').click();
+
+  await expect(page.getByRole('heading', { name: /Zelfservice/i })).toBeVisible();
+
+  await page.getByRole('button', { name: /indienen/i }).click();
+
+  // The BFF accepted it and the page shows the confirmation with the reference.
+  await expect(page.getByText(/ontvangen/i)).toBeVisible();
+
+  // Withdraw it. The confirmation of withdrawal appears only after the decide POST completes (204),
+  // so awaiting the "ingetrokken" text also proves the request landed — no premature navigation.
+  await page.getByRole('button', { name: /trek aanvraag in/i }).click();
+
+  await expect(page.getByText(/is ingetrokken/i)).toBeVisible();
+});

workflows/registratie.bpmn

@@ -11,7 +11,13 @@
        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. -->
+       variable so the werkbak can correlate each task back to its aggregate.
+       S-11 adds withdrawal: while parked at Beoordelen the citizen can trek de aanvraag in — an
+       interrupting message boundary event (RegistratieIngetrokken) cancels the task and ends the
+       process via a dedicated "ingetrokken" end (ADR-0014). The Workflow Client delivers the message
+       to the task's execution; the BPMN owns the cancellation path. -->
+  <message id="Message_Ingetrokken" name="RegistratieIngetrokken"/>
+
   <process id="registratie" name="Registratie ontvangen" isExecutable="true">
 
     <startEvent id="start" name="Registratie ontvangen"/>
@@ -29,6 +35,16 @@
     <sequenceFlow id="flow3" sourceRef="Beoordelen" targetRef="end"/>
 
     <endEvent id="end" name="Registratie beoordeeld"/>
+
+    <!-- Withdrawal (S-11): interrupting message boundary event on Beoordelen. On RegistratieIngetrokken
+         the task is cancelled and the process ends as "ingetrokken". -->
+    <boundaryEvent id="Ingetrokken" attachedToRef="Beoordelen" cancelActivity="true">
+      <messageEventDefinition messageRef="Message_Ingetrokken"/>
+    </boundaryEvent>
+
+    <sequenceFlow id="flow4" sourceRef="Ingetrokken" targetRef="endIngetrokken"/>
+
+    <endEvent id="endIngetrokken" name="Registratie ingetrokken"/>
   </process>
 
   <bpmndi:BPMNDiagram id="diagram">
@@ -57,6 +73,16 @@
         <omgdi:waypoint x="510" y="115"/>
         <omgdi:waypoint x="580" y="115"/>
       </bpmndi:BPMNEdge>
+      <bpmndi:BPMNShape id="s_ingetrokken" bpmnElement="Ingetrokken">
+        <omgdc:Bounds x="435" y="135" width="30" height="30"/>
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="s_endIngetrokken" bpmnElement="endIngetrokken">
+        <omgdc:Bounds x="435" y="220" width="30" height="30"/>
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNEdge id="e_flow4" bpmnElement="flow4">
+        <omgdi:waypoint x="450" y="165"/>
+        <omgdi:waypoint x="450" y="220"/>
+      </bpmndi:BPMNEdge>
     </bpmndi:BPMNPlane>
   </bpmndi:BPMNDiagram>
 </definitions>