feat(self-service): 'trek aanvraag in' withdraws the submitted registration (refs #12)

After submitting, a secondary action withdraws the registration via

postSelfServiceRegistrationsIdWithdraw(reference); success shows an ingetrokken confirmation, a

failure is surfaced and the action stays available to retry.

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

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

@@ -3,9 +3,29 @@
     <utrecht-heading-1>Zelfservice — BIG-registratie</utrecht-heading-1>
 
     @if (submitted()) {
+      @if (withdrawn()) {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.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+  protected readonly withdrawn = signal(false);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);
+      },
+    });
+  }
 }