refactor: extract toWizardErrors, adopted by all 3 wizards (RD-20)

Each wizard flattened its per-field error record into the shell's
WizardError[] summary with its own copy of the same loop. Extract one
pure helper, wizard-errors.ts, next to naarStapLabel. Add a spec that
covers a flat record, an empty record, skipped undefined/empty-string
values, the idPrefix, and a skipped nested object.

registratie-wizard.machine.ts changes Errors from an interface to a
type alias, because only a type alias gets an implicit index
signature and is assignable to the helper's Record<string, unknown>
parameter. The other two machines already declare their error maps as
type aliases, so this also makes the three consistent.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/ssp/src/app/herregistratie/ui/herregistratie-wizard/herregistratie-wizard.component.ts

@@ -9,6 +9,7 @@ import {
   WizardPhase,
   naarStapLabel,
 } from '@shared/layout/wizard-shell/wizard-shell.component';
+import { toWizardErrors } from '@shared/layout/wizard-shell/wizard-errors';
 import { ConfirmationComponent } from '@shared/ui/confirmation/confirmation.component';
 import { createStore } from '@shared/application/store';
 import { whenTag } from '@shared/kernel/fp';
@@ -251,12 +252,7 @@ export class HerregistratieWizardComponent {
     }
   });
   /** Current step's field errors, flattened for the shell's error summary. */
-  protected errorList = computed<WizardError[]>(() => {
-    const e = this.editing()?.errors ?? {};
-    return (Object.keys(e) as (keyof typeof e)[])
-      .filter((k) => e[k])
-      .map((k) => ({ id: k, message: e[k]! }));
-  });
+  protected errorList = computed<WizardError[]>(() => toWizardErrors(this.editing()?.errors ?? {}));
 
   constructor() {
     // An explicit seed (stories/tests) wins; otherwise resume the backend draft

apps/ssp/src/app/herregistratie/ui/intake-wizard/intake-wizard.component.ts

@@ -15,6 +15,7 @@ import {
   WizardPhase,
   naarStapLabel,
 } from '@shared/layout/wizard-shell/wizard-shell.component';
+import { toWizardErrors } from '@shared/layout/wizard-shell/wizard-errors';
 import { createStore } from '@shared/application/store';
 import { whenTag } from '@shared/kernel/fp';
 import { BigProfileStore } from '@registratie/application/big-profile.store';
@@ -360,12 +361,9 @@ export class IntakeWizardComponent {
   });
   /** Current step's field errors, flattened for the shell's error summary. The
       field ids match the answer keys, so the summary anchors jump to the field. */
-  protected errorList = computed<WizardError[]>(() => {
-    const e = this.answering()?.errors ?? {};
-    return (Object.keys(e) as (keyof Answers)[])
-      .filter((k) => e[k])
-      .map((k) => ({ id: k, message: e[k]! }));
-  });
+  protected errorList = computed<WizardError[]>(() =>
+    toWizardErrors(this.answering()?.errors ?? {}),
+  );
 
   protected err = (k: keyof Answers) => this.answering()?.errors[k] ?? '';
   protected set = (key: keyof Answers, value: string) =>

apps/ssp/src/app/registratie/domain/registratie-wizard.machine.ts

@@ -66,7 +66,7 @@ export type DraftField = 'straat' | 'postcode' | 'woonplaats' | 'email';
 
 /** Per-field error map. `antwoorden` holds per-policy-question errors, keyed by
     question id (a step can show several questions). */
-export interface Errors {
+export type Errors = {
   straat?: string;
   postcode?: string;
   woonplaats?: string;
@@ -75,7 +75,7 @@ export interface Errors {
   diploma?: string;
   documenten?: string;
   antwoorden?: Record<string, string>;
-}
+};
 
 export type RegistratieState =
   | { tag: 'Invullen'; draft: Draft; cursor: number; errors: Errors; upload: UploadState }

apps/ssp/src/app/registratie/ui/registratie-wizard/registratie-wizard.component.ts

@@ -17,6 +17,7 @@ import {
   WizardPhase,
   naarStapLabel,
 } from '@shared/layout/wizard-shell/wizard-shell.component';
+import { toWizardErrors } from '@shared/layout/wizard-shell/wizard-errors';
 import { ASYNC } from '@shared/ui/async/async.component';
 import { AddressFieldsComponent } from '@registratie/ui/address-fields/address-fields.component';
 import { createStore } from '@shared/application/store';
@@ -468,14 +469,7 @@ export class RegistratieWizardComponent {
   /** Current step's errors (incl. per-question), flattened for the error summary. */
   protected errorList = computed<WizardError[]>(() => {
     const e = this.invullen()?.errors ?? {};
-    const out: WizardError[] = [];
-    for (const [k, v] of Object.entries(e)) {
-      if (k !== 'antwoorden' && typeof v === 'string' && v) out.push({ id: k, message: v });
-    }
-    for (const [qid, msg] of Object.entries(e.antwoorden ?? {})) {
-      if (msg) out.push({ id: 'vraag-' + qid, message: msg });
-    }
-    return out;
+    return [...toWizardErrors(e), ...toWizardErrors(e.antwoorden ?? {}, 'vraag-')];
   });
   protected adresSamenvatting = computed(() => {
     const d = this.draft();