Step 3 (production-readiness): PII storage, validated reads, seams

Implement-now:
- G1: keep PII out of persistent storage — never persist BSN (only `naam`);
  move both wizard drafts (address/email, work data) localStorage → sessionStorage
  so they clear on tab close.
- G2: validate storage reads before trusting the cast — shape/tag guard in every
  restore() (mirrors the parse* HTTP boundary); corrupt/foreign shape → start fresh.
- G3: already satisfied (debug-state redacts via mask.ts).

Show-the-seam (hook + doc, not fully built):
- G4: problemFieldErrors() maps a server validation envelope (ASP.NET
  ValidationProblemDetails `errors`) to the field-keyed map the wizards already
  render; returns {} until the backend sends it. +spec.
- G5: documented the retry/backoff seam at the adapter GET loader; reads may
  retry, mutating submits never do.

Out of scope (named): unsaved-changes warning (persistence prevents data loss),
real auth/tokens, axe-core in CI.

Gate green: lint, check:tokens, build, test 79/79.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/shared/infrastructure/api-error.spec.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { problemDetail } from './api-error';
+import { problemDetail, problemFieldErrors } from './api-error';
 
 describe('problemDetail', () => {
   it('extracts the detail from an RFC-7807 ProblemDetails', () => {
@@ -12,3 +12,16 @@ describe('problemDetail', () => {
     expect(problemDetail(undefined, 'fallback')).toBe('fallback');
   });
 });
+
+describe('problemFieldErrors (G4 seam)', () => {
+  it('maps a ValidationProblemDetails errors dict to first-message-per-field', () => {
+    expect(problemFieldErrors({ errors: { straat: ['Verplicht.'], postcode: ['Ongeldig.', 'x'] } }))
+      .toEqual({ straat: 'Verplicht.', postcode: 'Ongeldig.' });
+  });
+
+  it('returns {} when there is no errors envelope (the current backend shape)', () => {
+    expect(problemFieldErrors({ detail: 'one banner' })).toEqual({});
+    expect(problemFieldErrors(new Error('boom'))).toEqual({});
+    expect(problemFieldErrors(undefined)).toEqual({});
+  });
+});

src/app/shared/infrastructure/api-error.ts

@@ -12,3 +12,25 @@ export function problemDetail(e: unknown, fallback: string): string {
   }
   return fallback;
 }
+
+/**
+ * SEAM (G4): map a server validation envelope to field-level errors.
+ *
+ * ASP.NET's ValidationProblemDetails carries `errors: { field: string[] }`. The
+ * backend today returns only `detail` (one banner message), so this returns `{}`.
+ * When the backend starts sending `errors`, a machine's `SubmitFailed` handler can
+ * merge this into its own `errors` map — the field-keyed shape the wizards already
+ * render — so a rejection shows inline per field, not just as a banner. The
+ * consumer hook is the only thing left to wire; the contract boundary lives here.
+ */
+export function problemFieldErrors(e: unknown): Record<string, string> {
+  if (!e || typeof e !== 'object' || !('errors' in e)) return {};
+  const errors = (e as { errors?: unknown }).errors;
+  if (!errors || typeof errors !== 'object') return {};
+  const out: Record<string, string> = {};
+  for (const [field, msgs] of Object.entries(errors as Record<string, unknown>)) {
+    const first = Array.isArray(msgs) ? msgs[0] : msgs;
+    if (typeof first === 'string') out[field] = first;
+  }
+  return out;
+}