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/registratie/ui/registratie-wizard/registratie-wizard.component.ts

@@ -41,7 +41,7 @@ const HANDMATIG = '__handmatig__'; // sentinel option: "my diploma isn't listed"
     the pure `reduce` (registratie-wizard.machine.ts). The BRP address prefills the
     draft via an effect; the DUO diploma list renders through <app-async>; choosing
     a diploma reveals its server-derived beroep. The draft is persisted to
-    localStorage so a reload keeps the user's progress. Built entirely from existing
+    sessionStorage so a reload keeps the user's progress (cleared on tab close). Built from existing
     atoms/molecules. */
 @Component({
   selector: 'app-registratie-wizard',
@@ -294,14 +294,15 @@ export class RegistratieWizardComponent {
   }
 
   constructor() {
-    // An explicit seed (stories) wins; otherwise resume from localStorage.
+    // An explicit seed (stories) wins; otherwise resume from sessionStorage.
     const seeded = this.seed();
     queueMicrotask(() => this.dispatch({ tag: 'Seed', state: seeded !== initial ? seeded : (this.restore() ?? initial) }));
-    // Persist only while filling in; clear once the flow is done.
+    // Persist only while filling in; clear once the flow is done. G1: sessionStorage
+    // (not localStorage) — the draft holds address/email and must not outlive the tab.
     effect(() => {
       const s = this.state();
-      if (s.tag === 'Invullen') localStorage.setItem(STORAGE_KEY, JSON.stringify(s));
-      else localStorage.removeItem(STORAGE_KEY);
+      if (s.tag === 'Invullen') sessionStorage.setItem(STORAGE_KEY, JSON.stringify(s));
+      else sessionStorage.removeItem(STORAGE_KEY);
     });
     // Prefill the address from the BRP lookup as it arrives. Track only the resource
     // value; untrack the dispatch (it reads the state signal, which would otherwise
@@ -325,10 +326,11 @@ export class RegistratieWizardComponent {
   }
 
   private restore(): RegistratieState | null {
-    const raw = localStorage.getItem(STORAGE_KEY);
+    const raw = sessionStorage.getItem(STORAGE_KEY);
     if (!raw) return null;
     try {
-      return JSON.parse(raw) as RegistratieState;
+      const parsed = JSON.parse(raw) as RegistratieState;
+      return parsed?.tag === 'Invullen' ? parsed : null; // G2: only resume a known shape.
     } catch {
       return null; // ponytail: corrupt entry -> start fresh, no migration.
     }