Step 2 (code quality): dedup + stop FE recomputing a server rule

- H1: tasksFromProfile takes the server's eligibleForHerregistratie decision
  instead of recomputing isHerregistratieEligible — the FE renders the rule,
  doesn't own it (ADR-0001). Policy reference impl kept for tests.
- M1: one shared runSubmit(fn, fallback) wrapper; the 4 submit-* commands keep
  only their payload mapping. +spec.
- M2: whenTag() kernel helper removes 10 repeated `as Extract<U,{tag}>` casts
  across the wizard/form components.

M4 (shared JA_NEE) folded into the upcoming i18n pass (clean dedup needs
$localize labels to sit in shared without breaking the English-shared-UI rule).
L1 already resolved by the restyle commit.

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

src/app/shared/application/submit.spec.ts

@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { runSubmit } from './submit';
+
+describe('runSubmit', () => {
+  it('folds a resolved call into ok(value)', async () => {
+    const r = await runSubmit(async () => 'BIG-123', 'fallback');
+    expect(r).toEqual({ ok: true, value: 'BIG-123' });
+  });
+
+  it('maps a ProblemDetails rejection to err(detail)', async () => {
+    const r = await runSubmit(async () => {
+      throw { detail: 'Aanvraag afgewezen.' };
+    }, 'fallback');
+    expect(r).toEqual({ ok: false, error: 'Aanvraag afgewezen.' });
+  });
+
+  it('falls back when the rejection has no detail', async () => {
+    const r = await runSubmit(async () => {
+      throw new Error('network');
+    }, 'fallback');
+    expect(r).toEqual({ ok: false, error: 'fallback' });
+  });
+});

src/app/shared/application/submit.ts

@@ -0,0 +1,20 @@
+import { Result, ok, err } from '@shared/kernel/fp';
+import { problemDetail } from '@shared/infrastructure/api-error';
+
+/**
+ * Run a mutating API call and fold it into a `Result` — the one place the
+ * try/catch + ProblemDetails-mapping lives, so every `submit-*` command is just
+ * its own payload mapping. The backend re-validates and returns a 422
+ * ProblemDetails on rejection, surfaced here as the error string.
+ */
+export async function runSubmit<T>(fn: () => Promise<T>, fallback: string): Promise<Result<string, T>> {
+  try {
+    return ok(await fn());
+  } catch (e) {
+    return err(problemDetail(e, fallback));
+  }
+}
+
+// ponytail: i18n in Step 3/M3 wraps this in $localize with a stable @@id, which
+// dedupes it at the translation layer; for now it's the single shared default.
+export const SUBMIT_FAILED = 'Het indienen is niet gelukt. Probeer het later opnieuw.';

src/app/shared/kernel/fp.ts

@@ -21,3 +21,13 @@ export const err = <E>(error: E): Result<E, never> => ({ ok: false, error });
 /** Nominal typing: Brand<string, 'Postcode'> is assignable from a plain string
     only through an explicit cast — so a smart constructor is the only minter. */
 export type Brand<T, B extends string> = T & { readonly __brand: B };
+
+/** Narrow a tagged union to one variant by its `tag`, or null. The single place
+    the cast lives — TS can't narrow through a runtime tag argument, so callers get
+    `whenTag(state, 'Editing')?.foo` instead of repeating `as Extract<…>`. */
+export function whenTag<U extends { tag: string }, K extends U['tag']>(
+  u: U,
+  tag: K,
+): Extract<U, { tag: K }> | null {
+  return u.tag === tag ? (u as Extract<U, { tag: K }>) : null;
+}