refactor: add successOr, sweep remaining inline unwraps (RD-17)

Eight sites hand-rolled `rd.tag === 'Success' ? rd.value : fallback`. Six
take the new `successOr(rd, fallback)`, one takes the existing `successOf`,
and one (`big-profile.store.ts`) uses the existing `map`, since it returns a
RemoteData rather than an unwrapped value.

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

libs/beheer/src/ui/audit.page.ts

@@ -5,6 +5,7 @@ import { AlertComponent } from '@shared/ui/alert/alert.component';
 import { ButtonComponent } from '@shared/ui/button/button.component';
 import { ASYNC } from '@shared/ui/async/async.component';
 import { AccessStore } from '@shared/application/access.store';
+import { successOr } from '@shared/application/remote-data';
 import { AuditStore } from '@beheer/application/audit.store';
 
 /**
@@ -94,10 +95,7 @@ export class AuditPage {
   protected access = inject(AccessStore);
 
   protected canRead = computed(() => this.access.can('cases:manage'));
-  protected entries = computed(() => {
-    const rd = this.store.entries();
-    return rd.tag === 'Success' ? rd.value : [];
-  });
+  protected entries = computed(() => successOr(this.store.entries(), []));
 
   protected heading = $localize`:@@audit.heading:Auditlog`;
   protected intro = $localize`:@@audit.intro:Toegangs- en inzagebeslissingen (autorisatie en het tonen van afgeschermde gegevens). Vastgelegd zonder persoonsgegevens.`;

libs/shared/docs/behaviour-spec.mdx

@@ -20,7 +20,7 @@ tested where._
 
 Every bullet below is a real test name from the suite — an `it()` title (frontend) or a test
 method name (backend), read as a sentence. Nothing here is hand-written prose: this page
-**is** the suite, reshaped for a business reader. 530 frontend behaviours across
+**is** the suite, reshaped for a business reader. 532 frontend behaviours across
 9 contexts; 261 backend behaviours across 42 test
 classes.
 
@@ -968,6 +968,11 @@ classes.
 - unwraps a Success value
 - is undefined for every other state
 
+#### successOr
+
+- unwraps a Success value
+- is the fallback for every other state
+
 #### upload lifecycle messages
 
 - queued → progress → complete

libs/shared/src/application/feature-flags.store.ts

@@ -1,5 +1,5 @@
 import { Injectable, computed, inject, signal } from '@angular/core';
-import { RemoteData } from '@shared/application/remote-data';
+import { RemoteData, successOr } from '@shared/application/remote-data';
 import { runSubmit } from '@shared/application/submit';
 import { Result, ok, err } from '@shared/kernel/fp';
 import { FeatureFlag } from '@shared/domain/feature-flag';
@@ -22,10 +22,7 @@ export class FeatureFlagStore {
 
   readonly flags = this.state.asReadonly();
   /** The resolved list (empty until loaded) — for the admin toggle UI. */
-  readonly all = computed(() => {
-    const rd = this.state();
-    return rd.tag === 'Success' ? rd.value : [];
-  });
+  readonly all = computed(() => successOr(this.state(), []));
 
   constructor() {
     void this.load();

libs/shared/src/application/remote-data.spec.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { RemoteData, fromLoadLifecycle, map2, map, successOf } from './remote-data';
+import { RemoteData, fromLoadLifecycle, map2, map, successOf, successOr } from './remote-data';
 import { loading, failure, empty, success } from '../testing/remote-data';
 
 const loadingRd: RemoteData<string, number> = loading();
@@ -34,6 +34,18 @@ describe('successOf', () => {
   });
 });
 
+describe('successOr', () => {
+  it('unwraps a Success value', () => {
+    expect(successOr(ok(2), 0)).toBe(2);
+  });
+
+  it('is the fallback for every other state', () => {
+    expect(successOr(loadingRd, [])).toEqual([]);
+    expect(successOr(failureRd, [])).toEqual([]);
+    expect(successOr(empty(), null)).toBeNull();
+  });
+});
+
 describe('fromLoadLifecycle', () => {
   it('maps Loading → Loading', () => {
     expect(fromLoadLifecycle({ tag: 'Loading' })).toEqual(loading());

libs/shared/src/application/remote-data.ts

@@ -109,3 +109,13 @@ export function andThen<E, A, B>(
 export function successOf<E, T>(rd: RemoteData<E, T>): T | undefined {
   return rd.tag === 'Success' ? rd.value : undefined;
 }
+
+/** Unwrap a Success value, or a caller-supplied `fallback` for every other state.
+    Reach for this over `successOf` when `undefined` is not a usable value at the
+    call site (e.g. a list the template iterates, which wants `[]`). Reach for
+    `map` instead when the site needs to stay a `RemoteData`, not an unwrapped
+    value. Three type parameters: `fallback` need not be assignable to `T`
+    (an empty array is not a `T[]` at the type level, only at the value level). */
+export function successOr<E, T, F>(rd: RemoteData<E, T>, fallback: F): T | F {
+  return rd.tag === 'Success' ? rd.value : fallback;
+}