feat(fp): WP-07 — brief on the shared idioms + RemoteData MDX

Collapse brief.store's busy signal + nullable lastError into one Idle |
Busy | Failed union (saveState gets matching tag-object style), and route
brief.page's load through RemoteData + <app-async> instead of a hand-rolled
@switch, via a BriefStore.remoteData projection of the machine's existing
loading/failed tags -- the machine keeps owning the letter's own status
lifecycle untouched. New brief.store.spec.ts covers the Busy->Idle/Failed
transitions; new Foundations/RemoteData & Async MDX page documents the
pattern and the WP-06 typed-loaded-slot fallback. Deviation from the
original plan recorded in the WP file.

src/app/brief/application/brief.store.spec.ts

@@ -0,0 +1,88 @@
+import { TestBed } from '@angular/core/testing';
+import { describe, it, expect } from 'vitest';
+import { Result } from '@shared/kernel/fp';
+import { Brief, BriefDecisions } from '@brief/domain/brief';
+import { BriefAdapter, BriefView } from '@brief/infrastructure/brief.adapter';
+import { BriefStore } from './brief.store';
+
+const decisions: BriefDecisions = {
+  canEdit: true,
+  canApprove: true,
+  canReject: true,
+  canSend: true,
+};
+
+const brief: Brief = {
+  briefId: 'b1',
+  beroep: 'arts',
+  templateId: 't1',
+  placeholders: [],
+  sections: [],
+  status: { tag: 'draft' },
+  drafterId: 'u1',
+};
+
+const view: BriefView = { brief, availablePassages: [], decisions };
+
+function setup(adapter: Partial<BriefAdapter>): BriefStore {
+  TestBed.configureTestingModule({ providers: [{ provide: BriefAdapter, useValue: adapter }] });
+  return TestBed.inject(BriefStore);
+}
+
+describe('BriefStore action state (Idle | Busy | Failed)', () => {
+  it('is Busy synchronously once a transition starts, then Idle on success', async () => {
+    const approved: BriefView = {
+      ...view,
+      brief: { ...brief, status: { tag: 'approved', approvedBy: 'u2', approvedAt: 't' } },
+    };
+    const store = setup({
+      load: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      save: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      approve: (): Promise<Result<string, BriefView>> =>
+        Promise.resolve({ ok: true, value: approved }),
+    });
+    await store.load();
+
+    const pending = store.approve();
+    expect(store.busy()).toBe(true); // set synchronously, before any await resolves
+
+    await pending;
+    expect(store.busy()).toBe(false);
+    expect(store.lastError()).toBeNull();
+  });
+
+  it('goes Busy then Failed on a failing transition, surfacing the error', async () => {
+    const store = setup({
+      load: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      save: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      approve: (): Promise<Result<string, BriefView>> =>
+        Promise.resolve({ ok: false, error: 'niet toegestaan' }),
+    });
+    await store.load();
+
+    await store.approve();
+    expect(store.busy()).toBe(false);
+    expect(store.lastError()).toBe('niet toegestaan');
+  });
+
+  it('a subsequent successful transition clears a prior Failed state', async () => {
+    let approveResult: Result<string, BriefView> = { ok: false, error: 'eerste poging mislukt' };
+    const store = setup({
+      load: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      save: (): Promise<Result<string, BriefView>> => Promise.resolve({ ok: true, value: view }),
+      approve: (): Promise<Result<string, BriefView>> => Promise.resolve(approveResult),
+    });
+    await store.load();
+
+    await store.approve();
+    expect(store.lastError()).toBe('eerste poging mislukt');
+
+    approveResult = {
+      ok: true,
+      value: { ...view, brief: { ...brief, status: { tag: 'approved', approvedBy: 'u2', approvedAt: 't' } } },
+    };
+    await store.approve();
+    expect(store.busy()).toBe(false);
+    expect(store.lastError()).toBeNull();
+  });
+});