Scaffold HIPCTF platform (NestJS + Angular)

- Backend: NestJS 10 + TypeORM (better-sqlite3) feature-modular layout.
  - Entities: user, setting, category, challenge, challenge_file, solve,
    refresh_token, blog_post. Auto-run migrations + idempotent 6-system-
    category seed on startup.
  - Argon2id password hashing with policy check; JWT access + rotating
    refresh tokens (HttpOnly cookie); CSRF middleware (SameSite + custom
    X-CSRF-Token header); global JWT auth guard with @Public() opt-out;
    per-IP login backoff + per-IP registration rate limit.
  - Endpoints: auth (login/refresh/logout/csrf), users (first-admin
    registration), system (bootstrap/event status/SSE), admin (guarded
    user CRUD with last-admin invariant), frontend module (uploads +
    SPA fallback).
  - Security: helmet+CSP+HSTS-gated-by-TLS, CORS allowlist, structured
    global exception filter, Zod request validation pipes, OpenAPI 3.1
    served at /api/docs and /api/docs-json, 10 canonical themes under
    backend/themes/.
- Frontend: Angular 17 standalone components, lazy-loaded feature routes,
  signals, functional HttpInterceptorFn (csrf + auth), functional
  CanActivateFn auth guard, HttpOnly-cookie-based auth service.
- Tests: Jest + supertest, 46 tests across 13 suites covering
  migrations, env schema, theme loader, event status, login backoff,
  registration rate limit, ApiError shape, bootstrap integration,
  auth refresh rotation, admin guard, last-admin invariant, SSE flat
  payloads. Single-command runner: `npm test`.

tests/backend/last-admin-invariant.spec.ts

@@ -0,0 +1,81 @@
+import { UsersService } from '../../backend/src/modules/users/users.service';
+import { DataSource } from 'typeorm';
+import { UserEntity } from '../../backend/src/database/entities/user.entity';
+import { ApiError } from '../../backend/src/common/errors/api-error';
+import { ERROR_CODES } from '../../backend/src/common/errors/error-codes';
+
+describe('UsersService.enforceLastAdminInvariant', () => {
+  let ds: DataSource;
+  let svc: UsersService;
+
+  beforeAll(async () => {
+    ds = new DataSource({
+      type: 'better-sqlite3',
+      database: ':memory:',
+      entities: [UserEntity],
+      synchronize: true,
+      logging: false,
+    });
+    await ds.initialize();
+    svc = new UsersService(ds.getRepository(UserEntity));
+  });
+
+  afterAll(async () => {
+    await ds.destroy();
+  });
+
+  beforeEach(async () => {
+    await ds.getRepository(UserEntity).clear();
+  });
+
+  it('throws LAST_ADMIN when demoting the only admin', async () => {
+    const repo = ds.getRepository(UserEntity);
+    const admin = repo.create({
+      id: 'a1', username: 'admin', passwordHash: 'x', role: 'admin', status: 'enabled', createdAt: new Date().toISOString(),
+    });
+    await repo.save(admin);
+
+    await expect(
+      ds.transaction(async (manager) => svc.enforceLastAdminInvariant(manager, 'a1', 'player')),
+    ).rejects.toMatchObject({
+      response: { code: ERROR_CODES.LAST_ADMIN },
+    });
+  });
+
+  it('throws LAST_ADMIN when deleting the only admin', async () => {
+    const repo = ds.getRepository(UserEntity);
+    const admin = repo.create({
+      id: 'a1', username: 'admin', passwordHash: 'x', role: 'admin', status: 'enabled', createdAt: new Date().toISOString(),
+    });
+    await repo.save(admin);
+
+    await expect(
+      ds.transaction(async (manager) => svc.enforceLastAdminInvariant(manager, 'a1')),
+    ).rejects.toMatchObject({
+      response: { code: ERROR_CODES.LAST_ADMIN },
+    });
+  });
+
+  it('does NOT throw when more than one admin exists', async () => {
+    const repo = ds.getRepository(UserEntity);
+    await repo.save([
+      repo.create({ id: 'a1', username: 'a1', passwordHash: 'x', role: 'admin', status: 'enabled', createdAt: new Date().toISOString() }),
+      repo.create({ id: 'a2', username: 'a2', passwordHash: 'x', role: 'admin', status: 'enabled', createdAt: new Date().toISOString() }),
+    ]);
+
+    await expect(
+      ds.transaction(async (manager) => svc.enforceLastAdminInvariant(manager, 'a1', 'player')),
+    ).resolves.toBeUndefined();
+  });
+
+  it('does NOT throw when demoting a non-admin', async () => {
+    const repo = ds.getRepository(UserEntity);
+    await repo.save([
+      repo.create({ id: 'a1', username: 'a1', passwordHash: 'x', role: 'admin', status: 'enabled', createdAt: new Date().toISOString() }),
+      repo.create({ id: 'p1', username: 'p1', passwordHash: 'x', role: 'player', status: 'enabled', createdAt: new Date().toISOString() }),
+    ]);
+    await expect(
+      ds.transaction(async (manager) => svc.enforceLastAdminInvariant(manager, 'p1', 'admin')),
+    ).resolves.toBeUndefined();
+  });
+});