Phase 0 — NestJS + Zod foundation harness (F1–F8) (#1050)

Co-hosted NestJS app behind the existing Express server via a strangler-fig dispatcher, sharing the same better-sqlite3 connection and JWT httpOnly cookie. Additive and dormant: default routing stays on Express, Nest only serves its own /api/_nest diagnostics until a module opts in.

F1 @trek/shared Zod contract package; F2 Nest bootstrap co-hosted (fall-through, single Dockerfile/port); F3 shared better-sqlite3 provider; F4 JWT cookie auth guard (+ @CurrentUser, admin guard); F5 Zod validation pipe + error-envelope parity; F6 Nest test + coverage gates; F7 per-prefix strangler toggle (env, default Express); F8 CI build/typecheck/test/coverage.

Remaining F4/F6/F8 checklist items (trip-access + permission levels + MFA policy, e2e harness/seed + 80% gate, Nest↔Express parity test, Playwright PR-comment workflow) are tracked on the first consuming module cards (L1/A1/C1).

server/src/nest/auth/admin.guard.ts

@@ -0,0 +1,19 @@
+import { CanActivate, ExecutionContext, HttpException, Injectable } from '@nestjs/common';
+import type { Request } from 'express';
+import type { User } from '../../types';
+
+/**
+ * Mirrors the legacy `adminOnly` middleware: requires an authenticated admin.
+ * Use together with JwtAuthGuard (which populates req.user):
+ * `@UseGuards(JwtAuthGuard, AdminGuard)`.
+ */
+@Injectable()
+export class AdminGuard implements CanActivate {
+  canActivate(context: ExecutionContext): boolean {
+    const req = context.switchToHttp().getRequest<Request & { user?: User }>();
+    if (!req.user || req.user.role !== 'admin') {
+      throw new HttpException({ error: 'Admin access required' }, 403);
+    }
+    return true;
+  }
+}