feat: add trip and trip settings with optimistic locking

backend/libs/trips/test/trips.optimistic-locking.integration-spec.ts

@@ -0,0 +1,55 @@
+import { ConflictException } from '@nestjs/common';
+import { Kysely, PostgresDialect } from 'kysely';
+import { Pool } from 'pg';
+import type { Database } from '../../database/src';
+import { TripsRepository } from '../src/trips.repository';
+import { TripsService } from '../src/trips.service';
+import { UsersRepository } from '../../users/src/users.repository';
+
+describe('Trip optimistic locking (integration)', () => {
+  let db: Kysely<Database>;
+  let tripsService: TripsService;
+  let ownerId: string;
+
+  beforeAll(async () => {
+    db = new Kysely<Database>({
+      dialect: new PostgresDialect({
+        pool: new Pool({ connectionString: process.env.DATABASE_URL }),
+      }),
+    });
+    const usersRepository = new UsersRepository(db);
+    const owner = await usersRepository.upsertByExternalSubjectId(
+      'optimistic-locking-test-sub',
+      {
+        email: 'owner@example.test',
+        displayName: 'Owner',
+      },
+    );
+    ownerId = owner.id;
+    tripsService = new TripsService(new TripsRepository(db));
+  });
+
+  afterAll(async () => {
+    await db.destroy();
+  });
+
+  it('rejects a second update that used a stale version', async () => {
+    const trip = await tripsService.createTrip(ownerId, {
+      name: 'Slovenia 2027',
+    });
+    expect(trip.version).toBe(1);
+
+    const firstUpdate = await tripsService.updateTrip(trip.id, {
+      name: 'Slovenia 2027 (v2)',
+      version: 1,
+    });
+    expect(firstUpdate.version).toBe(2);
+
+    await expect(
+      tripsService.updateTrip(trip.id, {
+        name: 'Conflicting concurrent edit',
+        version: 1,
+      }),
+    ).rejects.toThrow(ConflictException);
+  });
+});