diff --git a/tests/concurrency/ticket-status-race.test.ts b/tests/concurrency/ticket-status-race.test.ts
new file mode 100644
index 0000000..d5ca744
--- /dev/null
+++ b/tests/concurrency/ticket-status-race.test.ts
@@ -0,0 +1,121 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { buildApp } from '@/app';
+import { prismaClient } from '@/infrastructure/database';
+import { FastifyInstance } from 'fastify';
+import {
+  encryptCredential,
+  generateCredentialSecret,
+  issueIntegrationToken,
+} from '@/modules/catalog/products';
+import { ticketsRepository } from '@/modules/ticketing/tickets';
+
+/**
+ * specs/016-load-concurrency-testing User Story 4 / FR-004 / SC-004: proves — rather than
+ * assumes — that 003-ticketing's own optimistic-concurrency guarantee
+ * (TicketsRepository.updateStatus's atomic `updateMany({where:{id, version: expectedVersion}})`)
+ * actually holds under genuinely concurrent requests, not just the sequential checks that
+ * existed before this feature. research.md §4: no implementation change is expected here — this
+ * is a real Postgres, real concurrency proof of an already-sound mechanism.
+ */
+describe('Ticket status optimistic concurrency (User Story 4)', () => {
+  let app: FastifyInstance;
+  const externalProductId = `TEST_TICKET_STATUS_RACE_PROD_${Date.now()}`;
+  let productId: string;
+  let secret: string;
+  const createdTicketIds: string[] = [];
+
+  async function createTicket(): Promise<string> {
+    const token = issueIntegrationToken(secret, {
+      externalProductId,
+      tenantId: 'tenant-1',
+      userId: 'user-1',
+    });
+    const created = await app.inject({
+      method: 'POST',
+      url: '/v1/support/requests',
+      headers: { authorization: `Bearer ${token}` },
+      payload: {
+        productId: externalProductId,
+        tenantId: 'tenant-1',
+        userId: 'user-1',
+        source: 'test',
+        problem: `Ticket status race test ${Date.now()}-${Math.random()}`,
+      },
+    });
+    expect(created.statusCode).toBe(202);
+    const ticketId = created.json().data.ticketId as string;
+    createdTicketIds.push(ticketId);
+    return ticketId;
+  }
+
+  beforeAll(async () => {
+    app = await buildApp();
+
+    const product = await prismaClient.product.create({
+      data: { externalProductId, name: 'Ticket Status Race Test Product', status: 'active' },
+    });
+    productId = product.id;
+    secret = generateCredentialSecret();
+    await prismaClient.productIntegration.create({
+      data: {
+        productId,
+        credentialRef: encryptCredential(secret),
+        authMechanism: 'signed_token',
+        allowedScope: { tenantIds: ['tenant-1'] },
+        status: 'active',
+        rateLimitPerMinute: 1000,
+        rateLimitPerUserPerMinute: 1000,
+      },
+    });
+  });
+
+  afterAll(async () => {
+    await prismaClient.ticketMessage.deleteMany({ where: { ticketId: { in: createdTicketIds } } });
+    await prismaClient.ticket.deleteMany({ where: { id: { in: createdTicketIds } } });
+    await prismaClient.problem.deleteMany({ where: { productId } });
+    await prismaClient.productIntegration.deleteMany({ where: { productId } });
+    await prismaClient.product.deleteMany({ where: { id: productId } });
+    await app.close();
+  });
+
+  it('exactly one of 20 concurrent status updates from the same version succeeds', async () => {
+    const ticketId = await createTicket();
+    const original = await prismaClient.ticket.findUniqueOrThrow({ where: { id: ticketId } });
+    expect(original.status).toBe('NEW');
+
+    const attempts = 20;
+    const results = await Promise.all(
+      Array.from({ length: attempts }, () =>
+        ticketsRepository.updateStatus(ticketId, 'AI_ANALYZING', original.version),
+      ),
+    );
+
+    const successes = results.filter((r) => r !== null);
+    const failures = results.filter((r) => r === null);
+    expect(successes.length).toBe(1);
+    expect(failures.length).toBe(attempts - 1);
+
+    const finalTicket = await prismaClient.ticket.findUniqueOrThrow({ where: { id: ticketId } });
+    expect(finalTicket.status).toBe('AI_ANALYZING');
+    expect(finalTicket.version).toBe(original.version + 1);
+  });
+
+  it(
+    'holds consistently across 10 repeated runs (SC-004)',
+    async () => {
+      for (let run = 0; run < 10; run++) {
+        const ticketId = await createTicket();
+        const original = await prismaClient.ticket.findUniqueOrThrow({ where: { id: ticketId } });
+
+        const results = await Promise.all(
+          Array.from({ length: 20 }, () =>
+            ticketsRepository.updateStatus(ticketId, 'AI_ANALYZING', original.version),
+          ),
+        );
+
+        expect(results.filter((r) => r !== null).length).toBe(1);
+      }
+    },
+    60000,
+  );
+});