Copilot Workspace Tasks: Spec-Driven Changes Across Microservice Boundaries

## Task: Add idempotent refund endpoint

### Spec
- OpenAPI: `services/payments/openapi.yaml#/paths/@/v1/refunds`
- Event: `refund.completed.v1` in `asyncapi.yaml`

### Acceptance
- [ ] Handler matches generated types from OpenAPI
- [ ] Contract test `refunds.contract.test.ts` green against mock + sandbox
- [ ] Orders service consumes `refund.completed.v1` without schema drift
- [ ] No new paths outside the OpenAPI file in this PR

### Verify
```bash
pnpm --filter @acme/payments test:contract
pnpm --filter @acme/orders test:contract -- --grep refund
</code></pre>

<pre><code>
```markdown
❌ Bad task: "wire refunds between payments and orders somehow"

# ✅ Spec first → types → implementation
pnpm openapi-typescript services/payments/openapi.yaml -o packages/payments-client/src/types.ts
pnpm --filter @acme/payments-client build

// orders/src/refunds.ts
import type { paths } from "@acme/payments-client/types";

type RefundBody = paths["/v1/refunds"]["post"]["requestBody"]["content"]["application/json"];

export async function requestRefund(body: RefundBody) {
  // ✅ Only fields that exist on the generated type
  return paymentsFetch("/v1/refunds", { method: "POST", body });
}

// ❌ Model-invented client
await fetch("https://payments/api/refundOrder", { body: JSON.stringify({ order: id }) });

RULES:
- You may edit only: services/payments/** and packages/payments-client/**
- Spec PRs are separate: changes to openapi.yaml need label spec-change
- Do not add routes absent from openapi.yaml
- Prefer extending existing handlers over new micro-services

// payments/refunds.contract.test.ts
import { OpenAPIResponseValidator } from "openapi-response-validator";
import spec from "../openapi.yaml";

test("POST /v1/refunds matches response schema", async () => {
  const res = await app.inject({ method: "POST", url: "/v1/refunds", payload: fixture });
  const v = new OpenAPIResponseValidator({ responses: spec.paths["/v1/refunds"].post.responses });
  // ✅ Fail closed on schema drift
  expect(v.validateResponse(res.statusCode, res.json())).toBeUndefined();
});