Add spector integration test for payload/head HEAD operation response headers (#4789)

HEAD operations with response-header-only return types were generating
`Promise<void>`, making headers inaccessible in the returned value. The
`payload/head` spec from `@typespec/http-specs` exercises this — a HEAD
endpoint returning `Content-Type` and `x-ms-meta` headers.

## Changes

- **`test/commands/spector-list.js`** — Register `payload/head` for
client generation
-
**`test/azure-modular-integration/generated/payload/head/tspconfig.yaml`**
— New tspconfig with `include-headers-in-response: true` to surface
response headers in the return type
-
**`test/azure-modular-integration/generated/payload/head/src/index.d.ts`**
— Generated declarations; `contentTypeHeaderInResponse` now returns
`Promise<{ contentType?: string; metadata?: string }>` instead of
`Promise<void>`
- **`test/azure-modular-integration/payload-head.test.ts`** —
Integration test asserting headers are accessible on the returned object

```typescript
// Before: Promise<void> — headers inaccessible
// After: with include-headers-in-response: true
const result = await client.contentTypeHeaderInResponse();
assert.strictEqual(result.contentType, "text/plain; charset=utf-8");
assert.strictEqual(result.metadata, "hello");
```

The `include-headers-in-response` option is opt-in; this test makes the
per-service tspconfig the natural place to enable it, consistent with
existing usage in the storage data-plane specs.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: v-jiaodi <80496810+v-jiaodi@users.noreply.github.com>

Author: Copilot

.chronus/changes/typespec-ts-payload-head-spector-test-2026-7-1-5-0-0.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@azure-tools/typespec-ts"
+---
+
+Add spector integration test for `payload/head` HEAD operation with response headers, using `include-headers-in-response: true` to surface `contentType` and `metadata` headers in the return type.

packages/typespec-ts/test/azure-modular-integration/generated/payload/head/.gitignore

@@ -0,0 +1,6 @@
+/**
+!/src
+/src/**
+!/src/index.d.ts
+!/.gitignore
+!/tspconfig.yaml

packages/typespec-ts/test/azure-modular-integration/generated/payload/head/src/index.d.ts

@@ -0,0 +1,27 @@
+import { ClientOptions } from '@azure-rest/core-client';
+import { isRestError } from '@azure/core-rest-pipeline';
+import { OperationOptions } from '@azure-rest/core-client';
+import { Pipeline } from '@azure/core-rest-pipeline';
+import { RestError } from '@azure/core-rest-pipeline';
+
+export declare interface ContentTypeHeaderInResponseOptionalParams extends OperationOptions {
+}
+
+export declare class HeadClient {
+    private _client;
+    readonly pipeline: Pipeline;
+    constructor(options?: HeadClientOptionalParams);
+    contentTypeHeaderInResponse(options?: ContentTypeHeaderInResponseOptionalParams): Promise<{
+        contentType?: string;
+        metadata?: string;
+    }>;
+}
+
+export declare interface HeadClientOptionalParams extends ClientOptions {
+}
+
+export { isRestError }
+
+export { RestError }
+
+export { }

packages/typespec-ts/test/azure-modular-integration/generated/payload/head/tspconfig.yaml

@@ -0,0 +1,13 @@
+emit:
+  - "@azure-tools/typespec-ts"
+options:
+  "@azure-tools/typespec-ts":
+    emitter-output-dir: "{project-root}"
+    generate-metadata: true
+    generate-test: false
+    add-credentials: false
+    flavor: azure
+    include-headers-in-response: true
+    package-details:
+      name: "@msinternal/payload-head"
+      description: "Payload Head Test Service"

packages/typespec-ts/test/azure-modular-integration/payload-head.test.ts

@@ -0,0 +1,20 @@
+import { assert, beforeEach, describe, it } from "vitest";
+
+import { HeadClient } from "./generated/payload/head/src/index.js";
+
+describe("Payload Head Client", () => {
+  let client: HeadClient;
+
+  beforeEach(() => {
+    client = new HeadClient({
+      endpoint: "http://localhost:3002",
+      allowInsecureConnection: true,
+    });
+  });
+
+  it("should surface response headers for HEAD operation", async () => {
+    const result = await client.contentTypeHeaderInResponse();
+    assert.strictEqual(result.contentType, "text/plain; charset=utf-8");
+    assert.strictEqual(result.metadata, "hello");
+  });
+});

packages/typespec-ts/test/commands/spector-list.js

@@ -182,6 +182,10 @@ export const azureModularTsps = [
     outputPath: "payload/xml",
     inputPath: "payload/xml",
   },
+  {
+    outputPath: "payload/head",
+    inputPath: "payload/head",
+  },
   {
     outputPath: "server/versions/versioned",
     inputPath: "server/versions/versioned",