chore: Append language to user-agent header

FUTURE_COPYBARA_INTEGRATE_REVIEW=#596 from googleapis:release-please--branches--main--components--vertexai 489440d
PiperOrigin-RevId: 900425828

Author: sararob

src/genai/client.ts

@@ -35,7 +35,8 @@ export class Client {
       vertexai: true,
       httpOptions: options.apiEndpoint ? {baseUrl: options.apiEndpoint} :
                                          undefined,
-      userAgentExtra: `vertex-genai-modules/${SDK_VERSION}`,
+      userAgentExtra:
+          `vertex-genai-modules/${SDK_VERSION}`,  // gl-node/${process.version}
     });
 
     this._agentEnginesInternal = new AgentEngines(this.apiClient);

test/genai/_replay_client.ts

@@ -86,6 +86,18 @@ export class ReplayClient extends Client {
     }
 
     const [url, init] = actualArgs;
+
+
+    const actualHeaders = new Headers(init?.headers || {});
+    const xGoogApiClient = actualHeaders.get('x-goog-api-client') || '';
+    const userAgent = actualHeaders.get('user-agent') || '';
+
+    // Validate that the required identifiers are present
+    expect(xGoogApiClient).toContain('vertex-genai-modules/');
+    expect(xGoogApiClient).toContain('gl-node/');
+    expect(userAgent).toContain('vertex-genai-modules/');
+    expect(userAgent).toContain('gl-node/');
+
     const normalizedActual = normalizeRequest(init || {}, url.toString());
     assertMessagesEqual(normalizedActual, expectedRequestCamel);
   }