feat: add support for extendedAgentCard on client side

src/client/multitransport-client.ts

@@ -61,10 +61,17 @@ export interface RequestOptions {
 export class Client {
   constructor(
     public readonly transport: Transport,
-    public readonly agentCard: AgentCard,
+    public agentCard: AgentCard,
     public readonly config?: ClientConfig
   ) {}
 
+  async getAgentCard(): Promise<AgentCard> {
+    if (this.agentCard.supportsAuthenticatedExtendedCard) {
+      this.agentCard = await this.transport.getAuthenticatedExtendedAgentCard();
+    }
+    return this.agentCard;
+  }
+
   /**
    * Sends a message to an agent to initiate a new interaction or to continue an existing one.
    * Uses blocking mode by default.

src/client/transports/json_rpc_transport.ts

@@ -28,6 +28,7 @@ import {
   CancelTaskSuccessResponse,
   AgentCard,
   GetTaskPushNotificationConfigParams,
+  GetAuthenticatedExtendedCardSuccessResponse,
 } from '../../types.js';
 import { A2AStreamEventData, SendMessageResult } from '../client.js';
 import { RequestOptions } from '../multitransport-client.js';
@@ -48,6 +49,14 @@ export class JsonRpcTransport implements Transport {
     this.customFetchImpl = options.fetchImpl;
   }
 
+  async getAuthenticatedExtendedAgentCard(idOverride?: number): Promise<AgentCard> {
+    const rpcResponse = await this._sendRpcRequest<
+      unknown,
+      GetAuthenticatedExtendedCardSuccessResponse
+    >('agent/getAuthenticatedExtendedCard', {}, idOverride, undefined);
+    return rpcResponse.result;
+  }
+
   async sendMessage(
     params: MessageSendParams,
     options?: RequestOptions,

src/client/transports/transport.ts

@@ -13,6 +13,8 @@ import { A2AStreamEventData, SendMessageResult } from '../client.js';
 import { RequestOptions } from '../multitransport-client.js';
 
 export interface Transport {
+  getAuthenticatedExtendedAgentCard(): Promise<AgentCard>;
+
   sendMessage(params: MessageSendParams, options?: RequestOptions): Promise<SendMessageResult>;
 
   sendMessageStream(

test/client/factory.spec.ts

@@ -14,6 +14,7 @@ describe('ClientFactory', () => {
 
   beforeEach(() => {
     mockTransport = {
+      getAuthenticatedExtendedAgentCard: sinon.stub(),
       sendMessage: sinon.stub(),
       sendMessageStream: sinon.stub(),
       setTaskPushNotificationConfig: sinon.stub(),

test/client/multitransport-client.spec.ts

@@ -26,6 +26,7 @@ describe('Client', () => {
 
   beforeEach(() => {
     transport = {
+      getAuthenticatedExtendedAgentCard: sinon.stub(),
       sendMessage: sinon.stub(),
       sendMessageStream: sinon.stub(),
       setTaskPushNotificationConfig: sinon.stub(),
@@ -53,6 +54,21 @@ describe('Client', () => {
     client = new Client(transport, agentCard);
   });
 
+  it('should call transport.getAuthenticatedExtendedAgentCard', async () => {
+    const agentCardWithExtendedSupport = { ...agentCard, supportsAuthenticatedExtendedCard: true };
+    const extendedAgentCard: AgentCard = {
+      ...agentCard,
+      capabilities: { ...agentCard.capabilities, stateTransitionHistory: true },
+    };
+    client = new Client(transport, agentCardWithExtendedSupport);
+
+    transport.getAuthenticatedExtendedAgentCard.resolves(extendedAgentCard);
+    const result = await client.getAgentCard();
+
+    expect(transport.getAuthenticatedExtendedAgentCard.calledOnce).to.be.true;
+    expect(result).to.equal(extendedAgentCard);
+  });
+
   it('should call transport.sendMessage with default blocking=true', async () => {
     const params: MessageSendParams = {
       message: {