diff --git a/packages/core/src/agents/a2aUtils.test.ts b/packages/core/src/agents/a2aUtils.test.ts
index f0ea746025..2bcdad2c40 100644
--- a/packages/core/src/agents/a2aUtils.test.ts
+++ b/packages/core/src/agents/a2aUtils.test.ts
@@ -10,6 +10,7 @@ import {
   extractIdsFromResponse,
   isTerminalState,
   A2AResultReassembler,
+  AUTH_REQUIRED_MSG,
 } from './a2aUtils.js';
 import type { SendMessageResult } from './a2a-client-manager.js';
 import type {
@@ -285,6 +286,66 @@ describe('a2aUtils', () => {
       );
     });
 
+    it('should handle auth-required state with a message', () => {
+      const reassembler = new A2AResultReassembler();
+
+      reassembler.update({
+        kind: 'status-update',
+        status: {
+          state: 'auth-required',
+          message: {
+            kind: 'message',
+            role: 'agent',
+            parts: [{ kind: 'text', text: 'I need your permission.' }],
+          } as Message,
+        },
+      } as unknown as SendMessageResult);
+
+      expect(reassembler.toString()).toContain('I need your permission.');
+      expect(reassembler.toString()).toContain(AUTH_REQUIRED_MSG);
+    });
+
+    it('should handle auth-required state without relying on metadata', () => {
+      const reassembler = new A2AResultReassembler();
+
+      reassembler.update({
+        kind: 'status-update',
+        status: {
+          state: 'auth-required',
+        },
+      } as unknown as SendMessageResult);
+
+      expect(reassembler.toString()).toContain(AUTH_REQUIRED_MSG);
+    });
+
+    it('should not duplicate the auth instruction OR agent message if multiple identical auth-required chunks arrive', () => {
+      const reassembler = new A2AResultReassembler();
+
+      const chunk = {
+        kind: 'status-update',
+        status: {
+          state: 'auth-required',
+          message: {
+            kind: 'message',
+            role: 'agent',
+            parts: [{ kind: 'text', text: 'You need to login here.' }],
+          } as Message,
+        },
+      } as unknown as SendMessageResult;
+
+      reassembler.update(chunk);
+      // Simulate multiple updates with the same overall state
+      reassembler.update(chunk);
+      reassembler.update(chunk);
+
+      const output = reassembler.toString();
+      // The substring should only appear exactly once
+      expect(output.split(AUTH_REQUIRED_MSG).length - 1).toBe(1);
+
+      // Crucially, the agent's actual custom message should ALSO only appear exactly once
+      expect(output.split('You need to login here.').length - 1).toBe(1);
+    });
+
     it('should fallback to history in a task chunk if no message or artifacts exist and task is terminal', () => {
       const reassembler = new A2AResultReassembler();
 
diff --git a/packages/core/src/agents/a2aUtils.ts b/packages/core/src/agents/a2aUtils.ts
index 52817f4971..dc39f4e660 100644
--- a/packages/core/src/agents/a2aUtils.ts
+++ b/packages/core/src/agents/a2aUtils.ts
@@ -16,6 +16,8 @@ import type {
 } from '@a2a-js/sdk';
 import type { SendMessageResult } from './a2a-client-manager.js';
 
+export const AUTH_REQUIRED_MSG = `[Authorization Required] The agent has indicated it requires authorization to proceed. Please follow the agent's instructions.`;
+
 /**
  * Reassembles incremental A2A streaming updates into a coherent result.
  * Shows sequential status/messages followed by all reassembled artifacts.
@@ -33,6 +35,7 @@ export class A2AResultReassembler {
 
     switch (chunk.kind) {
       case 'status-update':
+        this.appendStateInstructions(chunk.status?.state);
         this.pushMessage(chunk.status?.message);
         break;
 
@@ -65,6 +68,7 @@ export class A2AResultReassembler {
         break;
 
       case 'task':
+        this.appendStateInstructions(chunk.status?.state);
         this.pushMessage(chunk.status?.message);
         if (chunk.artifacts) {
           for (const art of chunk.artifacts) {
@@ -106,6 +110,17 @@ export class A2AResultReassembler {
     }
   }
 
+  private appendStateInstructions(state: TaskState | undefined) {
+    if (state !== 'auth-required') {
+      return;
+    }
+
+    // Prevent duplicate instructions if multiple chunks report auth-required
+    if (!this.messageLog.includes(AUTH_REQUIRED_MSG)) {
+      this.messageLog.push(AUTH_REQUIRED_MSG);
+    }
+  }
+
   private pushMessage(message: Message | undefined) {
     if (!message) return;
     const text = extractPartsText(message.parts, '\n');