From 12c8469b34c9b0bb3d61604f98250017d2bce59b Mon Sep 17 00:00:00 2001
From: Adam Weidman <65992621+adamfweidman@users.noreply.github.com>
Date: Fri, 8 May 2026 13:12:54 -0400
Subject: [PATCH] refactor(core): agent session protocol changes (#26661)

---
 packages/core/src/agent/content-utils.test.ts        | 9 ++++++++-
 packages/core/src/agent/content-utils.ts             | 4 ++++
 packages/core/src/agent/legacy-agent-session.test.ts | 1 +
 packages/core/src/agent/legacy-agent-session.ts      | 2 ++
 4 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/packages/core/src/agent/content-utils.test.ts b/packages/core/src/agent/content-utils.test.ts
index 7de54c56fa..acf8a4a329 100644
--- a/packages/core/src/agent/content-utils.test.ts
+++ b/packages/core/src/agent/content-utils.test.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, expect, it } from 'vitest';
+import { describe, expect, it, vi } from 'vitest';
 import {
   geminiPartsToContentParts,
   contentPartsToGeminiParts,
@@ -12,6 +12,7 @@ import {
 } from './content-utils.js';
 import type { Part } from '@google/genai';
 import type { ContentPart } from './types.js';
+import { debugLogger } from '../utils/debugLogger.js';
 
 describe('geminiPartsToContentParts', () => {
   it('converts text parts', () => {
@@ -191,11 +192,17 @@ describe('contentPartsToGeminiParts', () => {
     const content = [
       { type: 'custom_widget', payload: 123 },
     ] as unknown as ContentPart[];
+
+    const warnSpy = vi.spyOn(debugLogger, 'warn');
     const result = contentPartsToGeminiParts(content);
+
+    expect(warnSpy).toHaveBeenCalled();
     expect(result).toHaveLength(1);
     expect(result[0]).toEqual({
       text: JSON.stringify({ type: 'custom_widget', payload: 123 }),
     });
+
+    warnSpy.mockRestore();
   });
 });
 
diff --git a/packages/core/src/agent/content-utils.ts b/packages/core/src/agent/content-utils.ts
index aaf191fe8e..42b0b7fec7 100644
--- a/packages/core/src/agent/content-utils.ts
+++ b/packages/core/src/agent/content-utils.ts
@@ -6,6 +6,7 @@
 
 import type { Part } from '@google/genai';
 import type { ContentPart } from './types.js';
+import { debugLogger } from '../utils/debugLogger.js';
 
 /**
  * Converts Gemini API Part objects to framework-agnostic ContentPart objects.
@@ -93,6 +94,9 @@ export function contentPartsToGeminiParts(content: ContentPart[]): Part[] {
         result.push({ text: part.text });
         break;
       default:
+        debugLogger.warn(
+          `Unhandled ContentPart type: ${JSON.stringify(part)} fallback to serialization`,
+        );
         // Serialize unknown ContentPart variants instead of dropping them
         result.push({ text: JSON.stringify(part) });
         break;
diff --git a/packages/core/src/agent/legacy-agent-session.test.ts b/packages/core/src/agent/legacy-agent-session.test.ts
index db3c173983..525548e292 100644
--- a/packages/core/src/agent/legacy-agent-session.test.ts
+++ b/packages/core/src/agent/legacy-agent-session.test.ts
@@ -1330,6 +1330,7 @@ describe('LegacyAgentSession', () => {
       );
       expect(err?.message).toBe('Connection refused');
       expect(err?.fatal).toBe(true);
+      expect(err?._meta?.['stack']).toBeDefined();
 
       const streamEnd = events.find(
         (e): e is AgentEvent<'agent_end'> => e.type === 'agent_end',
diff --git a/packages/core/src/agent/legacy-agent-session.ts b/packages/core/src/agent/legacy-agent-session.ts
index d65c583b0b..e8d5e56ef5 100644
--- a/packages/core/src/agent/legacy-agent-session.ts
+++ b/packages/core/src/agent/legacy-agent-session.ts
@@ -166,6 +166,7 @@ export class LegacyAgentProtocol implements AgentProtocol {
       } else {
         this._emitErrorAndAgentEnd(err);
       }
+    } finally {
       this._clearActiveStream();
     }
   }
@@ -390,6 +391,7 @@ export class LegacyAgentProtocol implements AgentProtocol {
     const meta: Record<string, unknown> = {};
     if (err instanceof Error) {
       meta['errorName'] = err.constructor.name;
+      meta['stack'] = err.stack;
       if ('exitCode' in err && typeof err.exitCode === 'number') {
         meta['exitCode'] = err.exitCode;
       }