fix(patch): cherry-pick 0135b03 to release/v0.33.0-preview.2-pr-21171 [CONFLICTS] (#21336)

Co-authored-by: Shreya Keshive <shreyakeshive@google.com>

packages/cli/src/acp/acpErrors.test.ts

@@ -0,0 +1,45 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { getAcpErrorMessage } from './acpErrors.js';
+
+describe('getAcpErrorMessage', () => {
+  it('should return plain error message', () => {
+    expect(getAcpErrorMessage(new Error('plain error'))).toBe('plain error');
+  });
+
+  it('should parse simple JSON error response', () => {
+    const json = JSON.stringify({ error: { message: 'json error' } });
+    expect(getAcpErrorMessage(new Error(json))).toBe('json error');
+  });
+
+  it('should parse double-encoded JSON error response', () => {
+    const innerJson = JSON.stringify({ error: { message: 'nested error' } });
+    const outerJson = JSON.stringify({ error: { message: innerJson } });
+    expect(getAcpErrorMessage(new Error(outerJson))).toBe('nested error');
+  });
+
+  it('should parse array-style JSON error response', () => {
+    const json = JSON.stringify([{ error: { message: 'array error' } }]);
+    expect(getAcpErrorMessage(new Error(json))).toBe('array error');
+  });
+
+  it('should parse JSON with top-level message field', () => {
+    const json = JSON.stringify({ message: 'top-level message' });
+    expect(getAcpErrorMessage(new Error(json))).toBe('top-level message');
+  });
+
+  it('should handle JSON with trailing newline', () => {
+    const json = JSON.stringify({ error: { message: 'newline error' } }) + '\n';
+    expect(getAcpErrorMessage(new Error(json))).toBe('newline error');
+  });
+
+  it('should return original message if JSON parsing fails', () => {
+    const invalidJson = '{ not-json }';
+    expect(getAcpErrorMessage(new Error(invalidJson))).toBe(invalidJson);
+  });
+});