feat(core): improve subagent result display (#20378)

packages/core/src/agents/browser/browserAgentInvocation.ts

@@ -17,6 +17,7 @@
 import { randomUUID } from 'node:crypto';
 import type { Config } from '../../config/config.js';
 import { LocalAgentExecutor } from '../local-executor.js';
+import { safeJsonToMarkdown } from '../../utils/markdownUtils.js';
 import {
   BaseToolInvocation,
   type ToolResult,
@@ -414,6 +415,8 @@ export class BrowserAgentInvocation extends BaseToolInvocation<
 
       const output = await executor.run(this.params, signal);
 
+      const displayResult = safeJsonToMarkdown(output.result);
+
       const resultContent = `Browser agent finished.
 Termination Reason: ${output.terminate_reason}
 Result:
@@ -425,7 +428,7 @@ Browser Agent Finished
 Termination Reason: ${output.terminate_reason}
 
 Result:
-${output.result}
+${displayResult}
 `;
 
       if (updateOutput) {

packages/core/src/agents/local-invocation.ts

@@ -6,6 +6,7 @@
 
 import type { Config } from '../config/config.js';
 import { LocalAgentExecutor } from './local-executor.js';
+import { safeJsonToMarkdown } from '../utils/markdownUtils.js';
 import {
   BaseToolInvocation,
   type ToolResult,
@@ -245,6 +246,8 @@ export class LocalSubagentInvocation extends BaseToolInvocation<
         throw cancelError;
       }
 
+      const displayResult = safeJsonToMarkdown(output.result);
+
       const resultContent = `Subagent '${this.definition.name}' finished.
 Termination Reason: ${output.terminate_reason}
 Result:
@@ -256,7 +259,7 @@ Subagent ${this.definition.name} Finished
 Termination Reason:\n ${output.terminate_reason}
 
 Result:
-${output.result}
+${displayResult}
 `;
 
       return {

packages/core/src/agents/remote-invocation.ts

@@ -25,6 +25,7 @@ import { extractIdsFromResponse, A2AResultReassembler } from './a2aUtils.js';
 import { GoogleAuth } from 'google-auth-library';
 import type { AuthenticationHandler } from '@a2a-js/sdk/client';
 import { debugLogger } from '../utils/debugLogger.js';
+import { safeJsonToMarkdown } from '../utils/markdownUtils.js';
 import type { AnsiOutput } from '../utils/terminalSerializer.js';
 import { A2AAuthProviderFactory } from './auth-provider/factory.js';
 
@@ -222,7 +223,7 @@ export class RemoteAgentInvocation extends BaseToolInvocation<
 
       return {
         llmContent: [{ text: finalOutput }],
-        returnDisplay: finalOutput,
+        returnDisplay: safeJsonToMarkdown(finalOutput),
       };
     } catch (error: unknown) {
       const partialOutput = reassembler.toString();

packages/core/src/services/keychainService.ts

@@ -13,6 +13,7 @@ import {
   KeychainSchema,
   KEYCHAIN_TEST_PREFIX,
 } from './keychainTypes.js';
+import { isRecord } from '../utils/markdownUtils.js';
 
 /**
  * Service for interacting with OS-level secure storage (e.g. keytar).
@@ -111,7 +112,7 @@ export class KeychainService {
   private async loadKeychainModule(): Promise<Keychain | null> {
     const moduleName = 'keytar';
     const module: unknown = await import(moduleName);
-    const potential = (this.isRecord(module) && module['default']) || module;
+    const potential = (isRecord(module) && module['default']) || module;
 
     const result = KeychainSchema.safeParse(potential);
     if (result.success) {
@@ -126,10 +127,6 @@ export class KeychainService {
     return null;
   }
 
-  private isRecord(obj: unknown): obj is Record<string, unknown> {
-    return typeof obj === 'object' && obj !== null;
-  }
-
   // Performs a set-get-delete cycle to verify keychain functionality.
   private async isKeychainFunctional(keychain: Keychain): Promise<boolean> {
     const testAccount = `${KEYCHAIN_TEST_PREFIX}${crypto.randomBytes(8).toString('hex')}`;

packages/core/src/utils/markdownUtils.test.ts

@@ -0,0 +1,128 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect, it } from 'vitest';
+import { jsonToMarkdown, safeJsonToMarkdown } from './markdownUtils.js';
+
+describe('markdownUtils', () => {
+  describe('jsonToMarkdown', () => {
+    it('should handle primitives', () => {
+      expect(jsonToMarkdown('hello')).toBe('hello');
+      expect(jsonToMarkdown(123)).toBe('123');
+      expect(jsonToMarkdown(true)).toBe('true');
+      expect(jsonToMarkdown(null)).toBe('null');
+      expect(jsonToMarkdown(undefined)).toBe('undefined');
+    });
+
+    it('should handle simple arrays', () => {
+      const data = ['a', 'b', 'c'];
+      expect(jsonToMarkdown(data)).toBe('- a\n- b\n- c');
+    });
+
+    it('should handle simple objects and convert camelCase to Space Case', () => {
+      const data = { userName: 'Alice', userAge: 30 };
+      expect(jsonToMarkdown(data)).toBe(
+        '- **User Name**: Alice\n- **User Age**: 30',
+      );
+    });
+
+    it('should handle empty structures', () => {
+      expect(jsonToMarkdown([])).toBe('[]');
+      expect(jsonToMarkdown({})).toBe('{}');
+    });
+
+    it('should handle nested structures with proper indentation', () => {
+      const data = {
+        userInfo: {
+          fullName: 'Bob Smith',
+          userRoles: ['admin', 'user'],
+        },
+        isActive: true,
+      };
+      const result = jsonToMarkdown(data);
+      expect(result).toBe(
+        '- **User Info**:\n' +
+          '  - **Full Name**: Bob Smith\n' +
+          '  - **User Roles**:\n' +
+          '    - admin\n' +
+          '    - user\n' +
+          '- **Is Active**: true',
+      );
+    });
+
+    it('should render tables for arrays of similar objects with Space Case keys', () => {
+      const data = [
+        { userId: 1, userName: 'Item 1' },
+        { userId: 2, userName: 'Item 2' },
+      ];
+      const result = jsonToMarkdown(data);
+      expect(result).toBe(
+        '| User Id | User Name |\n| --- | --- |\n| 1 | Item 1 |\n| 2 | Item 2 |',
+      );
+    });
+
+    it('should handle pipe characters, backslashes, and newlines in table data', () => {
+      const data = [
+        { colInfo: 'val|ue', otherInfo: 'line\nbreak', pathInfo: 'C:\\test' },
+      ];
+      const result = jsonToMarkdown(data);
+      expect(result).toBe(
+        '| Col Info | Other Info | Path Info |\n| --- | --- | --- |\n| val\\|ue | line break | C:\\\\test |',
+      );
+    });
+
+    it('should fallback to lists for arrays with mixed objects', () => {
+      const data = [
+        { userId: 1, userName: 'Item 1' },
+        { userId: 2, somethingElse: 'Item 2' },
+      ];
+      const result = jsonToMarkdown(data);
+      expect(result).toContain('- **User Id**: 1');
+      expect(result).toContain('- **Something Else**: Item 2');
+    });
+
+    it('should properly indent nested tables', () => {
+      const data = {
+        items: [
+          { id: 1, name: 'A' },
+          { id: 2, name: 'B' },
+        ],
+      };
+      const result = jsonToMarkdown(data);
+      const lines = result.split('\n');
+      expect(lines[0]).toBe('- **Items**:');
+      expect(lines[1]).toBe('  | Id | Name |');
+      expect(lines[2]).toBe('  | --- | --- |');
+      expect(lines[3]).toBe('  | 1 | A |');
+      expect(lines[4]).toBe('  | 2 | B |');
+    });
+
+    it('should indent subsequent lines of multiline strings', () => {
+      const data = {
+        description: 'Line 1\nLine 2\nLine 3',
+      };
+      const result = jsonToMarkdown(data);
+      expect(result).toBe('- **Description**: Line 1\n  Line 2\n  Line 3');
+    });
+  });
+
+  describe('safeJsonToMarkdown', () => {
+    it('should convert valid JSON', () => {
+      const json = JSON.stringify({ keyName: 'value' });
+      expect(safeJsonToMarkdown(json)).toBe('- **Key Name**: value');
+    });
+
+    it('should return original string for invalid JSON', () => {
+      const notJson = 'Not a JSON string';
+      expect(safeJsonToMarkdown(notJson)).toBe(notJson);
+    });
+
+    it('should handle plain strings that look like numbers or booleans but are valid JSON', () => {
+      expect(safeJsonToMarkdown('123')).toBe('123');
+      expect(safeJsonToMarkdown('true')).toBe('true');
+    });
+  });
+});

packages/core/src/utils/markdownUtils.ts

@@ -0,0 +1,147 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Converts a camelCase string to a Space Case string.
+ * e.g., "camelCaseString" -> "Camel Case String"
+ */
+function camelToSpace(text: string): string {
+  const result = text.replace(/([A-Z])/g, ' $1');
+  return result.charAt(0).toUpperCase() + result.slice(1).trim();
+}
+
+/**
+ * Converts a JSON-compatible value into a readable Markdown representation.
+ *
+ * @param data The data to convert.
+ * @param indent The current indentation level (for internal recursion).
+ * @returns A Markdown string representing the data.
+ */
+export function jsonToMarkdown(data: unknown, indent = 0): string {
+  const spacing = '  '.repeat(indent);
+
+  if (data === null) {
+    return 'null';
+  }
+
+  if (data === undefined) {
+    return 'undefined';
+  }
+
+  if (Array.isArray(data)) {
+    if (data.length === 0) {
+      return '[]';
+    }
+
+    if (isArrayOfSimilarObjects(data)) {
+      return renderTable(data, indent);
+    }
+
+    return data
+      .map((item) => {
+        if (
+          typeof item === 'object' &&
+          item !== null &&
+          Object.keys(item).length > 0
+        ) {
+          const rendered = jsonToMarkdown(item, indent + 1);
+          return `${spacing}-\n${rendered}`;
+        }
+        const rendered = jsonToMarkdown(item, indent + 1).trimStart();
+        return `${spacing}- ${rendered}`;
+      })
+      .join('\n');
+  }
+
+  if (typeof data === 'object') {
+    const entries = Object.entries(data);
+    if (entries.length === 0) {
+      return '{}';
+    }
+
+    return entries
+      .map(([key, value]) => {
+        const displayKey = camelToSpace(key);
+        if (
+          typeof value === 'object' &&
+          value !== null &&
+          Object.keys(value).length > 0
+        ) {
+          const renderedValue = jsonToMarkdown(value, indent + 1);
+          return `${spacing}- **${displayKey}**:\n${renderedValue}`;
+        }
+        const renderedValue = jsonToMarkdown(value, indent + 1).trimStart();
+        return `${spacing}- **${displayKey}**: ${renderedValue}`;
+      })
+      .join('\n');
+  }
+
+  if (typeof data === 'string') {
+    return data
+      .split('\n')
+      .map((line, i) => (i === 0 ? line : spacing + line))
+      .join('\n');
+  }
+
+  return String(data);
+}
+
+/**
+ * Safely attempts to parse a string as JSON and convert it to Markdown.
+ * If parsing fails, returns the original string.
+ *
+ * @param text The text to potentially convert.
+ * @returns The Markdown representation or the original text.
+ */
+export function safeJsonToMarkdown(text: string): string {
+  try {
+    const parsed: unknown = JSON.parse(text);
+    return jsonToMarkdown(parsed);
+  } catch {
+    return text;
+  }
+}
+
+export function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+function isArrayOfSimilarObjects(
+  data: unknown[],
+): data is Array<Record<string, unknown>> {
+  if (data.length === 0) {
+    return false;
+  }
+  if (!data.every(isRecord)) return false;
+  const firstKeys = Object.keys(data[0]).sort().join(',');
+  return data.every((item) => Object.keys(item).sort().join(',') === firstKeys);
+}
+
+function renderTable(data: Array<Record<string, unknown>>, indent = 0): string {
+  const spacing = '  '.repeat(indent);
+  const keys = Object.keys(data[0]);
+  const displayKeys = keys.map(camelToSpace);
+  const header = `${spacing}| ${displayKeys.join(' | ')} |`;
+  const separator = `${spacing}| ${keys.map(() => '---').join(' | ')} |`;
+  const rows = data.map(
+    (item) =>
+      `${spacing}| ${keys
+        .map((key) => {
+          const val = item[key];
+          if (typeof val === 'object' && val !== null) {
+            return JSON.stringify(val)
+              .replace(/\\/g, '\\\\')
+              .replace(/\|/g, '\\|');
+          }
+          return String(val)
+            .replace(/\\/g, '\\\\')
+            .replace(/\|/g, '\\|')
+            .replace(/\n/g, ' ');
+        })
+        .join(' | ')} |`,
+  );
+  return [header, separator, ...rows].join('\n');
+}