fix(agent-office): render TaskTab result_data when it's already an object

Old code assumed result_data was a JSON string and ran JSON.parse on it,
falling back to returning the value verbatim on parse error. When the
backend ships result_data as a dict (e.g. compose tasks return
{music_task_id, tracks}), JSON.parse threw, the catch returned the raw
object, and React threw error #31 'Objects are not valid as a React
child' the moment the user expanded the task row.

Extract formatResultData helper: object → JSON.stringify, JSON string
→ parse then pretty-print, plain string → as-is.

Regression tests cover all three input shapes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pages/agent-office/components/TaskTab.jsx

@@ -11,6 +11,22 @@ const STATUS_STYLE = {
   rejected:  { bg: '#7f1d1d', fg: '#fca5a5' }
 };
 
+// result_data는 백엔드에서 dict 또는 string 둘 다 올 수 있다.
+// React child로 직접 못 그리는 객체는 stringify, string은 parse 시도 후 pretty,
+// 둘 다 안 되면 원본 문자열을 그대로 표시.
+function formatResultData(rd) {
+  if (rd == null) return '';
+  if (typeof rd === 'object') {
+    try { return JSON.stringify(rd, null, 2); }
+    catch { return String(rd); }
+  }
+  if (typeof rd === 'string') {
+    try { return JSON.stringify(JSON.parse(rd), null, 2); }
+    catch { return rd; }
+  }
+  return String(rd);
+}
+
 function formatTime(ts) {
   if (!ts) return '';
   const d = new Date(ts);
@@ -46,10 +62,7 @@ export default function TaskTab({ agentId, refreshTrigger }) {
             </div>
             {expanded === task.id && task.result_data && (
               <pre className="ao-task-result">
-                {(() => {
-                  try { return JSON.stringify(JSON.parse(task.result_data), null, 2); }
-                  catch { return task.result_data; }
-                })()}
+                {formatResultData(task.result_data)}
               </pre>
             )}
           </div>

src/pages/agent-office/components/TaskTab.test.jsx

@@ -1,5 +1,5 @@
 import { describe, it, expect, vi } from 'vitest';
-import { render, screen, waitFor } from '@testing-library/react';
+import { render, screen, waitFor, fireEvent } from '@testing-library/react';
 import TaskTab from './TaskTab.jsx';
 
 const mockGetAgentTasks = vi.fn();
@@ -33,4 +33,55 @@ describe('TaskTab response shape handling', () => {
     render(<TaskTab agentId="music" refreshTrigger={0} />);
     await waitFor(() => expect(screen.getByText('No tasks yet')).toBeInTheDocument());
   });
+
+  it('task 클릭 → result_data가 객체일 때도 stringify되어 안전하게 렌더', async () => {
+    mockGetAgentTasks.mockResolvedValueOnce({
+      tasks: [{
+        id: 't_compose',
+        task_type: 'compose',
+        status: 'succeeded',
+        created_at: '2026-05-18T08:00:00Z',
+        result_data: { music_task_id: 'abc-123', tracks: [] },
+      }],
+    });
+    render(<TaskTab agentId="music" refreshTrigger={0} />);
+    const row = await screen.findByText('compose');
+    fireEvent.click(row.closest('.ao-task-item'));
+    const pre = await screen.findByText(/music_task_id/);
+    expect(pre.textContent).toContain('"music_task_id": "abc-123"');
+    expect(pre.textContent).toContain('"tracks": []');
+  });
+
+  it('task 클릭 → result_data가 JSON 문자열일 때 parse 후 pretty 렌더', async () => {
+    mockGetAgentTasks.mockResolvedValueOnce({
+      tasks: [{
+        id: 't_str',
+        task_type: 'compose',
+        status: 'succeeded',
+        created_at: '2026-05-18T08:00:00Z',
+        result_data: '{"foo":"bar"}',
+      }],
+    });
+    render(<TaskTab agentId="music" refreshTrigger={0} />);
+    const row = await screen.findByText('compose');
+    fireEvent.click(row.closest('.ao-task-item'));
+    const pre = await screen.findByText(/foo/);
+    expect(pre.textContent).toContain('"foo": "bar"');
+  });
+
+  it('task 클릭 → result_data가 plain string이면 그대로 표시 (parse 실패 fallback)', async () => {
+    mockGetAgentTasks.mockResolvedValueOnce({
+      tasks: [{
+        id: 't_plain',
+        task_type: 'fetch_news',
+        status: 'succeeded',
+        created_at: '2026-05-18T08:00:00Z',
+        result_data: 'Just a log line',
+      }],
+    });
+    render(<TaskTab agentId="music" refreshTrigger={0} />);
+    const row = await screen.findByText('fetch_news');
+    fireEvent.click(row.closest('.ao-task-item'));
+    expect(await screen.findByText('Just a log line')).toBeInTheDocument();
+  });
 });