Scheduled prompts remain queued and do not fire

### Describe the bug

Scheduled prompts in GitHub Copilot CLI did not fire overnight. They appeared to remain queued/active, but no scheduled prompt was delivered back into the session and no assistant turn was started.

This looks like a regression from this week. I expected the scheduled monitor prompt to wake the agent every 20 minutes, but from ~23:04 to ~08:10 local time no scheduled prompt fired.

### Affected version

1.0.71-1

### Steps to reproduce the behavior

1. Start a Copilot CLI session on Windows.
2. Create a recurring scheduled prompt, for example every 20 minutes, intended to monitor a long-running task.
3. Confirm the schedule is listed as active.
4. Leave the session running overnight.
5. Observe that no scheduled prompt is delivered and the agent is not woken by the schedule. In my session, the prompt remained queued/active but no scheduled turns fired.

I saw this with two schedules during the same session:
- an every-15m monitor schedule created first, which appeared queued and did not fire
- an every-20m overnight monitor schedule created later, which also did not fire overnight

### Expected behavior

The scheduled prompt should be delivered at the configured interval and wake/start an assistant turn each time, or it should fail visibly if the schedule cannot execute.

### Additional context

- OS: Windows_NT
- Shell/tooling context: PowerShell-based Copilot CLI session
- Workaround used: a separate PowerShell monitor loop writing to a log, because the scheduled prompt did not wake the agent
- Impact: scheduled monitoring is unreliable for unattended long-running tasks; user expected results by morning and no schedule-fired checks occurred

Bắt đầu bằng cách tái hiện prompt được lên lịch lặp lại trong một phiên Windows PowerShell Copilot CLI, sử dụng các kịch bản qua đêm hoặc khoảng thời gian ngắn được mô tả trong issue. Theo dõi trình giám sát prompt được lên lịch và đường dẫn đánh thức phiên, sau đó xác minh rằng mỗi khoảng thời gian đã cấu hình đều gửi một prompt và bắt đầu một lượt của trợ lý, hoặc báo cáo lỗi thực thi có thể nhìn thấy.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.