Agents window does not show the TODO checklist in Agent mode

- Copilot Chat Extension Version: Not provided
- VS Code Version: Not provided
- OS Version: Windows
- Feature: Agents window / Agent mode
- Selected model: GPT-5.6 Luna

## Steps to Reproduce

1. Open the VS Code Agents window.
2. Start a new session in Agent mode.
3. Ask Copilot to perform a task involving multiple steps that produces a TODO list.
4. Observe the Agents window while the agent works.

## Actual Behavior

The Agents window does not display the TODO checklist or task progress list. There is no visible list of pending and completed items, and no progress count for the current agent task.

## Expected Behavior

The Agents window should display the agent's TODO checklist, including pending, active, and completed items, with the progress count updated as the agent works.

## Impact

Without the checklist, users cannot tell which planned steps have been completed, what the agent is currently doing, or whether any tasks remain.

Related issues:
- #322561 — Agent Todos aren't showing as done
- #314703 — Copilot Chat - Todos Never update

This TODO check list is completely missing in Agent mode. It's available for Local harness tho.