Agents window: follow-up prompt in completed Copilot CLI session is not dispatched and disappears after reopening

# Agents window: follow-up prompt in completed Copilot CLI session is not dispatched and disappears after reopening

- VS Code: 1.135.0
- Bundled Copilot CLI: 1.0.81-0
- OS: macOS, arm64
- Feature: Agents window, local Copilot CLI session

## Description

After a Copilot CLI session that ran for multiple hours completes normally, a follow-up prompt appears in the transcript but receives no response. After switching sessions and reopening the affected session, the prompt disappears.

## Steps to reproduce

1. Let a local Copilot CLI session complete.
2. Reopen it from the Agents window.
3. Submit a follow-up prompt.
4. Observe that no response arrives.
5. Switch sessions, then return.

## Expected

The prompt is persisted and dispatched, or an actionable error is shown.

## Actual

The prompt appears temporarily, receives no response, and disappears after reopening.

## Diagnostic evidence

The local session log records the reopen and subsequent routine shutdown, but no corresponding user message, assistant turn, tool call, permission request, or error. The agent-host process remains alive and the previous turn completed cleanly.

Raw logs cannot be shared because they contain confidential information.

Related but different reports: #322314, #327029, and #332648.

Reproduce the issue in the Agents window with a completed local Copilot CLI session, then inspect the session log around reopening and submitting the follow-up prompt. Trace whether the prompt is persisted or dispatched; done means it receives a response or an actionable error and remains present after switching sessions.

Written by the indexing model from the issue text.