GitHub Copilot chat "Copy All" does nothing in one chat

I need to extract and save a chat conversation. Usually I use "Copy All":

1. Open a long chat.
2. Right click on the chat.
3. Select "Copy All".

**Expected:** The entire chat is copied to the clipboard as Markdown.

**Actual:** Nothing happens for about six seconds. _The context menu even stays on the screen._ Then the context menu goes away, but nothing was added to the clipboard. If I then paste in another editor, what is pasted is what was already in the clipboard.

There is no error message or anything

This is completely different behavior from #302908, which actually put something in the clipboard but truncated it.

```
Version: 1.136.2 (user setup)
Commit: 88e44fa0e00b08f7758b4f6d05632e4fd5e4df6f
Date: 2026-09-04T21:40:42Z
Electron: 42.10.0
ElectronBuildId: 15109253
Chromium: 148.0.7778.280
Node.js: 24.18.1
V8: 14.8.178.38-electron.0
@github/copilot: 1.0.81-0
@github/copilot-sdk: 1.0.11
OS: Windows_NT x64 10.0.26200
```