Unable to Open CLI Chat from Copilot Session Pane (Right Side) Error: Failed to open chat session: Illegal argument: character must be non-negative

### Describe the bug

I am unable to open a CLI chat from the Copilot session panel on the right side of VS Code.
Whenever I try, the following error is shown:

Failed to open chat session: Illegal argument: character must be non-negative
This blocks me from starting a CLI chat session from the Copilot UI.

### Affected version

GitHub Copilot CLI 1.0.61.

### Steps to reproduce the behavior

1. Open VS Code.
2. Open Copilot chat/session panel on the right side.
3. Attempt to start or open a CLI chat session.
4. Observe the error popup/message.

### Expected behavior

A new CLI chat session should open successfully.

### Additional context

The operation fails with:
Failed to open chat session: Illegal argument: character must be non-negative

similar to this one: https://github.com/microsoft/vscode/issues/319726

Start by reproducing the failure in VS Code with GitHub Copilot CLI 1.0.61 from the right-side Copilot session panel, then compare the behavior with the linked VS Code issue. Trace the CLI chat-session opening entry point and identify where the non-negative character argument is produced; done means a new CLI chat opens successfully without the error.

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