Windows Terminal key-binding offer is preselected "Yes", so the first Enter of a typed prompt rewrites Windows Terminal settings.json

[glmn]

Describe the bug

When Copilot CLI starts inside Windows Terminal (WT_SESSION is set), it shows the modal "Set up terminal for multi-line input support" right after the folder-trust dialog, with "1. Yes" preselected. The modal takes focus without any keystroke from the user, so if the user (or a program driving the CLI in a pseudo-terminal) starts typing a prompt, the letters are dropped and the first Enter accepts the offer. Copilot then rewrites the user's global Windows Terminal settings.json (adds a shift+enter → sendInput "\u001b\r" action) and the typed prompt is lost.

So a global terminal config file is edited by an Enter that was meant to submit a prompt. It is easy to hit when the CLI runs in an embedded/nested terminal (an editor panel, a terminal multiplexer, or a desktop app that hosts terminals) that inherits WT_SESSION from the parent Windows Terminal. A backup file is written, but the user never saw the question.

Affected version

1.0.93

Steps to reproduce the behavior

To avoid touching a real config, point LOCALAPPDATA at an empty folder with a stub Windows Terminal settings file:

1. Create <tmp>\la\Packages\Microsoft.WindowsTerminal_8wekyb3d8bbwe\LocalState\settings.json containing { "profiles": { "list": [] }, "actions": [] }.
2. In a terminal (any pty), set LOCALAPPDATA=<tmp>\la, COPILOT_HOME=<tmp>\home, WT_SESSION=<any guid>, and a BYOK provider (COPILOT_PROVIDER_BASE_URL, COPILOT_PROVIDER_API_KEY, COPILOT_MODEL) so no login is needed.
3. Run copilot in a new folder and answer the folder-trust dialog with Enter ("1. Yes").
4. The "Set up terminal for multi-line input support" modal appears with "1. Yes" selected.
5. Type hello and press Enter, as you would for a first prompt.

Result: "Updated Windows Terminal key bindings: added key binding for shift+enter." The stub settings.json now has the new actions entry and a settings.json.<timestamp>.backup is next to it; hello never reaches the prompt.

Expected behavior

One of:

• the offer defaults to "No" (or requires an explicit choice such as y), so a stray Enter cannot change a global config file;
• the offer is shown as a non-modal hint (e.g. "run /terminal-setup to enable Shift+Enter") instead of a modal at startup;
• the offer is skipped when stdin is not the Windows Terminal session itself (e.g. the CLI is a child of another terminal host).

COPILOT_SETUP_TERMINAL=false turns the offer off, which is what we use now, but it is not documented in copilot help environment as far as I can see, so other hosts will hit this.

Additional context

• Windows 10 22H2 (19045), x64
• Found while running Copilot CLI in a pty-hosted terminal inside a desktop app (NeuroSquad) started from Windows Terminal; reproduced above with a plain pty and a stub settings file.
• Related: /terminal-setup inside Dev Container and Codespaces writes keybindings to wrong file #657 (/terminal-setup writing keybindings to the wrong file in containers).