Console left in raw/VT mode after copilot.exe exits - arrow keys show `^[[A` (Windows)

[machish]

Describe the bug

Description:

After copilot.exe exits (normally or abnormally), the Windows console is sometimes left in virtual terminal input mode instead of being restored to the default cooked mode.

Symptoms:

- Pressing Up arrow shows ^[[A instead of navigating command history
- Pressing Down arrow shows ^[[B
- Backspace behaves like Ctrl+Backspace (deletes whole words)
- Other arrow keys show their escape sequences (^[[C, ^[[D)

Workaround:

Running any external executable (e.g., xcopy a a ) restores normal console behavior.

Root Cause (as analyzed by Copilot):

The application enables ENABLE_VIRTUAL_TERMINAL_INPUT via SetConsoleMode() but fails to restore the original console mode on exit. This can happen if:

- The process is terminated unexpectedly
- Signal handlers don't properly clean up
- There's a race condition in the cleanup code

Expected Behaviour:

Console input mode should be saved on startup and restored on exit (including via atexit handlers and signal handlers for SIGINT/SIGTERM).

Environment:

- OS: Windows
- Shell: cmd

Affected version

GitHub Copilot CLI 0.0.407-1.

Steps to reproduce the behavior

• Leave Copilot running for a while (e.g. overnight)
• Have it abruptly exit (timeout?)
• Console is left in a state where cursor keys output Escape sequences (e.g. ^[[A), backspace acts as ctrl+backpace.

Expected behavior

Console should behave normally.

Additional context

- OS: Windows
- Shell: cmd
- Chip: `x86-64`
- Console: Classing windows console (NOT windows terminal)