[Windows] Raw ANSI escape codes printed after Ctrl+C exit #13301

Description

On Windows, pressing Ctrl+C to exit the application causes raw ANSI escape sequences (color codes) to be printed to the terminal after the process terminates. Exiting via the exit command works cleanly without this issue.

Root Cause

The @opentui/core renderer registers SIGINT (and other signal) handlers by default via addExitListeners(). On Windows, the app disables ENABLE_PROCESSED_INPUT so that Ctrl+C is delivered as a keyboard event instead of a signal. However, a race condition exists in the 100ms polling guard — Bun's runtime can momentarily re-enable the flag between polls. When Ctrl+C is pressed during this window, it generates SIGINT instead of a keyboard event, and opentui's handler calls renderer.destroy() directly, bypassing the app's graceful exit flow (process.exit, unguard, worker shutdown).

Steps to reproduce

1. Run opencode on Windows (PowerShell or Windows Terminal)
2. Press Ctrl+C to exit
3. Observe raw ANSI escape codes printed in the terminal after exit

Expected behavior

The application should exit cleanly without printing any ANSI escape codes, the same as when using the exit command.

OpenCode version

v1.1.60

Operating System

Windows 11

Terminal

Windows Terminal / PowerShell