Stale stdin bytes leak to shell after exit on POSIX (space on prompt, blocks ctrl+d) #17081

Description

After exiting opencode on Linux/macOS, stale bytes sometimes remain in the kernel's tty input buffer and are read by the parent shell. The most common symptom is a space character appearing on the shell prompt line, which blocks ctrl+d (EOF) from terminating the shell since readline requires an empty line.

Related Issues

• After exiting opencode, there is residual output left on the screen. #12257 — residual output after exit (Alacritty + tmux + Fish)
• macOS: Terminal becomes unusable after opencode exits ("dead terminal") #7861 — terminal unusable after exit on macOS
• OpenCode for macOS displays garbled characters upon exit. #15084 — garbled characters ("ppppp") after Ctrl+C exit on macOS
• bug: exiting tui on windows has improper exit sequence handling #5070 — escape codes leak after exit on Windows (git bash)
• After using /exit to exit opencode and then using exit to exit the PowerShell terminal, the terminal gets stuck. #8395 — PowerShell terminal hangs after /exit

Root Cause

During @opentui/core's finalizeDestroy(), the stdin data listener is removed and raw mode is disabled, but the kernel's tty input buffer is not flushed. Any bytes that arrived between the last stdin read and the mode switch (e.g. key release events from the Kitty keyboard protocol, or other in-flight terminal data) persist in the cooked-mode line discipline buffer. When the process exits, the shell inherits these bytes.

On Windows this was already handled — win32FlushInputBuffer() calls FlushConsoleInputBuffer via kernel32 FFI after renderer.destroy(). There was no POSIX equivalent.

Notably, @opentui/core's own resume() method drains stdin (while (this.stdin.read() !== null) {}), but finalizeDestroy() does not — nor does it call stdin.pause() like suspend() does.

Fix

Add a cross-platform flushInputBuffer() that calls tcflush(STDIN_FILENO, TCIFLUSH) on POSIX via libc FFI (libc.so.6 on Linux, libSystem.B.dylib on macOS), alongside the existing Windows FlushConsoleInputBuffer path. Call it after renderer.destroy() in both exit paths (exit.tsx and the ErrorComponent in app.tsx).

Also rename win32.ts → console.ts since it now contains cross-platform code, and drop the win32 prefix from flushInputBuffer (the two Windows-only functions retain their prefix).

Environment

• OS: Linux (also affects macOS)
• Terminal: Konsole (likely affects most terminals)
• Shell: Any (readline sees the stale bytes)