fix(tui v2): stop tool subprocesses inheriting TTY stdin (multi-session key-eating on macOS/Linux)

[ggandmee-cloud]

Symptom

Running ga tui2 with several concurrent sessions on macOS randomly swallows typed input — letters, digits, space and Enter vanish while agents are running tools. A single idle session is mostly unaffected, so it presents as a "multi-session" bug.

Environment

• macOS (Apple Silicon), zsh, Ghostty terminal, frontends/tuiapp_v2.py (Textual)
• Not terminal-specific: any POSIX platform is affected
• Windows never shows this — by accident (see below)

Root cause

code_run (ga.py) spawns tool subprocesses with stdout/stderr piped but stdin left untouched, so every bash/python child inherits the TUI's terminal as fd 0, in the same foreground process group as Textual. Any child that reads stdin — input(), interactive prompts, stdin-probing tools, or readline's tcsetattr on import — races Textual for the same keyboard bytes and can flip the tty out of raw mode. More sessions → more concurrent children → more collisions.

Windows is immune because the existing creationflags=CREATE_NO_WINDOW branch detaches children from the console, so they can never touch its input buffer. The POSIX branch passes 0 — no isolation at all. This fix gives POSIX the same isolation Windows already had; Windows behavior is unchanged.

Fix

Pass stdin=subprocess.DEVNULL wherever no child legitimately needs the terminal:

• ga.py code_run Popen — the main path every tool call goes through
• tuiapp_v2.py !shell inline command (30s window)
• tuiapp_v2.py clipboard helper (only when no input= is fed; pbcopy/xclip data path unaffected)
• checklist_helper.py _PK spawns (long-lived worker/master/bbs processes)

Verification

• py_compile clean on all three files
• code_run('echo ...') output unchanged
• code_run('read -t 5 x; echo rc=$?') child now gets immediate EOF (~1s) instead of holding the tty for 5 seconds
• Manually tested ga tui2 with multiple concurrent sessions running tools while typing — no more swallowed keystrokes