Windows: hook commands spawn visible conhost.exe window on every execution

Summary

On Windows, every hook command in settings.json causes a brief conhost.exe console window to flash on screen. This happens because Claude Code spawns bash.exe (Git Bash) for each hook without the CREATE_NO_WINDOW flag, so Windows allocates a new visible console for each execution.

Environment

• OS: Windows 11
• Claude Code: latest
• Shell: Git Bash (C:\Program Files\Git\bin\bash.exe)

Steps to Reproduce

1. Configure any hook in ~/.claude/settings.json, e.g.:

``json
"Stop": [{ "matcher": "", "hooks": [{ "type": "command", "command": "echo done" }] }]
``

1. Start a Claude Code session and send any message.
2. Observe a conhost.exe console window flash briefly on screen after each response.

Root Cause

Claude Code calls CreateProcess for bash.exe without passing CREATE_NO_WINDOW in dwCreationFlags. Windows therefore allocates a new visible console for each hook invocation.

In Node.js, this is a one-line fix:

// Current behavior (creates conhost.exe flash)
spawn(bashPath, ['-c', command])

// Fixed (no console window created)
spawn(bashPath, ['-c', command], { windowsHide: true })

The windowsHide option passes CREATE_NO_WINDOW to CreateProcess on Windows.

Impact

• Hooks that fire frequently (e.g. Stop, UserPromptSubmit, PostToolUse) cause constant screen flashing that is jarring and disruptive during normal use.
• Each hook entry in a matcher group is a separate bash.exe spawn, multiplying the effect.
• Affects all Windows users who use hooks.

Workaround

A GUI-subsystem wrapper executable (hidden-bash.exe) can be built and pointed to via CLAUDE_CODE_GIT_BASH_PATH. Since it compiles as a Windows GUI app (no console subsystem), Node.js spawns it without creating a conhost.exe. It then spawns bash with CREATE_NO_WINDOW:

cmd.SysProcAttr = &syscall.SysProcAttr{
    HideWindow:    true,
    CreationFlags: 0x08000000, // CREATE_NO_WINDOW
}

Built with: go build -ldflags="-H windowsgui" -o hidden-bash.exe .

This workaround works but requires users to build and maintain a custom binary. The proper fix is { windowsHide: true } on the Node.js spawn call in Claude Code itself.

Requested Fix

Pass windowsHide: true when spawning hook processes on Windows. This is a well-known Node.js pattern for suppressing console windows for child processes on Windows.