[Windows] Hook subprocess spawning creates visible console window flashes on every tool call

Environment

• Platform: Windows 11 Enterprise
• Claude Code: VS Code extension
• Node.js: v24.14.0

Problem

On Windows, every hook invocation (PreToolUse, PostToolUse, SessionStart, etc.) causes a console window (PowerShell or cmd) to briefly flash on screen. This happens because Claude Code's hook subprocess spawner does not set windowsHide: true (or equivalent CREATE_NO_WINDOW flag) when spawning hook processes on Windows.

Hook commands like node "path/to/hook.mjs" are spawned without suppressing the console window, causing a visible flash for every tool call. With plugins like context-mode that register hooks for Bash, Read, Grep, WebFetch, Agent, and multiple MCP tools, this results in dozens of console flashes per conversation turn — extremely distracting during normal use.

Expected Behavior

Hook processes run silently in the background with no visible console windows.

Steps to Reproduce

1. Install Claude Code VS Code extension on Windows
2. Install any plugin that registers a Node.js-based hook (e.g. context-mode)
3. Trigger a tool call that matches the hook (e.g. a Bash or Read)
4. Observe console window flash

Proposed Fix

The subprocess spawner for hooks should use:

spawn(cmd, args, { windowsHide: true, ...rest })

This maps to CREATE_NO_WINDOW on Windows and eliminates the console flash without affecting hook stdin/stdout piping.

Workaround

Wrapping hook commands with powershell.exe -WindowStyle Hidden -NonInteractive -NoProfile -ExecutionPolicy Bypass -File <wrapper.ps1> partially mitigates the issue but adds ~200ms latency per hook call, gets overwritten on plugin upgrade, and is fragile. The correct fix is in Claude Code's hook process spawner.