[Bug] Windows: terminal/cmd windows flash on every subprocess spawn across multiple CCD sessions

Description

On Windows, Claude Code spawns visible terminal windows (conhost.exe + cmd.exe / bash.exe) for every subprocess operation — MCP server startup, tool execution (Bash), subagent spawning, etc. These windows flash briefly but are extremely disruptive, especially when multiple Claude Code sessions run concurrently under Claude Desktop.

Environment

• OS: Windows 11 (not WSL)
• Claude Desktop version: 1.11187.4 (Electron 41.6.1)
• Claude Code version: 2.1.165
• Shell: Git Bash (default on Windows install)

Steps to Reproduce

1. Open Claude Desktop on Windows
2. Create a Claude Code session with MCP servers (e.g., codegraph, tavily)
3. Use the session — every tool call that spawns a subprocess (Bash, MCP stdio, subagent) flashes a terminal window
4. With 2+ concurrent CCD sessions, the flashing is near-constant

Expected Behavior

Subprocesses should be spawned with windowsHide: true (Node.js) or CREATE_NO_WINDOW / STARTF_USESHOWWINDOW flags so they run in the background without visible terminal windows.

Actual Behavior

Every child_process.spawn() / child_process.exec() call creates a visible conhost.exe + cmd.exe/bash.exe window that flashes on screen. In a multi-session scenario (Claude Desktop with 3-5 CCD project sessions, each with MCP servers), this produces a constant stream of black terminal windows popping up and closing.

Root Cause

Claude Code's subprocess spawning on Windows does not set the windowsHide: true option in Node.js child_process APIs, nor does it use CREATE_NO_WINDOW for the spawned processes. This is a standard Windows development practice to prevent terminal flashing.

Specific code paths that trigger this:

• MCP stdio servers: Each MCP server (codegraph, tavily, etc.) spawns via cmd.exe
• Bash tool execution: Every Bash tool call spawns a new bash.exe via cmd.exe
• Subagent spawning: Agent tool spawns child processes
• Codex plugin: Additional process spawning for the codex companion

Impact

With N concurrent CCD sessions, each with M MCP servers, every tool call creates M + 1 visible terminal windows. For a typical setup with 2 MCP servers and 3 active sessions, that's potentially dozens of window flashes per minute during active use.

Suggested Fix

In all Windows subprocess spawning code paths, add windowsHide: true:

child_process.spawn(command, args, {
  windowsHide: true,
  // ...other options
});

Or for exec/execSync:

child_process.exec(command, { windowsHide: true }, callback);

This is a one-line fix per spawn call site and has zero functional impact — it only prevents the terminal window from being shown.

Additional Context

• This is not a Git Bash issue — replacing the shell with PowerShell produces the same behavior
• This is not an MCP server issue — the servers themselves run fine; it's the spawning mechanism
• The problem is amplified by the fact that Claude Desktop keeps old CCD sessions alive in the background even when the user is only interacting with one session