claude mcp add on Windows expands /c flag to C:/ path

Description

When using claude mcp add on Windows with cmd /c as the command (required for running npx via stdio MCP servers on Windows), the /c argument is incorrectly expanded to C:/ by the CLI.

Steps to Reproduce

Run any of these commands on Windows:

claude mcp add --scope local my-server -- cmd /c npx -y some-mcp-server
claude mcp add --scope user my-server -- cmd /c npx -y some-mcp-server
claude mcp add my-server -- cmd "/c" npx -y some-mcp-server

Expected Behavior

The resulting config in ~/.claude.json should be:

{
  "command": "cmd",
  "args": ["/c", "npx", "-y", "some-mcp-server"]
}

Actual Behavior

The /c is expanded to a Windows path:

{
  "command": "cmd",
  "args": ["C:/", "npx", "-y", "some-mcp-server"]
}

The CLI even reports the mangled result:

Added stdio MCP server my-server with command: cmd C:/ npx -y some-mcp-server

Quoting /c does not help — the expansion happens regardless.

Impact

This is particularly problematic because Claude Code itself warns that Windows requires cmd /c wrapper to execute npx for MCP servers. But the CLI tool to add MCP servers cannot produce a correct cmd /c configuration. Users must manually edit ~/.claude.json to fix C:/ back to /c after every claude mcp add.

Environment

• Claude Code version: 2.1.x (installed via native method)
• OS: Windows 11 Pro 10.0.26200
• Bun: Canary v1.3.9-canary.51