DEFAULT_INHERITED_ENV_VARS

[pkailas]

Summary

The Windows branch of DEFAULT_INHERITED_ENV_VARS in src/client/stdio.ts is missing several variables that Windows needs to resolve and execute common commands. As a result, MCP servers that try to spawn npm, git, .bat/.cmd files, or use cmd.exe features can fail in non-obvious ways even when PATH is correctly inherited.

Current state

src/client/stdio.ts (identical on main):

export const DEFAULT_INHERITED_ENV_VARS =
    process.platform === 'win32'
        ? [
              'APPDATA', 'HOMEDRIVE', 'HOMEPATH', 'LOCALAPPDATA',
              'PATH', 'PROCESSOR_ARCHITECTURE', 'SYSTEMDRIVE',
              'SYSTEMROOT', 'TEMP', 'USERNAME', 'USERPROFILE',
              'PROGRAMFILES'
          ]
        : ['HOME', 'LOGNAME', 'PATH', 'SHELL', 'TERM', 'USER'];

Missing variables

• PATHEXT — Windows uses this to determine which file extensions count as executable when resolving a bare command name. Without it, spawning npm, git, or any .cmd/.bat shim by name fails with ENOENT even when PATH is set correctly.
• COMSPEC — Path to cmd.exe. Required by Node's child_process.spawn({ shell: true }), by npm run scripts internally, and by anything that shells out via cmd.exe.
• PROGRAMFILES(X86) — 32-bit Program Files path on 64-bit Windows. Tools that probe both paths get inconsistent results when only one is inherited.
• PROGRAMW6432 — Resolves to the 64-bit Program Files path even from 32-bit processes.
• WINDIR — Path to the Windows directory. Used as a fallback by some legacy tooling and PowerShell modules.

Proposed change

Add these five variables to the Windows branch of DEFAULT_INHERITED_ENV_VARS. They're non-secret, system-defined, and pose no privacy or security concern beyond what's already inherited (PATH, SYSTEMROOT, etc.).

The same gap exists on both main and v1.x.