[BUG] Windows/Cowork: built-in Node.js not used for local MCP plugin servers → spawn node ENOENT (Windows repro of #35175)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Local plugin MCP servers that run on Node.js ("command": "node" in a plugin's
.mcp.json) fail silently in Cowork / Claude Desktop on machines that have
no system-installed Node.js. The app ships a built-in Node.js (Settings →
Extensions shows "Built-in: 24.15.0") and the "Use built-in Node.js for MCP"
toggle is ON, but plugin MCP servers do not use it — they are spawned via the
system PATH only. The server never starts, exposes no tools, and nothing is
shown in the UI.

What Should Happen?

With the built-in Node.js present (and "Use built-in Node.js for MCP" enabled),
a plugin's "command": "node" should resolve to the bundled runtime — the same
mechanism the Chat tab already uses. At minimum, a connection failure should
surface a clear error instead of failing silently.

Error Messages/Logs

- No error in the Cowork UI (silent).
- The plugin's MCP server reports 0 tools / is omitted from the connected list,
  while all built-in servers connect normally.
- Host log: `Failed to spawn node: spawn node ENOENT` (bare `node` not on PATH).
- Settings → Extensions: `Node.js: Not found (Built-in: 24.15.0)`.

Steps to Reproduce

1. On Windows with no system Node.js (where node returns nothing).
2. Install a plugin whose .mcp.json uses

"command": "node", "args": ["${CLAUDE_PLUGIN_ROOT}/server/index.mjs"].

1. Open Cowork → plugin installs OK, but its MCP server exposes no tools.
2. Install system Node.js, ensure it's on PATH, restart Cowork → the same

plugin's tools now appear. (confirms root cause + workaround)

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.11187.4.0 (Claude Desktop)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

• The identical plugin zip works on macOS where Node.js is on PATH — the bundle

itself is fine; the gap is the spawn environment.

• The Chat tab works for the same users (built-in Node via UtilityProcess);

only Cowork plugin MCP is affected.

• Workaround: install system Node.js on the host and ensure it's on PATH.
• Related: #35175.