mcp command fails on Windows: fileURLToPath returns POSIX path /C:/... causing C:\C:\ doubling

[jiaweing]

Bug

expect mcp crashes on Windows with:

Error: Cannot find module 'C:\C:\Users\...\expect-cli\dist\browser-mcp.js'

Root cause

In dist/index.js, the mcp command spawns browser-mcp.js using:

let v = fileURLToPath(new URL('./browser-mcp.js', import.meta.url))
// then: execFileSync(process.execPath, [v], ...)

On Windows, fileURLToPath returns a POSIX-style path /C:/Users/.../browser-mcp.js instead of C:\Users\...\browser-mcp.js. When this is passed as a CLI argument to node.exe, Windows interprets /C:/... relative to the current drive root, producing C:\C:\....

Repro

npm install -g expect-cli
echo '{"jsonrpc":"2.0","method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test","version":"1"}},"id":1}' | expect mcp

Environment

• OS: Windows 11
• Node.js: v22.22.2
• expect-cli: 0.1.3
• Shell: Git Bash (bash via MINGW64)

Fix suggestion

Wrap the path with a Windows path normalization before passing to execFileSync:

import { fileURLToPath } from 'node:url';
import path from 'node:path';

let v = path.resolve(fileURLToPath(new URL('./browser-mcp.js', import.meta.url)));

path.resolve will normalize /C:/... → C:\... on Windows.

This blocks Claude Code MCP integration on Windows entirely — the MCP server can never start.

[jiaweing]

Root cause identified

The bug is in apps/cli/src/index.tsx line 254:

const mcpBin = new URL("./browser-mcp.js", import.meta.url).pathname;

.pathname gives the raw URL path component — on Windows that's /C:/Users/..., not a valid Windows file path. Passing it to node.exe makes Windows resolve it as C:\C:\....

One-line fix

const { fileURLToPath } = await import("node:url");
const mcpBin = fileURLToPath(new URL("./browser-mcp.js", import.meta.url));

fileURLToPath is the standard Node.js way to convert import.meta.url to a file path — it correctly handles the Windows drive letter.

I tried opening a PR but the repo is set to collaborators_only for PRs. Fork with the fix is at: https://github.com/jiaweing/expect/tree/fix/windows-mcp-path