Fix npm start on Windows: spawn via shell so npx resolves to npx.cmd

[ivan-ottinger]

Related issues

• Fixes STU-1761

How AI was used in this PR

Diagnosed and patched with Claude Code. I reviewed the one-line change and verified it locally on Windows.

Proposed Changes

scripts/start-studio.mjs spawns npx vite ... and npx electron-vite ... with raw child_process.spawn(...). On Windows, npx is npx.cmd (a batch file), and Node's spawn without shell: true only resolves real executables — so npm start immediately throws Error: spawn npx ENOENT and the dev server never starts. macOS/Linux are unaffected because npx is a real binary there.

Fix: pass shell: true to the default spawn options inside spawnCommand. The shell resolves npx → npx.cmd on Windows and finds npx the usual way on macOS/Linux.

This was a latent bug in the predecessor scripts/start-new-ui.mjs (only reachable via the opt-in npm run start:new). #3537 promoted that script to default npm start, turning it into a Windows-wide blocker.

Why this is safe on macOS/Linux

• All spawn args are hardcoded literals ('vite', '--port', '5200', etc.), so there's no shell-quoting risk.
• stdio: 'inherit' still works through the shell wrapper.
• SIGINT/SIGTERM handlers in the script already call .kill() on the child references, so Ctrl+C still works.

Caveat (not a regression vs. current state, but worth knowing): with shell: true the immediate child is the shell wrapper. If the parent script is killed abruptly, the inner vite/electron-vite may briefly outlive the wrapper until they notice their parent is gone. The script's own SIGINT/SIGTERM handlers cover the normal Ctrl+C path.

Testing Instructions

Windows (the regression):

1. git checkout stu-1761-fix-windows-npm-start-enoent
2. npm install && npm start
3. Expected: prestart build runs, then Starting @studio/ui dev server on port 5200... followed by VITE vX ready in ... ms, then Electron launches.
4. On trunk the same command throws Error: spawn npx ENOENT and exits with code 1.

macOS / Linux (regression check):

1. npm start from this branch should behave identically to trunk — vite on 5200, then Electron.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[Copilot]

Pull request overview

This PR fixes npm start on Windows by allowing Node’s spawn calls in the Studio startup script to resolve shell commands such as npx.cmd.

Changes:

• Adds shell: true to the shared spawnCommand options used for launching Vite and Electron Vite.

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[fredrikekelund]

Works great 👍 Thanks for fixing this, @ivan-ottinger

[wpmobilebot]

📊 Performance Test Results

Comparing 32a0ab5 vs trunk

app-size

Metric	trunk	32a0ab5	Diff	Change
App Size (Mac)	1336.16 MB	1336.16 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	32a0ab5	Diff	Change
load	1749 ms	1717 ms	32 ms	⚪ 0.0%

site-startup

Metric	trunk	32a0ab5	Diff	Change
siteCreation	9036 ms	9038 ms	+2 ms	⚪ 0.0%
siteStartup	4387 ms	4378 ms	9 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)