[unplugin] Vite adapter leaks a setInterval under Vitest (no httpServer to clear it), tests hang 10s on exit

[gdegas]

Describe the issue

@stylexjs/unplugin's Vite adapter keeps the process alive after tests finish when used under Vitest. Every vitest run ends with:

close timed out after 10000ms
Tests closed successfully but something prevents Vite server from exiting

Cause (in the published @stylexjs/unplugin@0.19.0, lib/vite.js, configureServer): when shared is set, the adapter starts a 150 ms setInterval to broadcast stylex:css-update over server.ws, and clears it only via server.httpServer?.once('close', ...). Vitest's Vite server has no httpServer, so the once is skipped and the interval is never cleared.

const interval = setInterval(() => { /* ... server.ws.send(...) */ }, 150);
server.httpServer?.once('close', () => clearInterval(interval));

Vitest's --reporter=hanging-process shows the leaked handles. Suite wall time goes from ~4.5 s to ~15 s.

devMode: 'off' is not a workaround: it also skips the transform, so stylex.defineVars / stylex.create throw Unexpected 'stylex.defineVars' call at runtime in tests. devMode: 'css-only' still leaks the interval.

Expected behavior

vitest run exits immediately after tests complete, or the plugin does not start dev-only timers when there is no HTTP server to attach to.

Steps to reproduce

1. Vite 6.4 + @vitejs/plugin-react + Vitest 3.2 project.
2. vite.config.ts: plugins: [stylex.vite(), react()] with stylex from @stylexjs/unplugin@0.19.0.
3. Any component using stylex.create and a Vitest test that renders it (jsdom).
4. npx vitest run → tests pass, then the 10 s close timeout above.

Test case

Minimal component + test that reproduces it:

// Card.tsx
import * as stylex from '@stylexjs/stylex';
const styles = stylex.create({ card: { padding: '16px' } });
export function Card() { return <div {...stylex.props(styles.card)} />; }

// Card.test.tsx  (// @vitest-environment jsdom)
import { render } from '@testing-library/react';
import { it } from 'vitest';
import { Card } from './Card';
it('renders', () => { render(<Card />); });

Additional comments

Proposed fixes, either works:

• Guard the timer on the server actually having an HTTP server / WebSocket to notify: if (server.httpServer) { ... }.
• Or use interval.unref?.() so a leaked timer cannot keep Node alive, and additionally clear it in a buildEnd/closeBundle hook.

Workaround we are using: skip the unplugin adapter when process.env.VITEST is set and compile through @stylexjs/babel-plugin via @vitejs/plugin-react's babel.plugins instead. Works, but means two compile paths in one config.

Environment: Node 24.13, Vite 6.4.2, Vitest 3.2.4, @stylexjs/unplugin 0.19.0, @stylexjs/stylex 0.19.0, macOS.