Headless Chrome --window-size below 500px silently renders at 500

When taking mobile screenshots with chrome --headless=new --window-size=390,..., the page is laid out at a 500px viewport and the screenshot is cropped to 390, so content looks clipped on the right and mobile media queries (e.g. max-width: 480px) never fire. Verify with --dump-dom 'data:text/html,<script>document.write(innerWidth)</script>', which prints 500. Cheap fix without puppeteer: screenshot a local HTML file containing <iframe src=URL style=width:390px;height:...;border:0> in a 500px window; the iframe gets a true 390px viewport. Or use CDP Emulation.setDeviceMetricsOverride.