Server rendering

The lightbox is safe to render on the server and in React Server Component trees.

• The bundle starts with "use client".
• Nothing reads window, document or navigator during render. Measurements, listeners and the portal are set up in effects.
• The dialog is portalled into container (document.body by default) after the first client render, so server HTML and the first client render match and there is no hydration warning.
• useLightboxHash reads -1 on the server and during hydration. A page opened from a deep link renders closed, then opens right after hydration.

The grids do render on the server. They lay out for defaultContainerWidth until they are measured, and write item positions as style attributes, which matters under a strict CSP.

Opening a slide during server rendering is not supported, because the dialog lives in a portal. If you need the image in the HTML for search engines, render it in your grid, which you control.

The test suite renders an open lightbox with react-dom/server in a Node environment, with no browser globals, and expects empty HTML.