Working with react-dom

Description

Use, advise on, and review react-dom — client roots (createRoot/hydrateRoot), hydration and hydration-mismatch debugging, portals, flushSync, form APIs (useFormStatus, form actions), resource hints (preload/preinit/preconnect), document metadata hoisting, and server rendering (react-dom/server streaming, react-dom/static prerender). Use whenever the user mounts a React app, sees "hydration failed" or "text content does not match", builds modals/tooltips with portals, does custom SSR, upgrades from ReactDOM.render, or touches DOM-specific React behavior — even when they just say "my page flickers" or "the modal is clipped".