Live preview and editor share one container

You're tweaking a Next.js component. Your editor opens at code-1.../?folder=/app. Your preview opens at http-3000....: the same container, exposed on a different port. Both bookmarked.

You change a button color in the editor. The dev server inside the container picks up the file change. The preview tab refreshes. There's no "publish" step, no preview deploy, no Vercel build.

You drag the preview window to the second monitor. You drag the editor to the first. The whole iteration loop lives in two browser tabs and one container. When you ship, you copy the preview URL straight into Slack: your colleague sees what you see, instantly, no auth, no setup.