The e-ink frame never renders the dashboard

An e-paper frame on the kitchen wall shows today's sales, the CI status, and the temperature in the server room. The ESP32 driving it has 520 KB of RAM and cannot render a web page. It doesn't have to.

Every ten minutes, a cron line in the container screenshots the dashboard through the browser service, a real Chromium loading the real page, and writes the PNG into a folder. The frame fetches that file with a query string: ?thumbnail=&format=bmp&grayscale=&size=800x480&resize=fill. The files service resizes, converts, and desaturates on the way out. The board receives a BMP the exact size of its panel and draws it.

Change the dashboard and nothing on the board changes. The page is the design tool; the URL is the rendering pipeline.