The debug UART, as the draw block sees it. These were direct calls into IS-uart.js, imported into the renderer bundle. That file requires the native `usb` module, which a renderer without node integration cannot load at all, so it now lives in the main process and these are messages to it - see src/Main/Bridge.fs. The signatures are unchanged, which is the whole reason this port was cheap: the operations were already asynchronous, already took nothing but a viewer count, and already shared no objects with their caller. Nothing in SheetUpdate.fs had to change.