new UART characteristic write for each new line in forEach loop

Which after execution, should always print > as a newline?

Yes, ish. Although in a way if you really do need to mark the end of what you're sending then just adding a print("END")/similar to the end of the line might be best.

The reason is, if you had some other code running in an event like setInterval then if that executed and printed something then that could print code before you received the >. Maybe if you have control of everything you can be sure that doesn't happen though