> and most terminals have a hard time using the mouse to reliably edit a cURL command
This is true. Even though I'm not much of a mouse user for it, I tend to edit curl commands of much length in a text editor when I'm doing things by hand, then pasting into the terminal.
> especially if the last command didn't do a final "\n" output
Or if your prompt outputs something to stderr instead of stdout so it doesn't get counted when the shell is trying to position where you are in editing the stream. Ubuntu's default prompt under byobu is a pain for this when I move to a different machine and forget to carry my tweaks for that.
For the missing final \n I just hit [enter] an extra time, but getting round the stderr thing isn't quite that simple.