@how if I understand correctly you want to simulate what the keyboard does, without needing a keyboard, so you can demonstrate different scenarios. Yes we can do this. I think a TCP socket would work better than signals, also because it needs to work between machines and not just on the same machine.
So your ‘file.txt’ consists of, say:
# --- contents of file.txt:
n
n
n
and then you want to do
cat file.txt | upsycle-send mr-a.dream.public.cat
and it will have the same effect as if you had pressed ‘n n n’ on the keyboard. Is this correct?