The list's been very quiet and I need this badly, so here it goes. I'm not sure it is the right fix. The (concat input "\n") thing in slime-repl-send-input unconditionally appends a \n to the input, maybe it should just ensure there is one.
CL-USER> (list (read-line) (read-line)) 1 2 ("1" "2") CL-USER>