* contrib/sly-mrepl.el (sly-mrepl-shortcut-key): New variable.
(sly-mrepl-mode-map): New entry for `sly-mrepl-shortcut-key'
(sly-mrepl--shortcut-location-p): New helper.
(sly-mrepl-shortcut-alist): New variable.
(sly-mrepl-set-package, sly-mrepl-set-directory): New functions.
(sly-mrepl-shortcut): New interactive command.

* contrib/slynk-mrepl.lisp (:sync-package-and-default-directory):
Use new GUESS-AND-SET-PACKAGE.
(guess-and-set-package): New slyfun.
(with-eval-for-repl): Accept an extra MREPL-SYM arg
(eval-for-mrepl): Send prompt after evaluating slave slyfun.