Bookmarks run at your own shell’s prompt. Inside ssh, tmux or any other
program, the shell is not The Textsmith’s, so #@, Alt+Enter and Alt+M do
not apply there. The bookmark list does: while a program runs, choosing a
bookmark types its command into the program without pressing Enter, so you
can hear it and then press Enter yourself. A bookmark that takes arguments
is typed with its places (<file>) for you to replace.
Inside ssh forge, a bookmark with a command per machine shows one row per
machine (“update, for forge: …”), with the machine you are connected to
first. The Textsmith finds it from the ssh that is really running, however
you started it (an alias, a bookmark), and matches the name you gave ssh or
the host name from your ~/.ssh/config.