zsh offers cross-shell command history on the same server, but of course not between two servers. iTerm has "broadcast input", but that's not quite what I want. I'd like to try a command on a staging server, see that it works, then cut-and-paste that last command to the production server.
You mentioned that this could be part of shell integration; ideally, it wouldn't require any change to the server-side shell, since most production servers are not going to include an iTerm module! But maybe you meant more like "shell detection"... hey, that last line ended with /[$#%]\d/ and waited for input, maybe we're in a shell..