Whenever I ran @rails server@ from within a tmux shell window, I’d get rubygem dependency errors from bundler, but the ZSH prompt and command-completion were working, so I knew the right shell was getting loaded.
The last line of my user-level @.zshrc@ file is @rvm use default@ (currently ruby 1.9.2), and tmux was using 1.9.2, so that was fine as well.
However, RVM apparently ignored my local .rvmrc file, which uses a local gemset, so none of my gems were found.
@source .rvmrc@ in the shell window allowed me to run @rails server@ with no problem, but that’s a hassle to do every time.
Appending @source .rvmrc@ to the end of my @.zshrc@ file explicitly causes the local gemset to be loaded if the file exists, and is a no-op if not. My terminal windows act the same as always, but now every tmux window/pane acts just like it does from the command-line.