Compound startup command didn't work as expected

I added my server `server` in bink with a compound startup command: `"tmux attach || tmux new"`, including the double quotes -- I want to automatically create a new tmux session when there is none, otherwise I would like to attach the existing one.

When I issued `mosh server` in blink terminal, it worked exactly as I expected when there was a mosh-server session running in my server. But when there was none mosh-server running, I got `execvp: no such file or directory
Mosh session finished!`

I also tried `"tmux attach \|\| tmux new"` and `"-- sh -c 'tmux attach || tmux new'"` -- the latter works on my local laptop, but no luck.

My server configuration:
mosh-server: 1.2.4
shell: zsh 5.0.2

Please advice.

Start by reproducing the configured compound startup command with tmux and `mosh server`, using the reported mosh-server and zsh versions. Compare the behavior when a tmux session exists and when it does not; done means both cases launch the intended session without the reported execvp error.

Written by the indexing model from the issue text.