@julian The problem is if I don't use npm then the plugins will be lost in the next deploy, since the server will clean and rebuild.
I just checked the plugin's commit history and it indeed shows an api change that will make it incompatible with 0.8.x branch(
action:send.email has been changed to
filter:send.email). So I guess the solution for me would be to stick to up to the commit where the api didn't change.