Normally your ssh agent persists even when you log out of PUMA. However, from time to time it can vanish.
If you are prompted for your passphrase, this means the ssh-agent has stopped for some reason. The agent should have been re-initialised when you logged into PUMA, but you will need to re-associate your ssh keys to the agent.
To do so, run the following command:
puma$ ssh-add