This describes a method for maintaining a separate ssh-agent to hold your ssh key for connecting to Toolforge/CloudVPS.
The problem
You use an ssh-agent to connect to your personal or company systems. You want to connect to Toolforge/CloudVPS using an agent and you created a separate ssh key to connect to Toolforge/CloudVPS, but you don't want to forward your personal key to Toolforge/CloudVPS systems. If you just add both keys to your existing agent, they both get forwarded to Toolforge/CloudVPS. It's a pain to constantly remove your personal key from your agent each time you want to connect to Toolforge/CloudVPS. Additionally, you might be connected to both your personal system and Toolforge/CloudVPS simultaneously, so just removing the key is insufficent; you must run a separate ssh-agent. You don't want to run one agent per connection because then you have to type your passphrase on every connection (and you have a nice long secure passphrase on your key).
This page describes a method for getting your shell to maintain two agents, your primary agent and your Toolforge/CloudVPS agent. When you connect to Toolforge/CloudVPS you connect to the existing Toolforge/CloudVPS agent (or create one if it doesn't exist) and the rest of the time you use your default agent.