Adding and removing keys to the agent:
```
waja at Brotschneidemaschine in ~
$ eval "$(ssh-agent -s)"
Agent pid 7715

waja at Brotschneidemaschine in ~
$ ssh-add -L
The agent has no identities.

waja at Brotschneidemaschine in ~
$ ssh-add ~/.ssh/id_rsa
Identity added: /Users/waja/.ssh/id_rsa (waja@Brotschneidemaschine.local)

waja at Brotschneidemaschine in ~
$ ssh-add -L
ssh-rsa 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 waja@Brotschneidemaschine.local

waja at Brotschneidemaschine in ~
$ tail -2 .ssh/config 
Host *
  ForwardAgent yes

waja at Brotschneidemaschine in ~
$ ssh-add -d ~/.ssh/id_rsa
Identity removed: /Users/waja/.ssh/id_rsa RSA (waja@Brotschneidemaschine.local)
```
Identities are not permanent, Desktop-Managers reads keys from `basename -s .pub ~/.ssh/*.pub`.
```
waja in 🌐 jumphost in ~
✦ ❯ kill -9 7715

waja in 🌐 jumphost in ~
✦ ❯ ssh-add -L
Error connecting to agent: Connection refused

waja in 🌐 jumphost in ~
✦ ❯ eval "$(ssh-agent -s)"
Agent pid 7795

waja in 🌐 jumphost in ~
✦ ❯ ssh-add -L
The agent has no identities.
```

https://www.maketecheasier.com/kill-unresponsive-ssh-session/