ssh-agent -s does not export SSH_AUTH_SOCK in current a-shell session

Hello everybody,

I’m using a-shell on iPad and noticed inconsistent behavior with `ssh-agent`.

Today:

```bash
$ ssh-agent -s
I have set SSH_AUTH_SOCK to /private/var/mobile/Containers/Data/Application/.../tmp/agent.8769; you can now run ssh-add.

$ env | grep SSH
SSH_HOME=/var/mobile/Containers/Data/Application/.../Documents
CURLOPT_SSH_KNOWNHOSTS=/var/mobile/Containers/Data/Application/.../Documents/.ssh/known_hosts

$ ssh-add
Could not open a connection to your authentication agent.
```

`SSH_AUTH_SOCK` is not exported into the shell environment after running `ssh-agent -s`.

Yesterday the same workflow worked without manually exporting the variable, so I’m not sure whether this is:

* a regression,
* shell/session-specific behavior,
* or expected behavior in a-shell.

Environment:

* iPad
* a-shell
* using OpenSSH keys (`~/.ssh/id_ed25519`)