ssh-askpass is a great tool in these situations. It intercedes and allows you to manually control all key usage attempts.
`ssh-add -c` will cause your ssh agent to pop up with ssh-askpass every time it does an authentication. This is fiddly; You need to have configured your ssh-agent right, and there's a slightly different version to use keychains on macos that's equivalent.
This trick has been used in the past by blackhats to escalate from a compromised CI environment to full production takeover.
GauntletWizard probably meant to respond to your parent in this thread.