SSH stops at 'SSH2_MSG_SERVICE_ACCEPT received'
Running unset SSH_AUTH_SOCK in Terminal worked for me, though I'm currently unsure why. One thing I did not mention in the body of my question was that I had to modify /System/Library/LaunchAgents/org.openbsd.ssh-agent.plist in order to get sshd to work: here's a link to my org.openbsd.ssh-agent.plist in case anyone in the future thinks they know what caused the problem.