use dynamic ssh agent

roles/base.nix

@@ -53,9 +53,19 @@ in {
       export EDITOR=nvim
       export STARSHIP_CONFIG=/etc/starship.toml
 
-      if [ -z "$SSH_AUTH_SOCK" ]; then
-          eval $(ssh-agent)
+      if [ -f ~/.ssh/agent.env ] ; then
+          . ~/.ssh/agent.env > /dev/null
+          if ! kill -0 "$SSH_AGENT_PID" > /dev/null 2>&1; then
+              echo "Stale agent file found. Spawning a new agent. "
+              eval `ssh-agent | tee ~/.ssh/agent.env`
+              ssh-add
           fi
+      else
+          echo "Starting ssh-agent"
+          eval `ssh-agent | tee ~/.ssh/agent.env`
+          ssh-add
+      fi
+
 
       set_win_title() {
         echo -ne "\033]0;$USER@$HOSTNAME: $PWD\007"