Improve SSH_AUTH_SOCK handling.

dotfiles/shenv

@@ -97,6 +97,8 @@ export LVM_SUPPRESS_FD_WARNINGS=1
 export EARTHLY_SSH_AUTH_SOCK=""
 
 # Handle SSH_AUTH_SOCK for tmux consistency
+case "$-" in
+  *i*)
     _SSH_AUTH_LINK="${HOME}/.ssh/ssh_auth_sock"
 
     # Helper to check if a path is our link or points to it
@@ -115,10 +117,19 @@ _is_link_path() {
       return 1
     }
 
-# Helper to check if an SSH socket is valid and useful via ssh-add return codes
+    # Helper to check if an SSH socket is valid and useful
     _is_valid_ssh_sock() {
       [ -z "$1" ] && return 1
       [ -S "$1" ] || return 1
+
+      if command -v nc >/dev/null 2>&1; then
+        # Use nc to quickly check if the socket is listening.
+        # We use -N to shutdown the socket after EOF on stdin (for OpenBSD netcat compatibility).
+        if echo '' | nc -w 1 -N -U "$1" >/dev/null 2>&1; then
+          return 0
+        fi
+      fi
+
       if command -v ssh-add >/dev/null 2>&1; then
         SSH_AUTH_SOCK="$1" ssh-add -l >/dev/null 2>&1
         case "$?" in
@@ -126,6 +137,10 @@ _is_valid_ssh_sock() {
           *)   return 1 ;;
         esac
       fi
+
+      if command -v nc >/dev/null 2>&1; then
+        return 1
+      fi
       return 0
     }
 
@@ -234,6 +249,8 @@ elif _is_valid_ssh_sock "${_SSH_AUTH_LINK}"; then
     fi
 
     unset _SSH_AUTH_LINK _CANDIDATE
+    ;;
+esac
 
 # Setup XDG-like dirs on MacOS
 # Based on https://leebyron.com/til/mac-xdg/