fix(shell): reuse sudo session during deployment

configs/nixos/modules/shell/fish/functions/deploy-to.fish

@@ -47,6 +47,8 @@ or begin
     return $status
 end
 
+set remote_nar
+
 if test (count $missing_paths) -gt 0
     set nar_file (mktemp --suffix=.nar)
     or return $status
@@ -70,26 +72,23 @@ if test (count $missing_paths) -gt 0
         return $scp_status
     end
 
-    echo "deploy-to: importing closure on $host" >&2
-    ssh -t $host "sudo sh -c 'nix-store --import < $remote_nar' && rm -f $remote_nar"
-    or begin
-        echo "deploy-to: closure import failed for $host" >&2
-        return $status
-    end
+    echo "deploy-to: importing the closure, recording $system_path, and activating it on $host" >&2
 else
     echo "deploy-to: $host already has the full closure for $system_path" >&2
+    echo "deploy-to: recording $system_path and activating it on $host" >&2
 end
 
-echo "deploy-to: recording $system_path as the system profile on $host" >&2
-ssh -t $host sudo nix-env --profile /nix/var/nix/profiles/system --set $system_path
-or begin
-    echo "deploy-to: system profile update failed for $host" >&2
-    return $status
-end
+set remote_script (
+    string join '; ' \
+        'system_path=$1' \
+        'remote_nar=$2' \
+        'if test -n "$remote_nar"; then nix-store --import < "$remote_nar"; rm -f "$remote_nar"; fi' \
+        'nix-env --profile /nix/var/nix/profiles/system --set "$system_path"' \
+        '"$system_path/bin/switch-to-configuration" switch'
+)
 
-echo "deploy-to: activating $system_path on $host" >&2
-ssh -t $host sudo "$system_path/bin/switch-to-configuration" switch
+ssh -t $host sudo sh -e -c (string escape -- $remote_script) sh (string escape -- $system_path $remote_nar)
 or begin
-    echo "deploy-to: activation failed for $host" >&2
+    echo "deploy-to: deployment failed for $host" >&2
     return $status
 end