diff --git a/justfile b/justfile
index 633263c..8afb7e6 100644
--- a/justfile
+++ b/justfile
@@ -21,5 +21,23 @@ run-vm machine=`just _a_machine`:
     | xargs -L 1 nix flake lock --update-input
 
 
+
+# helpers
+
+[no-exit-message]
 _a_machine:
-  nix eval .#nixosConfigurations --apply builtins.attrNames --json | jq .[] -r | gum filter
+  #!/usr/bin/env -S sh -euo pipefail
+  machines="$(
+    nix eval {{nix_eval_opts}} .#nixosConfigurations --apply builtins.attrNames --json | jq .[] -r
+  )"
+  [ -n "$machines" ] || { echo >&2 "ERROR: no machines found"; false; }
+  if [ -s .direnv/vars/last-machine.txt ]; then
+    machines="$(
+      grep <<<"$machines" -xF  "$(cat .direnv/vars/last-machine.txt)" ||:
+      grep <<<"$machines" -xFv "$(cat .direnv/vars/last-machine.txt)" ||:
+    )"
+  fi
+  choice="$(gum filter <<<"$machines")"
+  mkdir -p .direnv/vars
+  cat <<<"$choice" >.direnv/vars/last-machine.txt
+  cat <<<"$choice"