diff --git a/scripts/setup/machine-setup/lib/packages.sh b/scripts/setup/machine-setup/lib/packages.sh
index c7a31a30..f4613d73 100644
--- a/scripts/setup/machine-setup/lib/packages.sh
+++ b/scripts/setup/machine-setup/lib/packages.sh
@@ -51,7 +51,14 @@ LAST_SKIPPED=()
 # are the environment: nothing calls them, they are here because a box you use
 # should have them.
 #
-# Three entries reach beyond simply existing on the machine.
+# Four entries earn a note.
+#
+# python3 is not a tool anybody here calls — it is node-gyp's build dependency,
+# and node-gyp is not optional on Linux. node-pty ships prebuilt binaries for
+# darwin and win32 ONLY, so on Linux its install script always falls through to
+# `node-gyp rebuild` and compiles from source. Without python3 that fails, and
+# the failure surfaces as a broken terminal sidecar rather than as a missing
+# package. build-essential below is the other half of the same requirement.
 #
 # unattended-upgrades installs updates on a timer with nobody watching. apt only:
 # it is a Debian and Ubuntu package, dnf's equivalent is dnf-automatic and pacman
@@ -82,17 +89,17 @@ pkgs_core() {
       # fastfetch PPA. They have no counterpart on the other systems.
       echo curl ca-certificates gnupg git jq unzip \
         apt-transport-https lsb-release software-properties-common \
-        wget zip build-essential btop htop tree tmux ripgrep fd-find net-tools \
+        wget zip build-essential python3 btop htop tree tmux ripgrep fd-find net-tools \
         fail2ban unattended-upgrades
       ;;
     pacman)
       echo curl ca-certificates gnupg git jq unzip \
-        wget zip base-devel btop htop tree tmux ripgrep fd net-tools \
+        wget zip base-devel python btop htop tree tmux ripgrep fd net-tools \
         fail2ban
       ;;
     dnf)
       echo curl ca-certificates gnupg2 git jq unzip \
-        wget zip btop htop tree tmux ripgrep fd-find net-tools \
+        wget zip python3 btop htop tree tmux ripgrep fd-find net-tools \
         fail2ban
       ;;
     brew)