diff --git a/pkgs/nomarchy-install/nomarchy-install.sh b/pkgs/nomarchy-install/nomarchy-install.sh
index 0d7b27d..de0e730 100644
--- a/pkgs/nomarchy-install/nomarchy-install.sh
+++ b/pkgs/nomarchy-install/nomarchy-install.sh
@@ -464,10 +464,13 @@ success "System installed (bootloader in place)"
 # fully themed desktop, not bare Hyprland. Best-effort: a failure here
 # only costs the user one `home-manager switch` after logging in.
 section "Baking the desktop"
-cat > /mnt/tmp/nomarchy-hm-activate.sh <<EOF
-set -e
+# NOT /mnt/tmp: nixos-enter mounts a fresh tmpfs over /tmp inside the
+# chroot, which silently vaporizes any script staged there (cost us a
+# full verification round to find). /root persists into the chroot.
+cat > /mnt/root/nomarchy-hm-activate.sh <<EOF
+set -ex
+exec > /var/log/nomarchy-hm-preactivate.log 2>&1
 export PATH=/run/current-system/sw/bin:\$PATH
-export NIX_CONFIG=$(printf '%q' "$NIX_CONFIG")
 out=\$(nix --extra-experimental-features "nix-command flakes" \
     build --no-link --print-out-paths \
     --option substituters "" \
@@ -476,13 +479,15 @@ install -d -o "$USERNAME" -g users /nix/var/nix/profiles/per-user/$USERNAME
 install -d -o "$USERNAME" -g users /nix/var/nix/gcroots/per-user/$USERNAME
 runuser -u "$USERNAME" -- bash -lc "USER=$USERNAME HOME=/home/$USERNAME \$out/activate"
 EOF
-if nixos-enter --root /mnt -- bash /tmp/nomarchy-hm-activate.sh; then
+if nixos-enter --root /mnt -- bash /root/nomarchy-hm-activate.sh; then
     success "Desktop pre-activated — first boot is fully themed"
 else
-    warn "Desktop pre-activation failed; after first login run:"
+    warn "Desktop pre-activation failed (see /var/log/nomarchy-hm-preactivate.log"
+    warn "on the installed system); after first login run:"
     warn "  home-manager switch --flake ~/.nomarchy -b bak"
+    tail -n 5 /mnt/var/log/nomarchy-hm-preactivate.log 2>/dev/null || true
 fi
-rm -f /mnt/tmp/nomarchy-hm-activate.sh
+rm -f /mnt/root/nomarchy-hm-activate.sh
 
 header "Nomarchy installed on $TARGET_DISK" \
        "User: $USERNAME @ $HOSTNAME_" \