smoketest: install the baselines with herdr-bin for herdr

Every baseline installs herdr from source, which pins zig 0.16, and Arch
now has 0.17, so their installs fail. Install them with herdr-bin (which
provides herdr, and is what HEAD installs) in a commit on top, then put
the clone back at the baseline itself, since update pulls --ff-only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

smoketest/scenarios/30-upgrade-from-baseline.sh

@@ -9,9 +9,23 @@ scenario() {
   [ -f "$(reference_fingerprint)" ] \
     || skip "needs the fingerprint 10-fresh-install saves; run both in the same run"
 
-  upstream_set "$VARIANT"
+  local sha
+  sha="$(git -C "$SMOKETEST_REPO" rev-parse "$VARIANT^{commit}")"
+  upstream_set "$sha"
+
+  # Older installers ask for packages that no longer build. Install those
+  # baselines with a fix on top, then put the clone back at the baseline
+  # itself, as on a machine installed back then: update pulls --ff-only.
+  # The source-built herdr pins a zig version Arch has moved on from;
+  # herdr-bin provides herdr, and is what HEAD installs instead
+  if git -C "$SMOKETEST_REPO" show "$sha:packages.conf" | grep -qx '[[:space:]]*herdr'; then
+    upstream_commit "Smoketest: herdr-bin for herdr" '
+      sed -i "s/^\([[:space:]]*\)herdr$/\1herdr-bin/" packages.conf'
+  fi
   cd_install
   assert_status 0
+  run_in_vm reset "git -C ~/.local/share/coredesktop reset -q --hard $(q "$sha")"
+  assert_status 0
   vm_reboot
 
   upstream_set "$SMOKETEST_REF"