fix artifact extraction and previous version check

Author: timothypratley

.github/workflows/render-and-publish.yml

@@ -75,10 +75,21 @@ jobs:
       - name: Detect changed Clojure sources
         if: github.event_name == 'push'
         id: changed_clj
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
         run: |
           set -euo pipefail
           git fetch origin main:refs/remotes/origin/main
-          changed=$(git diff --name-only --diff-filter=ACMR origin/main...HEAD -- 'src/**/*.clj' | tr '\n' ' ')
+          # Get the commit of the previous successful run (where the artifact came from)
+          latest_run=$(gh api "/repos/$REPO/actions/workflows/render-and-publish.yml/runs?branch=main&status=success&per_page=1" --jq '.workflow_runs[0].head_commit' || true)
+          if [ -z "${latest_run:-}" ] || [ "${latest_run}" = "null" ]; then
+            echo "No previous commit found; doing full rebuild."
+            echo "files=" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          echo "Comparing against previous artifact commit: $latest_run"
+          changed=$(git diff --name-only --diff-filter=ACMR "$latest_run" HEAD -- 'src/**/*.clj' | tr '\n' ' ')
           if [ -z "$changed" ]; then
             echo "No changed Clojure sources detected."
             echo "files=" >> "$GITHUB_OUTPUT"