ci: release a stack once, when its last PR merges (#248)

Author: dazzatronus

.github/workflows/release.yml

@@ -70,7 +70,21 @@ jobs:
         working-directory: shotstack-studio-extended-regression-suite
         run: npm test
 
+      # A stack releases once, when its last PR merges: semantic-release then reads every commit since the
+      # last release. Earlier PRs in the stack, titled [n/m] with n < m, hold the release.
+      - name: Hold the release for an unfinished stack
+        id: stack
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          title=$(gh api "repos/${{ github.repository }}/commits/${{ github.sha }}/pulls" --jq '.[0].title // ""')
+          if [[ "$title" =~ ^\[([0-9]+)/([0-9]+)\] ]] && (( BASH_REMATCH[1] < BASH_REMATCH[2] )); then
+            echo "hold=true" >> "$GITHUB_OUTPUT"
+            echo "Holding the release until the stack's last PR merges: $title"
+          fi
+
       - name: Release
+        if: steps.stack.outputs.hold != 'true'
         working-directory: shotstack-studio-sdk
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}