fix(ci): Trigger Docker build step on pull request close (#330)

Author: iambriccardo

.github/workflows/docker-ci.yml

@@ -1,16 +1,55 @@
 name: Docker CI
 
 on:
-  push:
-    branches: [main]
+  pull_request:
+    types: [closed]
   workflow_dispatch:
+    inputs:
+      ref:
+        description: "Git ref to build (branch, tag, or SHA)"
+        type: string
+        required: false
 
 permissions:
   contents: read
 
 jobs:
+  resolve-ref:
+    name: Resolve Checkout Ref
+    runs-on: ubuntu-latest
+    outputs:
+      ref: ${{ steps.pick.outputs.ref }}
+    steps:
+      - name: Pick ref
+        id: pick
+        shell: bash
+        run: |
+          set -euo pipefail
+          EVENT_NAME="${GITHUB_EVENT_NAME}"
+          MERGE_SHA=$(jq -r '.pull_request.merge_commit_sha // empty' "$GITHUB_EVENT_PATH")
+          INPUT_REF=$(jq -r '.inputs.ref // empty' "$GITHUB_EVENT_PATH")
+          
+          if [[ "$EVENT_NAME" == "pull_request" && -n "$MERGE_SHA" ]]; then
+            REF="$MERGE_SHA"
+          elif [[ -n "$INPUT_REF" ]]; then
+            REF="$INPUT_REF"
+          else
+            echo "Error: no merge commit or input ref provided" >&2
+            exit 1
+          fi
+          
+          echo "ref=$REF" >> "$GITHUB_OUTPUT"
+
   build:
     name: Build and Push Images
+    needs: resolve-ref
+    # Run only when the PR is merged and is NOT a release PR, or manual run.
+    if: |
+      github.event_name == 'workflow_dispatch' || (
+        github.event_name == 'pull_request' &&
+        github.event.pull_request.merged == true &&
+        !contains(github.event.pull_request.labels.*.name, 'release')
+      )
     strategy:
       matrix:
         image: [etl-api, etl-replicator]
@@ -22,3 +61,5 @@ jobs:
       file: ./${{ matrix.image }}/Dockerfile
       push: true
       tag_with_version: false
+      # Build from the resolved ref: merge commit for PRs, or provided ref, fallback to current SHA.
+      checkout_ref: ${{ needs.resolve-ref.outputs.ref }}