fix(ci): two-phase multi-arch publish with per-digest build and manifest merge

.github/workflows/publish.yml

@@ -9,7 +9,7 @@ env:
   IMAGE: ghcr.io/${{ github.repository_owner }}/trawl
 
 jobs:
-  publish:
+  build:
     strategy:
       matrix:
         include:
@@ -38,20 +38,76 @@ jobs:
         id: meta
         with:
           images: ${{ env.IMAGE }}
-          tags: |
-            type=raw,value=latest,enable={{is_default_branch}}
-            type=semver,pattern={{version}}
-            type=sha,prefix=sha-
+
+      - name: Sanitize platform name
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
 
       - uses: docker/build-push-action@v6
+        id: build
         with:
           context: .
           file: apps/api/Dockerfile
           platforms: ${{ matrix.platform }}
           push: true
-          tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+          outputs: type=image,name=${{ env.IMAGE }},push-by-digest=true,name-canonical=true
+          cache-from: type=gha,scope=${{ env.PLATFORM_PAIR }}
+          cache-to: type=gha,scope=${{ env.PLATFORM_PAIR }},mode=max
           secrets: |
             GITHUB_TOKEN=${{ secrets.GITHUB_TOKEN }}
+
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    runs-on: ubuntu-latest
+    needs: build
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/metadata-action@v5
+        id: meta
+        with:
+          images: ${{ env.IMAGE }}
+          tags: |
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=semver,pattern={{version}}
+            type=sha,prefix=sha-
+
+      - name: Create and push multi-arch manifest
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create \
+            $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.IMAGE }}@sha256:%s ' *)
+
+      - name: Inspect manifest
+        run: docker buildx imagetools inspect ${{ env.IMAGE }}:${{ steps.meta.outputs.version }}