ci(docker): avoid gha cache on arm64 PR builds

.github/workflows/docker-publish.yml

@@ -196,10 +196,26 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f  # v3
 
-      # Build once, load into the local daemon for smoke testing.  Cached
-      # to gha with a per-arch scope; the push step below reuses every
-      # layer from this build.
-      - name: Build image (arm64, smoke test)
+      # Build once, load into the local daemon for smoke testing. PR arm64
+      # builds deliberately avoid the gha cache: cold-cache arm64 builds can
+      # outlive GitHub's short-lived Azure cache SAS token, then fail while
+      # reading or writing cache blobs before the smoke test can run.
+      - name: Build image (arm64, smoke test, uncached PR)
+        if: github.event_name == 'pull_request'
+        uses: docker/build-push-action@bcafcacb16a39f128d818304e6c9c0c18556b85f  # v7.1.0
+        with:
+          context: .
+          file: Dockerfile
+          load: true
+          platforms: linux/arm64
+          tags: ${{ env.IMAGE_NAME }}:test
+          build-args: |
+            HERMES_GIT_SHA=${{ github.sha }}
+
+      # Main/release builds still use the per-arch gha cache so the digest
+      # push below can reuse layers from this smoke-test build.
+      - name: Build image (arm64, smoke test, cached publish)
+        if: github.event_name != 'pull_request'
         uses: docker/build-push-action@bcafcacb16a39f128d818304e6c9c0c18556b85f  # v7.1.0
         with:
           context: .