fix(ci): lowercase image ref before push-by-digest

[strausmann]

What broke

After #40 was merged, the first run on the native-arm64 pipeline failed in all four build legs with:

ERROR: failed to build: failed to solve: failed to parse ref
  \"ghcr.io/strausmann/Label-Printer-Hub-frontend\":
  invalid reference format: repository name
  (strausmann/Label-Printer-Hub-frontend) must be lowercase

Root cause

The GitHub repository is named Label-Printer-Hub (mixed case). \${{ github.repository }} keeps that casing, but OCI/Docker registry refs must be all-lowercase. The old single-phase workflow accidentally side-stepped this because docker/metadata-action lowercases the values it emits in outputs.tags / outputs.labels. The new two-phase workflow pushes by digest via build-push-action's outputs: name=… field, which is a raw passthrough — the mixed-case repo path reached buildx unchanged.

Fix

Both phases get an early Compute lowercase image ref step that does:

repo_lc=\"\${REPO,,}\"
echo \"ref=\${{ env.REGISTRY_GHCR }}/\${repo_lc}-\${{ matrix.service }}\" >> \"\$GITHUB_OUTPUT\"

(\${VAR,,} is bash's lowercase parameter expansion — POSIX shell would need tr, but the runner is bash.)

Every place the workflow needed a registry ref now uses \${{ steps.image.outputs.ref }}:

• metadata-action images: (build + merge)
• build-push-action outputs: name=… (build)
• DIGEST_REPO env in the merge step

Verification (after merge)

gh workflow run docker-publish.yml -f tag=0.2.0 --ref main
gh run watch <new-run-id>

Expect: 4 native build jobs in ~30-45 s each, 2 merge jobs in ~10 s each, total run ~1:30 (vs. ~3:54 on the QEMU pipeline).

[gemini-code-assist]

Note

Gemini is unable to generate a summary for this pull request due to the file types involved not being currently supported.

[Copilot]

Pull request overview

Fixes the Docker publish workflow failing on mixed-case GitHub repo names by normalizing the GHCR image reference to lowercase before using it in push-by-digest and manifest-merge operations.

Changes:

• Add a Compute lowercase image ref step (in both build + merge phases) and route all GHCR image refs through steps.image.outputs.ref.
• Update the build phase to use the computed lowercase ref in build-push-action’s outputs: type=image,name=… (push-by-digest).
• Update metadata/merge steps to also use the computed lowercase image ref when assembling and tagging the multi-arch manifest.

Comments suppressed due to low confidence (1)

.github/workflows/docker-publish.yml:105

• In the build phase, the Docker Hub login step appears unused now (the build only pushes by digest to the GHCR name=... reference). Consider removing this login from the build job and keeping Docker Hub auth only in the merge job where tags/manifests are pushed.

      - name: Log in to Docker Hub
        env:
          DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_USERNAME }}
          DOCKERHUB_TOKEN: ${{ secrets.DOCKERHUB_TOKEN }}
        if: env.DOCKERHUB_USERNAME != '' && env.DOCKERHUB_TOKEN != ''