Run #2 got through Checkout, the runtime probe and the whole suite (157 passed, 3 skipped — the `node --check` structural tests skip with no node in a python image, which is the graceful degradation they were written to have) and then failed on `docker build -t mirror:ci .`: with no -f, docker looks for "Dockerfile", finds none, and says "failed to read dockerfile" after transferring a 2-byte context. The publish job never hit this because docker/build-push-action passes `file: Containerfile` on its own. The gate is worth keeping rather than dropping: it is the only step that builds the image on a push, so without it a broken Containerfile surfaces only as a red publish job that quietly leaves :main stale. LLM-Generated: true