Why: The runner cannot reach github.com, so cloning actions/checkout timed out before any test ran. Evidence: mirrors.aliyun.com/golang/go1.27.1.linux-amd64.tar.gz returned HTTP 200. The workflow now fetches GITHUB_SHA with the job token and installs Go from that mirror. Impact: Submodule checkout still requires SUBMODULE_TOKEN. A missing secret fails the job with that message. Refs: feature/agent-stack-r0-r1 Co-authored-by: Cursor <cursoragent@cursor.com>