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Any repository code running earlier in the job that holds the key could reach it (a build patched through Cargo.toml, or a step writing $GITHUB_ENV or $GITHUB_PATH for the next one). The `sign` job checks out only tools/ci/sign_release.sh, which signs with the runner's OpenSSL; the publish job, without the key, checks the result with horizon-release-sign as launchers will. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>