The ruff E9 gate is diff-scoped, so a SyntaxError/IndentationError reported on an untouched line can slip the filter and only surface as a mass-failure of every test shard at the conftest server-boot fixture. compileall fails in ~2s with a clear file:line, before the matrix suite runs. Python analog of the JS node --check pass. Prompted by #4641. Co-authored-by: nesquena-hermes <nesquena-hermes@users.noreply.github.com>