GitHub Actions summary silently dropped when GITHUB_STEP_SUMMARY exceeds 1024 KiB

GitHub Actions refuses to attach a step summary file that exceeds a fixed cap of 1024 kibibytes, reporting the failure as an annotation rather than a step result. The result is a red annotation on an otherwise passing job, with no summary visible on the run page. The cap is a constant built into the runner and does not vary by plan, runner, or repository. The same symptom can also appear when the summary file is empty or when a summary was written in a different step, and neither of those cases produces any message. Recommended fixes include checking the two sizes in the error line, uploading large reports as artifacts and linking to them, and keeping summaries to headline figures.