Function extractOutputTail

actions/setup/js/copilot_harness.cjs:315–334

* Extract a compact tail preview from combined process output for failure logs. * @param {string} output * @param {{ maxChars?: number, maxLines?: number }} [options] * @returns {string}

(output, options)

 * @returns {string}
 */
function extractOutputTail(output, options) {
  if (typeof output !== "string" || !output) return "";
  const maxChars = options?.maxChars ?? OUTPUT_TAIL_MAX_CHARS;
  const maxLines = options?.maxLines ?? OUTPUT_TAIL_MAX_LINES;
  const normalized = output.replace(/\0/g, "").replace(/\r\n/g, "\n").replace(/\r/g, "\n").trim();
  if (!normalized) return "";
  // filter(Boolean) removes empty strings from blank lines after trimEnd(); maxLines therefore counts non-empty lines.
  const tailLines = normalized
    .split("\n")
    .map(line => line.trimEnd())
    .filter(Boolean)
    .slice(-maxLines);
  if (tailLines.length === 0) return "";
  let tail = tailLines.join("\n");
  if (tail.length > maxChars) {
    const keep = maxChars - 1;
    tail = keep > 0 ? `…${tail.slice(-keep)}` : "…";
  }
  return tail;
}

/**
 * Classify a failed Copilot attempt into a short, named failure class.