Method streamChat

backend/src/chat/chat.service.ts:24–34

(
    input: ChatInput,
  )

 * that is what this folds. An unrecognised role is the caller being wrong
 * about something this function cannot guess, and is refused rather than
 * silently relabelled.
 *
 * ponytail: one guard on the single write path, rather than validation in
 * each of saveMessage's callers.
 */
export function normaliseRole(role: string): MessageRole {
  const found = Object.values(MessageRole).find(
    (r) => r.toLowerCase() === String(role).toLowerCase(),
  );
  if (!found) {
    throw new NotFoundException(
      `Unknown message role "${role}" — expected one of ${Object.values(
        MessageRole,
      ).join(', ')}`,