```ts
export function traceRelay(links: Record<string, string>, start: string): string[] {
  if (typeof links !== 'object' || !links) {
    throw new Error('Links must be a non-empty object');
  }
  if (!Object.keys(links).includes(start)) {
    throw new Error(`Start post '${start}' is not in the links`);
  }

  const visited = new Set<string>();
  const path: string[] = [start];

  let currentPost = start;
  while (currentPost !== '') {
    if (visited.has(currentPost)) {
      throw new Error('Handoffs form a cycle');
    }
    visited.add(currentPost);

    const nextPost = links[currentPost];
    if (!nextPost || typeof nextPost !== 'string') {
      throw new Error(`Invalid handoff from '${currentPost}'`);
    }

    path.push(nextPost);
    currentPost = nextPost;
  }

  return path;
}
```