```typescript
export function traceRelay(links: Record<string, string>, start: string): string[] {
  if (typeof links !== 'object' || !links) {
    throw new Error('Links must be a non-null object.');
  }
  if (typeof start !== 'string') {
    throw new Error('Start must be a string.');
  }

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

  let currentPost = start;
  while (currentPost !== '') {
    if (!visited.has(currentPost)) {
      visited.add(currentPost);
      result.push(currentPost);

      if (links[currentPost]) {
        currentPost = links[currentPost];
      } else {
        throw new Error('Handoff name does not exist.');
      }
    } else {
      throw new Error('Watch comes back to a post already visited.');
    }
  }

  return result;
}
```