```python
def trace_relay(links: dict, start: str) -> list:
    if not isinstance(links, dict):
        raise ValueError("links must be a dictionary")
    if start not in links:
        raise ValueError(f"start '{start}' is not a post named in links")
    
    visited = set()
    current_post = start
    path = []
    
    while True:
        if current_post in visited:
            raise ValueError("handoff comes back to a post already visited")
        visited.add(current_post)
        path.append(current_post)
        
        next_post = links[current_post]
        if next_post == "":
            break
        if next_post not in links:
            raise ValueError(f"handoff naming a post that links does not name: '{next_post}'")
        
        current_post = next_post
    
    return path
```