```python
def trace_relay(links: dict, start: str) -> list:
    if not isinstance(links, dict) or any(not isinstance(k, str) or not isinstance(v, str) for k, v in links.items()):
        raise ValueError("links must be a dictionary mapping post names to other post names")
    if start not in links:
        raise ValueError(f"start post '{start}' is not named in the links")
    
    visited = set()
    path = []
    current_post = start
    
    while current_post:
        if current_post in visited:
            raise ValueError("watch comes back to a post already visited")
        visited.add(current_post)
        path.append(current_post)
        current_post = links.get(current_post, None)
    
    return path
```