```python
def fork_paths(pattern: str) -> list:
    """
    Expand a deployment pattern into full paths by handling forks.
    
    :param pattern: A string representing the deployment pattern with slashes and curly braces.
    :return: A list of expanded paths.
    """
    if not isinstance(pattern, str) or not pattern:
        raise ValueError("Pattern must be a non-empty string.")
    
    def expand_segment(segment: str) -> list:
        if "{" in segment:
            options = segment.split("{")[1].split(",")[:-1]
            return [f"{segment.split("{")[0]}{option}" for option in options]
        else:
            return [segment]
    
    def expand_pattern(pattern: str) -> list:
        segments = pattern.split("/")
        if any(segment == "" or "{" in segment for segment in segments):
            raise ValueError("Invalid pattern format.")
        
        paths = []
        current_paths = [""]
        
        for segment in segments:
            new_paths = []
            for path in current_paths:
                expanded_segment = expand_segment(segment)
                new_paths.extend([f"{path}/{option}" for option in expanded_segment])
            current_paths = new_paths
        
        return paths
    
    try:
        return expand_pattern(pattern)
    except ValueError as e:
        raise ValueError(f"Pattern error: {e}")
```