```python
def drain_frames(chunks: list, marker: str) -> dict:
    if not isinstance(marker, str) or len(marker) != 1:
        raise ValueError("marker must be a single character")
    
    buffer = "".join(chunks)
    frames = []
    pending = ""
    i = 0
    
    while i < len(buffer):
        if buffer[i:i+2] == marker * 2:
            frames.append(pending)
            pending = marker
            i += 2
        elif buffer[i] == marker:
            frames.append(pending)
            pending = ""
            i += 1
        else:
            pending += buffer[i]
            i += 1
    
    if buffer.endswith(marker):
        pending += marker
    
    return {"frames": frames, "pending": pending}
```