```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)
    pending = ""
    frames = []
    for i in range(len(buffer)):
        if buffer[i] == marker:
            if i > 0 and buffer[i-1] == marker:
                pending += marker
            else:
                if pending:
                    frames.append(pending)
                    pending = ""
                frames.append(buffer[i])
        else:
            pending += buffer[i]
    if pending:
        frames.append(pending)
    return {"frames": frames, "pending": ""}
```