Not sure this invalidate your scenario but consider this:
You can’t request a chunk you hold because you don’t know what its XOR chunk ID is. The local chunk ID that you see in your vault is different then the XOR chunk ID a user needs to request the chunk. Only your Data Manager knows the real XOR chunk ID. It hashes it before giving it to you and keeps a dictionary mapping the real ID with your local one.
You can find more info in this discussion.