Proxy Re-Encryption with provable re-encryption target Suppose Alice has encrypted some plaintext $P$ to Bob. Bob wishes to re-encrypt this information to Charlie via proxy, in such a manner that:


The proxy cannot obtain $P$
The proxy can prove that Bob has provided a valid re-encryption key, meaning that Charlie will be able to obtain $P$ by decrypting with his private key
The proxy can prove that the ciphertext originated from Alice


Is such a scheme possible?
PRE schemes guarantee Q1, if they are even remotely worthwhile.
Alice could add a signature over her public signing key and the ciphertext to accomplish Q3.
I haven't seen any works that guarantee a re-encryption key from B to C is valid.