Proof-of-stake is not a consensus algorithm on the same level as proof-of-work. When faced with two blockchains, one in which I control 100% of coins -- and th

Proof-of-stake is not a consensus algorithm on the same level as proof-of-work. When faced with two blockchains, one in which I control 100% of coins -- and thus 100% of the stake -- and some other chain, which chain do you choose, and why? You can't use stake to make the choice, because that's a property of a chain, so you need to decide which chain to use before stake has meaning. Also, what happens if an attacker exploits a bug in the Ethereum implementation, and uses it to replace all nodes' chains with his own copy? How can we ever return to the correct chain unless we just use trust/majority vote?