Compute a failsafe check for consensus

[aeyakovenko]

Problem

Summary of Changes

Fixes #8113

tag: @sakridge @carllin

[aeyakovenko]

@carllin @sakridge @sagar-solana

I don't think blocktree is the right approach. I think we need to rely on a hard to censor protocol for a watchdog.

watchdog:

1. scan gossip for EpochSlots
2. scan gossip for Votes
3. Store bankhash from each vote, Slot/Pubkey.
4. Assert that X% of the network agrees on the root slots.
5. Assert that X% of the network agrees on BankHash for root slots (this may be hard because nodes may skip some of the votes)

replay should stop voting if watchdog fails. X should be 75%?

[carllin]

@aeyakovenko, I'm fine with this as long as we're careful that gossip failures don't lead to the network stalling.

For #3, Store bankhash from each vote, Slot/Pubkey, from the other steps you listed, it seems we only care about the bank hashes for the roots, why not just gossip that as part of EpochSlots? You think people will lie about that?

Also I'm sitting on a few changes, one of which is to store the confirmed blockhashes in blocktree, which will give you all the blockhashes for previous roots. Do you want to leverage that? If so I can check it in.

[aeyakovenko]

@carllin this is trying to watchdog for an attack, so we have to assume attacker will lie. I think the block propagation is weaker than gossip.

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