Why can 512 validators mislead every light client on Ethereum today?

Ethereum's light client protocol trusts a rotating committee of 512 validators to attest to the chain head, but their combined stake is roughly 16,000 ETH, a fraction of a percent of total validator stake, and their ETH is non-slashable in the light-client context. A dishonest supermajority of the committee could feed light clients an invalid chain head without facing penalties proportional to what they could steal. Mobile wallets, bridge relayers, and cross-chain oracles increasingly rely on these light clients rather than full nodes, so the attack surface is expanding with each quarter. A 2024 Princeton paper formally identifies the gap and proposes stake-matched security levels as a fix, and EIP-8390 proposes removing the sync committee entirely in favor of ZK proofs, but neither is implemented on mainnet. A user relying on a light client today has no way to know their security guaran