AMP: Arc Multi-Proposer Protocol with Bounded Inclusion Guarantees
Blockchain systems that settle financial transactions face a structural tension: the validator that assembles each block holds unilateral power over transaction inclusion and ordering. Traditional markets curb this power through laws that prevent front-running and market manipulation. Regulators have flagged the absence of such rules as a first-order concern for blockchain-based financial infrastructure. To address this tension, we introduce AMP, Arc multi-proposer protocol where no single validator fully controls the flow of transactions into blocks. AMP composes with a broad class of BFT consensus algorithms in which explicit validator votes determine decisions. Any node can act as a proposer, collecting user transactions, bundling them into payloads, and broadcasting those payloads to all validators. Validators attest to received payloads by embedding payload identifiers in the votes cast to reach a consensus decision. This yields the key guarantee, bounded inclusion: any payload attested by more than $2f$ validators at height $h$ must appear in the block finalized at height $h+1$. A deterministic ordering function over finalized payloads curbs any single validator's ordering discretion. AMP decouples dissemination from agreement, inherits safety and liveness from the underlying BFT algorithm, and removes the need for a shared transaction pool (mempool). We prove correctness formally, including the bounded-inclusion guarantee within one consensus height.