Sedna is a coded multi-proposer consensus protocol in which a sender shards a transaction payload into rateless symbols and disseminates them across parallel proposer lanes, providing high throughput and ``until decode'' privacy. This paper studies a sharp incentive failure in such systems. A cartel of lane proposers can withhold the bundles addressed to its lanes, slowing the chain's symbol accumulation while privately pooling the missing symbols. Because finalized symbols become public, the cartel's multi-slot information lead is governed by a chain level delay event where the chain fails to accumulate the $κ$ bundles needed for decoding by the honest horizon $t^\star=\lceil κ/m\rceil$. We characterize the resulting delay probability with KL-type large deviation bounds and show a knife edge pathology when the slack $Δ=t^\star m-κ$ is zero such that withholding a single bundle suffices to push inclusion into the next slot with high probability. We propose \textsf{PIVOT-$K$}, a Sedna native pivotal bundle bounty that concentrates rewards on the $κ$ bundles that actually trigger decoding, and we derive explicit incentive compatibility conditions against partial and coalition deviations. We further show that an adaptive sender ``ratchet'' that excludes lanes whose tickets were not redeemed collapses multi-slot withholding into a first slot deficit when $t^\star\ge 2$, reducing the required bounty by orders of magnitude. We close by bounding irreducible within slot decode races and providing parameter guidance and numerical illustrations. Our results show that for realistic parameters Sedna can reduce MEV costs to 0.04\% of the transaction value.

翻译：Sedna是一种编码多提议者共识协议，其中发送方将交易负载分片为无速率符号，并通过并行提议者通道分发，从而提供高吞吐量和“解码前”隐私。本文研究了此类系统中一个严峻的激励失效问题。由通道提议者组成的卡特尔可以扣留发往其通道的数据包，减缓链的符号累积速度，同时私下汇集缺失的符号。由于最终确定的符号变为公开，卡特尔的跨时段信息优势取决于链级延迟事件：链未能按诚实视界t^⋆=⌈κ/m⌉累积解码所需的κ个数据包。我们利用KL型大偏差界刻画了由此产生的延迟概率，并展示了当余量Δ=t^⋆m-κ为零时的临界病理现象——此时扣留单个数据包便足以高概率地将包含推迟至下一时段。我们提出Sedna原生关键数据包赏金机制\textsf{PIVOT-$K$}，将奖励集中在实际触发解码的κ个数据包上，并推导了针对部分偏离和联盟偏离的显式激励相容条件。进一步证明，当t^⋆≥2时，一种排除票据未被赎回通道的自适应发送方“棘轮”机制可将多时段扣留简化为首时段短缺，从而将所需赏金降低数个数量级。最后我们界定了时段内不可约的解码竞争，并给出了参数指导和数值示例。结果表明，在现实参数下Sedna可将MEV成本降至交易价值的0.04%。