P-Chain as Superchain L2 – OP Stack Rollup Integration

Abstract

This LP presents a feasibility blueprint showing how Lux P-Chain can operate as an OP Stack rollup on Ethereum mainnet—joining the Superchain—without discarding Lux Consensus or our eight-chain architecture. P-Chain’s stake-weighted proposer set replaces a centralized sequencer key, and finalized P-Blocks are batched to Ethereum via the OptimismPortal and L2OutputOracle.

Motivation

By merging P-Chain with OP Stack, Lux achieves:

• Decentralized Sequencing: P-Chain’s Lux consensus++ consensus (≥ ⅔ stake) orders blocks instead of a single sequencer.
• Native Settlement: Batches of P-Chain transactions commit on L1 via Optimism contracts.
• Seamless Integration: All Lux chains (C/X/M/Z) remain L3 Superchain appchains.
• Shared Security: Lux validators secure both base-chain and rollup state with the same stake.

Specification

1. Big-Picture Topology

Ethereum L1
│   ▲              ▲
│   │ (ETH deposits│L2 outputs, fraud/zk proofs)
│   │              │
│ ┌─┴──────────────┴────────────────┐
│ │  P-Chain  (Lux  ↔  OP-Stack L2) │
│ │  ─ Lux Consensus (≥⅔ stake)     │
│ │  ─ op-geth state engine         │
│ │  ─ lux-batcher & lux-proposer   │
│ └─┬───────────────────────────────┘
│   │ Warp / IBC / SDK
│   ▼
┌───┴───────────┬───────────┬────────────┐
│ C-Chain (EVM) │ X-Chain   │ T-Chain    │ Z-Chain    │
│               │ (AMM)     │ (MPC)      │ (zk/FHE)   │
└───────────────┴───────────┴────────────┴────────────┘

2. P-Chain Component Changes

Component	Current	After Upgrade
Execution	PlatformVM (UTXO + staking)	op-geth (EVM + OP Stack modifications)
Ordering	Lux consensus++ proposer rotation	Unchanged (stake-weighted proposer; exposed via op-node API)
L2 Contracts	none	Deploy OptimismPortal, L2OutputOracle, StandardBridge on L1
Batcher	n/a	lux-batcher service batches P-Blocks and posts to portal
Proposer	n/a	lux-proposer submits output roots to L2OutputOracle every N blocks
Fraud/Validity	Lux slashing only	Start with OP fault-proof; later replace with ZK proofs

Rationale

This design preserves Lux Consensus ordering and finality, anchors P-Chain state natively on Ethereum, and reuses proven OP Stack contracts for settlement. It aligns with Superchain standards while retaining decentralization and low-latency UX.

Backwards Compatibility

This upgrade is fully additive and opt-in. Nodes not launched in OP-Stack mode behave as before, and existing Lux applications are unaffected unless they explicitly enable rollup features.

Implementation

P-Chain as OP Stack Rollup Integration

Location: ~/work/lux/geth/rollup/optimism/ GitHub: github.com/luxfi/geth/tree/main/rollup/optimism

Core Components:

• plugin.go - OP Stack plugin
• consensus/sequencer.go - Stake-weighted sequencer
• contracts/OptimismPortal.sol - L1 settlement
• contracts/L2OutputOracle.sol - Output validation

Lux-specific Components:

• Location: ~/work/lux/stack/
• lux-batcher - Batch posting service
• lux-proposer - Output root proposer

Stake-Weighted Proposer Implementation:

// From consensus/sequencer.go
type ProposerRotation struct {
    validators ValidatorSet
    currentIdx uint32
    stake      map[ids.NodeID]uint64
}

func (pr *ProposerRotation) NextProposer() ids.NodeID {
    // Select next proposer weighted by stake
    totalStake := pr.TotalStake()
    selected := rand.Int64() % totalStake
    cumulative := int64(0)

    for nodeID, nodeStake := range pr.stake {
        cumulative += int64(nodeStake)
        if selected < cumulative {
            return nodeID
        }
    }
}

Testing:

cd ~/work/lux/geth
go test ./rollup/optimism/... -v
go test ./contracts/... -v

cd ~/work/lux/stack
go test ./lux-batcher/... -v
go test ./lux-proposer/... -v

RPC Extensions

P-Chain Rollup RPC methods:

• rollup_getCurrentSequencer - Get active sequencer
• rollup_getProposerCommitment - Get proposed output root
• rollup_estimateL1Cost - Estimate L1 settlement cost

Test Cases

1. Commit and verify a known P-Chain state root and inclusion proofs.
2. Submit and validate batches under different block sizes and time intervals.
3. Simulate fault-proof challenges via OP Stack test harness.
4. Ensure C-Chain and other Lux chains operate normally when rollup mode is disabled.
5. Verify stake-weighted proposer selection is correct.
6. Test validator set updates trigger new DKG for MPC signers.

Reference Implementation

Proof-of-concept modules:

• /work/lux/geth/rollup/optimism (OP plugin)
• /work/lux/evm with op-geth feature under Lux consensus++ harness
• lux-batcher and lux-proposer binaries in /work/lux/stack

Security Considerations

• Relayer authority must be permissioned (e.g. multisig) to guard against malicious commits.
• Batch submissions only after P-Chain finality (≥ ⅔ stake) to prevent reorg attacks.
• Strict gas limits on proof verification to mitigate DoS.
• Isolate rollup state from base-chain state to avoid cross-chain contamination.

Economic Impact (optional)

At 50 gwei and 100 000 gas per batch, L1 cost ≈ 0.0025 ETH (~ $4.50). Batching 200 L2 txs yields ~$0.0225 per tx. EIP‑4844 proto‑dank cuts this by ≈ 10×.

Open Questions (optional)

1. Optimal batch window (size vs latency)?
2. Dynamic fee‑market or fixed sequencer margin?
3. L1 proof challenge window vs ZK proof replacement?