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?

Copyright

Copyright and related rights waived via CC0.