Layer 2 Scaling Solutions: Technical Implementation Guide for Ethereum

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// Simplified Optimistic Rollup implementation
pragma solidity ^0.8.19;

contract OptimisticRollup {
    struct StateRoot {
        bytes32 root;
        uint256 blockNumber;
        uint256 timestamp;
        address proposer;
        bool finalized;
    }
    
    struct Challenge {
        bytes32 stateRoot;
        address challenger;
        uint256 deposit;
        uint256 deadline;
        bool resolved;
    }
    
    StateRoot[] public stateRoots;
    mapping(bytes32 => Challenge) public challenges;
    
    uint256 public constant CHALLENGE_PERIOD = 7 days;
    uint256 public constant CHALLENGE_DEPOSIT = 1 ether;
    
    event StateRootProposed(bytes32 indexed root, address proposer);
    event ChallengeInitiated(bytes32 indexed root, address challenger);
    event ChallengeResolved(bytes32 indexed root, bool valid);
    
    function proposeStateRoot(bytes32 _stateRoot) external {
        require(_stateRoot != bytes32(0), "Invalid state root");
        
        StateRoot memory newRoot = StateRoot({
            root: _stateRoot,
            blockNumber: block.number,
            timestamp: block.timestamp,
            proposer: msg.sender,
            finalized: false
        });
        
        stateRoots.push(newRoot);
        emit StateRootProposed(_stateRoot, msg.sender);
    }
    
    function challengeStateRoot(bytes32 _stateRoot) external payable {
        require(msg.value >= CHALLENGE_DEPOSIT, "Insufficient deposit");
        require(challenges[_stateRoot].challenger == address(0), "Already challenged");
        
        // Find the state root
        bool found = false;
        for (uint i = 0; i < stateRoots.length; i++) {
            if (stateRoots[i].root == _stateRoot && !stateRoots[i].finalized) {
                require(
                    block.timestamp <= stateRoots[i].timestamp + CHALLENGE_PERIOD,
                    "Challenge period expired"
                );
                found = true;
                break;
            }
        }
        require(found, "State root not found or finalized");
        
        challenges[_stateRoot] = Challenge({
            stateRoot: _stateRoot,
            challenger: msg.sender,
            deposit: msg.value,
            deadline: block.timestamp + 1 days,
            resolved: false
        });
        
        emit ChallengeInitiated(_stateRoot, msg.sender);
    }
    
    function resolveChallenge(
        bytes32 _stateRoot,
        bytes calldata _proof,
        bool _isValid
    ) external {
        Challenge storage challenge = challenges[_stateRoot];
        require(challenge.challenger != address(0), "No challenge exists");
        require(!challenge.resolved, "Already resolved");
        require(block.timestamp <= challenge.deadline, "Challenge expired");
        
        // Verify the fraud proof (simplified)
        bool proofValid = verifyFraudProof(_stateRoot, _proof);
        
        if (proofValid && !_isValid) {
            // Invalid state root, challenger wins
            payable(challenge.challenger).transfer(challenge.deposit * 2);
            _markStateRootInvalid(_stateRoot);
        } else {
            // Valid state root, proposer wins
            address proposer = _getProposer(_stateRoot);
            payable(proposer).transfer(challenge.deposit);
        }
        
        challenge.resolved = true;
        emit ChallengeResolved(_stateRoot, _isValid);
    }
    
    function finalizeStateRoots() external {
        uint256 cutoff = block.timestamp - CHALLENGE_PERIOD;
        
        for (uint i = 0; i < stateRoots.length; i++) {
            if (!stateRoots[i].finalized && 
                stateRoots[i].timestamp <= cutoff &&
                challenges[stateRoots[i].root].challenger == address(0)) {
                
                stateRoots[i].finalized = true;
            }
        }
    }
    
    function verifyFraudProof(bytes32 _stateRoot, bytes calldata _proof) 
        internal 
        pure 
        returns (bool) 
    {
        // Simplified fraud proof verification
        // Real implementation would verify state transition validity
        return keccak256(_proof) != bytes32(0);
    }
    
    function _getProposer(bytes32 _stateRoot) internal view returns (address) {
        for (uint i = 0; i < stateRoots.length; i++) {
            if (stateRoots[i].root == _stateRoot) {
                return stateRoots[i].proposer;
            }
        }
        return address(0);
    }
    
    function _markStateRootInvalid(bytes32 _stateRoot) internal {
        for (uint i = 0; i < stateRoots.length; i++) {
            if (stateRoots[i].root == _stateRoot) {
                // Remove invalid state root
                stateRoots[i] = stateRoots[stateRoots.length - 1];
                stateRoots.pop();
                break;
            }
        }
    }
}

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// Interactive fraud proof implementation
class InteractiveFraudProof {
    constructor(disputed_transition, original_state, claimed_state) {
        this.disputed_transition = disputed_transition;
        this.original_state = original_state;
        this.claimed_state = claimed_state;
        this.challenge_steps = [];
    }
    
    // Binary search to isolate the exact instruction causing disagreement
    async initiateBinarySearch(challenger, defender) {
        let left = 0;
        let right = this.disputed_transition.instructions.length - 1;
        
        while (left < right) {
            const mid = Math.floor((left + right) / 2);
            
            // Request intermediate state at midpoint
            const challengerState = await challenger.getStateAtStep(mid);
            const defenderState = await defender.getStateAtStep(mid);
            
            if (this.statesEqual(challengerState, defenderState)) {
                // Agreement up to midpoint, disagreement is after
                left = mid + 1;
            } else {
                // Disagreement is at or before midpoint
                right = mid;
            }
            
            this.challenge_steps.push({
                step: mid,
                challenger_state: challengerState,
                defender_state: defenderState,
                agreement: this.statesEqual(challengerState, defenderState)
            });
        }
        
        // Now we know the exact instruction causing disagreement
        return this.disputed_transition.instructions[left];
    }
    
    async executeOnChainVerification(disputed_instruction, pre_state) {
        // Execute single instruction on-chain to determine correct result
        const contract = new ethers.Contract(
            FRAUD_PROOF_CONTRACT_ADDRESS,
            FRAUD_PROOF_ABI,
            provider
        );
        
        const result = await contract.executeInstruction(
            disputed_instruction.opcode,
            disputed_instruction.inputs,
            pre_state
        );
        
        return {
            post_state: result.post_state,
            is_valid: result.is_valid,
            gas_used: result.gas_used
        };
    }
    
    statesEqual(state1, state2) {
        return state1.merkle_root === state2.merkle_root &&
               state1.block_number === state2.block_number;
    }
}

// Usage in rollup operator
const fraudProofHandler = async (challenge) => {
    const proof = new InteractiveFraudProof(
        challenge.disputed_transition,
        challenge.pre_state,
        challenge.post_state
    );
    
    const disputed_instruction = await proof.initiateBinarySearch(
        challenge.challenger,
        challenge.defender
    );
    
    const verification_result = await proof.executeOnChainVerification(
        disputed_instruction,
        challenge.pre_state
    );
    
    if (verification_result.is_valid) {
        // Defender wins, slash challenger
        await slashChallenger(challenge.challenger);
    } else {
        // Challenger wins, slash defender and revert state
        await slashDefender(challenge.defender);
        await revertInvalidState(challenge.disputed_transition);
    }
};

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// Circom circuit for simple token transfer verification
pragma circom 2.0.0;

template TokenTransfer() {
    // Private inputs
    signal private input sender_balance;
    signal private input sender_nonce;
    signal private input sender_private_key;
    
    // Public inputs
    signal input recipient;
    signal input amount;
    signal input new_sender_balance;
    signal input new_sender_nonce;
    signal input merkle_root_before;
    signal input merkle_root_after;
    
    // Outputs
    signal output valid;
    
    // Components
    component poseidon_hash = Poseidon(4);
    component ecdsa_verify = ECDSAVerify();
    component merkle_verify_before = MerkleTreeInclusionProof(8);
    component merkle_verify_after = MerkleTreeInclusionProof(8);
    
    // Verify sender has sufficient balance
    component balance_check = GreaterEqualThan(64);
    balance_check.in[0] <== sender_balance;
    balance_check.in[1] <== amount;
    
    // Verify balance update is correct
    component balance_update_check = IsEqual();
    balance_update_check.in[0] <== new_sender_balance;
    balance_update_check.in[1] <== sender_balance - amount;
    
    // Verify nonce increment
    component nonce_check = IsEqual();
    nonce_check.in[0] <== new_sender_nonce;
    nonce_check.in[1] <== sender_nonce + 1;
    
    // Create transaction hash for signature verification
    poseidon_hash.inputs[0] <== recipient;
    poseidon_hash.inputs[1] <== amount;
    poseidon_hash.inputs[2] <== sender_nonce;
    poseidon_hash.inputs[3] <== 1; // Transaction type
    
    // Verify ECDSA signature
    ecdsa_verify.message <== poseidon_hash.out;
    ecdsa_verify.private_key <== sender_private_key;
    
    // Verify merkle tree inclusion before and after
    merkle_verify_before.root <== merkle_root_before;
    merkle_verify_after.root <== merkle_root_after;
    
    // All checks must pass
    valid <== balance_check.out * 
              balance_update_check.out * 
              nonce_check.out * 
              ecdsa_verify.valid * 
              merkle_verify_before.valid * 
              merkle_verify_after.valid;
}

component main = TokenTransfer();

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// ZK-Rollup verifier contract
pragma solidity ^0.8.19;

import "./verifier.sol"; // Generated from circom circuit

contract ZKRollup {
    using SafeMath for uint256;
    
    struct Block {
        bytes32 stateRoot;
        bytes32 transactionsHash;
        uint256 blockNumber;
        uint256 timestamp;
        address operator;
    }
    
    Block[] public blocks;
    mapping(bytes32 => bool) public processedTransactions;
    
    Verifier public immutable verifier;
    bytes32 public currentStateRoot;
    uint256 public blockCount;
    
    event BlockCommitted(uint256 indexed blockNumber, bytes32 stateRoot);
    event TransactionProcessed(bytes32 indexed txHash);
    
    constructor(Verifier _verifier, bytes32 _genesisStateRoot) {
        verifier = _verifier;
        currentStateRoot = _genesisStateRoot;
        
        // Genesis block
        blocks.push(Block({
            stateRoot: _genesisStateRoot,
            transactionsHash: bytes32(0),
            blockNumber: 0,
            timestamp: block.timestamp,
            operator: msg.sender
        }));
    }
    
    function commitBlock(
        bytes32 _newStateRoot,
        bytes32 _transactionsHash,
        uint[2] memory _pA,
        uint[2][2] memory _pB,
        uint[2] memory _pC,
        uint[2] memory _publicSignals
    ) external {
        // Verify the ZK proof
        require(
            verifier.verifyTx(_pA, _pB, _pC, _publicSignals),
            "Invalid proof"
        );
        
        // Public signals should match current and new state
        require(
            bytes32(_publicSignals[0]) == currentStateRoot,
            "Invalid previous state root"
        );
        require(
            bytes32(_publicSignals[1]) == _newStateRoot,
            "State root mismatch"
        );
        
        // Create new block
        Block memory newBlock = Block({
            stateRoot: _newStateRoot,
            transactionsHash: _transactionsHash,
            blockNumber: blockCount + 1,
            timestamp: block.timestamp,
            operator: msg.sender
        });
        
        blocks.push(newBlock);
        currentStateRoot = _newStateRoot;
        blockCount++;
        
        emit BlockCommitted(blockCount, _newStateRoot);
    }
    
    function verifyInclusion(
        bytes32 _leaf,
        bytes32[] memory _proof,
        uint256 _index
    ) public view returns (bool) {
        bytes32 computedHash = _leaf;
        
        for (uint256 i = 0; i < _proof.length; i++) {
            bytes32 proofElement = _proof[i];
            
            if (_index % 2 == 0) {
                computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
            } else {
                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
            }
            
            _index = _index / 2;
        }
        
        return computedHash == currentStateRoot;
    }
    
    function withdraw(
        uint256 _amount,
        uint256 _nonce,
        bytes32[] memory _merkleProof,
        uint256 _merkleIndex
    ) external {
        // Construct leaf from withdrawal data
        bytes32 leaf = keccak256(abi.encodePacked(
            msg.sender,
            _amount,
            _nonce,
            "withdrawal"
        ));
        
        // Verify inclusion in current state
        require(
            verifyInclusion(leaf, _merkleProof, _merkleIndex),
            "Invalid merkle proof"
        );
        
        // Prevent double withdrawal
        require(!processedTransactions[leaf], "Already withdrawn");
        processedTransactions[leaf] = true;
        
        // Transfer funds
        payable(msg.sender).transfer(_amount);
        
        emit TransactionProcessed(leaf);
    }
}

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// Bidirectional payment channel implementation
pragma solidity ^0.8.19;

contract PaymentChannel {
    address public alice;
    address public bob;
    uint256 public aliceDeposit;
    uint256 public bobDeposit;
    uint256 public expirationTime;
    uint256 public nonce;
    
    bool public channelClosed;
    mapping(address => uint256) public withdrawnAmounts;
    
    struct ChannelState {
        uint256 aliceBalance;
        uint256 bobBalance;
        uint256 nonce;
    }
    
    event ChannelOpened(address alice, address bob, uint256 totalDeposit);
    event ChannelClosed(uint256 aliceFinal, uint256 bobFinal);
    event DisputeInitiated(address initiator, uint256 nonce);
    
    modifier onlyParticipants() {
        require(msg.sender == alice || msg.sender == bob, "Not participant");
        _;
    }
    
    modifier channelOpen() {
        require(!channelClosed, "Channel closed");
        require(block.timestamp < expirationTime, "Channel expired");
        _;
    }
    
    constructor(
        address _alice,
        address _bob,
        uint256 _duration
    ) {
        alice = _alice;
        bob = _bob;
        expirationTime = block.timestamp + _duration;
    }
    
    function deposit() external payable {
        require(msg.sender == alice || msg.sender == bob, "Not participant");
        require(!channelClosed, "Channel closed");
        
        if (msg.sender == alice) {
            aliceDeposit += msg.value;
        } else {
            bobDeposit += msg.value;
        }
        
        emit ChannelOpened(alice, bob, aliceDeposit + bobDeposit);
    }
    
    function cooperativeClose(
        uint256 _aliceFinal,
        uint256 _bobFinal,
        bytes memory _aliceSignature,
        bytes memory _bobSignature
    ) external onlyParticipants {
        require(_aliceFinal + _bobFinal == aliceDeposit + bobDeposit, "Invalid amounts");
        
        // Verify both signatures
        bytes32 message = keccak256(abi.encodePacked(
            _aliceFinal,
            _bobFinal,
            "close"
        ));
        
        require(
            recoverSigner(message, _aliceSignature) == alice &&
            recoverSigner(message, _bobSignature) == bob,
            "Invalid signatures"
        );
        
        channelClosed = true;
        
        if (_aliceFinal > 0) payable(alice).transfer(_aliceFinal);
        if (_bobFinal > 0) payable(bob).transfer(_bobFinal);
        
        emit ChannelClosed(_aliceFinal, _bobFinal);
    }
    
    function initiateDispute(
        uint256 _aliceBalance,
        uint256 _bobBalance,
        uint256 _nonce,
        bytes memory _signature
    ) external onlyParticipants channelOpen {
        require(_aliceBalance + _bobBalance == aliceDeposit + bobDeposit, "Invalid balances");
        require(_nonce > nonce, "Outdated state");
        
        // Verify signature from the other party
        address expectedSigner = msg.sender == alice ? bob : alice;
        bytes32 stateHash = keccak256(abi.encodePacked(
            _aliceBalance,
            _bobBalance,
            _nonce
        ));
        
        require(
            recoverSigner(stateHash, _signature) == expectedSigner,
            "Invalid signature"
        );
        
        nonce = _nonce;
        
        // Start challenge period
        expirationTime = block.timestamp + 1 days;
        
        emit DisputeInitiated(msg.sender, _nonce);
    }
    
    function challengeDispute(
        uint256 _aliceBalance,
        uint256 _bobBalance,
        uint256 _nonce,
        bytes memory _signature
    ) external onlyParticipants {
        require(_nonce > nonce, "Not a newer state");
        require(_aliceBalance + _bobBalance == aliceDeposit + bobDeposit, "Invalid balances");
        
        address expectedSigner = msg.sender == alice ? bob : alice;
        bytes32 stateHash = keccak256(abi.encodePacked(
            _aliceBalance,
            _bobBalance,
            _nonce
        ));
        
        require(
            recoverSigner(stateHash, _signature) == expectedSigner,
            "Invalid signature"
        );
        
        nonce = _nonce;
        
        // Reset challenge period
        expirationTime = block.timestamp + 1 days;
    }
    
    function finalizeDispute() external {
        require(block.timestamp >= expirationTime, "Challenge period active");
        require(!channelClosed, "Already closed");
        
        channelClosed = true;
        
        // Use last known valid state
        // This is simplified - real implementation would store the disputed state
        uint256 aliceFinal = aliceDeposit; // Placeholder
        uint256 bobFinal = bobDeposit;     // Placeholder
        
        if (aliceFinal > 0) payable(alice).transfer(aliceFinal);
        if (bobFinal > 0) payable(bob).transfer(bobFinal);
        
        emit ChannelClosed(aliceFinal, bobFinal);
    }
    
    function recoverSigner(bytes32 _message, bytes memory _signature)
        internal
        pure
        returns (address)
    {
        bytes32 ethSignedMessageHash = keccak256(abi.encodePacked(
            "\x19Ethereum Signed Message:\n32",
            _message
        ));
        
        (bytes32 r, bytes32 s, uint8 v) = splitSignature(_signature);
        return ecrecover(ethSignedMessageHash, v, r, s);
    }
    
    function splitSignature(bytes memory _signature)
        internal
        pure
        returns (bytes32 r, bytes32 s, uint8 v)
    {
        require(_signature.length == 65, "Invalid signature length");
        
        assembly {
            r := mload(add(_signature, 32))
            s := mload(add(_signature, 64))
            v := byte(0, mload(add(_signature, 96)))
        }
    }
}

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// L1 to L2 message passing
contract L1ToL2MessageBridge {
    struct Message {
        address sender;
        address target;
        bytes data;
        uint256 value;
        uint256 gasLimit;
        uint256 nonce;
    }
    
    mapping(bytes32 => bool) public sentMessages;
    mapping(bytes32 => bool) public relayedMessages;
    
    uint256 public nonce;
    
    event MessageSent(
        address indexed sender,
        address indexed target,
        bytes32 indexed messageHash,
        bytes data
    );
    
    function sendMessage(
        address _target,
        bytes calldata _data,
        uint256 _gasLimit
    ) external payable {
        require(_gasLimit >= 21000, "Gas limit too low");
        
        Message memory message = Message({
            sender: msg.sender,
            target: _target,
            data: _data,
            value: msg.value,
            gasLimit: _gasLimit,
            nonce: nonce++
        });
        
        bytes32 messageHash = hashMessage(message);
        sentMessages[messageHash] = true;
        
        emit MessageSent(msg.sender, _target, messageHash, _data);
    }
    
    function relayMessage(
        address _sender,
        address _target,
        bytes calldata _data,
        uint256 _value,
        uint256 _gasLimit,
        uint256 _nonce
    ) external {
        Message memory message = Message({
            sender: _sender,
            target: _target,
            data: _data,
            value: _value,
            gasLimit: _gasLimit,
            nonce: _nonce
        });
        
        bytes32 messageHash = hashMessage(message);
        
        require(sentMessages[messageHash], "Message not sent");
        require(!relayedMessages[messageHash], "Message already relayed");
        
        relayedMessages[messageHash] = true;
        
        // Execute the message on L2
        (bool success, ) = _target.call{value: _value, gas: _gasLimit}(
            abi.encodePacked(_data, _sender)
        );
        
        require(success, "Message execution failed");
    }
    
    function hashMessage(Message memory _message) 
        internal 
        pure 
        returns (bytes32) 
    {
        return keccak256(abi.encode(
            _message.sender,
            _message.target,
            _message.data,
            _message.value,
            _message.gasLimit,
            _message.nonce
        ));
    }
}

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// Performance benchmarking script
class L2PerformanceAnalyzer {
    constructor() {
        this.metrics = {
            optimistic_rollup: {
                tps: 2000,
                finality_time: 604800, // 7 days in seconds
                gas_cost_reduction: 10,
                security_assumptions: 'honest majority'
            },
            zk_rollup: {
                tps: 2000,
                finality_time: 600, // 10 minutes
                gas_cost_reduction: 40,
                security_assumptions: 'cryptographic proof'
            },
            state_channel: {
                tps: 'unlimited',
                finality_time: 1, // Instant
                gas_cost_reduction: 1000,
                security_assumptions: 'both parties online'
            },
            ethereum_l1: {
                tps: 15,
                finality_time: 900, // 15 minutes
                gas_cost_reduction: 1,
                security_assumptions: 'full consensus'
            }
        };
    }
    
    calculateCostSavings(solution, transactions_per_day) {
        const l1_cost_per_tx = 50; // USD
        const reduction_factor = this.metrics[solution].gas_cost_reduction;
        
        const l2_cost_per_tx = l1_cost_per_tx / reduction_factor;
        const daily_savings = (l1_cost_per_tx - l2_cost_per_tx) * transactions_per_day;
        
        return {
            l1_daily_cost: l1_cost_per_tx * transactions_per_day,
            l2_daily_cost: l2_cost_per_tx * transactions_per_day,
            daily_savings: daily_savings,
            annual_savings: daily_savings * 365
        };
    }
    
    analyzeScalabilityLimits(solution) {
        const metrics = this.metrics[solution];
        
        return {
            theoretical_max_tps: metrics.tps,
            practical_bottlenecks: this.getBottlenecks(solution),
            scaling_factors: this.getScalingFactors(solution)
        };
    }
    
    getBottlenecks(solution) {
        const bottlenecks = {
            optimistic_rollup: ['sequencer capacity', 'L1 data availability'],
            zk_rollup: ['proof generation time', 'prover hardware requirements'],
            state_channel: ['routing liquidity', 'watchtower availability'],
            ethereum_l1: ['block gas limit', 'consensus time']
        };
        
        return bottlenecks[solution] || [];
    }
    
    getScalingFactors(solution) {
        return {
            optimistic_rollup: {
                data_compression: 8,
                computation_offchain: 100,
                batch_processing: 10
            },
            zk_rollup: {
                data_compression: 40,
                computation_offchain: 100,
                batch_processing: 10
            },
            state_channel: {
                data_compression: 1000,
                computation_offchain: 1000,
                batch_processing: 1
            }
        }[solution] || {};
    }
}

// Usage example
const analyzer = new L2PerformanceAnalyzer();

const solutions = ['optimistic_rollup', 'zk_rollup', 'state_channel'];
const daily_transactions = 10000;

solutions.forEach(solution => {
    console.log(`\n=== ${solution.toUpperCase()} ANALYSIS ===`);
    
    const cost_analysis = analyzer.calculateCostSavings(solution, daily_transactions);
    console.log('Cost Analysis:', cost_analysis);
    
    const scalability = analyzer.analyzeScalabilityLimits(solution);
    console.log('Scalability:', scalability);
});

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// Security patterns for L2 implementations
contract L2SecurityPatterns {
    // Prevent sequencer censorship
    mapping(address => uint256) public lastInclusionBlock;
    uint256 public constant MAX_CENSORSHIP_TIME = 1 days;
    
    function enforceInclusion(bytes calldata _transaction) external {
        require(
            block.timestamp - lastInclusionBlock[msg.sender] > MAX_CENSORSHIP_TIME,
            "Censorship period not exceeded"
        );
        
        // Force include transaction in next batch
        _forceIncludeTransaction(_transaction);
    }
    
    // Prevent data availability attacks
    function commitBatch(
        bytes32 _batchRoot,
        bytes calldata _batchData
    ) external {
        require(_batchData.length > 0, "Batch data required");
        require(
            keccak256(_batchData) == _batchRoot,
            "Batch data mismatch"
        );
        
        // Store batch data for availability
        _storeBatchData(_batchRoot, _batchData);
    }
    
    // MEV protection for L2 transactions
    function commitWithMEVProtection(
        bytes32 _commitment,
        uint256 _revealDeadline
    ) external {
        require(_revealDeadline > block.timestamp + 1 hours, "Reveal too soon");
        
        // Two-phase commit to prevent MEV
        _storeCommitment(msg.sender, _commitment, _revealDeadline);
    }
    
    function revealTransaction(
        bytes calldata _transaction,
        uint256 _nonce
    ) external {
        bytes32 commitment = keccak256(abi.encodePacked(_transaction, _nonce));
        
        require(_verifyCommitment(msg.sender, commitment), "Invalid commitment");
        require(block.timestamp >= _getRevealTime(msg.sender), "Too early");
        
        _executeTransaction(_transaction);
    }
    
    // Emergency circuit breaker
    bool public emergencyPaused;
    address public emergencyOperator;
    
    modifier emergencyStop() {
        require(!emergencyPaused, "Emergency stop active");
        _;
    }
    
    function emergencyPause() external {
        require(msg.sender == emergencyOperator, "Unauthorized");
        emergencyPaused = true;
    }
    
    // Implementation stubs
    function _forceIncludeTransaction(bytes calldata) internal {}
    function _storeBatchData(bytes32, bytes calldata) internal {}
    function _storeCommitment(address, bytes32, uint256) internal {}
    function _verifyCommitment(address, bytes32) internal returns (bool) {}
    function _getRevealTime(address) internal returns (uint256) {}
    function _executeTransaction(bytes calldata) internal {}
}

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graph TD
    A[Ethereum L1] --> B[Optimistic Rollup L2]
    A --> C[ZK-Rollup L2]
    B --> D[State Channel L3]
    C --> E[Application-Specific L3]
    B --> F[Cross-Rollup Bridge]
    C --> F