L2ToL2CrossDomainMessengerGatewayAdapterStorage

struct L2ToL2CrossDomainMessengerGatewayAdapterStorage {
    /// @notice Trusted remote gateway adapter (the sibling adapter) per EVM chainId (0 = unset). APPEND-ONLY.
    mapping(uint256 chainId => address remoteAdapter) _remoteAdapters;
    /// @notice Replay guard: per source chainId, the set of consumed message ids. APPEND-ONLY.
    mapping(uint256 chainId => mapping(bytes32 id => bool used)) _executed;
    /// @notice Monotonic outbound counter. The OP messenger exposes no per-message id to the delivery target, so
    ///         each dispatched message carries this source-minted nonce, giving a globally-unique (source, nonce)
    ///         id on delivery (matching the unique-id semantics of the CCIP/LayerZero/Wormhole siblings).
    uint256 _outboundNonce;
}