CrosschainLinkStorage

struct CrosschainLinkStorage {
    /// @notice Per source-chain link, keyed by a "chain-only" interoperable address. APPEND-ONLY.
    mapping(bytes chain => Link) _links;
    /// @notice Inbound message handler per 4-byte payload tag. APPEND-ONLY.
    mapping(bytes4 tag => address handler) _handlers;
    /// @notice De-duplication set, keyed by `keccak256(abi.encode(gateway, receiveId))` — ERC-7786 only
    ///         guarantees receiveId uniqueness per-gateway, so the key is gateway-scoped. APPEND-ONLY.
    mapping(bytes32 usedKey => bool used) _used;
}