Payment Router

interface IPaymentRouter {
    /// @notice Pay for a checkout session
    function pay(
        bytes32 sessionId,
        address recipient,
        uint256 amount
    ) external;

    /// @notice Pay using EIP-2612 permit (approve + pay in one transaction)
    function payWithPermit(
        bytes32 sessionId,
        address recipient,
        uint256 amount,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    /// @notice Check if a session has already been paid on-chain
    function sessionPaid(bytes32 sessionId) external view returns (bool);

    /// @notice Get the USDC token address used by this router
    function usdc() external view returns (address);

    /// @notice Emitted on every successful payment
    event CheckoutPayment(
        bytes32 indexed sessionId,
        address indexed from,
        address indexed to,
        uint256 amount
    );

    error InvalidRecipient();
    error InvalidRecipientAddress();
    error InvalidAmount();
    error InvalidSessionId();
    error SessionAlreadyPaid();
}