// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

contract ReplayPermit {
    address public signer;
    mapping(address => uint256) public balances;

    constructor(address _signer) {
        signer = _signer;
    }

    function claim(uint256 amount, uint8 v, bytes32 r, bytes32 s) external {
        bytes32 msgHash = keccak256(abi.encodePacked(msg.sender, amount));
        address recovered = ecrecover(msgHash, v, r, s);
        require(recovered == signer, "bad sig");

        // no nonce, no deadline, replayable forever
        balances[msg.sender] += amount;
    }
}