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What you implement

Deploy one contract per token pair implementing the standard Rialto propAMM interface: a getAmountOut quote and a swapExactIn settle. Rialto calls them by their 4-byte selector, so match these signatures, or put a thin adapter in front if your AMM already exposes different ones. token0() and token1() are optional; Rialto never calls them, since the pair and ordering come from Rialto’s config. 
interface IPropPair {
    /// OPTIONAL — Rialto never calls these; pair & ordering come from config.
    function token0() external view returns (address);
    function token1() external view returns (address);

    /// QUOTE (read-only view). Exact-in only.
    /// zeroForOne = true  -> selling token0, receiving token1
    /// zeroForOne = false -> selling token1, receiving token0
    function getAmountOut(bool zeroForOne, uint256 amountIn)
        external view returns (uint256 amountOut);

    /// SETTLE (state-changing). Called by RialtoRouter only.
    function swapExactIn(
        bool zeroForOne,
        uint256 amountIn,
        uint256 amountOutMin,
        address to,
        uint256 deadline
    ) external payable returns (uint256 amountOut);
}
getAmountOut is sampled at quote time; swapExactIn settles. The trade direction zeroForOne is fixed by Rialto’s config ordering, not by token0() or token1(): zeroForOne = true means sell config-token0 and buy config-token1.

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Why the shape matters

The interface is a convention Rialto standardizes on, not a protocol constraint, but two things are coupled to the exact shape:
  • The settle selector is allowlisted onchain per pool, and the router patches the real input amount into the calldata at a fixed offset that assumes swapExactIn(bool, uint256 amountIn, …) with amountIn as the second argument. A different argument layout moves that offset.
  • The quote and settle selectors are currently a single shared interface across all propAMM pools.
payable is part of the standard signature so native-ETH pairs are possible.