[Contracts] open-market: Slippage protection (min_amount_out) on AMM swaps

[Olowodarey]

Problem
calculate_swap_output in liquidity.rs computes output from the constant-product formula, but swaps execute without a caller-supplied minimum. Between quote and execution, reserves can move (front-running/MEV or concurrent swaps), so a trader can receive far less than expected with no protection.

Requirements

• Add a min_amount_out: i128 parameter to the swap entrypoint; revert with a new SlippageExceeded error when amount_out < min_amount_out.
• Add an optional deadline (ledger timestamp) check; revert DeadlineExpired when env.ledger().timestamp() > deadline.
• Keep all math on the checked-arithmetic path already used in liquidity.rs.

Acceptance Criteria

• Swap succeeds at/above the minimum, reverts below it, and reverts past the deadline. Covered by tests.

Files

• contracts/open-market/src/liquidity.rs
• contracts/open-market/src/market.rs
• contracts/open-market/src/errors.rs
• contracts/open-market/tests/liquidity_tests.rs

[lordemaverick]

My name is MC Christ, and I am a Full-Stack and Smart Contract Developer with experience building web applications, backend services, and blockchain-based solutions. I would like to express my interest in working on this issue and contributing to the project.

What attracted me to this issue is the opportunity to contribute to a project that is actively creating value for its users while collaborating with a talented open-source community. Throughout my development journey, open source has been an important source of learning and growth, and I enjoy giving back by contributing high-quality code and helping improve projects that others rely on.

I am confident that my experience in software development and problem-solving will allow me to approach this issue effectively and deliver a reliable solution. I am committed to clear communication, timely updates, and writing maintainable code that aligns with the project's standards.

Thank you for considering my application. I would appreciate the opportunity to contribute and look forward to working with the team.

[safal207]

Hi! I'm interested in #1758.

My proposed scope is the min_amount_out guard, optional deadline validation, and focused regression tests covering exact boundaries and unchanged balances/reserves on rejection.

I noticed another contributor has expressed interest. Is this issue still available for assignment?

Before starting, could you confirm the funded reward amount and currency, acceptance criteria, payout timing, and the contribution/license terms? The issue currently says “Maybe Rewarded”, so I don't want to assume payment is agreed.

I would start by reproducing the current behavior against a pinned main commit and keep the PR limited to this issue.

Alexey Safonov
Independent QA — payment recovery and financial-state verification

[guptakumarranjeet150]

Hi maintainers,

I would love to take this on. My planned approach:

• Implement [Contracts] open-market: Slippage protection (min_amount_out) on AMM swaps with explicit require_auth checks, clean storage layouts, and robust Soroban contract logic.
• Add comprehensive unit tests verifying both happy-path invocations and unauthorized revert scenarios.

Happy to pick this up today—please assign to me!