Implement reentrancy guards utilizing transient storage for cross-contract fractional token swaps

[Damola-Sodiq]

Description

Secure the fractional token exchange functions against malicious reentrancy callbacks by leveraging ephemeral transient storage locks.

Architecture & Context

When the smart contract invokes an external token contract to perform a transfer, malicious tokens can execute a callback into the original vault before the state balances are updated. Using transient storage (state that clears automatically at the end of the transaction) provides an ultra-cheap, bulletproof mutex lock.

Technical Requirements

• Implement a non_reentrant modifier pattern in the Soroban SDK utilizing temporary storage keys.
• Wrap all state-mutating mint, burn, and swap functions within this lock.
• Ensure the lock is flawlessly released even if an internal sub-routine fails gracefully.

Acceptance Criteria

• Cross-contract reentrancy attempts immediately panic and revert the state.
• Normal, non-recursive execution flows flawlessly.
• Transient storage rent costs are mathematically negligible.

[Digitalasu]

Hello, this task aligns well with my experience, and I'm confident I can resolve it with a clean and maintainable implementation. Kindly assign it to me.

[Fatimasanusi]

Hi maintainer can i be assigned to work on this?

[grantfox-oss]

🦊 GrantFox — @Fatimasanusi has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #476)
2. Your PR will be reviewed by the Sahara-Pay maintainers

Good luck! Track your progress on GrantFox.