Implement MPC session replay protection against coordinator replay

[Marvy247]

MPC nodes maintain a set of processed session IDs. Reject duplicate session initiations from the coordinator. Use a nonce or timestamp for fresh session identification.

[TINEROW]

@TINEROW has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello Maintainer, I’ve reviewed the issue and understand the requirements. I’m confident I can implement an effective solution. Please consider assigning it to me.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @TINEROW to this issue.

[Davidemulo]

@Davidemulo has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i will love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Davidemulo to this issue.

[drips-wave]

Congratulations, @Davidemulo! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @Davidemulo: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @Davidemulo as part of the Stellar Wave Program's 8th Wave 🥳

😎 @Davidemulo: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.