Introduce strict validation against overlapping subscription tiers for a single account

[elizabetheonoja-art]

Task: Introduce strict validation against overlapping subscription tiers for a single account

Focus Area: Soroban Smart Contract Optimization, Security Hardening, and Reliability.

[blurbeast]

@blurbeast has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

hello my Boss, can i work on this issue please ?

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

[Tolais]

@Tolais has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello, I can do this.

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

[drips-wave]

Congratulations, @Tolais! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Tolais: 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.

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