[engine] Rule: Detect unchecked return values from external Soroban calls

[Gbangbolaoluwagbemiga]

Context

Ignoring Result from cross-contract calls can leave state inconsistent.

What to build

Implement S013 (Unchecked External Call). Ensure results are handled.

[Nanle-code]

@Nanle-code has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

let me work on this

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

[drips-wave]

Congratulations, @Nanle-code! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @Nanle-code: 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 marked as completed by a Drips Wave moderator for @Nanle-code as part of the Stellar Wave Program's 3rd Wave 🥳

Moderator's reason: [Auto-assessed] The contributor implemented the requested security rule (S019, originally S013 in the issue) to detect unchecked external calls. The PR was merged by maintainers, effectively completing the work for this issue despite the issue remaining open.

😎 @Nanle-code: 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.

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

ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.