Pair clear_all_invoices with backup and restore safety checks

[Baskarayelu]

Description

Ensure admin clear operations cannot leave orphan indexes; document restore ordering.

Requirements and context

• Must be secure, tested, and documented
• Should be efficient and easy to review
• Align with existing Soroban contract patterns in quicklendx-contracts

Suggested execution

• Fork the repo and create a branch
• git checkout -b feature/clear-invoices-restore-safety
• Implement changes
• Write contract: src/invoice.rs, src/backup.rs
• Write comprehensive tests: src/test_backup.rs, src/test_storage.rs
• Add documentation: docs/contracts/backup.md
• Include NatSpec-style comments (Rust doc comments on public items)
• Validate security assumptions

Test and commit

• Run tests
• Cover edge cases
• Include test output and security notes

Example commit message

feat: pair clear_all_invoices with restore safety

Guidelines

• Minimum 95 percent test coverage
• Clear documentation
• Timeframe: 96 hours

[blessme247]

@blessme247 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @blessme247 to this issue.

[drips-wave]

Congratulations, @blessme247! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @blessme247: 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

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🌊 Happy Wave 🌊

[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @blessme247 as part of the Stellar Wave Program's 3rd Wave 🥳

Moderator's reason: [Auto-assessed] The contributor implemented the requested safety checks for invoice clearing and backup restoration, specifically fixing a bug in index erasure and documenting the process. PR #767 has been open for over 48 hours without maintainer objections and provides high-quality code, documentation, and comprehensive tests.

😎 @blessme247: 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.

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