Add invoice contract monitoring hooks

[Kingsman-99]

Label: complexity: high
Points: 200

Description

Production contracts need structured observability for real-time monitoring dashboards. This issue adds a comprehensive monitoring event emitted on every state change — monitor_event with fields for function name, invoice ID, actor, gas used estimate, and timestamp — enabling real-time contract health observability.

Technical Context

Involves events.rs — add monitor_event(env, function: Symbol, invoice_id: u64, actor: &Address, timestamp: u64). Call from every public entry point in lib.rs (create_invoice, pay, release, refund) as the first operation. Use topic (symbol_short!("monitor"), function) for easy filtering.

Acceptance Criteria

• monitor_event emitted at the start of every public entry point
• Event topic is (symbol_short!("monitor"), function_name)
• Event data includes invoice ID, actor address, and ledger timestamp
• All 4 public functions emit monitoring events
• Test verifies monitoring event emitted with correct function name on each call
• All existing cargo tests pass
• cargo clippy passes with zero warnings

[Glam26]

I'd be happy to take this on.

I've worked on similar issues across multiple open-source and production projects, including feature development, refactoring, testing, documentation, performance improvements, and bug fixes. My approach is to first understand the existing architecture and conventions, then deliver a solution that is clean, maintainable, and aligned with the project's standards.

I'll make sure the implementation is thoroughly tested, well-documented where necessary, and covers relevant edge cases. I'm comfortable collaborating during review, incorporating feedback quickly, and ensuring the final result is production-ready.

[IyanuOluwaJesuloba]

Hello Maintainer.

I am a full stack web3 developer with professional experience in software development, integration and smart contract writing.

I understand the criticality of this task and I am confident that I will deliver accordingly.
I'll ensure to monitor_event emitted at the start of every public entry point, event topic is (symbol_short!("monitor"), function_name), that event data includes invoice ID, actor address, and ledger timestampe, and also ensure all 4 public functions emit monitoring events

I'd love to contribute my expertise to your project. Kindly assign this issue to me.

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[Nuwe10]

@Nuwe10 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I will like to work on this issue please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Nuwe10 to this issue.

[grantfox-oss]

🦊 GrantFox — @Nuwe10 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #180)
2. Your PR will be reviewed by the Stellar-split maintainers

Good luck! Track your progress on GrantFox.

[drips-wave]

Congratulations, @Nuwe10! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Nuwe10: 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.

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