Add withdrawer allowlist enforcement

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox campaign. This is a smart-contract issue for the GrantFox campaign. Optional allowlist of addresses allowed to withdraw on behalf of recipient.

Requirements and Context

• Implement per the description
• Add focused tests
• Document any API changes
• Run the standard verification for this domain
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b feature/withdrawer-allowlist

2. Implement changes
   • contracts/contracts/streampay-stream/src/withdrawer.rs (new)
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

feat: add withdrawer allowlist enforcement

Acceptance Criteria

• Implementation matches design
• Tests pass for the domain
• Code review approved
• Docs updated

Guidelines

• Minimum 95% test coverage with cargo test
• require_auth on every state-changing entrypoint
• Overflow-safe math; no unwrap() in production paths
• Clear NatSpec-style /// rustdoc
• Timeframe: 96 hours

[MK0042]

@MK0042 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I will like to apply. I understand that it can be difficult to trust someone without a track record, but I will really appreciate the opportunity to demonstrate my skills. I would also be grateful for the chance to earn some points along the way.

Thank you for considering my application.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @MK0042 to this issue.

[drips-wave]

Congratulations, @MK0042! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @MK0042: 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 🌊

[mosharraftimes2018-dev]

@mosharraftimes2018-dev has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue because it matches my interest in front of development and open source of contribution.I have some experience with react,java script,html,CSS and Git/GitHub

ℹ️ Repo Maintainers: To accept this application, review their application or assign @mosharraftimes2018-dev to this issue.

[Blaqkenny]

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

Hello Maintainer, please can I work on this issue and give you a better result

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

[ifygreg01-best]

@ifygreg01-best has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi Maintainer, I'd like to work on this issue by implementing withdrawer allowlist enforcement with tests and documentation.

Thanks!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ifygreg01-best to this issue.