[CT-16] Implement Cancellation Policy Enforcer for Flexible/Moderate/Strict policies in Rust

[devwums]

Problem

Cancellation policy enforcement is inconsistently applied across booking types. Different refund amounts are computed in different places with no single codified source of truth.

Proposed Solution

Create contracts/cntr/cancellation_policy.rs defining #[derive(Debug, PartialEq, Clone)] pub enum CancellationPolicy { Flexible, Moderate, Strict } and implementing pub fn apply_policy(policy: CancellationPolicy, hours_before_start: u64, amount_stroops: i128) -> i128. Rules — Flexible: always 100% refund. Moderate: 100% if 48h+, 50% if 24–47h, 0% if <24h. Strict: 100% if 96h+, 0% otherwise. Integer arithmetic only. All implementation must live inside contracts/cntr/.

Acceptance Criteria

• File at contracts/cntr/cancellation_policy.rs
• All 3 policies implemented correctly
• CancellationPolicy derives Debug, PartialEq, Clone
• Flexible always returns amount_stroops
• At least 9 unit tests (3 per policy, one per refund rule per policy)
• No floating-point arithmetic
• Compiles with cargo test

[42natus]

@42natus has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi

Please assign me this task. I’ll implement the CancellationPolicy enum and apply_policy function with correct rule-based refund logic using integer arithmetic, and add comprehensive unit tests covering all policy scenarios.

ETA: 1–2 hours

ℹ️ Repo Maintainers: To accept this application, review their application or assign @42natus to this issue.

[RennyThompson]

@RennyThompson has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would love to take on this issue.

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

[drips-wave]

Congratulations, @RennyThompson! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @RennyThompson: 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 🌊