Validate velocity_window is non-zero when velocity_limit is set

[Kingsman-99]

Description

velocity_limit and velocity_window together enforce a per-payer spend rate limit. If velocity_window == 0 but velocity_limit > 0, division by zero or undefined behaviour could occur when computing whether a payer has exceeded their limit.

Acceptance Criteria

• create_invoice returns ContractError::InvalidAmount when velocity_limit > 0 and velocity_window == 0
• No error when velocity_limit == 0 regardless of velocity_window
• Unit test verifies rejection for velocity_limit=1000, velocity_window=0
• Unit test verifies acceptance for velocity_limit=1000, velocity_window=3600
• cargo test passes

Context

• Target file: contracts/split/src/lib.rs

[Wiseman52]

@Wiseman52 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, kindly assign task. I’ve carefully reviewed the requirements and understand what is needed to resolve the issue.

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[baling-1]

@baling-1 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

hey maintainer kindly assign this to me

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[CodedBay]

@CodedBay has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

please assign

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[drips-wave]

Congratulations, @CodedBay! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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