Add minimum funding amount before release

[Kingsman-99]

Description

Allow creators to set a minimum funding amount (absolute value) that must be reached before an invoice can be released. If the invoice is fully paid but below the threshold, it stays pending.

Acceptance Criteria

• InvoiceOptions accepts an optional min_funding_amount: Option<i128> field
• _pay checks invoice.funded >= min_funding_amount before triggering auto-release
• If threshold not met, invoice remains Pending even when funded >= total
• A test test_min_funding_amount_delays_release verifies release is blocked below threshold
• A test test_min_funding_amount_releases_when_met verifies release triggers when met

Context

Note: min_funding_bps (percentage-based) already exists. This is an absolute amount alternative. Auto-release logic is at the bottom of _pay in contracts/split/src/lib.rs.

[bashir1738]

Hello, I'm a smart contract and full stack developer, open for contributions. contributed to over 20 project on OnlyDust and Drips , with expertise in Solidity, Cairo, JavaScript, TypeScript, and RUST. I am passionate about building secure and scalable blockchain solutions, and I would love the opportunity to contribute my skills toward solving this issue.

[Phantomcall]

I’d like to take this on. I’ve been contributing to Rust/Soroban projects across multiple Stellar Waves, and I’m comfortable working with contract payment and release logic. I’ll add support for an absolute min_funding_amount, update the auto-release flow in _pay to respect the threshold, and add comprehensive tests covering both delayed and successful release scenarios. I’ll make sure the implementation remains compatible with the existing min_funding_bps behavior and that all tests pass before submitting the PR.

[grantfox-oss]

🦊 GrantFox — @bashir1738 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 #165)
2. Your PR will be reviewed by the Stellar-split maintainers

Good luck! Track your progress on GrantFox.