Add invoice metadata field for off-chain content hash (IPFS)

[Kingsman-99]

Overview

Invoice descriptions, attachments, and rich metadata cannot fit in contract storage cost-efficiently. Add a metadata_hash field to point to off-chain content (IPFS CID or SHA-256 hash) stored alongside the invoice.

Acceptance Criteria

• InvoiceParams gains metadata_hash: Option<BytesN<32>>
• Hash stored in per-invoice persistent storage
• get_invoice returns metadata_hash in the invoice struct
• update_metadata_hash(invoice_id, new_hash: BytesN<32>) callable only by the creator; emits MetadataUpdated event
• metadata_hash is optional — existing invoices without it return None
• Contract does NOT validate or fetch the off-chain content — hash is stored as-is
• MetadataUpdated { invoice_id, old_hash, new_hash, ledger } event emitted on update
• Integration tests: create with hash, create without hash, update hash, verify stored value

[DevSolex]

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

Hi Maintainer,

I’m a smart contract and full-stack developer and would love to contribute to this issue. I’m an experienced contributor with hands-on expertise in Rust, Soroban, Cairo, and TypeScript.

I’m passionate about building secure, scalable blockchain solutions, with a strong emphasis on writing clean and maintainable code. Based on the scope of this issue, I’m confident I can deliver a complete solution within 24 hours of assignment.

I’d greatly appreciate the opportunity to contribute and help move this forward.

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[emteebug12-jpg]

@emteebug12-jpg has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainers! I’d love to help out with this issue. I’ve checked the current codebase/documentation and know exactly what needs to be updated to make this clearer. I will ensure everything aligns perfectly with your existing contribution guidelines.

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[dhareymu]

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

Hi maintainer,

Please, I would love to work on this project to fix the issues for you. I promise to work on it swiftly and create a PR for it in no time.

I look forward to working with you. Thank you.

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[jasmine874]

@jasmine874 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello dear maintainer i would love to work along side you on this task sir.

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[iamkingvalor]

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

please, can i work on this?

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[Caneryy]

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

Hello, may I work on this issue?

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[drips-wave]

Congratulations, @jasmine874! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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