Implement invoice cross-contract composability

[Kingsman-99]

Label: complexity: high
Points: 200

Description

Other Soroban contracts cannot programmatically create StellarSplit invoices without knowing internal storage details. This issue adds a standardised IInvoiceFactory trait interface with create_invoice_for() — allowing any authorised external contract to create invoices on behalf of users.

Technical Context

Involves lib.rs — new create_invoice_for(env, caller: Address, creator: Address, recipients, amounts, token, deadline) -> u64. Requires caller.require_auth(). Store authorised_factories: Vec<Address> in persistent storage. Assert caller is in the list. Then execute standard create_invoice() logic with creator.

Acceptance Criteria

• authorise_factory(env, address) requires admin auth
• create_invoice_for() requires caller auth and caller must be authorised factory
• Unauthorised caller panics with "not authorised factory"
• Invoice created with correct creator (not the factory address)
• Test authorises factory contract, creates invoice via factory, verifies creator field
• All existing cargo tests pass
• cargo clippy passes with zero warnings

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[TheBigWealth89]

@TheBigWealth89 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I have gone through the task description and will like to work on this please. Thank you

ℹ️ Repo Maintainers: To accept this application, review their application or assign @TheBigWealth89 to this issue.

[Jonathan-ai9]

@Jonathan-ai9 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi,I’d like to work on this issue. I will implement the invoice factory interface with authorized factory management, secure access control, and invoice creation on behalf of users, along with comprehensive tests to verify authorization and creator ownership behavior.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Jonathan-ai9 to this issue.

[ahmadadebayo78-boop]

@ahmadadebayo78-boop has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @ahmadadebayo78-boop to this issue.

[drips-wave]

Congratulations, @ahmadadebayo78-boop! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @ahmadadebayo78-boop: 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.

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