Add cross-contract composability interface for DeFi protocol integration

[Chuks-coderr]

Overview

External Soroban contracts such as lending protocols or DAOs cannot currently integrate with SoroStream streams programmatically, limiting composability within the Stellar DeFi ecosystem.

Problem

There is no standardized interface that external contracts can call to create, query, or interact with streams, preventing SoroStream from becoming a composable primitive in the Stellar DeFi stack.

Proposed Solution

• Define a StreamInterface trait exposing create_stream, withdraw, cancel_stream, get_stream, and get_claimable with standardized types
• Implement the trait on the SoroStream contract
• Document the interface as the canonical integration target for external contracts
• Provide a minimal cross-contract call example in the test suite

Acceptance Criteria

• StreamInterface trait defined in a dedicated module
• All listed functions exposed through the trait with correct signatures
• Cross-contract call integration test demonstrates an external contract creating and withdrawing from a stream
• Interface documented with parameter types and error codes
• ABI types remain backward compatible

[drips-wave]

Congratulations, @Abigail6168! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Abigail6168: 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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