Add Cross-Contract Transfer-Out Call in `withdraw_to_replace` Before Deleting Custody Record

[Oluwaseyi89]

Summary

Update the buffer_pool contract so that the withdraw_to_replace function performs a cross-contract transfer-out call to the relevant asset contract before deleting the custody record, ensuring atomicity and traceability of asset movement.

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Technical Context

• Motivation: Currently, custody records may be deleted before the actual asset transfer is confirmed, risking asset loss or inconsistent state. Performing the transfer-out as a cross-contract call before deletion ensures that assets are safely moved and the custody record is only removed upon successful transfer.
• Current State: The withdraw_to_replace function deletes the custody record without first performing a cross-contract transfer-out, which can lead to state inconsistencies or asset loss if the transfer fails.

Requirements

Contract Changes

• Refactor withdraw_to_replace to:
  • Initiate a cross-contract transfer-out call to the asset contract for the specified token/amount.
  • Only delete the custody record after the transfer-out call returns success.
• Ensure error handling is robust: if the transfer fails, the custody record must remain intact and no state is lost.
• Emit events for both the transfer-out action and the custody record deletion for off-chain traceability.

Acceptance Criteria

• Custody records are only deleted after a successful cross-contract transfer-out.
• All error paths leave custody records intact.
• Events are emitted for transfer-out and deletion.
• Unit tests cover:
  • Successful transfer-out and custody deletion
  • Failed transfer-out with custody record retention
  • Event emission and off-chain traceability

Definition of Done

• PR with contract code changes and tests
• Documentation updated to describe the new transfer-out flow
• Team review completed

Working Directory:

stellar-core/carbon-asset-factory/contracts/buffer_pool

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[brodapeethar]

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[Francis6-git]

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