Issue 152: defi: Build the formal Flash Loan callback interface

[AlAfiz]

Description

We previously scaffolded the fee for flash loans, but to actually execute them, we need a standard cross-contract callback interface.
When a borrower requests a flash loan, our contract must send them the tokens, and then immediately call a specific execute_operation function on their smart contract.
If their contract fails to return the principal plus the fee by the end of that specific call, our contract must panic and revert the entire ledger state.
This is complex, synchronous DeFi architecture that requires deep knowledge of Soroban's cross-contract invocation.

Requirements

• Define a FlashLoanReceiver trait that external borrower contracts must implement.
• Update the flash_loan function to transfer the requested tokens to the borrower's address.
• Use env.invoke_contract() to trigger the borrower's callback function.
• Assert that the pool's token balance after the callback is >= the balance before the loan + the flash loan fee.

[LaahAbba]

@LaahAbba has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

I'm a full stack develop I'll like to work on this issue because It picks my interest and Ive got experience with similar projects I'll have it solved in 24 hours or less

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

[T-kesh]

@T-kesh has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

i can work on this

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

[drips-wave]

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

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