feat(backend): fix #812 implement trigger payout endpoint with grace …

[fhayvy]

Closes #812

PR Description

This Pull Request implements the POST /api/plans/payout endpoint in the Axum backend to resolve the issue.

How the Flow Works Now:

1. Request Reception: The endpoint /api/plans/payout receives a PayoutRequest containing the plan owner's wallet address.
2. Authentication: The request passes through the signature_auth_middleware, which verifies the cryptographic signature (Ed25519) of the request body to ensure authenticity.
3. Database Transaction & Pessimistic Locking: A database transaction is started, and the active plan is retrieved using FOR UPDATE to lock the row and prevent concurrent trigger requests.
4. Grace Period Verification: The handler checks if the grace period has elapsed (now >= last_ping + grace_period_seconds). If the owner is still active (within the grace period), the request is rejected with 400 Bad Request.
5. Yield Projection: The handler calculates the final accrued yield up to the current time using compute_projected_accrued_yield and adds it to the principal to get the total payout amount.
6. Pro-rata Beneficiary Distribution:
   • The handler loads all beneficiaries associated with the plan.
   • The total payout amount is split based on each beneficiary's allocation_bps (basis points).
   • Any remainder/dust from integer division is allocated to the last beneficiary to ensure 100% of the funds are distributed.
7. Payout Record Insertion: An entry is inserted into the payouts table for each beneficiary, specifying the type (fiat or crypto) and status (processing).
8. Distribution Initiation:
   • If the beneficiary has fiat_anchor_info set, the handler parses the details and triggers a fiat payout via the simulated Stellar Anchor off-ramp (state.anchor.create_payout).
   • If it is a crypto payout, the handler logs the transaction to simulate the on-chain transfer.
9. Plan Deactivation: The plan is updated in the database, setting is_active = false and status = 'PAID_OUT'.
10. Cache Invalidation: The Redis/memory cache is invalidated for both the owner and the beneficiaries.

---

Changed

• backend/src/api.rs:
  • Implemented the trigger_payout handler to process payouts, calculate yields, insert payout records, and deactivate plans.
  • Implemented the parse_fiat_anchor_info helper to parse anchor details for the AnchorPayoutRequest.
• backend/tests/api_tests.rs:
  • Added test_trigger_payout_invalid_signature to verify signature auth failure.
  • Added test_trigger_payout_valid_signature_not_found to verify successful signature auth and routing to the database handler.

---

Testing

The changes were verified by running the backend integration test suite.

cd backend
cargo test

All 25 tests compiled and passed successfully:

running 10 tests
test test_router_compiles ... ok
test test_create_plan_validation_negative_amount ... ok
test test_create_plan_validation_empty_owner ... ok
test test_create_plan_validation_invalid_bps ... ok
test test_get_plans_returns_cached_response_without_db_access ... ok
test test_ping_plan_invalid_signature ... ok
test test_trigger_payout_invalid_signature ... ok
test test_trigger_payout_valid_signature_not_found ... ok
test test_get_plans_is_public ... ok
test test_create_plan_with_valid_signature ... ok

test result: ok. 10 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.01s

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[ONEONUORA]

Great job @fhayvy
Thank you for your contribution