[Osaodion]

Overview

This PR adds a low refund-reserve alert to the refund contract so merchants are warned before their reserve is exhausted. A RefundReserveLow event is emitted when a withdrawal or refund causes the reserve to cross below a merchant-set warning level, firing once on the crossing rather than on every subsequent operation while the reserve stays low.

Related Issue

Changes

🔔 Low Reserve Alerts

• [MODIFY] contracts/refund/src/lib.rs

  • Emits RefundReserveLow when a withdrawal or refund leaves the reserve below the merchant-set warning level.
  • Tracks the crossing so the event fires only when the reserve transitions below the level, not on every refund while it remains low.

• [ADD] contracts/refund/src/test_refund_reserve.rs

  • Tests covering the event firing on the crossing and staying silent on subsequent operations while the reserve remains low.

• [MODIFY] contracts/refund/README.md

  • Documents the new function(s), parameters, errors and the RefundReserveLow event.

Verification Results

cargo fmt --all -- --check
cargo clippy -- -D warnings
cargo test --workspace

Acceptance Criteria	Status
The event fires when the reserve crosses below the level, not on every refund while it stays low	✅ Crossing-only emission covered by test_refund_reserve.rs
cargo fmt --all -- --check, cargo clippy -- -D warnings and cargo test --workspace pass	✅ All checks pass
The contract's README documents the new function(s), parameters, errors and events	✅ README updated with RefundReserveLow

Closes #814