Add on-chain credit redemption contract for converting credits to rewards

[prodbycorne]

Overview

Credits accrued via the farming-pool (get_credits, calculate_credits) have no on-chain redemption mechanism. They exist as an accounting value in storage but cannot currently be converted to any reward token. A CreditRedeemer contract is needed to close this loop.

Design

CreditRedeemer
  ├── initialize(admin, reward_token, pool: Address, credits_per_token: u128)
  ├── redeem(user)          — burns user credits, transfers reward tokens
  ├── set_credits_per_token(admin, new_rate)
  └── redemption_info() -> RedemptionInfo

Redemption Flow

1. User calls redeem
2. Redeemer reads user's total credits from the farming-pool contract via cross-contract call
3. Computes reward_amount = total_credits / credits_per_token
4. Marks credits as redeemed (stores redeemed_credits for the user)
5. Transfers reward_amount of reward_token to user
6. Emits redeemed event

Credit Snapshot Problem

Credits accrue continuously — the redeemer cannot "burn" them from the pool contract. Instead, use a snapshot model:

• CreditRedeemer stores credits_at_last_redemption per user
• On redeem: redeemable_credits = current_credits - credits_at_last_redemption
• Updates the snapshot after redemption

pub struct RedeemKey {
    pub user: Address,
    pub last_redeemed_credits: i128,
}

Token Supply Consideration

The admin must fund the CreditRedeemer contract address with enough reward_token balance before redemptions can proceed. Add a reward_balance() getter.

Acceptance Criteria

• contracts/credit-redeemer/ created
• Cross-contract call to FarmingPoolClient::get_credits (or calculate_credits)
• Snapshot model prevents double-redemption without burning credits
• set_credits_per_token admin function for rate adjustment
• reward_balance getter returns contract's current token balance
• Tests: first redeem, second redeem (only new credits), zero redeemable credits
• Test: insufficient reward token balance returns typed error

[GazzyLee]

hey boss, I’d be happy to take this on. I can implement the redemption flow end-to-end, ensuring credits can be redeemed safely and efficiently while preventing double-redemptions through a robust snapshot-based approach. I’ll also cover the cross-contract interactions, admin controls, edge cases, and test scenarios to make sure the contract is secure, reliable, and easy to review. Please assign this issue to me.

[grantfox-oss]

🦊 GrantFox — @GazzyLee has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #31)
2. Your PR will be reviewed by the SmartDropLabs maintainers

Good luck! Track your progress on GrantFox.