Quest Engine: Staking Multiplier Implementation

Overview

Implemented staking multiplier feature that applies a boost to learner payouts based on their stake in the StakeVault contract.

Changes

1. Contract Implementation

Files:

• contracts/quest-engine/src/lib.rs
• contracts/quest-engine/src/types.rs

Added:

• StakeVaultClient interface to fetch multiplier from StakeVault contract
• StakeVault address to initialization parameters and storage
• Multiplier logic in review_submission function

Multiplier Logic:

• Fetches multiplier from StakeVault (basis points: 100 = 1.0x, 120 = 1.2x)
• Applies multiplier to base learner amount (after 15% fee)
• Caps boosted amount to available funds to prevent overflow
• Formula: boosted_amount = (base_amount * multiplier) / 100

Note: Current implementation caps boost to available quest funds. In production, employers should fund quests accounting for potential multipliers, or boosts should come from a separate authorized reward pool contract.

2. Tests

File: contracts/quest-engine/src/test.rs

Added:

• MockStakeVault contract returning 100 (1.0x) by default
• MockStakeVaultWithMultiplier returning 120 (1.2x)
• setup_with_multiplier() helper function
• 4 new tests:
  • test_review_submission_with_no_multiplier - Verifies 1.0x multiplier
  • test_review_submission_with_120_multiplier - Verifies 1.2x multiplier (capped)
  • test_review_submission_with_80_multiplier - Verifies 1.0x baseline
  • test_multiplier_math_correctness - Validates calculation logic

3. Updated Initialization

Breaking Change: initialize() now requires stake_vault parameter:

pub fn initialize(
    env: Env,
    admin: Address,
    token: Address,
    reward_pool: Address,
    stake_vault: Address, // NEW
)

Math Examples

Verification

✅ All tests pass (111 total across all contracts)
✅ Clippy clean
✅ Formatting correct
✅ Wasm builds successfully
✅ CI ready

Future Enhancements

• Implement authorized reward pool contract to fund multiplier boosts
• Allow employers to specify max multiplier when creating quests
• Add events for multiplier application
  Closes [QuestEngine] Apply staking multiplier to quests #55