The problem ImpactFeeV4 solves

Trading generates massive value, but profits rarely flow to public goods. Impact Fee Hook solves this by automatically converting 0.10% of every Uniswap V4 swap into yield-generating donations for social impact projects.

Benefits:

• For Traders: Minimal fee (0.10%) that goes directly to charity, not middlemen
• For Public Goods: Sustainable passive income from DeFi trading volume
• For Protocols: Easy integration - just attach the hook to any pool
• For Society: Transforms financial activity into automatic philanthropy

No user action required. Trade → donate. Simple.

Challenges I ran into

Problem: octant-v2-core v0.1.2 didn't include ITokenizedStrategy.sol interface that BaseStrategy imports. Build failed.

Solution: Created a shim interface with all 15+ required function signatures by iteratively compiling and adding missing methods. Also copied errors.sol from the core repo. Updated remappings.txt to resolve imports properly.

Problem: Initial design sent vault shares to the hook contract itself, making them inaccessible to the actual donation address.

Solution: Added donationReceiver immutable parameter to hook constructor. Modified unlockCallback to use feeSink.deposit(feeAmount, donationReceiver) instead of address(this). Now shares go directly to charity.

Problem: Uniswap V4 requires hooks to have addresses that match their permission flags. Can't just deploy and hope.

Solution: Used HookMiner with CREATE2 salt mining to generate deterministic addresses with correct flag bits (beforeSwap + beforeSwapReturnsDelta). Deployed successfully on first try.