Decent Paymaster V1

[adamgall]

Closes https://linear.app/decent-labs/issue/ENG-147/gasless-voting-paymaster-contract

Depends on #137, so if you're here for a review, please review that one first.

DecentPaymaster Implementation for Account Abstraction Gasless Voting

This PR implements a paymaster contract that enables DAOs to subsidize specific function calls on whitelisted strategy contracts. The implementation follows EIP-4337 (Account Abstraction) standards and provides a flexible way for DAOs to manage which functions they want to sponsor.

Key Features

1. Custom BasePaymaster Implementation

   • Created our own version of BasePaymaster.sol instead of using the one from @account-abstraction/contracts
   • Reasons for custom implementation:
     • Compatibility with OpenZeppelin v4 (avoiding conflicts with OZ v5 required by account-abstraction)
     • Support for our proxy-based deployment strategy using ModuleProxyFactory
     • Replaced constructor-based initialization with initializer pattern
     • Modified Ownable implementation to use OZ's upgradeable variant

2. Strategy Function Whitelisting

   • DAOs can whitelist specific function selectors for specific strategy contracts
   • Fine-grained control over which functions can be sponsored
   • Zero-address checks and array length validation for safety

3. ERC165 Support

   • Full ERC165 interface detection support
   • Implements IPaymaster and custom IDecentPaymaster interfaces
   • Proper interface inheritance and detection

4. Robust Validation

   • Validates UserOp calldata format and length
   • Extracts and verifies function selectors and target addresses
   • Ensures only approved function calls are sponsored

Technical Details

• Uses ModuleProxyFactory for deploying minimal proxies of a master copy
• Initialization through setUp pattern instead of constructors
  • Inherits from OpenZeppelin's upgradeable contracts where needed
• Uses custom errors for gas optimization and better error reporting
• Comprehensive test suite with 100% coverage for new contract

Architectural Decisions

1. Proxy Pattern

   • Master copy deployment followed by minimal proxy instances
   • Initialization via setUp function instead of constructors
   • Compatible with our existing deployment infrastructure

2. OpenZeppelin Compatibility

   • Uses OZ v4 instead of v5 required by account-abstraction
   • Modified BasePaymaster to work with our OZ version
   • Maintains consistency with project's dependency structure

3. Deployment Strategy

   • Follows the project's standard deployment pattern using ModuleProxyFactory
   • Enables gas-efficient proxy deployments
   • Maintains upgradeability pattern consistent with other contracts

Security Considerations

• All state-changing functions are owner-only
• Input validation for all external functions
• No reentrancy vulnerabilities
• Gas-optimized calldata parsing
• Proper initialization checks for proxy pattern

Testing

The implementation includes extensive tests covering:

• Initialization and ownership
• Function approval management
• UserOp validation
• Deposit handling
• ERC165 interface support
• Proxy deployment and setup

Dependencies

• Added @account-abstraction/contracts v0.7.0 (for interfaces only)
• Uses OpenZeppelin v4 contracts for standard implementations
• Maintains compatibility with existing project dependencies

[linear]

ENG-147 Gasless voting - Paymaster contract

[adamgall]

I'm actually going to just merge this as-is right now, so it doesn't get in my way as I tear apart this codebase for the refactoring and rebuilding work that I need to do on the "long term" contracts.