Add CLAUDE.md for Claude Code guidance

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Repository Overview
+
+This is Coinbase's ERC-4337 compliant smart contract wallet implementation, featuring:
+- Multiple owner support (both Ethereum addresses and passkey public keys)
+- Cross-chain replayable transactions
+- WebAuthn/passkey integration for authentication
+- Factory pattern for deterministic deployments
+
+## Key Commands
+
+### Testing
+```bash
+forge test                    # Run all tests
+forge test --match-test <name>  # Run specific test
+forge test -vvv              # Run with verbose output
+```
+
+### Building & Linting  
+```bash
+forge build                  # Compile contracts
+forge fmt                    # Format Solidity code
+```
+
+### Deployment
+```bash
+make deploy                  # Deploy factory and implementation (requires .env setup)
+```
+
+## Core Architecture
+
+### Main Contracts (src/)
+- **CoinbaseSmartWallet.sol** - The main wallet implementation inheriting from MultiOwnable, ERC1271, UUPSUpgradeable
+- **CoinbaseSmartWalletFactory.sol** - Factory for deterministic wallet creation using LibClone
+- **MultiOwnable.sol** - Multi-owner auth system supporting both addresses and public keys
+- **ERC1271.sol** - Signature validation with anti-replay protection
+
+### Key Design Patterns
+1. **Multi-Owner Architecture**: Owners stored as `bytes` to support both Ethereum addresses and secp256r1 public keys
+2. **Cross-Chain Replayability**: Special `executeWithoutChainIdValidation()` function for cross-chain owner updates
+3. **Signature Wrapping**: Uses `SignatureWrapper` struct with `ownerIndex` to identify signers
+4. **Factory Pattern**: Deterministic deployment via Safe Singleton Factory
+
+### Dependencies
+- **account-abstraction**: ERC-4337 interfaces and EntryPoint integration  
+- **solady**: Core utilities (LibClone, UUPSUpgradeable, SignatureCheckerLib, Receiver)
+- **webauthn-sol**: WebAuthn signature verification for passkeys
+- **p256-verifier**: secp256r1 signature verification
+- **openzeppelin-contracts**: Standard implementations
+
+### Test Structure
+- **test/CoinbaseSmartWallet/**: Core wallet functionality tests
+- **test/MultiOwnable/**: Multi-owner system tests  
+- **test/mocks/**: Mock contracts for testing
+- **SmartWalletTestBase.sol**: Shared test utilities and setup
+
+### Cross-Chain Features
+- Uses `REPLAYABLE_NONCE_KEY` for sequential cross-chain operations
+- Whitelisted functions: owner management and upgrades via `canSkipChainIdValidation()`
+- Chain ID excluded from signature validation for replayable operations
+
+### Development Notes
+- Uses Foundry for build/test (foundry.toml config)
+- Solidity 0.8.23 with optimizer enabled for deployment profile
+- Safe Singleton Factory for consistent cross-chain addresses
+- Factory deployed at: `0xBA5ED110eFDBa3D005bfC882d75358ACBbB85842`