Add CLAUDE.md file for Claude Code development guidance (#19)

This file provides comprehensive guidance for future Claude Code instances working in this repository, including:
- Essential development commands (build, test, lint)
- High-level architecture overview
- Berachain-specific modifications and their locations
- Network-specific usage examples
- Development workflow best practices

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

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.
+
+## Project Overview
+
+This is **bera-geth**, Berachain's fork of go-ethereum that implements the Berachain blockchain network. Key differences from upstream:
+
+- **Custom base fee mechanism**: 1 gwei minimum with 6x faster adjustments via Prague1 fork
+- **Networks**: Berachain mainnet (Chain ID 80094) and Bepolia testnet (Chain ID 80069)
+- **Optimized for faster block times** while maintaining Ethereum compatibility
+
+## Development Commands
+
+### Building
+```bash
+make geth                    # Build main geth binary
+make all                     # Build all executables
+make evm                     # Build EVM utility
+```
+
+### Testing
+```bash
+make test                    # Run all tests
+go test ./path/to/package    # Run specific package tests
+go test -run TestName        # Run specific test
+```
+
+### Code Quality
+```bash
+make lint                    # Run linters
+make fmt                     # Format code with gofmt
+```
+
+### Development Tools
+```bash
+make devtools                # Install development dependencies
+```
+
+### Cleaning
+```bash
+make clean                   # Clean build artifacts
+```
+
+## Codebase Architecture
+
+### Core Components
+
+**Core Blockchain Logic** (`/core/`)
+- `blockchain.go` - Main blockchain state management
+- `state_processor.go` - Transaction execution
+- `types/` - Core data structures (blocks, transactions, receipts)
+- `vm/` - Ethereum Virtual Machine implementation
+- `txpool/` - Transaction pool management
+
+**Consensus Layer** (`/consensus/`)
+- `beacon/` - Proof-of-stake consensus (primary)
+- `misc/eip1559/` - Base fee calculation with Berachain modifications
+- `clique/` - Proof-of-authority for testing
+
+**Network Protocol** (`/eth/`)
+- `backend.go` - Main Ethereum service
+- `downloader/` - Block/state synchronization
+- `protocols/` - Network protocol handlers
+
+**P2P Networking** (`/p2p/`)
+- `discover/` - Node discovery protocols
+- `rlpx/` - Encrypted communication
+
+### Key Entry Points
+
+**Main Binary**: `/cmd/geth/main.go`
+- CLI application setup
+- Network selection logic
+- Node initialization
+
+**Other Executables**: `/cmd/`
+- `clef/` - Account management
+- `abigen/` - ABI binding generator
+- `evm/` - Standalone EVM executor
+
+### Configuration Management
+
+**Chain Configs**: `/params/config.go`
+- Network parameters and fork schedules
+- Berachain/Bepolia network definitions
+- Prague1 fork configuration
+
+**Network Discovery**: `/params/bootnodes.go`
+- Bootstrap nodes for peer discovery
+
+### Berachain-Specific Modifications
+
+**Base Fee Changes** (`/consensus/misc/eip1559/eip1559.go:116-121`)
+- Prague1 fork enforces 1 gwei minimum base fee
+- BaseFeeChangeDenominator set to 48 (6x faster adjustment)
+
+**Network Configurations** (`/params/config.go:77-99, 107-129`)
+- BerachainChainConfig with Chain ID 80094
+- BepoliaChainConfig with Chain ID 80069
+- Custom Prague1 fork activation parameters
+
+### Test Organization
+
+Tests follow Go conventions with `*_test.go` files alongside source code:
+- Unit tests in package directories
+- Integration tests in `/tests/`
+- Consensus tests for Ethereum specification compliance
+- EVM operation tests in `/core/vm/testdata/`
+
+### Build System
+
+**Primary Build**: `/build/ci.go`
+- Cross-platform compilation
+- Docker image building
+- Release packaging
+
+**Simple Builds**: `/Makefile`
+- Development-focused targets
+- Requires Go 1.23+ and C compiler
+
+## Development Workflow
+
+1. **Architecture Understanding**: The codebase follows Ethereum's layered architecture (consensus → state → networking → application)
+2. **Testing Strategy**: Always run tests after changes with `make test`
+3. **Code Style**: Use `make fmt` and `make lint` before committing
+4. **Network Testing**: Use `--bepolia` flag for testnet development
+5. **Debugging**: Use `./build/bin/geth --help` for comprehensive CLI options
+
+## Network-Specific Usage
+
+### Berachain Mainnet
+```bash
+./build/bin/geth --berachain
+```
+
+### Bepolia Testnet
+```bash
+./build/bin/geth --bepolia
+```
+
+### Development Mode
+```bash
+./build/bin/geth --dev
+```