docs: Add CLAUDE.md

Author: vilsonrodrigues

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code when working with code in this repository.
+
+## Overview
+
+**msgspec-ext** is a high-performance settings management library built on top of msgspec. It provides a pydantic-like API for loading settings from environment variables and .env files, with **3.8x better performance** than pydantic-settings.
+
+## Project Structure
+
+```
+msgspec-ext/
+├── src/msgspec_ext/       # Source code
+│   ├── settings.py        # Core BaseSettings implementation
+│   └── version.py         # Version string
+├── tests/                 # Test suite
+│   └── test_settings.py   # Comprehensive unit tests (22 tests)
+├── examples/              # Practical examples
+│   ├── 01_basic_usage.py
+│   ├── 02_env_prefix.py
+│   ├── 03_dotenv_file.py
+│   ├── 04_advanced_types.py
+│   ├── 05_serialization.py
+│   └── README.md
+├── scripts/               # Automation scripts
+│   ├── release.sh         # Release automation (use this!)
+│   └── setup-branch-protection.sh
+└── benchmark.py           # Performance benchmarks
+
+## Common Commands
+
+### Development
+
+```bash
+# Install dependencies
+uv sync
+
+# Install with dev dependencies
+uv sync --group dev
+
+# Add new dependency
+uv add <package>
+
+# Run tests
+uv run pytest tests/ -v
+
+# Run specific test
+uv run pytest tests/test_settings.py::test_name -v
+
+# Run linter (only checks src/)
+uv run ruff check src/
+
+# Format code
+uv run ruff format
+
+# Run benchmark
+uv run python benchmark.py
+```
+
+### Testing
+
+All tests are in `tests/test_settings.py`:
+- 22 comprehensive unit tests
+- Tests cover: basic usage, env vars, type conversion, .env files, validation, serialization
+- Run with: `uv run pytest tests/ -v`
+- Should complete in < 0.1s
+
+### Releases
+
+**IMPORTANT**: Always use the release script:
+
+```bash
+# Create a new release
+./scripts/release.sh <version>
+
+# Example:
+./scripts/release.sh 0.2.0
+```
+
+The script will:
+1. Update `src/msgspec_ext/version.py`
+2. Create git tag
+3. Push to upstream
+4. Trigger GitHub Actions for PyPI publishing
+
+**Never manually edit version.py** - always use the release script!
+
+## Architecture
+
+### Core Implementation (`settings.py`)
+
+**Key optimization**: Uses bulk JSON decoding instead of field-by-field validation.
+
+```python
+# Old approach (slow):
+for field in fields:
+    value = msgspec.convert(env_value, field_type)  # Python loop
+
+# New approach (fast):
+json_bytes = encoder.encode(all_values)  # Cached encoder
+return decoder.decode(json_bytes)  # Cached decoder, all in C!
+```
+
+**Important classes**:
+- `BaseSettings`: Wrapper factory that creates msgspec.Struct instances
+- `SettingsConfigDict`: Configuration (env_file, env_prefix, etc.)
+
+**Performance optimizations**:
+- Cached encoders/decoders (ClassVar)
+- Automatic field ordering (required before optional)
+- Bulk JSON decoding in C
+- Zero Python loops for validation
+
+### Type Handling
+
+Environment variables are always strings, but we need proper types:
+
+```python
+_preprocess_env_value(env_value: str, field_type: type) -> Any
+```
+
+Handles:
+- `bool`: "true"/"false"/"1"/"0" → True/False
+- `int`/`float`: String to number conversion
+- `list`/`dict`: JSON parsing for complex types
+- `Optional[T]`: Unwraps Union types correctly
+
+### Field Ordering
+
+`msgspec.defstruct` requires required fields before optional fields. We handle this automatically in `_create_struct_class()`:
+
+```python
+required_fields = [(name, type), ...]
+optional_fields = [(name, type, default), ...]
+fields = required_fields + optional_fields  # Correct order
+```
+
+## Linting & Code Style
+
+**Ruff configuration** (`pyproject.toml`):
+- Target: Python 3.10+
+- Line length: 88
+- Strict linting for `src/`
+- Relaxed rules for `tests/` and `examples/`
+
+**Running lint**:
+```bash
+# Check only src/ (recommended for quick checks)
+uv run ruff check src/
+
+# Check everything
+uv run ruff check
+
+# Auto-fix issues
+uv run ruff check --fix
+
+# Format code
+uv run ruff format
+```
+
+**Important per-file ignores**:
+- `tests/`: Ignores D (docstrings), S104 (binding), S105 (passwords), etc.
+- `examples/`: Ignores D, S101, S104, S105, T201, F401
+- `benchmark.py`: Ignores D, S101, S105, T201, etc.
+
+## Examples
+
+5 practical examples in `examples/`:
+1. **Basic usage**: Defaults, env vars, explicit values
+2. **Environment prefixes**: Organizing settings with `env_prefix`
+3. **.env files**: Loading from dotenv files
+4. **Advanced types**: Optional, lists, dicts, JSON parsing
+5. **Serialization**: `model_dump()`, `model_dump_json()`, `schema()`
+
+Run examples:
+```bash
+uv run python examples/01_basic_usage.py
+```
+
+## Benchmarking
+
+```bash
+uv run python benchmark.py
+```
+
+Expected results:
+- msgspec-ext: ~0.7ms per load
+- pydantic-settings: ~2.7ms per load (if installed)
+- **Speedup**: 3.8x faster than pydantic-settings
+
+## CI/CD
+
+GitHub Actions workflows:
+- **CI**: Runs on every push (Ruff, Tests, Build)
+- **Publish**: Publishes to PyPI on new tags
+- **Release Drafter**: Auto-generates release notes
+
+**Creating a PR**:
+1. Create feature branch from main
+2. Make changes
+3. Run tests: `uv run pytest tests/ -v`
+4. Run lint: `uv run ruff check src/`
+5. Format: `uv run ruff format`
+6. Push and create PR
+7. Ensure CI passes (Ruff, Tests, Build)
+
+## Common Workflows
+
+### Adding a new feature
+
+1. Create branch: `git checkout -b feat/feature-name`
+2. Implement feature in `src/msgspec_ext/settings.py`
+3. Add tests in `tests/test_settings.py`
+4. Add example in `examples/` (if user-facing)
+5. Run tests: `uv run pytest tests/ -v`
+6. Run lint: `uv run ruff check src/`
+7. Create PR
+
+### Fixing a bug
+
+1. Add failing test in `tests/test_settings.py`
+2. Fix bug in `src/msgspec_ext/settings.py`
+3. Verify test passes
+4. Run full test suite
+5. Create PR
+
+### Updating dependencies
+
+```bash
+# Update specific package
+uv add package@latest
+
+# Update all dependencies
+uv sync --upgrade
+```
+
+## Performance Tips
+
+- **Always use cached encoder/decoder**: Don't create new instances
+- **Bulk operations**: Process all fields at once via JSON decode
+- **Avoid Python loops**: Let msgspec handle validation in C
+- **Field ordering**: Required before optional (automatic)
+- **Type hints**: Proper annotations enable better performance
+
+## Troubleshooting
+
+**Tests failing**:
+```bash
+uv run pytest tests/ -v  # See detailed output
+```
+
+**Lint errors**:
+```bash
+uv run ruff check src/  # Check src only
+uv run ruff check --fix  # Auto-fix
+```
+
+**Import errors**:
+```bash
+uv sync  # Reinstall dependencies
+```
+
+**Performance regression**:
+```bash
+uv run python benchmark.py  # Compare with baseline
+```
+
+## Key Files
+
+- `src/msgspec_ext/settings.py` - Core implementation (most important)
+- `src/msgspec_ext/version.py` - Version (updated by release script)
+- `tests/test_settings.py` - Test suite (22 tests)
+- `benchmark.py` - Performance benchmarks
+- `scripts/release.sh` - Release automation (**use this for releases!**)
+- `pyproject.toml` - Project config, dependencies, ruff settings
+
+## Documentation
+
+- `README.md` - User-facing docs with quickstart
+- `examples/README.md` - Example gallery guide
+- `CONTRIBUTING.md` - Contribution guidelines
+- `CLAUDE.md` - This file (for Claude Code)
+
+## Notes for Claude Code
+
+- **Releases**: Always use `./scripts/release.sh <version>`, never edit version.py manually
+- **Linting**: Focus on `src/` only (`uv run ruff check src/`)
+- **Tests**: Must maintain 100% pass rate (22/22)
+- **Performance**: Benchmark should show ~0.7ms per load, 3.8x vs pydantic
+- **Examples**: Update if changing user-facing APIs
+- **Breaking changes**: Require major version bump