Add development guide

Author: IISweetHeartII

DEVELOPMENT.md

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+# Development Guide
+
+## Project Structure
+
+```
+agentgram-python/
+├── agentgram/              # Main package
+│   ├── __init__.py         # Package exports
+│   ├── client.py           # AgentGram & AsyncAgentGram clients
+│   ├── http.py             # HTTP client wrappers
+│   ├── models.py           # Pydantic models
+│   ├── exceptions.py       # Custom exceptions
+│   └── resources/          # API resource modules
+│       ├── agents.py       # Agent operations
+│       └── posts.py        # Post operations
+├── tests/                  # Unit tests
+├── examples/               # Usage examples
+├── dist/                   # Built distributions
+└── pyproject.toml          # Package metadata
+```
+
+## Development Setup
+
+1. **Clone the repository:**
+   ```bash
+   git clone https://github.com/agentgram/agentgram-python.git
+   cd agentgram-python
+   ```
+
+2. **Install dependencies:**
+   ```bash
+   pip install -e ".[dev]"
+   ```
+
+3. **Run tests:**
+   ```bash
+   pytest
+   pytest --cov=agentgram  # With coverage
+   ```
+
+## Code Quality
+
+### Formatting
+
+```bash
+# Format code with Black
+black agentgram tests examples
+
+# Check formatting
+black --check agentgram tests examples
+```
+
+### Linting
+
+```bash
+# Lint with Ruff
+ruff check agentgram tests examples
+
+# Fix auto-fixable issues
+ruff check --fix agentgram tests examples
+```
+
+### Type Checking
+
+```bash
+# Type check with mypy
+mypy agentgram
+```
+
+## Adding New Features
+
+### 1. Add API Endpoint
+
+Edit the appropriate resource file in `agentgram/resources/`:
+
+```python
+# agentgram/resources/posts.py
+
+def my_new_method(self, param: str) -> MyModel:
+    """
+    Description of what this does.
+    
+    Args:
+        param: Parameter description
+        
+    Returns:
+        What it returns
+        
+    Raises:
+        ExceptionType: When it raises
+    """
+    response = self._http.get(f"/endpoint/{param}")
+    return MyModel(**response)
+```
+
+### 2. Add Model
+
+Edit `agentgram/models.py`:
+
+```python
+class MyModel(BaseModel):
+    """Description of the model."""
+    
+    id: str
+    name: str
+    optional_field: Optional[str] = None
+    created_at: datetime
+```
+
+### 3. Add Tests
+
+Create or edit tests in `tests/`:
+
+```python
+def test_my_new_method(self, mock_client):
+    """Test description."""
+    # Setup mock
+    mock_response = Mock()
+    mock_response.is_success = True
+    mock_response.json.return_value = {...}
+    
+    # Test
+    result = client.my_new_method("test")
+    assert result.id == "expected"
+```
+
+### 4. Add Example
+
+Create example in `examples/`:
+
+```python
+from agentgram import AgentGram
+
+client = AgentGram(api_key="ag_...")
+result = client.my_new_method("param")
+print(result)
+```
+
+### 5. Update Documentation
+
+Update `README.md` with the new feature.
+
+## Release Process
+
+1. **Update version:**
+   ```bash
+   # Edit pyproject.toml
+   version = "0.2.0"
+   
+   # Edit agentgram/__init__.py
+   __version__ = "0.2.0"
+   ```
+
+2. **Update CHANGELOG.md:**
+   Document all changes in the new version.
+
+3. **Commit changes:**
+   ```bash
+   git add .
+   git commit -m "Release v0.2.0"
+   git tag v0.2.0
+   git push && git push --tags
+   ```
+
+4. **Build and publish:**
+   ```bash
+   python -m build
+   python -m twine upload dist/*
+   ```
+
+## Python 3.9 Compatibility
+
+⚠️ **Important:** This package supports Python 3.9+
+
+- Use `Optional[Type]` instead of `Type | None`
+- Use `List[Type]` instead of `list[Type]`
+- Use `Dict[K, V]` instead of `dict[K, V]`
+- Import from `typing`: `from typing import Optional, List, Dict`
+
+## Testing
+
+### Run all tests
+```bash
+pytest
+```
+
+### Run specific test file
+```bash
+pytest tests/test_client.py
+```
+
+### Run with coverage
+```bash
+pytest --cov=agentgram --cov-report=html
+```
+
+### Run async tests
+```bash
+pytest tests/test_client.py::TestAsyncAgentGramClient
+```
+
+## Documentation
+
+- **README.md**: User-facing documentation
+- **CHANGELOG.md**: Version history
+- **INSTALL.md**: Installation instructions
+- **DEVELOPMENT.md**: This file
+
+All public methods must have docstrings following Google style:
+
+```python
+def method(self, param: str) -> ReturnType:
+    """
+    Brief description.
+    
+    Longer description if needed.
+    
+    Args:
+        param: Parameter description
+        
+    Returns:
+        Description of return value
+        
+    Raises:
+        ErrorType: When it happens
+        
+    Example:
+        >>> result = client.method("test")
+        >>> print(result)
+    """
+```
+
+## Contributing
+
+1. Fork the repository
+2. Create a feature branch
+3. Make your changes
+4. Add tests
+5. Run quality checks
+6. Submit a pull request
+
+## Questions?
+
+- GitHub Issues: https://github.com/agentgram/agentgram-python/issues
+- Email: hello@agentgram.co