Add Copilot instructions for repository (#298)

* Initial plan

* Add GitHub Copilot instructions for repository

Co-authored-by: naorpeled <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: naorpeled <[email protected]>

Author: Copilot

.github/copilot-instructions.md

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+# GitHub Copilot Instructions for lambda-api
+
+This repository contains **lambda-api**, a lightweight web framework for AWS Lambda serverless applications. This framework has **ZERO dependencies** and is designed specifically for serverless applications using AWS Lambda and API Gateway.
+
+## Project Overview
+
+Lambda API is a web framework that closely mirrors Express.js and Fastify but is significantly stripped down to maximize performance with Lambda's stateless, single-run executions. It provides routing, HTML serving, redirects, binary file serving, middleware, error handling, and more.
+
+## Architecture & Code Structure
+
+- **`index.js`** - Main API class and entry point
+- **`lib/`** - Core library modules:
+  - `request.js` - Request handling and parsing
+  - `response.js` - Response formatting and methods
+  - `utils.js` - Utility functions
+  - `logger.js` - Built-in logging engine
+  - `errors.js` - Custom error classes
+  - `compression.js` - Response compression handling
+  - `s3-service.js` - S3 integration for file operations
+  - `statusCodes.js` - HTTP status code mappings
+  - `mimemap.js` - MIME type mappings
+  - `prettyPrint.js` - Route debugging and visualization
+- **`__tests__/`** - Jest unit tests for all functionality
+- **`index.d.ts`** - TypeScript type definitions
+
+## Development Guidelines
+
+### Code Style & Conventions
+
+- **Style**: Use JavaScript ES6+ features, strict mode (`'use strict'`)
+- **Quotes**: Single quotes for strings (enforced by Prettier)
+- **Code quality**: ESLint with `eslint:recommended` and Prettier integration
+- **Comments**: Use JSDoc style for file headers with author and license
+- **Error handling**: Use custom error classes from `lib/errors.js` (ConfigurationError, ApiError, FileError)
+- **Async patterns**: Support both async/await and Promises
+- **No external dependencies**: This is a core principle - do not add external npm packages
+
+### Testing
+
+- **Framework**: Jest
+- **Test files**: `__tests__/*.unit.js`
+- **Test structure**: Each module has corresponding unit tests
+- **Coverage**: Aim for high test coverage
+- **Run tests**: `npm test` (runs both type tests and unit tests)
+  - Type tests: `npm run test:types`
+  - Unit tests only: `npm run test:unit`
+  - With coverage: `npm run test-cov`
+
+### Build & Development Commands
+
+```bash
+# Install dependencies
+npm ci
+
+# Run all tests (TypeScript types + Jest unit tests)
+npm test
+
+# Linting
+npm run lint:check      # Check for lint errors
+npm run lint:fix        # Auto-fix lint errors
+
+# Code formatting
+npm run prettier:check  # Check formatting
+npm run prettier:write  # Auto-format code
+
+# CI test command (includes linting, formatting, tests, and coverage)
+npm run test-ci
+```
+
+### Key Features & Patterns
+
+1. **Route definition**: Similar to Express.js
+
+   ```javascript
+   api.get('/path', async (req, res) => {
+     return { status: 'ok' };
+   });
+   ```
+
+2. **Middleware support**: Method-based and global middleware
+3. **Error handling**: Built-in error middleware system
+4. **Binary support**: Automatic base64 encoding/decoding
+5. **Compression**: Built-in gzip/brotli compression
+6. **S3 integration**: Pre-signed URL generation via `getLink()`
+7. **Logger**: Configurable logging with sampling support
+8. **Multi-version support**: API Gateway v1/v2 and ALB payload formats
+
+### AWS Integration
+
+- Designed for AWS Lambda Proxy Integration and ALB Lambda Target Support
+- Parses API Gateway and ALB event formats (v1 and v2)
+- Automatically handles request parsing and response formatting
+- Supports binary file uploads/downloads via base64 encoding
+
+### TypeScript Support
+
+- Type definitions in `index.d.ts`
+- Type tests in `index.test-d.ts` using `tsd`
+- Ensure changes maintain TypeScript compatibility
+
+### Making Changes
+
+1. **Minimal dependencies**: Never add external npm dependencies without strong justification
+2. **Test coverage**: Add unit tests for new features in `__tests__/`
+3. **Type definitions**: Update `index.d.ts` for public API changes
+4. **Documentation**: Update README.md for user-facing changes
+5. **Backwards compatibility**: Avoid breaking changes when possible
+6. **Performance**: Keep the framework lightweight and fast
+7. **Serverless-first**: Design with Lambda's stateless execution model in mind
+
+### Security Considerations
+
+- Validate all user inputs
+- Sanitize HTML output (use `escapeHtml` from `lib/utils.js`)
+- Be cautious with file operations and S3 integrations
+- Ensure proper error handling to avoid information leakage
+- Use secure defaults for cookies and headers
+
+### Common Patterns
+
+- **Route handlers**: Accept `(req, res, next)` parameters
+- **Async responses**: Can return values directly or use `res.send()`, `res.json()`, etc.
+- **Error propagation**: Use `res.error()` or throw errors to trigger error middleware
+- **Path parameters**: Extracted automatically (e.g., `/user/:id`)
+- **Middleware chaining**: Use `next()` to continue to next middleware/handler
+
+### CI/CD
+
+- GitHub Actions workflows in `.github/workflows/`
+- Automated testing on push to main branch
+- Coverage reports sent to Coveralls
+- Requires Node.js 14+ (currently testing on 14.x)
+
+## Notes for Copilot
+
+- This is a production library used by many serverless applications
+- Prioritize backwards compatibility and stability
+- Keep the codebase simple and maintainable
+- Performance is critical - avoid adding overhead
+- The zero-dependency philosophy is non-negotiable
+- When suggesting changes, ensure they align with Express.js-like API patterns
+- Test thoroughly with both API Gateway v1/v2 and ALB event formats