chore(Copilot) Adds copilot instructions

.github/copilot-instructions.md

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+# LeafyGreen UI - Copilot Instructions
+
+This document provides comprehensive guidance for coding agents working on the LeafyGreen UI design system repository. Following these instructions will minimize build failures, validation errors, and rejected pull requests.
+
+## Repository Overview
+
+LeafyGreen UI is MongoDB's React component library and design system consisting of:
+
+- **100+ workspace packages** across 4 scopes: `@leafygreen-ui`, `@lg-charts`, `@lg-chat`, and `@lg-tools`
+- **Languages/Frameworks**: TypeScript, React 18, Emotion (CSS-in-JS), Storybook
+- **Build System**: Turbo monorepo with pnpm workspaces
+
+### Project Structure
+
+```
+leafygreen-ui/
+├── packages/        # @leafygreen-ui core components (button, modal, etc.)
+├── charts/          # @lg-charts data visualization components
+├── chat/            # @lg-chat conversational UI components
+├── tools/           # @lg-tools build system, CLI, linting, etc.
+├── stories/         # Storybook files unrelated to a specific component
+└── scripts/         # Repository maintenance scripts
+```
+
+## Build System & Development Commands
+
+### Required Environment
+
+Refer to `package.json` for the required Node and pnpm versions.
+
+MUST use pnpm, not npm or yarn
+
+### Development Workflow & Commands
+
+Follow this workflow for all development tasks:
+
+1. **Initial Setup** (required after clone or when switching branches):
+
+   ```bash
+   pnpm run init  # Installs dependencies and builds all packages
+   ```
+
+   - ALWAYS run this before any development work
+
+2. **Making Changes**:
+
+   - Edit component files in `src/`
+   - Add/update tests in `.spec.tsx` files
+   - Update stories in `.stories.tsx` files
+
+3. **Development Commands**:
+
+   ```bash
+   # Build all packages (uses Turbo, typically 6-10 seconds with cache)
+   pnpm build
+
+   # Start Storybook for development
+   pnpm start          # Starts on port 9001
+
+   # Run tests
+   pnpm test                              # All tests
+   pnpm test --filter="@leafygreen-ui/*"  # Specific scope
+
+   # Linting
+   pnpm lint           # Check only
+   pnpm run fix        # Auto-fix issues
+   ```
+
+4. **Before Committing**:
+
+   ```bash
+   pnpm build          # Ensure builds pass
+   pnpm lint           # Check for issues
+   pnpm test           # Run test suite
+   pnpm changeset      # Document changes for release
+   ```
+
+   - **CRITICAL**: Always use `pnpm run fix` instead of manual formatting fixes
+   - Runs ESLint, Prettier, and npmPkgJsonLint
+
+5. **PR Submission**:
+   - All checks must pass in CI
+   - Include meaningful test coverage
+   - Update documentation as needed
+
+### Package-Level Commands
+
+Each package supports these scripts (defined in individual `package.json`):
+
+```json
+{
+  "scripts": {
+    "build": "lg-build bundle",
+    "tsc": "lg-build tsc",
+    "docs": "lg-build docs"
+  }
+}
+```
+
+## Validation Pipeline
+
+The CI/CD system runs validations on every PR
+
+For regular PRs, refer to `.github/workflows/pr.yml`
+
+### PR Requirements
+
+Refer to `.github/pull_request_template.md` for PR requirements
+
+## Package Development Guidelines
+
+### Creating New Components
+
+```bash
+pnpm create-package my-new-component
+```
+
+This scaffolds:
+
+- Package structure with TypeScript configs
+- Test setup with Jest/React Testing Library
+- Storybook stories
+- Build configuration
+
+### Package Structure
+
+Each package follows this structure:
+
+```
+packages/component-name/
+├── src/
+│   ├── Component/
+│   │   ├── Component.tsx
+│   │   ├── Component.styles.ts
+│   │   ├── Component.spec.tsx
+│   │   └── index.ts
+│   ├── Component.stories.tsx
+│   ├── index.ts
+│   └── types.ts
+├── package.json
+├── README.md
+└── CHANGELOG.md
+```
+
+### Workspace Dependencies
+
+- Use `workspace:^` for internal dependencies (Example: `"@leafygreen-ui/palette": "workspace:^"`)
+- External dependencies use specific versions with caret `^` version notation.
+- External dependencies in `@lg-tools/*` packages use explicit dependency versions (with no caret `^` or tilde `~`)
+
+### TypeScript Configuration
+
+- Extends `@lg-tools/build/config/package.tsconfig.json`
+- Path mapping configured in root `tsconfig.json`:
+  ```json
+  {
+    "paths": {
+      "@leafygreen-ui/*": ["packages/*/src"],
+      "@lg-charts/*": ["charts/*/src"],
+      "@lg-chat/*": ["chat/*/src"],
+      "@lg-tools/*": ["tools/*/src"]
+    }
+  }
+  ```
+
+## File Locations & Configurations
+
+### Key Configuration Files
+
+- `eslint.config.mjs` - Linting rules (extends `@lg-tools/lint`)
+- `prettier.config.js` - Code formatting (extends `@lg-tools/lint`)
+- `turbo.json` - Build orchestration
+- `tsconfig.json` - TypeScript path mapping and compilation
+- `.github/workflows/` - CI/CD pipeline definitions
+
+### Build Tools
+
+- **Main CLI**: `@lg-tools/cli` provides `lg` command
+- **Build System**: `@lg-tools/build` provides `lg-build` commands
+- **Validation**: `@lg-tools/validate` checks dependencies and structure
+- **Testing**: `@lg-tools/test` provides Jest configuration
+
+## Performance Notes
+
+- **Build caching**: Turbo extensively caches builds - clean cache if issues arise
+- **Icon package**: Has special build caching due to SVG generation complexity
+- **Storybook**: Large application - expect 30+ second build times
+
+## Code Style guide
+
+Refer to `STYLEGUIDE.md` for code style guidelines
+
+## Additional instructions
+
+- For Storybook files `**/*.stories.ts`, do not comment on the inclusion of `console` logs.
+
+## Trust These Instructions
+
+These instructions are based on comprehensive exploration and testing of the actual codebase. Only search for additional information if:
+
+- These instructions are incomplete for your specific task
+- You encounter errors not covered in the troubleshooting section
+- The codebase has changed since these instructions were created
+
+**Always prefer following these established patterns over creating new approaches.**