chore: init CLAUDE.md (#9563)

* chore: init CLAUDE.md

* Add Copilot instructions

* update gitignore

* simplify

---------

Co-authored-by: Mark Tolmacs <mark@lazycat.hu>

.github/copilot-instructions.md

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+# Project coding standards
+
+## Generic Communication Guidelines
+
+- Be succint and be aware that expansive generative AI answers are costly and slow
+- Avoid providing explanations, trying to teach unless asked for, your chat partner is an expert
+- Stop apologising if corrected, just provide the correct information or code
+- Prefer code unless asked for explanation
+- Stop summarizing what you've changed after modifications unless asked for
+
+## TypeScript Guidelines
+
+- Use TypeScript for all new code
+- Where possible, prefer implementations without allocation
+- When there is an option, opt for more performant solutions and trade RAM usage for less CPU cycles
+- Prefer immutable data (const, readonly)
+- Use optional chaining (?.) and nullish coalescing (??) operators
+
+## React Guidelines
+
+- Use functional components with hooks
+- Follow the React hooks rules (no conditional hooks)
+- Keep components small and focused
+- Use CSS modules for component styling
+
+## Naming Conventions
+
+- Use PascalCase for component names, interfaces, and type aliases
+- Use camelCase for variables, functions, and methods
+- Use ALL_CAPS for constants
+
+## Error Handling
+
+- Use try/catch blocks for async operations
+- Implement proper error boundaries in React components
+- Always log errors with contextual information
+
+## Testing
+
+- Always attempt to fix #problems
+- Always offer to run `yarn test:app` in the project root after modifications are complete and attempt fixing the issues reported
+
+## Types
+
+- Always include `packages/math/src/types.ts` in the context when your write math related code and always use the Point type instead of { x, y}

.gitignore

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 dev-dist
 html
 meta*.json
+.claude

CLAUDE.md

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+# CLAUDE.md
+
+## Project Structure
+
+Excalidraw is a **monorepo** with a clear separation between the core library and the application:
+
+- **`packages/excalidraw/`** - Main React component library published to npm as `@excalidraw/excalidraw`
+- **`excalidraw-app/`** - Full-featured web application (excalidraw.com) that uses the library
+- **`packages/`** - Core packages: `@excalidraw/common`, `@excalidraw/element`, `@excalidraw/math`, `@excalidraw/utils`
+- **`examples/`** - Integration examples (NextJS, browser script)
+
+## Development Workflow
+
+1. **Package Development**: Work in `packages/*` for editor features
+2. **App Development**: Work in `excalidraw-app/` for app-specific features
+3. **Testing**: Always run `yarn test:update` before committing
+4. **Type Safety**: Use `yarn test:typecheck` to verify TypeScript
+
+## Development Commands
+
+```bash
+yarn test:typecheck  # TypeScript type checking
+yarn test:update     # Run all tests (with snapshot updates)
+yarn fix             # Auto-fix formatting and linting issues
+```
+
+## Architecture Notes
+
+### Package System
+
+- Uses Yarn workspaces for monorepo management
+- Internal packages use path aliases (see `vitest.config.mts`)
+- Build system uses esbuild for packages, Vite for the app
+- TypeScript throughout with strict configuration