docs: add CLAUDE.md for Claude Code guidance

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ctrlplusb

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Easy Peasy (v6.1.0) is a React state management library built on Redux + Immer. Source is JavaScript with handwritten TypeScript definitions in `index.d.ts`.
+
+## Commands
+
+```bash
+yarn install              # Install dependencies
+yarn build                # Rollup build (ESM + CJS → dist/)
+yarn lint                 # ESLint with auto-fix
+yarn test                 # Jest (jsdom)
+yarn test -- tests/actions.test.js          # Single test file
+yarn test -- --testNamePattern="some test"  # Single test by name
+yarn test:watch           # Watch mode
+yarn test:coverage        # Coverage report
+yarn dtslint              # TypeScript type tests (tests/typescript/)
+```
+
+## Architecture
+
+**Redux wrapper with symbol-based type detection.** Models are plain JS objects; helpers (`action`, `thunk`, `computed`, etc.) tag properties with symbols (`$_a`, `$_t`, `$_c`, etc.) that `extract-data-from-model.js` uses to build dispatch routing and metadata maps during store creation.
+
+### Middleware chain (in order)
+
+Computed properties → user middleware → Redux Thunk → listeners → effects → persistence
+
+### Key source files
+
+- `src/create-store.js` — Store factory. Assembles middleware, initializes state, handles `addModel`/`removeModel`/`reconfigure`.
+- `src/hooks.js` — React hooks (`useStoreState`, `useStoreActions`, etc.) using `useSyncExternalStoreWithSelector`.
+- `src/helpers.js` — Public model definition API (`action`, `thunk`, `computed`, `effectOn`, `persist`, `reducer`, `debug`, `generic`).
+- `src/extract-data-from-model.js` — Recursive model traversal; builds action/thunk/listener/effect metadata and lookup maps.
+- `src/computed-properties.js` — Lazy evaluation via `Object.defineProperty` getters with memoization (`fast-deep-equal`).
+- `src/persistence.js` — Async/sync storage adapters, transformation pipeline, migration support.
+- `src/lib.js` — Internal utilities (`get`, `set`, `clone`, `createSimpleProduce` wrapping Immer with `autoFreeze: false`).
+
+### Type definitions
+
+All TypeScript types live in the root `index.d.ts` (not generated — hand-maintained). Uses `ts-toolbelt` for advanced type manipulation. Type tests are in `tests/typescript/` and run via `dtslint`.
+
+## Conventions
+
+- Node >= 14 (`.nvmrc` specifies 14), Yarn for package management
+- Babel transpiles source; no TypeScript compiler for source code
+- Tests use `@testing-library/react` and Jest with jsdom
+- ESLint extends airbnb + prettier
+- Husky pre-commit hooks run lint and tests
+- Immer configured with `autoFreeze: false` for mixed mutability