Add CLAUDE.md

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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.
+
+## Commands
+
+```bash
+npm run inst             # Install deps (uses npm ci --ignore-scripts — do NOT use npm install)
+npm run dev              # Run client + server in dev mode with hot reload
+npm run start:client     # Client only
+npm run start:server-dev # Server only
+npm test                 # Run all tests (Vitest)
+npm run test:coverage    # Tests with coverage
+npm run lint             # ESLint
+npm run lint:fix         # ESLint with auto-fix
+npm run format           # Prettier
+npm run build-prod       # Production build
+```
+
+**Run a single test file:**
+
+```bash
+npx vitest tests/YourTest.test.ts --run
+npx vitest NationAllianceBehavior --run # match by name pattern
+```
+
+## Architecture
+
+OpenFront.io is a real-time multiplayer territorial strategy game. There are four components:
+
+1. **`src/core/`** — Deterministic game simulation. Pure TypeScript with **no external dependencies**. Must remain fully deterministic (seeded PRNG, no floating-point math). Runs in a Web Worker thread. All `src/core` changes **must** include tests.
+2. **`src/client/`** — Rendering (Pixi.js/WebGL), UI (Lit web components + Tailwind CSS 4), WebSocket communication.
+3. **`src/server/`** — Game coordination, intent relay, WebSocket management (Node.js/Express/ws).
+4. **API** — Closed-source Cloudflare Worker handling auth, stats, cosmetics, monetization. Not in this repo.
+
+### Simulation Flow (Intent → Execution)
+
+The game simulation runs **on each client**, not the server. The server only relays intents.
+
+1. Player action → client creates an **Intent** → sent to server
+2. Server bundles all intents for the tick into a **Turn** → relays to all clients
+3. Client forwards Turn to the Core worker
+4. Core creates an **Execution** for each intent
+5. Core calls `executeNextTick()` — all executions run and mutate game state
+6. Core sends **GameUpdates** back to client → client renders
+
+Intents and all wire messages are Zod-validated schemas defined in `src/core/Schemas.ts`.
+
+### CDN / Static Assets
+
+The game server only serves `index.html` and the WebSocket. All other assets (JS bundle, images, maps, worker) come from a CDN bucket. `CDN_BASE` is an empty string in dev (falls back to same-origin) and a full origin (e.g. `https://cdn.example.com`) in production. It is set as both a Vite build-time variable and a server runtime env var.
+
+## Key Files
+
+| File                        | Purpose                                |
+| --------------------------- | -------------------------------------- |
+| `src/core/Schemas.ts`       | All intent/message types (Zod schemas) |
+| `src/core/GameRunner.ts`    | Simulation orchestrator                |
+| `src/core/game/GameImpl.ts` | Game state implementation              |
+| `src/server/GameServer.ts`  | Main WebSocket server, game loop       |
+| `src/server/Master.ts`      | Lobby and game registry                |
+| `tests/util/Setup.ts`       | Test helper — creates test games       |
+| `docs/Architecture.md`      | Architecture overview                  |
+| `docs/Auth.md`              | JWT/auth flow                          |
+| `docs/API.md`               | Public API endpoints                   |
+| `vite.config.ts`            | Build config, CDN handling             |
+
+## UI Text / i18n
+
+All user-visible text must go through `translateText()` and have a corresponding entry added to `resources/lang/en.json`. Translations are managed via Crowdin. DO NOT modify any other translation files.
+
+## Testing Patterns
+
+Tests use a `setup()` helper from `tests/util/Setup.ts` that creates a full game instance with map data from `tests/testdata/maps/`. Write tests that exercise the core simulation directly — not mocks.
+
+## Tech Stack
+
+- **Bundler:** Vite + TypeScript 5.7
+- **Rendering:** Pixi.js (WebGL)
+- **UI Components:** Lit (LitElement) + Tailwind CSS 4
+- **Audio:** Howler.js
+- **Schemas/Validation:** Zod
+- **Testing:** Vitest
+- **Server:** Node.js, Express, ws (WebSocket)