diff --git a/README.md b/README.md
index e6cd94f..0ba8f76 100644
--- a/README.md
+++ b/README.md
@@ -1,47 +1,30 @@
-# Svelte + TS + Vite
+# Duplicate Chess
 
-This template should help get you started developing with Svelte and TypeScript in Vite.
+A local, single-operator browser sandbox for **duplicate chess** — a four-player
+chess variant invented by Andrew Freiberg. Four players (North, South, East, West)
+and four boards (NW, NE, SW, SE); each player controls one colour on two boards and
+must play the identical move on both. A captured piece leaves a frozen "ghost" twin
+on the player's other board.
 
-## Recommended IDE Setup
+This tool puts all four boards on one screen as a rotated "compass", enforces the
+synchronized-move coupling, renders ghosts, shows the move-legality intersection,
+and detects the endgame.
 
-[VS Code](https://code.visualstudio.com/) + [Svelte](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode).
+## Develop
 
-## Need an official Svelte framework?
-
-Check out [SvelteKit](https://github.com/sveltejs/kit#readme), which is also powered by Vite. Deploy anywhere with its serverless-first approach and adapt to various platforms, with out of the box support for TypeScript, SCSS, and Less, and easily-added support for mdsvex, GraphQL, PostCSS, Tailwind CSS, and more.
-
-## Technical considerations
-
-**Why use this over SvelteKit?**
-
-- It brings its own routing solution which might not be preferable for some users.
-- It is first and foremost a framework that just happens to use Vite under the hood, not a Vite app.
-
-This template contains as little as possible to get started with Vite + TypeScript + Svelte, while taking into account the developer experience with regards to HMR and intellisense. It demonstrates capabilities on par with the other `create-vite` templates and is a good starting point for beginners dipping their toes into a Vite + Svelte project.
-
-Should you later need the extended capabilities and extensibility provided by SvelteKit, the template has been structured similarly to SvelteKit so that it is easy to migrate.
-
-**Why `global.d.ts` instead of `compilerOptions.types` inside `jsconfig.json` or `tsconfig.json`?**
-
-Setting `compilerOptions.types` shuts out all other types not explicitly listed in the configuration. Using triple-slash references keeps the default TypeScript setting of accepting type information from the entire workspace, while also adding `svelte` and `vite/client` type information.
-
-**Why include `.vscode/extensions.json`?**
-
-Other templates indirectly recommend extensions via the README, but this file allows VS Code to prompt the user to install the recommended extension upon opening the project.
-
-**Why enable `allowJs` in the TS template?**
-
-While `allowJs: false` would indeed prevent the use of `.js` files in the project, it does not prevent the use of JavaScript syntax in `.svelte` files. In addition, it would force `checkJs: false`, bringing the worst of both worlds: not being able to guarantee the entire codebase is TypeScript, and also having worse typechecking for the existing JavaScript. In addition, there are valid use cases in which a mixed codebase may be relevant.
-
-**Why is HMR not preserving my local component state?**
-
-HMR state preservation comes with a number of gotchas! It has been disabled by default in both `svelte-hmr` and `@sveltejs/vite-plugin-svelte` due to its often surprising behavior. You can read the details [here](https://github.com/rixo/svelte-hmr#svelte-hmr).
-
-If you have state that's important to retain within a component, consider creating an external store which would not be replaced by HMR.
-
-```ts
-// store.ts
-// An extremely simple external store
-import { writable } from 'svelte/store'
-export default writable(0)
 ```
+pnpm install
+pnpm dev      # run the dev server
+pnpm build    # production build
+pnpm test     # run the engine test suite (vitest)
+```
+
+`pnpm exec svelte-check --tsconfig ./tsconfig.json` typechecks the Svelte/TS code.
+
+## Design
+
+See `docs/superpowers/specs/2026-05-19-duplicate-chess-design.md` for the full design,
+and `docs/superpowers/plans/2026-05-19-duplicate-chess-sandbox.md` for the build plan.
+
+This is v1 — a local sandbox. Networked multiplayer, AI opponents, and a free
+position editor are explicitly out of scope (see the spec, §7).
diff --git a/src/engine/notation.test.ts b/src/engine/notation.test.ts
index b876093..c6b1e66 100644
--- a/src/engine/notation.test.ts
+++ b/src/engine/notation.test.ts
@@ -20,4 +20,8 @@ describe('notation', () => {
   it('rejects a file that is not a duplicate-chess save', () => {
     expect(() => deserialize('{"variant":"chess","version":1,"moves":[]}')).toThrow();
   });
+
+  it('rejects an unsupported save version', () => {
+    expect(() => deserialize('{"variant":"duplicate-chess","version":99,"moves":[]}')).toThrow();
+  });
 });
diff --git a/src/engine/notation.ts b/src/engine/notation.ts
index 9648e7b..a14de22 100644
--- a/src/engine/notation.ts
+++ b/src/engine/notation.ts
@@ -21,5 +21,8 @@ export function deserialize(json: string): HistoryEntry[] {
   if (data.variant !== 'duplicate-chess' || !Array.isArray(data.moves)) {
     throw new Error('Not a duplicate-chess save file');
   }
+  if (data.version !== 1) {
+    throw new Error('Unsupported save version');
+  }
   return data.moves;
 }