SNAKE game v0.3: round screen, swipe control

- 16x16 grid, 320px board centered on round 466 screen, designWidth 466
- pure snake logic in src/common/snake.js (step/turn/rotateDir/spawnFood, TDD'd)
- for-directive segment rendering, show-gated game-over overlay, 300ms tick
- swipe direction input (crown rotation confirmed unsupported on Vela S4)
- tests: snake logic + page wiring

.gitignore

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+node_modules/
+build/
+dist/
+sign/*.pem
+

README.md

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+# Xiaomi Vela Hello World for Watch S4
+
+This is the smallest practical Xiaomi Vela JS watch application. It shows two centered lines on a round black screen:
+
+```text
+Hello World!
+Xiaomi Watch S4
+```
+
+It compiles entirely from a Linux terminal. Xiaomi AIoT-IDE is not required.
+
+## 1. What you need
+
+- A 64-bit Linux system
+- Node.js and npm
+- OpenSSL, but only if you want a signed release package
+- Internet access for the first `npm install`
+
+Node.js 20 LTS is a conservative choice. The included project has also been build-tested with Node.js 24 and npm 11.
+
+On Ubuntu or Debian, install the basic tools:
+
+```bash
+sudo apt update
+sudo apt install -y curl openssl
+```
+
+Install Node.js using your preferred package manager or a version manager such as `nvm`. Confirm that it works:
+
+```bash
+node --version
+npm --version
+```
+
+## 2. Understand the tiny project
+
+```text
+xiaomi-vela-s4-hello-world/
+├── package.json
+├── README.md
+├── sign/
+└── src/
+    ├── app.ux
+    ├── manifest.json
+    ├── common/
+    │   ├── icon.png
+    │   └── icon.svg
+    └── pages/
+        └── index/
+            └── index.ux
+```
+
+- `package.json` installs Xiaomi's command-line build tool and defines the build commands.
+- `src/manifest.json` defines the package, icon, watch target, design width, and start page.
+- `src/app.ux` contains application lifecycle hooks.
+- `src/pages/index/index.ux` contains the UI and its styles.
+- `sign/` is where release certificate files go. Keep private keys private.
+
+Vela `.ux` files resemble small single-file web components. A page may contain `template`, `style`, and `script` blocks. This Hello World page needs only `template` and `style`.
+
+## 3. Compile a debug RPK without Xiaomi's IDE
+
+Open a terminal in the project folder and run:
+
+```bash
+npm install
+npm run build
+```
+
+The important output is created under `dist/` and ends in `.debug.rpk`:
+
+```bash
+find dist -maxdepth 1 -type f -name '*.rpk' -print
+```
+
+The `build/` directory contains intermediate generated files. You normally do not edit either `build/` or `dist/`.
+
+To include a separate source map while debugging:
+
+```bash
+npm run build:source-map
+```
+
+To see every compiler option supported by your installed toolkit:
+
+```bash
+npm run help
+```
+
+## 4. Create a signed release RPK
+
+The release builder expects these two files:
+
+```text
+sign/private.pem
+sign/certificate.pem
+```
+
+Generate a local development certificate from the project root:
+
+```bash
+openssl req \
+  -newkey rsa:2048 \
+  -nodes \
+  -keyout sign/private.pem \
+  -x509 \
+  -days 3650 \
+  -out sign/certificate.pem \
+  -subj '/CN=Hello Vela Development/O=Example/C=US'
+```
+
+Then compile the release package:
+
+```bash
+npm run release
+find dist -maxdepth 1 -type f -name '*.release.*.rpk' -print
+```
+
+Do not commit or share `sign/private.pem`. If a companion Android application communicates with the watch app, Xiaomi's wearable integration may require matching signing identity; changing certificates later can also prevent an update from being accepted as the same app.
+
+## 5. Change the app
+
+Edit `src/pages/index/index.ux`. For example, replace:
+
+```xml
+<text class="hello">Hello World!</text>
+```
+
+with:
+
+```xml
+<text class="hello">My first app</text>
+```
+
+Then rebuild:
+
+```bash
+npm run build
+```
+
+When publishing an update, increase `versionCode` in `src/manifest.json`. Also update `versionName` when you want the visible version string to change.
+
+## 6. Important Vela rules
+
+- A template must have exactly one root element.
+- Visible text must be inside a `<text>` component.
+- Vela uses flex layout, but its CSS support is smaller than a browser's CSS support.
+- Package names should use reverse-domain form, such as `com.yourname.hello`.
+- `designWidth: 480` lets Vela scale the 480-pixel design to the physical display.
+- APIs such as sensors, storage, network, or vibration must usually be declared in the manifest's `features` array before use. This Hello World app requests no APIs.
+
+## 7. Installing on a real Watch S4
+
+Compilation and installation are separate. The terminal workflow above reliably creates the `.rpk`; transferring it to a physical watch depends on the exact Watch S4 model, firmware region, Mi Fitness version, and whether developer or debugging access is enabled for that firmware.
+
+Do not treat the `.rpk` as an Android APK, and do not flash random firmware. Use Xiaomi's supported wearable deployment route for your device/account. Some retail or global firmware builds do not expose the same development or sideload controls as Chinese developer setups.
+
+## 8. Troubleshooting
+
+### `aiot: command not found`
+
+Always run the local tool through npm:
+
+```bash
+npm install
+npm run build
+```
+
+Do not rely on a global `aiot` installation.
+
+### Dependency installation fails
+
+Clear only this project's installed dependencies and retry:
+
+```bash
+rm -rf node_modules
+npm install
+```
+
+If you use a company proxy, configure npm for that proxy instead of disabling TLS verification.
+
+### No `.rpk` appears
+
+Read the first compiler error, then verify:
+
+```bash
+npx aiot build -h
+find src -maxdepth 4 -type f -print
+```
+
+The required files are `src/manifest.json`, `src/app.ux`, and the routed page component.
+
+### Release build says signing files are missing
+
+Run the OpenSSL command in section 4 and confirm:
+
+```bash
+test -s sign/private.pem && test -s sign/certificate.pem && echo 'Signing files exist'
+```
+
+## Official references
+
+- Xiaomi Vela JS documentation: <https://iot.mi.com/vela/quickapp/en/>
+- Project structure: <https://iot.mi.com/vela/quickapp/zh/guide/start/project-overview.html>
+- Manifest configuration: <https://iot.mi.com/vela/quickapp/zh/guide/framework/manifest.html>
+- Compiler parameters: <https://iot.mi.com/vela/quickapp/zh/guide/start/toolkit-params.html>
+- UI introduction: <https://iot.mi.com/vela/quickapp/zh/guide/start/user-interface.html>
+
+The project intentionally uses only the public `aiot-toolkit` command-line package. It does not require Xiaomi AIoT-IDE.

node_modules

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+/tmp/hw/node_modules

package.json

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+{
+  "name": "xiaomi-vela-s4-hello-world",
+  "version": "1.0.0",
+  "private": true,
+  "description": "Minimal Xiaomi Vela JS Hello World app for Xiaomi Watch S4",
+  "scripts": {
+    "build": "aiot build",
+    "release": "aiot release",
+    "build:source-map": "aiot build --devtool=source-map",
+    "help": "aiot build -h"
+  },
+  "devDependencies": {
+    "aiot-toolkit": "2.0.5"
+  }
+}

src/app.ux

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+<script>
+export default {
+  onCreate() {
+    console.log('Hello Vela app created')
+  },
+  onDestroy() {
+    console.log('Hello Vela app destroyed')
+  }
+}
+</script>

src/common/icon.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="192" height="192" viewBox="0 0 192 192">
+  <rect width="192" height="192" rx="48" fill="#ff6900"/>
+  <text x="96" y="116" text-anchor="middle" font-family="DejaVu Sans, sans-serif" font-size="72" font-weight="700" fill="#ffffff">Hi</text>
+</svg>

src/common/snake.js

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+// Snake core — pure functions, no Vela APIs. Exports: initialSnake, step, turn, spawnFood.
+function initialSnake() {
+  return [
+    { x: 6, y: 7 },
+    { x: 5, y: 7 },
+    { x: 4, y: 7 }
+  ]
+}
+
+// Advance the snake one cell in `dir` ({x,y} unit vector). Returns { snake, ate, alive }.
+function step(snake, dir, food, N) {
+  const head = snake[0]
+  const nx = head.x + dir.x
+  const ny = head.y + dir.y
+  if (nx < 0 || ny < 0 || nx >= N || ny >= N) {
+    return { snake, ate: false, alive: false }
+  }
+  const ate = (nx === food.x && ny === food.y)
+  // tail cell vacates unless we grew, so exclude it from self-collision check
+  const body = ate ? snake : snake.slice(0, snake.length - 1)
+  for (let i = 0; i < body.length; i++) {
+    if (body[i].x === nx && body[i].y === ny) {
+      return { snake, ate: false, alive: false }
+    }
+  }
+  const next = [{ x: nx, y: ny }].concat(snake)
+  if (!ate) next.pop()
+  return { snake: next, ate, alive: true }
+}
+
+// Reject a 180° reversal; otherwise accept the new direction.
+function turn(current, desired) {
+  if (current.x + desired.x === 0 && current.y + desired.y === 0) return current
+  return desired
+}
+
+// Rotate a direction 90°: clockwise order right->down->left->up. Always ±90°, never a reversal.
+function rotateDir(dir, clockwise) {
+  const order = [{ x: 1, y: 0 }, { x: 0, y: 1 }, { x: -1, y: 0 }, { x: 0, y: -1 }]
+  let i = 0
+  for (let k = 0; k < 4; k++) {
+    if (order[k].x === dir.x && order[k].y === dir.y) { i = k; break }
+  }
+  return clockwise ? order[(i + 1) % 4] : order[(i + 3) % 4]
+}
+
+// Random empty cell, avoiding the snake.
+function spawnFood(snake, N) {
+  const occupied = new Set(snake.map(s => s.x + ',' + s.y))
+  if (occupied.size >= N * N) return null
+  let x, y
+  do {
+    x = Math.floor(Math.random() * N)
+    y = Math.floor(Math.random() * N)
+  } while (occupied.has(x + ',' + y))
+  return { x, y }
+}
+
+module.exports = { initialSnake, step, turn, rotateDir, spawnFood }

src/manifest.json

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+{
+  "package": "com.ilias.snake",
+  "name": "SNAKE",
+  "icon": "/common/icon.png",
+  "versionName": "0.3",
+  "versionCode": 3,
+  "minAPILevel": 1,
+  "deviceTypeList": [
+    "watch"
+  ],
+  "config": {
+    "logLevel": "debug",
+    "designWidth": 466
+  },
+  "router": {
+    "entry": "pages/index",
+    "pages": {
+      "pages/index": {
+        "component": "index",
+        "path": "/"
+      }
+    }
+  },
+  "display": {
+    "backgroundColor": "#000000"
+  },
+  "features": [
+    {
+      "name": "system.router"
+    }
+  ]
+}

src/pages/index/index.ux

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+<template>
+  <div class="page" onswipe="onSwipe">
+    <stack class="dial">
+      <div class="board"></div>
+      <div class="food" style="left: {{ food.left }}px; top: {{ food.top }}px;"></div>
+      <div class="{{ seg.cls }}" for="{{ seg in snake }}" style="left: {{ seg.left }}px; top: {{ seg.top }}px;"></div>
+      <div class="overlay" show="{{ over }}" onclick="onTap">
+        <text class="overText">GAME OVER</text>
+        <text class="overSub">{{ scoreText }}</text>
+        <text class="overHint">tap to play again</text>
+      </div>
+      <text class="score">{{ scoreText }}</text>
+      <text class="hint">swipe to move</text>
+    </stack>
+  </div>
+</template>
+<script>
+import snake from '../../common/snake.js'
+
+const CELL = 20
+const GRID = 16
+const OFFSET = 73
+
+export default {
+  private: {
+    snake: [],
+    food: { left: '73px', top: '73px' },
+    scoreText: 'SCORE 0',
+    over: false
+  },
+  onInit() {
+    this.dir = { x: 1, y: 0 }
+    this.pending = null
+    this.reset()
+  },
+  onShow() {
+    this.timer = setInterval(() => this.tick(), 300)
+  },
+  onHide() {
+    clearInterval(this.timer)
+  },
+  onDestroy() {
+    clearInterval(this.timer)
+  },
+  reset() {
+    this.model = snake.initialSnake()
+    this.foodModel = snake.spawnFood(this.model, GRID)
+    this.dir = { x: 1, y: 0 }
+    this.pending = null
+    this.over = false
+    this.rebuild()
+  },
+  tick() {
+    if (this.over) return
+    if (this.pending) {
+      this.dir = snake.turn(this.dir, this.pending)
+      this.pending = null
+    }
+    const r = snake.step(this.model, this.dir, this.foodModel, GRID)
+    if (!r.alive) {
+      this.over = true
+      clearInterval(this.timer)
+      return
+    }
+    this.model = r.snake
+    if (r.ate) {
+      this.foodModel = snake.spawnFood(this.model, GRID)
+    }
+    this.rebuild()
+  },
+  restart() {
+    this.reset()
+    clearInterval(this.timer)
+    this.timer = setInterval(() => this.tick(), 300)
+  },
+  onSwipe(e) {
+    if (this.over) return
+    const d = e.direction
+    let v
+    if (d === 'left') v = { x: -1, y: 0 }
+    else if (d === 'right') v = { x: 1, y: 0 }
+    else if (d === 'up') v = { x: 0, y: -1 }
+    else if (d === 'down') v = { x: 0, y: 1 }
+    else return
+    this.pending = v
+  },
+  onTap() {
+    if (this.over) this.restart()
+  },
+  rebuild() {
+    const out = []
+    for (let i = 0; i < this.model.length; i++) {
+      const s = this.model[i]
+      out.push({
+        left: (OFFSET + s.x * CELL + 1) + 'px',
+        top: (OFFSET + s.y * CELL + 1) + 'px',
+        cls: i === 0 ? 'seg head' : 'seg'
+      })
+    }
+    this.snake = out
+    this.food = {
+      left: (OFFSET + this.foodModel.x * CELL + 3) + 'px',
+      top: (OFFSET + this.foodModel.y * CELL + 3) + 'px'
+    }
+    this.scoreText = 'SCORE ' + (this.model.length - 3)
+  }
+}
+</script>
+<style>
+.page {
+  width: 466px; height: 466px;
+  background-color: #000000;
+  align-items: center;
+  justify-content: center;
+}
+.dial {
+  width: 466px; height: 466px;
+}
+.board {
+  position: absolute; left: 71px; top: 71px;
+  width: 320px; height: 320px;
+  border-radius: 26px;
+  border-width: 2px;
+  border-color: #2a3040;
+  background-color: #0a0f1a;
+}
+.seg {
+  position: absolute;
+  width: 18px; height: 18px;
+  border-radius: 4px;
+  background-color: #35c26a;
+}
+.seg.head {
+  background-color: #7cf0a0;
+}
+.food {
+  position: absolute;
+  width: 14px; height: 14px;
+  border-radius: 7px;
+  background-color: #ff5a5a;
+}
+.score {
+  position: absolute; left: 0px; top: 24px;
+  width: 466px;
+  color: #9aa0aa;
+  font-size: 22px;
+  text-align: center;
+}
+.hint {
+  position: absolute; left: 0px; top: 408px;
+  width: 466px;
+  color: #3a4052;
+  font-size: 18px;
+  text-align: center;
+}
+.overlay {
+  position: absolute; left: 0px; top: 160px;
+  width: 466px;
+  flex-direction: column;
+  align-items: center;
+}
+.overText {
+  height: 40px;
+  color: #ffffff;
+  font-size: 32px;
+  text-align: center;
+}
+.overSub {
+  height: 32px;
+  color: #f3a633;
+  font-size: 24px;
+  text-align: center;
+}
+.overHint {
+  height: 30px;
+  color: #9aa0aa;
+  font-size: 20px;
+  text-align: center;
+}
+</style>

tests/page.cjs

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+// Page wiring test: drives the VM methods extracted from index.ux.
+const fs = require('node:fs');
+const vm = require('node:vm');
+const assert = require('node:assert/strict');
+const snake = require('../src/common/snake.js');
+
+const ux = fs.readFileSync('src/pages/index/index.ux', 'utf8');
+const body = ux.match(/<script>([\s\S]*?)<\/script>/)[1]
+  .replace(/import\s+snake\s+from\s+'[^']*';?/, '')
+  .replace(/^const\s+\w+\s*=[^\n]*\n/gm, '')
+  .replace('export default', '');
+
+const sandbox = { snake, Date, Math, String, Number, console, setInterval: () => 0, clearInterval: () => {},
+  CELL: 20, GRID: 16, OFFSET: 73 };
+vm.createContext(sandbox);
+const spec = vm.runInContext('(' + body + ')', sandbox);
+
+function mk() {
+  const o = Object.assign({}, spec, JSON.parse(JSON.stringify(spec.private)));
+  o.$element = () => null;
+  spec.onInit.call(o);
+  return o;
+}
+
+let c = mk();
+assert.equal(c.model.length, 3, 'initialized to length 3');
+assert.equal(c.snake.length, 3, 'rendered 3 segments');
+assert.equal(c.snake[0].cls, 'seg head', 'head flagged');
+assert.equal(c.snake[1].cls, 'seg', 'body flagged');
+assert.equal(c.scoreText, 'SCORE 0');
+assert.equal(c.snake[0].left, (73 + 6 * 20 + 1) + 'px', 'head x mapped to px');
+
+for (let i = 0; i < 5; i++) c.tick();
+assert.equal(c.model[0].x, 11, 'head moved right 5 steps from x=6');
+assert.equal(c.over, false);
+
+c.onSwipe({ direction: 'down' });
+c.tick();
+assert.equal(c.dir.x, 0, 'dir x');
+assert.equal(c.dir.y, 1, 'direction turned down');
+assert.equal(c.model[0].y, 8, 'head moved down');
+
+c.onSwipe({ direction: 'up' });
+c.tick();
+assert.equal(c.dir.x, 0, 'reversal keeps x');
+assert.equal(c.dir.y, 1, 'reversal blocked');
+
+// run into the wall to trigger game over (GRID=16, last column x=15)
+c.model = [{ x: 15, y: 5 }, { x: 14, y: 5 }, { x: 13, y: 5 }];
+c.dir = { x: 1, y: 0 };
+c.pending = null;
+c.tick();
+assert.equal(c.over, true, 'game over on wall hit');
+
+c.restart();
+assert.equal(c.over, false);
+assert.equal(c.model.length, 3);
+assert.equal(c.scoreText, 'SCORE 0');
+
+// template uses documented directives/events, no transforms, no crown remnants
+assert.match(ux, /for="\{\{ seg in snake \}\}"/);
+assert.match(ux, /show="\{\{ over \}\}"/);
+assert.match(ux, /onswipe="onSwipe"/);
+assert.doesNotMatch(ux, /crownrotationchanged/i);
+assert.doesNotMatch(ux, /transform\s*:/);
+
+console.log('PAGE WIRING PASS (movement, turn, reversal, game over, restart, directives)');

tests/snake.cjs

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+// TDD: Snake core — pure functions, no Vela APIs.
+const assert = require('node:assert/strict');
+const snake = require('../src/common/snake.js');
+
+// initial snake: head first, heading right, length 3
+const init = snake.initialSnake();
+assert.equal(init.length, 3, 'starts length 3');
+assert.deepEqual(init[0], { x: 6, y: 7 }, 'head at start cell');
+assert.deepEqual(init[1], { x: 5, y: 7 }, 'body behind head');
+assert.deepEqual(init[2], { x: 4, y: 7 }, 'tail');
+
+// move right into empty cell: alive, no food, length unchanged, tail advances
+let r = snake.step(init, { x: 1, y: 0 }, { x: 10, y: 10 }, 14);
+assert.equal(r.alive, true);
+assert.equal(r.ate, false);
+assert.equal(r.snake.length, 3);
+assert.deepEqual(r.snake[0], { x: 7, y: 7 }, 'head moved right');
+assert.deepEqual(r.snake[2], { x: 5, y: 7 }, 'tail advanced');
+
+// eat food: length grows by 1, tail retained
+r = snake.step(r.snake, { x: 1, y: 0 }, { x: 8, y: 7 }, 14);
+assert.equal(r.ate, true, 'ate the food ahead');
+assert.equal(r.snake.length, 4, 'grew by one');
+assert.deepEqual(r.snake[0], { x: 8, y: 7 });
+
+// wall collision: move left wall
+r = snake.step([{ x: 0, y: 5 }, { x: 1, y: 5 }], { x: -1, y: 0 }, { x: 3, y: 3 }, 14);
+assert.equal(r.alive, false, 'hit left wall');
+r = snake.step([{ x: 13, y: 5 }, { x: 12, y: 5 }], { x: 1, y: 0 }, { x: 3, y: 3 }, 14);
+assert.equal(r.alive, false, 'hit right wall');
+r = snake.step([{ x: 5, y: 0 }, { x: 5, y: 1 }], { x: 0, y: -1 }, { x: 3, y: 3 }, 14);
+assert.equal(r.alive, false, 'hit top wall');
+r = snake.step([{ x: 5, y: 13 }, { x: 5, y: 12 }], { x: 0, y: 1 }, { x: 3, y: 3 }, 14);
+assert.equal(r.alive, false, 'hit bottom wall');
+
+// self collision: run into own body
+const loop = [{ x: 5, y: 5 }, { x: 5, y: 6 }, { x: 6, y: 6 }, { x: 6, y: 5 }];
+r = snake.step(loop, { x: 0, y: -1 }, { x: 3, y: 3 }, 14); // head 5,5 -> 5,4? no, dir -y -> 5,4 empty
+assert.equal(r.alive, true, 'moving away from body is safe');
+// head at 5,5 move up into 5,4 (empty), then try to move into own neck is blocked by dir reversal
+// direct: build snake where head's next cell is body
+const sb = [{ x: 5, y: 5 }, { x: 4, y: 5 }, { x: 4, y: 4 }, { x: 5, y: 4 }];
+r = snake.step(sb, { x: 0, y: 1 }, { x: 9, y: 9 }, 14); // 5,5 -> 5,6 empty
+assert.equal(r.alive, true);
+r = snake.step([{ x: 5, y: 5 }, { x: 4, y: 5 }, { x: 4, y: 4 }, { x: 5, y: 4 }, { x: 6, y: 4 }, { x: 6, y: 5 }], { x: 0, y: 1 }, { x: 9, y: 9 }, 14);
+assert.equal(r.alive, true, 'moving into vacating tail cell is allowed');
+r = snake.step([{ x: 5, y: 5 }, { x: 5, y: 6 }, { x: 4, y: 6 }, { x: 4, y: 5 }], { x: 0, y: 1 }, { x: 9, y: 9 }, 14); // 5,5 -> 5,6 which is a middle body cell
+assert.equal(r.alive, false, 'run into body');
+
+// direction reversal guard
+assert.deepEqual(snake.turn({ x: 1, y: 0 }, { x: -1, y: 0 }), { x: 1, y: 0 }, 'cannot reverse into itself');
+assert.deepEqual(snake.turn({ x: 1, y: 0 }, { x: 0, y: 1 }), { x: 0, y: 1 }, 'turn down allowed');
+assert.deepEqual(snake.turn({ x: 1, y: 0 }, { x: 1, y: 0 }), { x: 1, y: 0 });
+
+// crown rotation: rotate direction ±90° (right->down->left->up, clockwise)
+assert.deepEqual(snake.rotateDir({ x: 1, y: 0 }, true), { x: 0, y: 1 }, 'clockwise right->down');
+assert.deepEqual(snake.rotateDir({ x: 0, y: 1 }, true), { x: -1, y: 0 }, 'clockwise down->left');
+assert.deepEqual(snake.rotateDir({ x: -1, y: 0 }, true), { x: 0, y: -1 }, 'clockwise left->up');
+assert.deepEqual(snake.rotateDir({ x: 0, y: -1 }, true), { x: 1, y: 0 }, 'clockwise up->right (wrap)');
+assert.deepEqual(snake.rotateDir({ x: 1, y: 0 }, false), { x: 0, y: -1 }, 'counterclockwise right->up');
+assert.deepEqual(snake.rotateDir({ x: 0, y: -1 }, false), { x: -1, y: 0 }, 'counterclockwise up->left');
+
+// spawnFood lands on an empty cell
+for (let i = 0; i < 50; i++) {
+  const f = snake.spawnFood([{ x: 0, y: 0 }], 14);
+  assert.ok(f.x >= 0 && f.x < 14 && f.y >= 0 && f.y < 14, 'in bounds');
+  assert.ok(!(f.x === 0 && f.y === 0), 'not on snake');
+}
+
+console.log('ALL SNAKE LOGIC PASS');