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

tests/snake.cjs

@@ -0,0 +1,70 @@
+// 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');