feat(snake): implement snake game with pure game logic, renderer, and IPC-based main loop

crates/apps/snake/src/tests/game.rs

@@ -0,0 +1,82 @@
+use crate::game::*;
+
+#[test]
+fn new_game_is_running() {
+    let game = Snake::new();
+    assert_eq!(game.state(), GameState::Running);
+}
+
+#[test]
+fn initial_snake_has_three_segments() {
+    let game = Snake::new();
+    assert_eq!(game.body().len(), 3);
+}
+
+#[test]
+fn initial_score_is_zero() {
+    let game = Snake::new();
+    assert_eq!(game.score(), 0);
+}
+
+#[test]
+fn tick_moves_head_right() {
+    let mut game = Snake::new();
+    let initial_head = game.head();
+    game.tick();
+    assert_eq!(game.head().x, initial_head.x + 1);
+    assert_eq!(game.head().y, initial_head.y);
+}
+
+#[test]
+fn set_direction_changes_movement() {
+    let mut game = Snake::new();
+    game.set_direction(Direction::Down);
+    game.tick();
+    let head = game.head();
+    assert_eq!(head.y, GRID_HEIGHT / 2 + 1);
+}
+
+#[test]
+fn cannot_reverse_direction() {
+    let mut game = Snake::new();
+    // moving right, try to go left — should be ignored
+    game.set_direction(Direction::Left);
+    game.tick();
+    assert_eq!(game.direction(), Direction::Right);
+}
+
+#[test]
+fn wall_collision_ends_game() {
+    let mut game = Snake::new();
+    // Move right until hitting the wall
+    for _ in 0..GRID_WIDTH {
+        if game.state() != GameState::Running { break; }
+        game.tick();
+    }
+    assert_eq!(game.state(), GameState::GameOver);
+}
+
+#[test]
+fn food_exists_on_grid() {
+    let game = Snake::new();
+    let food = game.food();
+    assert!(food.x < GRID_WIDTH);
+    assert!(food.y < GRID_HEIGHT);
+}
+
+#[test]
+fn body_length_preserved_without_food() {
+    let mut game = Snake::new();
+    let initial_len = game.body().len();
+    game.tick();
+    assert_eq!(game.body().len(), initial_len);
+}
+
+#[test]
+fn direction_up_moves_correctly() {
+    let mut game = Snake::new();
+    game.set_direction(Direction::Up);
+    let y_before = game.head().y;
+    game.tick();
+    assert_eq!(game.head().y, y_before - 1);
+}

crates/apps/snake/src/tests/mod.rs

@@ -0,0 +1,2 @@
+mod game;
+mod renderer;

crates/apps/snake/src/tests/renderer.rs

@@ -0,0 +1,32 @@
+use crate::game::Snake;
+use crate::renderer::{render, RenderCommand};
+
+#[test]
+fn render_produces_commands() {
+    let snake = Snake::new();
+    let mut commands = [RenderCommand { x: 0, y: 0, w: 0, h: 0, color: 0 }; 64];
+    let count = render(&snake, &mut commands);
+    // background + border + food + 3 body segments = 6
+    assert!(count >= 6);
+}
+
+#[test]
+fn first_command_is_background() {
+    let snake = Snake::new();
+    let mut commands = [RenderCommand { x: 0, y: 0, w: 0, h: 0, color: 0 }; 64];
+    render(&snake, &mut commands);
+    assert_eq!(commands[0].x, 0);
+    assert_eq!(commands[0].y, 0);
+    assert!(commands[0].w > 0);
+    assert!(commands[0].h > 0);
+}
+
+#[test]
+fn food_is_rendered() {
+    let snake = Snake::new();
+    let mut commands = [RenderCommand { x: 0, y: 0, w: 0, h: 0, color: 0 }; 64];
+    let count = render(&snake, &mut commands);
+    // Food is command index 2 (after bg and border)
+    assert!(count > 2);
+    assert_eq!(commands[2].color, 0xFF0040);
+}