feat(engine): add InputPlugin with keyboard and stock-click

Keyboard: U=undo, N=new game, D=draw, Escape=pause placeholder (logged
only until the pause screen lands). Mouse: left-click on the stock pile
fires DrawRequestEvent. Cursor coordinates are converted via the active
Camera2d's viewport_to_world_2d so the hit-test works under arbitrary
camera setups.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_engine/src/input_plugin.rs

@@ -0,0 +1,123 @@
+//! Keyboard + mouse input for the game board.
+//!
+//! - `U` → `UndoRequestEvent`
+//! - `N` → `NewGameRequestEvent { seed: None }`
+//! - `D` → `DrawRequestEvent`
+//! - `Esc` → logged as a pause placeholder (no event yet; wired up when the
+//!   pause screen lands in a later phase)
+//! - Left-click on the stock pile → `DrawRequestEvent`
+//!
+//! Drag-and-drop for tableau/waste/foundation moves is handled in Phase 3E.
+
+use bevy::input::ButtonInput;
+use bevy::math::Vec2;
+use bevy::prelude::*;
+use bevy::window::PrimaryWindow;
+use solitaire_core::pile::PileType;
+
+use crate::events::{DrawRequestEvent, NewGameRequestEvent, UndoRequestEvent};
+use crate::layout::LayoutResource;
+
+/// Registers the keyboard + mouse input systems.
+pub struct InputPlugin;
+
+impl Plugin for InputPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(Update, (handle_keyboard, handle_mouse_clicks));
+    }
+}
+
+fn handle_keyboard(
+    keys: Res<ButtonInput<KeyCode>>,
+    mut undo: EventWriter<UndoRequestEvent>,
+    mut new_game: EventWriter<NewGameRequestEvent>,
+    mut draw: EventWriter<DrawRequestEvent>,
+) {
+    if keys.just_pressed(KeyCode::KeyU) {
+        undo.send(UndoRequestEvent);
+    }
+    if keys.just_pressed(KeyCode::KeyN) {
+        new_game.send(NewGameRequestEvent { seed: None });
+    }
+    if keys.just_pressed(KeyCode::KeyD) {
+        draw.send(DrawRequestEvent);
+    }
+    if keys.just_pressed(KeyCode::Escape) {
+        // Pause placeholder — the pause screen hooks this up in a later phase.
+        info!("pause requested (not yet wired)");
+    }
+}
+
+fn handle_mouse_clicks(
+    buttons: Res<ButtonInput<MouseButton>>,
+    windows: Query<&Window, With<PrimaryWindow>>,
+    cameras: Query<(&Camera, &GlobalTransform)>,
+    layout: Option<Res<LayoutResource>>,
+    mut draw: EventWriter<DrawRequestEvent>,
+) {
+    if !buttons.just_pressed(MouseButton::Left) {
+        return;
+    }
+    let Some(layout) = layout else {
+        return;
+    };
+    let Ok(window) = windows.get_single() else {
+        return;
+    };
+    let Some(cursor) = window.cursor_position() else {
+        return;
+    };
+    let Ok((camera, camera_transform)) = cameras.get_single() else {
+        return;
+    };
+    let Ok(world) = camera.viewport_to_world_2d(camera_transform, cursor) else {
+        return;
+    };
+
+    let Some(&stock_pos) = layout.0.pile_positions.get(&PileType::Stock) else {
+        return;
+    };
+    if point_in_rect(world, stock_pos, layout.0.card_size) {
+        draw.send(DrawRequestEvent);
+    }
+}
+
+/// Axis-aligned rectangle hit-test with a center and full size.
+fn point_in_rect(point: Vec2, center: Vec2, size: Vec2) -> bool {
+    let half = size / 2.0;
+    point.x >= center.x - half.x
+        && point.x <= center.x + half.x
+        && point.y >= center.y - half.y
+        && point.y <= center.y + half.y
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn point_in_rect_inside_returns_true() {
+        let center = Vec2::new(10.0, 20.0);
+        let size = Vec2::new(40.0, 60.0);
+        assert!(point_in_rect(Vec2::new(10.0, 20.0), center, size));
+        assert!(point_in_rect(Vec2::new(29.0, 49.0), center, size));
+        assert!(point_in_rect(Vec2::new(-9.0, -9.0), center, size));
+    }
+
+    #[test]
+    fn point_in_rect_on_edge_returns_true() {
+        let center = Vec2::ZERO;
+        let size = Vec2::new(10.0, 10.0);
+        assert!(point_in_rect(Vec2::new(5.0, 5.0), center, size));
+        assert!(point_in_rect(Vec2::new(-5.0, -5.0), center, size));
+    }
+
+    #[test]
+    fn point_in_rect_outside_returns_false() {
+        let center = Vec2::ZERO;
+        let size = Vec2::new(10.0, 10.0);
+        assert!(!point_in_rect(Vec2::new(6.0, 0.0), center, size));
+        assert!(!point_in_rect(Vec2::new(0.0, 6.0), center, size));
+        assert!(!point_in_rect(Vec2::new(-100.0, 0.0), center, size));
+    }
+}

solitaire_engine/src/lib.rs

@@ -7,6 +7,7 @@
 pub mod card_plugin;
 pub mod events;
 pub mod game_plugin;
+pub mod input_plugin;
 pub mod layout;
 pub mod resources;
 pub mod table_plugin;
@@ -17,6 +18,7 @@ pub use events::{
     StateChangedEvent, UndoRequestEvent,
 };
 pub use game_plugin::{GameMutation, GamePlugin};
+pub use input_plugin::InputPlugin;
 pub use layout::{compute_layout, Layout, LayoutResource};
 pub use resources::{DragState, GameStateResource, SyncStatus, SyncStatusResource};
 pub use table_plugin::{PileMarker, TableBackground, TablePlugin};