feat(engine): Phase F touch action bar — thumb-reach Undo/Draw/Hint + hold-to-repeat undo

Touch layout (USE_TOUCH_UI_LAYOUT) restructures the bottom action bar
to five buttons: an enlarged Undo / Draw / Hint trio (96x64px targets,
1.35x labels) between compact Menu and Pause. Draw is new — it fires
the same DrawRequestEvent as tapping the stock, so the most frequent
action no longer needs a reach to the top of a tall folded screen.
Help, Modes, and New Game leave the touch bar (they live in Menu ->
System, the Home grid, and Home's hero respectively). Desktop keeps
the seven-button bar unchanged (decision 5: touch-only).

Holding Undo now steps back repeatedly after a 0.45s delay (5.5/s),
each step through the normal request path so the scoring penalty
applies. New self-ambiguous DrawRequestWriters set keeps the ambiguity
gate at zero with the fourth DrawRequestEvent writer.

6 new hud_plugin tests; workspace suite + clippy green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

solitaire_engine/src/hud_plugin/tests.rs

@@ -670,7 +670,7 @@ fn hud_elements_carry_expected_tooltip_strings() {
     );
     assert_eq!(
         tooltip_for::<UndoButton>(&mut app),
-        "Take back your last move. Costs points and blocks No Undo."
+        "Take back your last move. Hold to keep undoing. Costs points and blocks No Undo."
     );
     assert_eq!(
         tooltip_for::<PauseButton>(&mut app),
@@ -899,3 +899,157 @@ fn hud_focus_only_engages_when_button_hovered() {
         "Hud-engaged Tab must focus a Hud-grouped entity"
     );
 }
+
+// ---------------------------------------------------------------------------
+// Phase F: touch action bar + hold-to-repeat undo
+// ---------------------------------------------------------------------------
+
+/// Bare app (no `HudPlugin`) so bar-content assertions count only the
+/// buttons the tested spawn function creates — `headless_app` would
+/// pre-spawn the platform-default bar and pollute the counts.
+fn bar_only_app(touch: bool) -> App {
+    let mut app = App::new();
+    app.add_plugins(MinimalPlugins);
+    app.update();
+    let font = TextFont::default();
+    let world = app.world_mut();
+    let mut commands = world.commands();
+    commands.spawn(Node::default()).with_children(|row| {
+        if touch {
+            spawn_touch_action_bar(row, &font);
+        } else {
+            spawn_desktop_action_bar(row, &font);
+        }
+    });
+    app.update();
+    app
+}
+
+fn count_buttons<C: Component>(app: &mut App) -> usize {
+    app.world_mut()
+        .query_filtered::<(), With<C>>()
+        .iter(app.world())
+        .count()
+}
+
+#[test]
+fn touch_action_bar_has_thumb_trio_plus_menu_and_pause() {
+    let mut app = bar_only_app(true);
+
+    assert_eq!(count_buttons::<UndoButton>(&mut app), 1);
+    assert_eq!(count_buttons::<DrawButton>(&mut app), 1);
+    assert_eq!(count_buttons::<HintButton>(&mut app), 1);
+    assert_eq!(count_buttons::<MenuButton>(&mut app), 1);
+    assert_eq!(count_buttons::<PauseButton>(&mut app), 1);
+
+    // Utility actions live elsewhere on touch: Help in Menu → System,
+    // modes on the Home screen, New Game on Home's hero button.
+    assert_eq!(count_buttons::<HelpButton>(&mut app), 0);
+    assert_eq!(count_buttons::<ModesButton>(&mut app), 0);
+    assert_eq!(count_buttons::<NewGameButton>(&mut app), 0);
+}
+
+#[test]
+fn desktop_action_bar_keeps_all_seven_and_no_draw() {
+    let mut app = bar_only_app(false);
+
+    for (count, name) in [
+        (count_buttons::<MenuButton>(&mut app), "Menu"),
+        (count_buttons::<UndoButton>(&mut app), "Undo"),
+        (count_buttons::<PauseButton>(&mut app), "Pause"),
+        (count_buttons::<HelpButton>(&mut app), "Help"),
+        (count_buttons::<HintButton>(&mut app), "Hint"),
+        (count_buttons::<ModesButton>(&mut app), "Modes"),
+        (count_buttons::<NewGameButton>(&mut app), "New Game"),
+    ] {
+        assert_eq!(count, 1, "desktop bar must keep its {name} button");
+    }
+    assert_eq!(
+        count_buttons::<DrawButton>(&mut app),
+        0,
+        "Draw is touch-only (decision 5); desktop draws via stock click / D / Space"
+    );
+}
+
+#[test]
+fn draw_button_press_fires_draw_request() {
+    let mut app = headless_app();
+    app.world_mut()
+        .resource_mut::<Messages<DrawRequestEvent>>()
+        .clear();
+
+    app.world_mut().spawn((DrawButton, Interaction::Pressed));
+    app.update();
+
+    let events = app.world().resource::<Messages<DrawRequestEvent>>();
+    let mut cursor = events.get_cursor();
+    assert_eq!(
+        cursor.read(events).count(),
+        1,
+        "pressing the Draw button must fire exactly one DrawRequestEvent"
+    );
+}
+
+#[test]
+fn draw_button_press_is_noop_while_paused() {
+    let mut app = headless_app();
+    app.insert_resource(PausedResource(true));
+    app.world_mut()
+        .resource_mut::<Messages<DrawRequestEvent>>()
+        .clear();
+
+    app.world_mut().spawn((DrawButton, Interaction::Pressed));
+    app.update();
+
+    let events = app.world().resource::<Messages<DrawRequestEvent>>();
+    let mut cursor = events.get_cursor();
+    assert_eq!(
+        cursor.read(events).count(),
+        0,
+        "the Draw button must be inert while paused (mirrors the stock-click guard)"
+    );
+}
+
+/// The timing contract for hold-to-repeat undo, exercised through the
+/// pure boundary function so no wall-clock is involved. Delay = 0.45 s,
+/// interval = 0.18 s → boundaries at 0.45, 0.63, 0.81, …
+#[test]
+fn undo_hold_boundary_math() {
+    // A tap never repeats.
+    assert!(!undo_hold_crossed_fire_boundary(0.0, 0.05));
+    assert!(!undo_hold_crossed_fire_boundary(0.2, 0.44));
+    // Crossing the initial delay fires the first repeat.
+    assert!(undo_hold_crossed_fire_boundary(0.44, 0.46));
+    // Inside the first repeat interval: quiet.
+    assert!(!undo_hold_crossed_fire_boundary(0.46, 0.62));
+    // Each interval boundary fires exactly once.
+    assert!(undo_hold_crossed_fire_boundary(0.62, 0.64));
+    assert!(!undo_hold_crossed_fire_boundary(0.64, 0.80));
+    assert!(undo_hold_crossed_fire_boundary(0.80, 0.82));
+}
+
+#[test]
+fn undo_hold_state_accumulates_and_resets_on_release() {
+    let mut app = headless_app();
+    let button = app
+        .world_mut()
+        .spawn((UndoButton, Interaction::Pressed))
+        .id();
+    app.update();
+    app.update();
+    app.update();
+
+    assert!(
+        app.world().resource::<UndoHoldState>().held_secs > 0.0,
+        "held time must accumulate while the Undo button stays pressed"
+    );
+
+    app.world_mut().entity_mut(button).insert(Interaction::None);
+    app.update();
+
+    assert_eq!(
+        app.world().resource::<UndoHoldState>().held_secs,
+        0.0,
+        "releasing the Undo button must reset the hold state"
+    );
+}