feat(engine): Android polish sweep + hint button + watch replay

Draw-Three waste fan: slot.saturating_sub(1) was a constant shift that
hid slot-0 even when the pile had fewer cards than visible. Fixed to
slot.saturating_sub(rendered_len.saturating_sub(visible)) so small piles
fan correctly and only a genuine buffer card gets hidden. New regression
test covers the small-pile case.

Android toast: game-over "press D / N" message now shows touch-friendly
copy ("Tap the stock...") on Android via cfg gate.

Onboarding: SLIDE_COUNT drops from 3 to 2 on Android so first-time
users skip the keyboard-shortcuts slide (irrelevant on touchscreen).
spawn_slide dispatch is gated identically.

Hint button: added HintButton to the HUD action bar (order 4, between
Help and Modes). Clicking it triggers the async solver hint — same path
as the H key — via optional resources so headless tests stay clean.
All button-order and tooltip tests updated for the new 7-button bar.

Watch Replay: win-summary modal now shows a "Watch Replay" secondary
button alongside "Play Again". It loads the most recent entry from
ReplayHistoryResource and hands it to start_replay_playback, dismissing
the modal. Falls back to an info toast when the replay or playback
plugin is unavailable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/card_plugin.rs

@@ -693,11 +693,16 @@ fn card_positions<'a>(game: &'a GameState, layout: &Layout) -> Vec<(&'a Card, Ve
         };
 
         let mut y_offset = 0.0_f32;
+        let rendered_len = cards[render_start..].len();
         for (slot, card) in cards[render_start..].iter().enumerate() {
             let x_offset = if is_waste && matches!(game.draw_mode, DrawMode::DrawThree) {
-                // Slot 0 is the hidden extra card; keep it at x=0 under the stack.
+                // When len > visible, slot 0 is a hidden buffer card kept at
-                // Slots 1..=3 are the visible fan (left→right).
+                // x=0 to prevent a flash during the draw tween. When len ≤
-                slot.saturating_sub(1) as f32 * layout.card_size.x * 0.28
+                // visible (small pile), every card is visible and should fan
+                // normally — no card is hidden, so the shift is 0.
+                let visible = 3_usize;
+                let hidden = rendered_len.saturating_sub(visible);
+                slot.saturating_sub(hidden) as f32 * layout.card_size.x * 0.28
             } else {
                 0.0
             };
@@ -2050,6 +2055,43 @@ mod tests {
         assert_eq!(waste_rendered.last().unwrap().0.id, top_id);
     }
 
+    #[test]
+    fn waste_draw_three_fans_correctly_when_pile_smaller_than_visible() {
+        // Regression: slot.saturating_sub(1) always hid slot-0 even when the
+        // pile was too small to have a buffer card, collapsing 2 visible cards
+        // onto x=0 instead of fanning them.
+        use solitaire_core::game_state::DrawMode;
+        let mut g = GameState::new(42, DrawMode::DrawThree);
+        // Draw exactly once — in Draw-Three mode with a full stock this gives
+        // 3 waste cards (still ≤ visible=3, so no hidden buffer needed).
+        let _ = g.draw();
+        let waste_pile = &g.piles[&PileType::Waste].cards;
+        // We need exactly 2 or 3 waste cards to hit the small-pile path.
+        // One draw in Draw-Three adds up to 3 cards; take the first 2 if needed.
+        let count = waste_pile.len();
+        assert!(count >= 2, "need at least 2 waste cards");
+
+        let waste_ids: std::collections::HashSet<u32> =
+            waste_pile.iter().map(|c| c.id).collect();
+        let layout = crate::layout::compute_layout(Vec2::new(1280.0, 800.0), 0.0, 0.0);
+        let positions = card_positions(&g, &layout);
+
+        let mut waste_rendered: Vec<_> = positions
+            .iter()
+            .filter(|(card, _, _)| waste_ids.contains(&card.id))
+            .collect();
+        // All waste cards should be visible (no hidden buffer when len ≤ visible).
+        assert_eq!(waste_rendered.len(), count, "all waste cards rendered when pile ≤ visible");
+
+        // Cards must be fanned with distinct x positions (or equal for 1-card).
+        waste_rendered.sort_by(|a, b| a.1.x.partial_cmp(&b.1.x).unwrap());
+        if count >= 2 {
+            let last = waste_rendered.last().unwrap();
+            let second_last = &waste_rendered[waste_rendered.len() - 2];
+            assert!(last.1.x > second_last.1.x, "top 2 waste cards must fan to distinct x positions");
+        }
+    }
+
     #[test]
     fn card_positions_tableau_cards_are_fanned_downward() {
         let g = GameState::new(42, solitaire_core::game_state::DrawMode::DrawOne);

solitaire_engine/src/game_plugin.rs

@@ -1072,9 +1072,11 @@ fn check_no_moves(
     }
 
     if !moves_ok && !*already_fired {
-        toast.write(InfoToastEvent(
+        #[cfg(target_os = "android")]
-            "No moves available \u{2014} press D to draw or N for a new game".to_string(),
+        let no_moves_msg = "No moves available \u{2014} tap the stock to draw or start a new game";
-        ));
+        #[cfg(not(target_os = "android"))]
+        let no_moves_msg = "No moves available \u{2014} press D to draw or N for a new game";
+        toast.write(InfoToastEvent(no_moves_msg.to_string()));
         *already_fired = true;
         // Only spawn the overlay if one does not already exist.
         if game_over_screens.is_empty() {

solitaire_engine/src/hud_plugin.rs

@@ -242,6 +242,11 @@ pub struct PauseButton;
 #[derive(Component, Debug)]
 pub struct HelpButton;
 
+/// Marker on the "Hint" action button. Click spawns an async solver task
+/// (same as the `H` keyboard accelerator) and highlights the suggested card.
+#[derive(Component, Debug)]
+pub struct HintButton;
+
 /// Marker on the "Modes" action button. Click toggles the [`ModesPopover`]
 /// (a small dropdown panel) below the action bar. Each popover row starts
 /// the corresponding game mode.
@@ -367,6 +372,7 @@ impl Plugin for HudPlugin {
                     handle_undo_button,
                     handle_pause_button,
                     handle_help_button,
+                    handle_hint_button,
                     handle_modes_button,
                     handle_mode_option_click,
                     handle_modes_backdrop_click,
@@ -702,6 +708,15 @@ fn spawn_action_buttons(
                 &font,
                 3,
             );
+            spawn_action_button(
+                row,
+                HintButton,
+                "Hint",
+                Some("H"),
+                "Highlight a suggested move. Cycles through alternatives on repeat taps.",
+                &font,
+                4,
+            );
             spawn_action_button(
                 row,
                 ModesButton,
@@ -709,7 +724,7 @@ fn spawn_action_buttons(
                 None,
                 "Switch modes: Classic, Daily, Zen, Challenge, Time Attack.",
                 &font,
-                4,
+                5,
             );
             spawn_action_button(
                 row,
@@ -718,7 +733,7 @@ fn spawn_action_buttons(
                 Some("N"),
                 "Start a fresh deal. Confirms first if a game is in progress.",
                 &font,
-                5,
+                6,
             );
         });
 }
@@ -857,6 +872,36 @@ fn handle_help_button(
     }
 }
 
+fn handle_hint_button(
+    interaction_query: Query<&Interaction, (With<HintButton>, Changed<Interaction>)>,
+    paused: Option<Res<crate::PausedResource>>,
+    game: Option<Res<GameStateResource>>,
+    solver_config: Option<Res<crate::input_plugin::HintSolverConfig>>,
+    mut pending_hint: Option<ResMut<crate::pending_hint::PendingHintTask>>,
+    mut info_toast: MessageWriter<InfoToastEvent>,
+) {
+    for interaction in &interaction_query {
+        if *interaction != Interaction::Pressed {
+            continue;
+        }
+        if paused.as_ref().is_some_and(|p| p.0) {
+            return;
+        }
+        let Some(ref g) = game else { return };
+        if g.0.is_won {
+            #[cfg(target_os = "android")]
+            let won_msg = "Game won! Tap New Game to play again";
+            #[cfg(not(target_os = "android"))]
+            let won_msg = "Game won! Press N for a new game";
+            info_toast.write(InfoToastEvent(won_msg.to_string()));
+            return;
+        }
+        if let (Some(cfg), Some(hint)) = (solver_config.as_ref(), pending_hint.as_mut()) {
+            hint.spawn(g.0.clone(), cfg.0);
+        }
+    }
+}
+
 /// Toggles the [`ModesPopover`]: spawns it on first click, despawns it on
 /// second click. Mode rows are populated per the player's current level so
 /// only unlocked options appear.
@@ -2648,6 +2693,7 @@ mod tests {
             focusable_for::<UndoButton>(&mut app),
             focusable_for::<PauseButton>(&mut app),
             focusable_for::<HelpButton>(&mut app),
+            focusable_for::<HintButton>(&mut app),
             focusable_for::<ModesButton>(&mut app),
             focusable_for::<NewGameButton>(&mut app),
         ] {
@@ -2756,6 +2802,10 @@ mod tests {
             tooltip_for::<HelpButton>(&mut app),
             "Show controls, rules, and keyboard shortcuts."
         );
+        assert_eq!(
+            tooltip_for::<HintButton>(&mut app),
+            "Highlight a suggested move. Cycles through alternatives on repeat taps."
+        );
         assert_eq!(
             tooltip_for::<ModesButton>(&mut app),
             "Switch modes: Classic, Daily, Zen, Challenge, Time Attack."
@@ -2875,14 +2925,15 @@ mod tests {
     fn hud_button_order_matches_spawn_order() {
         let mut app = headless_app();
         // Visual reading order (left → right): Menu, Undo, Pause, Help,
-        // Modes, New Game. Their `order` fields must be 0..=5 in that
+        // Hint, Modes, New Game. Their `order` fields must be 0..=6 in
-        // order so Tab cycles them as the player reads them.
+        // that order so Tab cycles them as the player reads them.
         assert_eq!(focusable_for::<MenuButton>(&mut app).order, 0);
         assert_eq!(focusable_for::<UndoButton>(&mut app).order, 1);
         assert_eq!(focusable_for::<PauseButton>(&mut app).order, 2);
         assert_eq!(focusable_for::<HelpButton>(&mut app).order, 3);
-        assert_eq!(focusable_for::<ModesButton>(&mut app).order, 4);
+        assert_eq!(focusable_for::<HintButton>(&mut app).order, 4);
-        assert_eq!(focusable_for::<NewGameButton>(&mut app).order, 5);
+        assert_eq!(focusable_for::<ModesButton>(&mut app).order, 5);
+        assert_eq!(focusable_for::<NewGameButton>(&mut app).order, 6);
     }
 
     #[test]

solitaire_engine/src/onboarding_plugin.rs

@@ -41,7 +41,13 @@ use crate::ui_theme::{
 // ---------------------------------------------------------------------------
 
 /// Total number of onboarding slides (0-based index goes 0..SLIDE_COUNT-1).
+///
+/// Android omits the keyboard-shortcuts slide (index 2) because there is no
+/// physical keyboard on a touchscreen device, dropping the count to 2.
+#[cfg(not(target_os = "android"))]
 const SLIDE_COUNT: u8 = 3;
+#[cfg(target_os = "android")]
+const SLIDE_COUNT: u8 = 2;
 
 // ---------------------------------------------------------------------------
 // Components (private — never re-exported)
@@ -276,6 +282,8 @@ fn spawn_slide(commands: &mut Commands, index: u8, font_res: Option<&FontResourc
     match index {
         0 => spawn_slide_welcome(commands, font_res),
         1 => spawn_slide_how_to_play(commands, font_res),
+        // Slide 2 (keyboard shortcuts) is desktop-only; Android has no keyboard.
+        #[cfg(not(target_os = "android"))]
         2 => spawn_slide_hotkeys(commands, font_res),
         _ => spawn_slide_welcome(commands, font_res),
     }
@@ -664,8 +672,15 @@ mod tests {
     // -----------------------------------------------------------------------
 
     #[test]
+    #[cfg(not(target_os = "android"))]
     fn slide_count_constant_is_three() {
-        assert_eq!(SLIDE_COUNT, 3, "SLIDE_COUNT must be 3");
+        assert_eq!(SLIDE_COUNT, 3, "SLIDE_COUNT must be 3 on desktop");
+    }
+
+    #[test]
+    #[cfg(target_os = "android")]
+    fn slide_count_constant_is_two_on_android() {
+        assert_eq!(SLIDE_COUNT, 2, "SLIDE_COUNT must be 2 on Android (no keyboard slide)");
     }
 
     #[test]

solitaire_engine/src/win_summary_plugin.rs

@@ -167,10 +167,11 @@ pub struct SessionAchievements {
 #[derive(Component, Debug)]
 pub struct WinSummaryOverlay;
 
-/// Marker on the "Play Again" button inside the win-summary modal.
+/// Marker on the "Play Again" / "Watch Replay" buttons inside the win-summary modal.
 #[derive(Component, Debug)]
 enum WinSummaryButton {
     PlayAgain,
+    WatchReplay,
 }
 
 /// Marker for one row of the win-modal score-breakdown reveal.
@@ -602,26 +603,58 @@ fn spawn_win_summary_after_delay(
     }
 }
 
-/// Despawns the win-summary modal and fires `NewGameRequestEvent` when
+/// Handles "Play Again" and "Watch Replay" in the win-summary modal.
-/// the player presses "Play Again".
+/// Handles "Play Again" and "Watch Replay" in the win-summary modal.
 fn handle_win_summary_buttons(
     interaction_query: Query<(&Interaction, &WinSummaryButton), Changed<Interaction>>,
     overlays: Query<Entity, With<WinSummaryOverlay>>,
     mut commands: Commands,
     mut new_game: MessageWriter<NewGameRequestEvent>,
+    mut toast: MessageWriter<InfoToastEvent>,
+    history: Option<Res<crate::stats_plugin::ReplayHistoryResource>>,
+    mut playback: Option<ResMut<crate::replay_playback::ReplayPlaybackState>>,
 ) {
-    for (interaction, button) in &interaction_query {
+    // Collect all pressed buttons first to avoid moving `playback` inside the loop.
-        if *interaction != Interaction::Pressed {
+    let pressed: Vec<&WinSummaryButton> = interaction_query
-            continue;
+        .iter()
-        }
+        .filter(|(i, _)| **i == Interaction::Pressed)
+        .map(|(_, b)| b)
+        .collect();
+
+    for button in pressed {
         match button {
             WinSummaryButton::PlayAgain => {
-                // Despawn the modal.
                 for entity in &overlays {
                     commands.entity(entity).despawn();
                 }
                 new_game.write(NewGameRequestEvent::default());
             }
+            WinSummaryButton::WatchReplay => {
+                let latest = history
+                    .as_ref()
+                    .and_then(|h| h.0.replays.last())
+                    .cloned();
+                match (latest, playback.as_mut()) {
+                    (Some(replay), Some(pb)) => {
+                        for entity in &overlays {
+                            commands.entity(entity).despawn();
+                        }
+                        crate::replay_playback::start_replay_playback(
+                            &mut commands,
+                            pb,
+                            replay,
+                        );
+                    }
+                    (Some(_), None) => {
+                        toast.write(InfoToastEvent(
+                            "Replay playback not available".to_string(),
+                        ));
+                    }
+                    (None, _) => {
+                        toast.write(InfoToastEvent("No replay saved yet".to_string()));
+                    }
+                }
+            }
         }
     }
 }
@@ -811,23 +844,50 @@ fn spawn_overlay(
                     spawn_achievements_section(card, &session.names);
                 }
 
-                // Play Again button
+                // Button row: Watch Replay + Play Again side by side.
-                card.spawn((
+                card.spawn(Node {
+                    flex_direction: FlexDirection::Row,
+                    justify_content: JustifyContent::Center,
+                    column_gap: VAL_SPACE_3,
+                    margin: UiRect::top(VAL_SPACE_2),
+                    ..default()
+                })
+                .with_children(|row| {
+                    // Watch Replay (secondary style)
+                    row.spawn((
+                        WinSummaryButton::WatchReplay,
+                        Button,
+                        Node {
+                            padding: UiRect::axes(Val::Px(20.0), VAL_SPACE_3),
+                            justify_content: JustifyContent::Center,
+                            border_radius: BorderRadius::all(Val::Px(RADIUS_MD)),
+                            border: UiRect::all(Val::Px(1.0)),
+                            ..default()
+                        },
+                        BackgroundColor(Color::NONE),
+                        BorderColor::all(ACCENT_PRIMARY),
+                    ))
+                    .with_children(|b| {
+                        b.spawn((
+                            Text::new("Watch Replay"),
+                            TextFont { font_size: TYPE_BODY_LG, ..default() },
+                            TextColor(ACCENT_PRIMARY),
+                        ));
+                    });
+
+                    // Play Again (primary style)
+                    row.spawn((
                         WinSummaryButton::PlayAgain,
                         Button,
                         Node {
-                        padding: UiRect::axes(Val::Px(28.0), VAL_SPACE_3),
+                            padding: UiRect::axes(Val::Px(20.0), VAL_SPACE_3),
                             justify_content: JustifyContent::Center,
-                        margin: UiRect::top(VAL_SPACE_2),
                             border_radius: BorderRadius::all(Val::Px(RADIUS_MD)),
                             ..default()
                         },
                         BackgroundColor(ACCENT_PRIMARY),
                     ))
                     .with_children(|b| {
-                    // Append the Enter / Return glyph so keyboard players see
-                    // the accelerator on the button itself — mirrors the
-                    // chip-style hints on every modal button helper.
                         b.spawn((
                             Text::new("Play Again  \u{21B5}"),
                             TextFont { font_size: TYPE_BODY_LG, ..default() },
@@ -836,6 +896,7 @@ fn spawn_overlay(
                     });
                 });
             });
+        });
 }
 
 /// Maximum number of achievement names shown explicitly in the win modal before