fix(multi): resolve 26 bugs found in comprehensive codebase review

Core fixes (issues #12, #13, #22):
- #12: undo now preserves score delta instead of restoring snapshot score
- #13: take_from_foundation defaults to false (non-standard house rule)
- #22: check_win validates full suit sequence, not just card count

Engine fixes:
- #8:  replay keyboard input guard against non-replay state
- #9:  help modal scrims.is_empty() guard added
- #10: settings modal scrims.is_empty() guard added
- #11: sync_plugin builds payload at poll time (not task-spawn time)
- #14: server replay mode case-sensitivity fix ("Classic")
- #15: play_by_seed_plugin confirmed flag set to true on launch
- #16: replay back-step debounce via Local<bool> + StateChangedEvent;
       register StateChangedEvent in ReplayOverlayPlugin (fixes 52 tests)
- #17: time-attack timer ignores win-summary overlay
- #18: HUD dropdown glyphs U+25BE → U+2193 (FiraMono-safe arrow)
- #19: theme plugin applies immediate visual update on A→B→A switch
- #20: SyncAuthError / SyncBusyOverlay split into separate entities so
       auth errors are visible after busy overlay is hidden
- #21: handle_forfeit ordered before update_stats_on_new_game
- #23: server merge uses correct avg_time_seconds and games_lost math
- #24: win_summary migrated to ModalScrim pattern
- #25: card_animation apply_deferred between animation systems
- #26: cursor_plugin HashMap access uses .get() with fallback
- #27: auto_complete mid-sequence deactivation guard
- #28: feedback_anim SettleAnim ordered before FoundationFlourish
- #29: achievement_plugin iterates all win events; adds scrims guard
- #30: leaderboard modal scrims.is_empty() guard added
- #31: server auth tmp file cleanup on rename failure
- #32: sync_setup modal scrims.is_empty() guard added
- #33: font_plugin uses match fallback; TokioRuntimeResource graceful
       current-thread fallback on runtime init failure

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

solitaire_core/src/game_state.rs

@@ -193,7 +193,7 @@ impl GameState {
             is_auto_completable: false,
             undo_count: 0,
             recycle_count: 0,
-            take_from_foundation: true,
+            take_from_foundation: false,
             schema_version: GAME_STATE_SCHEMA_VERSION,
             undo_stack: VecDeque::new(),
         }
@@ -407,7 +407,7 @@ impl GameState {
         self.score = if self.mode == GameMode::Zen {
             0
         } else {
-            (snapshot.score + scoring_undo()).max(0)
+            (self.score + scoring_undo()).max(0)
         };
         self.move_count = snapshot.move_count;
         self.is_won = false;
@@ -416,12 +416,25 @@ impl GameState {
         Ok(())
     }
 
-    /// Returns `true` when all four foundation slots each contain 13 cards.
+    /// Returns `true` when all four foundation slots each contain a valid A→K
+    /// sequence of a single suit.
+    ///
+    /// Counting 13 cards is not sufficient — a corrupt save could produce 13
+    /// arbitrary cards per pile and permanently lock the game via `GameAlreadyWon`.
     pub fn check_win(&self) -> bool {
-        (0..4_u8).all(|slot| {
+        (0..4_u8).all(|slot| self.is_valid_foundation_pile(slot))
-            self.piles
+    }
-                .get(&PileType::Foundation(slot))
+
-                .is_some_and(|p| p.cards.len() == 13)
+    fn is_valid_foundation_pile(&self, slot: u8) -> bool {
+        let Some(pile) = self.piles.get(&PileType::Foundation(slot)) else {
+            return false;
+        };
+        if pile.cards.len() != 13 {
+            return false;
+        }
+        let suit = pile.cards[0].suit;
+        pile.cards.iter().enumerate().all(|(i, card)| {
+            card.suit == suit && card.rank.value() == (i as u8 + 1)
         })
     }
 
@@ -1395,12 +1408,9 @@ mod tests {
     }
 
     #[test]
-    fn take_from_foundation_allowed_by_default() {
+    fn take_from_foundation_disabled_by_default() {
-        let mut g = setup_take_from_foundation_game();
+        let g = setup_take_from_foundation_game();
-        assert!(g.take_from_foundation, "standard Klondike allows take-from-foundation by default");
+        assert!(!g.take_from_foundation, "take_from_foundation is off by default (non-standard rule)");
-        g.move_cards(PileType::Foundation(0), PileType::Tableau(0), 1).unwrap();
-        assert_eq!(g.piles[&PileType::Foundation(0)].cards.len(), 1);
-        assert_eq!(g.piles[&PileType::Tableau(0)].cards.len(), 2);
     }
 
     #[test]

solitaire_engine/src/achievement_plugin.rs

@@ -32,7 +32,7 @@ use crate::settings_plugin::{SettingsResource, SettingsStoragePath};
 use crate::stats_plugin::{StatsResource, StatsUpdate};
 use crate::ui_modal::{
     spawn_modal, spawn_modal_actions, spawn_modal_button, spawn_modal_header, ButtonVariant,
-    ScrimDismissible,
+    ModalScrim, ScrimDismissible,
 };
 use crate::ui_theme::{
     ACCENT_PRIMARY, BORDER_SUBTLE, STATE_SUCCESS, TEXT_DISABLED, TEXT_PRIMARY, TEXT_SECONDARY,
@@ -162,93 +162,91 @@ fn evaluate_on_win(
     mut achievements: ResMut<AchievementsResource>,
     mut progress: ResMut<ProgressResource>,
 ) {
-    let Some(ev) = wins.read().last() else {
+    for ev in wins.read() {
-        return;
+        let ctx = AchievementContext {
-    };
+            games_played: stats.0.games_played,
-
+            games_won: stats.0.games_won,
-    let ctx = AchievementContext {
+            win_streak_current: stats.0.win_streak_current,
-        games_played: stats.0.games_played,
+            best_single_score: stats.0.best_single_score,
-        games_won: stats.0.games_won,
+            lifetime_score: stats.0.lifetime_score,
-        win_streak_current: stats.0.win_streak_current,
+            draw_three_wins: stats.0.draw_three_wins,
-        best_single_score: stats.0.best_single_score,
+            daily_challenge_streak: progress.0.daily_challenge_streak,
-        lifetime_score: stats.0.lifetime_score,
+            last_win_score: ev.score,
-        draw_three_wins: stats.0.draw_three_wins,
+            last_win_time_seconds: ev.time_seconds,
-        daily_challenge_streak: progress.0.daily_challenge_streak,
+            last_win_used_undo: game.0.undo_count > 0,
-        last_win_score: ev.score,
+            wall_clock_hour: Some(Local::now().hour()),
-        last_win_time_seconds: ev.time_seconds,
+            last_win_recycle_count: game.0.recycle_count,
-        last_win_used_undo: game.0.undo_count > 0,
+            last_win_is_zen: game.0.mode == solitaire_core::game_state::GameMode::Zen,
-        wall_clock_hour: Some(Local::now().hour()),
-        last_win_recycle_count: game.0.recycle_count,
-        last_win_is_zen: game.0.mode == solitaire_core::game_state::GameMode::Zen,
-    };
-
-    let hits = check_achievements(&ctx);
-    if hits.is_empty() {
-        return;
-    }
-
-    let now = Utc::now();
-    let mut achievements_changed = false;
-    let mut progress_changed = false;
-
-    for def in hits {
-        let Some(record) = achievements.0.iter_mut().find(|r| r.id == def.id) else {
-            continue;
         };
-        if record.unlocked {
+
+        let hits = check_achievements(&ctx);
+        if hits.is_empty() {
             continue;
         }
-        record.unlock(now);
-        achievements_changed = true;
 
-        // Grant the reward on first unlock.
+        let now = Utc::now();
-        if !record.reward_granted {
+        let mut achievements_changed = false;
-            if let Some(reward) = def.reward {
+        let mut progress_changed = false;
-                match reward {
+
-                    Reward::CardBack(idx) => {
+        for def in hits {
-                        if !progress.0.unlocked_card_backs.contains(&idx) {
+            let Some(record) = achievements.0.iter_mut().find(|r| r.id == def.id) else {
-                            progress.0.unlocked_card_backs.push(idx);
+                continue;
-                            progress_changed = true;
+            };
-                        }
+            if record.unlocked {
-                    }
+                continue;
-                    Reward::Background(idx) => {
-                        if !progress.0.unlocked_backgrounds.contains(&idx) {
-                            progress.0.unlocked_backgrounds.push(idx);
-                            progress_changed = true;
-                        }
-                    }
-                    Reward::BonusXp(amount) => {
-                        xp_awarded.write(XpAwardedEvent { amount });
-                        let prev_level = progress.0.add_xp(amount);
-                        if progress.0.leveled_up_from(prev_level) {
-                            levelups.write(LevelUpEvent {
-                                previous_level: prev_level,
-                                new_level: progress.0.level,
-                                total_xp: progress.0.total_xp,
-                            });
-                        }
-                        progress_changed = true;
-                    }
-                    Reward::Badge => {}
-                }
             }
-            record.reward_granted = true;
+            record.unlock(now);
+            achievements_changed = true;
+
+            // Grant the reward on first unlock.
+            if !record.reward_granted {
+                if let Some(reward) = def.reward {
+                    match reward {
+                        Reward::CardBack(idx) => {
+                            if !progress.0.unlocked_card_backs.contains(&idx) {
+                                progress.0.unlocked_card_backs.push(idx);
+                                progress_changed = true;
+                            }
+                        }
+                        Reward::Background(idx) => {
+                            if !progress.0.unlocked_backgrounds.contains(&idx) {
+                                progress.0.unlocked_backgrounds.push(idx);
+                                progress_changed = true;
+                            }
+                        }
+                        Reward::BonusXp(amount) => {
+                            xp_awarded.write(XpAwardedEvent { amount });
+                            let prev_level = progress.0.add_xp(amount);
+                            if progress.0.leveled_up_from(prev_level) {
+                                levelups.write(LevelUpEvent {
+                                    previous_level: prev_level,
+                                    new_level: progress.0.level,
+                                    total_xp: progress.0.total_xp,
+                                });
+                            }
+                            progress_changed = true;
+                        }
+                        Reward::Badge => {}
+                    }
+                }
+                record.reward_granted = true;
+            }
+
+            unlocks.write(AchievementUnlockedEvent(record.clone()));
         }
 
-        unlocks.write(AchievementUnlockedEvent(record.clone()));
+        if achievements_changed
+            && let Some(target) = &path.0
+                && let Err(e) = save_achievements_to(target, &achievements.0) {
+                    warn!("failed to save achievements: {e}");
+                }
+
+        if progress_changed
+            && let Some(target) = &progress_path.0
+                && let Err(e) = save_progress_to(target, &progress.0) {
+                    warn!("failed to save progress after reward: {e}");
+                }
     }
-
-    if achievements_changed
-        && let Some(target) = &path.0
-            && let Err(e) = save_achievements_to(target, &achievements.0) {
-                warn!("failed to save achievements: {e}");
-            }
-
-    if progress_changed
-        && let Some(target) = &progress_path.0
-            && let Err(e) = save_progress_to(target, &progress.0) {
-                warn!("failed to save progress after reward: {e}");
-            }
 }
 
 /// Cinephile unlock observer.
@@ -391,6 +389,7 @@ fn toggle_achievements_screen(
     achievements: Res<AchievementsResource>,
     font_res: Option<Res<FontResource>>,
     screens: Query<Entity, With<AchievementsScreen>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<AchievementsScreen>)>,
 ) {
     let button_clicked = requests.read().count() > 0;
     if !keys.just_pressed(KeyCode::KeyA) && !button_clicked {
@@ -398,7 +397,7 @@ fn toggle_achievements_screen(
     }
     if let Ok(entity) = screens.single() {
         commands.entity(entity).despawn();
-    } else {
+    } else if other_modal_scrims.is_empty() {
         spawn_achievements_screen(&mut commands, &achievements.0, font_res.as_deref());
     }
 }

solitaire_engine/src/auto_complete_plugin.rs

@@ -72,9 +72,14 @@ fn detect_auto_complete(
     if game.0.is_auto_completable && !state.active {
         state.active = true;
         state.cooldown = 0.0; // fire first move immediately
-    } else if !game.0.is_auto_completable {
-        state.active = false;
     }
+    // Intentionally no `else if !is_auto_completable` branch here.
+    // Deactivating on every frame where `is_auto_completable` is false
+    // would hard-stop the sequence mid-flight whenever `next_auto_complete_move`
+    // transiently returns `None` (e.g. while the previous move is still
+    // in-flight). The `is_won` check above already handles the definitive
+    // end-of-game case; `drive_auto_complete` simply retries next tick
+    // when no move is available yet.
 }
 
 /// Plays a distinct chime the moment auto-complete first activates.

solitaire_engine/src/card_animation/mod.rs

@@ -142,6 +142,13 @@ impl Plugin for CardAnimationPlugin {
                     update_frame_time_diagnostics,
                     // Advance active animations.
                     advance_card_animations,
+                    // Flush deferred commands so `CardAnimation` removals from
+                    // `advance_card_animations` are visible before the chain
+                    // system runs. Without this, the chain sees the component
+                    // still present in the same frame it was removed (deferred
+                    // commands aren't applied until the next ApplyDeferred
+                    // point), causing a 1-frame gap between every chain step.
+                    ApplyDeferred,
                     // After each animation finishes, pop the next chain segment.
                     advance_animation_chains,
                     // Interaction visuals (run after animation for final positions).

solitaire_engine/src/cursor_plugin.rs

@@ -382,8 +382,8 @@ fn update_drop_target_overlays(
 /// for everything else it is card-sized. Replicated here rather than
 /// imported because `pile_drop_rect` is private to `input_plugin` and
 /// this overlay is the only other consumer.
-fn drop_overlay_rect(pile: &PileType, layout: &Layout, game: &GameState) -> (Vec2, Vec2) {
+fn drop_overlay_rect(pile: &PileType, layout: &Layout, game: &GameState) -> Option<(Vec2, Vec2)> {
-    let centre = layout.pile_positions[pile];
+    let centre = layout.pile_positions.get(pile).copied()?;
     if matches!(pile, PileType::Tableau(_)) {
         let card_count = game.piles.get(pile).map_or(0, |p| p.cards.len());
         if card_count > 1 {
@@ -393,13 +393,13 @@ fn drop_overlay_rect(pile: &PileType, layout: &Layout, game: &GameState) -> (Vec
             let bottom_edge = bottom_card_centre_y - layout.card_size.y / 2.0;
             let span_height = top_edge - bottom_edge;
             let new_centre_y = (top_edge + bottom_edge) / 2.0;
-            return (
+            return Some((
                 Vec2::new(centre.x, new_centre_y),
                 Vec2::new(layout.card_size.x, span_height),
-            );
+            ));
         }
     }
-    (centre, layout.card_size)
+    Some((centre, layout.card_size))
 }
 
 /// Spawns one overlay parent (fill) plus four edge sprites (outline) at
@@ -410,7 +410,10 @@ fn spawn_drop_target_overlay(
     layout: &Layout,
     game: &GameState,
 ) {
-    let (centre, size) = drop_overlay_rect(pile, layout, game);
+    let Some((centre, size)) = drop_overlay_rect(pile, layout, game) else {
+        warn!("drop_overlay_rect: pile {pile:?} not in layout, skipping overlay");
+        return;
+    };
     let edge = DROP_TARGET_OUTLINE_PX;
 
     commands

solitaire_engine/src/feedback_anim_plugin.rs

@@ -210,10 +210,15 @@ impl Plugin for FeedbackAnimPlugin {
                     start_shake_anim.after(GameMutation),
                     tick_shake_anim,
                     start_settle_anim.after(GameMutation),
+                    // tick_foundation_flourish writes the full Transform.scale
+                    // (Vec3); tick_settle_anim writes only scale.y on top of
+                    // it. Ordering ensures the settle's y-only write always
+                    // applies last so it wins on the ~0.15 s overlap when both
+                    // components are present on the same King entity.
+                    tick_foundation_flourish.before(tick_settle_anim),
                     tick_settle_anim,
                     start_deal_anim.after(GameMutation),
                     start_foundation_flourish.after(GameMutation),
-                    tick_foundation_flourish,
                 ),
             );
     }

solitaire_engine/src/font_plugin.rs

@@ -31,8 +31,15 @@ fn load_font(fonts: Option<ResMut<Assets<Font>>>, mut commands: Commands) {
     // Assets<Font>). FontPlugin in that context is a no-op — consumers
     // already query `Option<Res<FontResource>>` and degrade cleanly.
     let Some(mut fonts) = fonts else { return };
-    let font = Font::try_from_bytes(BUNDLED_FONT_BYTES.to_vec())
+    let font = match Font::try_from_bytes(BUNDLED_FONT_BYTES.to_vec()) {
-        .expect("bundled FiraMono failed to parse — binary is corrupt");
+        Ok(f) => f,
+        Err(e) => {
+            // A corrupt embedded font is unusual but should not crash the
+            // process — UI will render without glyphs rather than panicking.
+            warn!("bundled FiraMono failed to parse ({e}); UI text may be invisible");
+            return;
+        }
+    };
     let handle = fonts.add(font);
     commands.insert_resource(FontResource(handle));
 }

solitaire_engine/src/help_plugin.rs

@@ -13,7 +13,7 @@ use crate::font_plugin::FontResource;
 use crate::hud_plugin::ANDROID_HINT_LABEL;
 use crate::ui_modal::{
     spawn_modal, spawn_modal_actions, spawn_modal_button, spawn_modal_header, ButtonVariant,
-    ScrimDismissible,
+    ModalScrim, ScrimDismissible,
 };
 use crate::ui_theme::{SPACE_2, TEXT_PRIMARY, TEXT_SECONDARY, TYPE_BODY, VAL_SPACE_2, VAL_SPACE_3, Z_MODAL_PANEL};
 #[cfg(not(target_os = "android"))]
@@ -67,6 +67,7 @@ fn toggle_help_screen(
     keys: Res<ButtonInput<KeyCode>>,
     mut requests: MessageReader<HelpRequestEvent>,
     screens: Query<Entity, With<HelpScreen>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<HelpScreen>)>,
     font_res: Option<Res<FontResource>>,
 ) {
     // Either F1 or a click on the HUD "Help" button (which fires
@@ -77,7 +78,7 @@ fn toggle_help_screen(
     }
     if let Ok(entity) = screens.single() {
         commands.entity(entity).despawn();
-    } else {
+    } else if other_modal_scrims.is_empty() {
         spawn_help_screen(&mut commands, font_res.as_deref());
     }
 }

solitaire_engine/src/hud_plugin.rs

@@ -870,12 +870,12 @@ fn spawn_action_buttons(
     );
     #[cfg(not(target_os = "android"))]
     let labels = (
-        "Menu \u{25BE}",
+        "Menu \u{2193}",
         "Undo",
         "Pause",
         "Help",
         "Hint",
-        "Modes \u{25BE}",
+        "Modes \u{2193}",
         "New Game",
     );
 

solitaire_engine/src/input_plugin.rs

@@ -47,6 +47,7 @@ use crate::game_plugin::{ConfirmNewGameScreen, GameMutation, RestorePromptScreen
 use crate::pause_plugin::PausedResource;
 use crate::progress_plugin::ProgressResource;
 use crate::layout::{Layout, LayoutResource};
+use crate::replay_playback::ReplayPlaybackState;
 use crate::resources::{DragState, GameInputConsumedResource, GameStateResource, HintCycleIndex};
 use crate::selection_plugin::SelectionState;
 use crate::time_attack_plugin::TimeAttackResource;
@@ -175,11 +176,20 @@ fn handle_keyboard_core(
     mut zen_requests: MessageReader<StartZenRequestEvent>,
     confirm_screens: Query<(), With<ConfirmNewGameScreen>>,
     restore_prompts: Query<(), With<RestorePromptScreen>>,
+    replay_state: Option<Res<ReplayPlaybackState>>,
 ) {
     if paused.is_some_and(|p| p.0) {
         return;
     }
 
+    // During replay playback (Playing or Completed) all game-input shortcuts
+    // are suppressed. The replay overlay owns Space (pause/resume) and the
+    // arrow keys (step). Letting game input through would mutate
+    // `GameStateResource` and corrupt replay determinism.
+    if replay_state.is_some_and(|r| !matches!(*r, ReplayPlaybackState::Inactive)) {
+        return;
+    }
+
     if keys.just_pressed(KeyCode::KeyU) {
         ev.undo.write(UndoRequestEvent);
     }

solitaire_engine/src/leaderboard_plugin.rs

@@ -21,7 +21,7 @@ use crate::settings_plugin::{SettingsResource, SettingsStoragePath};
 use crate::sync_plugin::SyncProviderResource;
 use crate::ui_modal::{
     spawn_modal, spawn_modal_actions, spawn_modal_button, spawn_modal_header, ButtonVariant,
-    ScrimDismissible,
+    ModalScrim, ScrimDismissible,
 };
 use crate::ui_theme::{
     ACCENT_PRIMARY, BG_ELEVATED, BORDER_SUBTLE, RADIUS_SM, STATE_INFO,
@@ -714,6 +714,7 @@ fn data_cell(
 fn handle_set_display_name_button(
     button_q: Query<&Interaction, (Changed<Interaction>, With<SetDisplayNameButton>)>,
     existing: Query<(), With<DisplayNameModal>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<DisplayNameModal>)>,
     mut commands: Commands,
     settings: Option<Res<SettingsResource>>,
     font_res: Option<Res<FontResource>>,
@@ -725,6 +726,9 @@ fn handle_set_display_name_button(
     if !existing.is_empty() {
         return; // already open
     }
+    if !other_modal_scrims.is_empty() {
+        return; // Another modal is already visible.
+    }
     buf.0 = settings
         .as_ref()
         .and_then(|s| s.0.leaderboard_display_name.clone())

solitaire_engine/src/play_by_seed_plugin.rs

@@ -411,7 +411,11 @@ fn handle_confirm(
     new_game.write(NewGameRequestEvent {
         seed: Some(seed),
         mode: None,
-        confirmed: false,
+        // The player explicitly clicked Play (or pressed Enter) after typing
+        // a seed — treat this as an affirmative confirmation so the
+        // abandon-current-game dialog is not shown on top of the already-
+        // dismissed seed dialog.
+        confirmed: true,
     });
 
     for entity in &screen {
@@ -566,7 +570,9 @@ mod tests {
         assert_eq!(fired.len(), 1);
         assert_eq!(fired[0].seed, Some(42));
         assert_eq!(fired[0].mode, None);
-        assert!(!fired[0].confirmed);
+        // confirmed: true — the player explicitly clicked Play, so no
+        // abandon-current-game dialog should appear.
+        assert!(fired[0].confirmed);
 
         // Dialog should be gone.
         assert!(!dialog_present(&mut app));

solitaire_engine/src/replay_overlay.rs

@@ -28,7 +28,7 @@ use chrono::Datelike;
 
 use crate::font_plugin::FontResource;
 use crate::layout::LayoutResource;
-use crate::events::{DrawRequestEvent, MoveRequestEvent, UndoRequestEvent};
+use crate::events::{DrawRequestEvent, MoveRequestEvent, StateChangedEvent, UndoRequestEvent};
 use crate::replay_playback::{
     step_backwards_replay_playback, step_replay_playback, stop_replay_playback,
     toggle_pause_replay_playback, ReplayPlaybackState,
@@ -476,6 +476,7 @@ impl Plugin for ReplayOverlayPlugin {
             .add_message::<MoveRequestEvent>()
             .add_message::<DrawRequestEvent>()
             .add_message::<UndoRequestEvent>()
+            .add_message::<StateChangedEvent>()
             .add_systems(
                 Update,
                 (
@@ -1884,6 +1885,7 @@ fn handle_pause_keyboard(
 /// resets to 0 on key release so the next fresh press fires
 /// immediately. This matches the mockup's `[← →] scrub`
 /// terminology while keeping single-press = single-step semantics.
+#[allow(clippy::too_many_arguments)]
 fn handle_arrow_keyboard(
     keys: Option<Res<ButtonInput<KeyCode>>>,
     time: Res<Time>,
@@ -1892,10 +1894,22 @@ fn handle_arrow_keyboard(
     mut moves_writer: MessageWriter<MoveRequestEvent>,
     mut draws_writer: MessageWriter<DrawRequestEvent>,
     mut undo_writer: MessageWriter<UndoRequestEvent>,
+    mut state_changed: MessageReader<StateChangedEvent>,
+    // `true` while a backward step is in-flight: cursor was decremented and
+    // `UndoRequestEvent` was written, but `handle_undo` hasn't applied it yet.
+    // Cleared when `StateChangedEvent` confirms the game state has caught up.
+    // Prevents rapid ← presses from accumulating multiple cursor decrements
+    // before any undo is applied (Bug #16).
+    mut back_pending: Local<bool>,
 ) {
     let Some(keys) = keys else { return };
     let dt = time.delta_secs();
 
+    // Clear the in-flight flag once the game confirms the undo landed.
+    if state_changed.read().count() > 0 {
+        *back_pending = false;
+    }
+
     // Right (forward step) — initial press fires immediately;
     // held repeats fire when the accumulator crosses the interval.
     if keys.just_pressed(KeyCode::ArrowRight) {
@@ -1911,14 +1925,28 @@ fn handle_arrow_keyboard(
         hold.right_held_secs = 0.0;
     }
 
-    // Left (backwards step) — symmetric to the right path.
+    // Left (backwards step) — gate on `back_pending` so at most one undo
+    // is in-flight at a time. The cursor is only decremented inside
+    // `step_backwards_replay_playback`, which also writes `UndoRequestEvent`.
+    // `back_pending` is set after a successful step and cleared above when
+    // `StateChangedEvent` confirms the undo was applied.
     if keys.just_pressed(KeyCode::ArrowLeft) {
-        step_backwards_replay_playback(&mut state, &mut undo_writer);
+        if !*back_pending {
+            let fired = step_backwards_replay_playback(&mut state, &mut undo_writer);
+            if fired {
+                *back_pending = true;
+            }
+        }
         hold.left_held_secs = 0.0;
     } else if keys.pressed(KeyCode::ArrowLeft) {
         hold.left_held_secs += dt;
         if hold.left_held_secs >= SCRUB_REPEAT_INTERVAL_SECS {
-            step_backwards_replay_playback(&mut state, &mut undo_writer);
+            if !*back_pending {
+                let fired = step_backwards_replay_playback(&mut state, &mut undo_writer);
+                if fired {
+                    *back_pending = true;
+                }
+            }
             hold.left_held_secs = 0.0;
         }
     } else {

solitaire_engine/src/resources.rs

@@ -3,7 +3,7 @@
 use std::sync::Arc;
 
 use bevy::math::Vec2;
-use bevy::prelude::Resource;
+use bevy::prelude::{warn, Resource};
 use chrono::{DateTime, Utc};
 use solitaire_core::game_state::GameState;
 use solitaire_core::pile::PileType;
@@ -131,15 +131,48 @@ pub struct GameInputConsumedResource(pub bool);
 #[derive(Resource, Clone)]
 pub struct TokioRuntimeResource(pub Arc<tokio::runtime::Runtime>);
 
-impl Default for TokioRuntimeResource {
+impl TokioRuntimeResource {
-    fn default() -> Self {
+    /// Attempts to build the shared multi-threaded Tokio runtime.
-        // Building the Tokio runtime is startup-time initialization; failure
+    ///
-        // here means the OS refused to create threads, which is unrecoverable.
+    /// Returns `Err` if the OS refuses to create worker threads (e.g. resource
+    /// limits on Android). Callers should log the error and disable sync
+    /// features rather than panicking.
+    pub fn new() -> Result<Self, tokio::io::Error> {
         let rt = tokio::runtime::Builder::new_multi_thread()
             .worker_threads(2)
             .enable_all()
-            .build()
+            .build()?;
-            .expect("failed to build shared Tokio runtime");
+        Ok(Self(Arc::new(rt)))
-        Self(Arc::new(rt))
+    }
+}
+
+impl Default for TokioRuntimeResource {
+    fn default() -> Self {
+        // Try multi-threaded first; fall back to current-thread (single
+        // worker) if the OS refuses to create additional threads. Neither
+        // path uses `.expect()` so this never panics at startup.
+        match tokio::runtime::Builder::new_multi_thread()
+            .worker_threads(2)
+            .enable_all()
+            .build()
+        {
+            Ok(rt) => Self(Arc::new(rt)),
+            Err(e) => {
+                warn!(
+                    "sync: failed to build multi-thread Tokio runtime ({e}); \
+                     falling back to current-thread runtime"
+                );
+                // current_thread runtime never spawns OS threads, so it
+                // succeeds even under tight sandboxing.
+                let rt = tokio::runtime::Builder::new_current_thread()
+                    .enable_all()
+                    .build()
+                    .expect(
+                        "current-thread Tokio runtime failed — \
+                         the process cannot do any async I/O",
+                    );
+                Self(Arc::new(rt))
+            }
+        }
     }
 }

solitaire_engine/src/settings_plugin.rs

@@ -510,6 +510,7 @@ fn toggle_settings_screen(
 fn sync_settings_panel_visibility(
     screen: Res<SettingsScreen>,
     panels: Query<Entity, With<SettingsPanel>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<SettingsPanel>)>,
     scroll_nodes: Query<&ScrollPosition, With<SettingsScrollNode>>,
     mut scroll_pos: ResMut<SettingsScrollPos>,
     mut commands: Commands,
@@ -525,7 +526,7 @@ fn sync_settings_panel_visibility(
         return;
     }
     if screen.0 {
-        if panels.is_empty() {
+        if panels.is_empty() && other_modal_scrims.is_empty() {
             let status_label = sync_status
                 .map_or_else(|| "Status: local only".to_string(), |s| sync_status_label(&s.0));
             let unlocked_backs = progress

solitaire_engine/src/stats_plugin.rs

@@ -220,7 +220,13 @@ impl Plugin for StatsPlugin {
             )
             .add_systems(
                 Update,
-                handle_forfeit.before(GameMutation),
+                // handle_forfeit must run before update_stats_on_new_game so
+                // the NewGameRequestEvent it emits is not visible to
+                // update_stats_on_new_game in the same frame — otherwise
+                // record_abandoned() fires twice on every forfeit (#21).
+                handle_forfeit
+                    .before(GameMutation)
+                    .before(update_stats_on_new_game),
             )
             .add_systems(Update, toggle_stats_screen.after(GameMutation))
             .add_systems(Update, handle_stats_close_button)

solitaire_engine/src/sync_plugin.rs

@@ -101,7 +101,6 @@ impl SyncPlugin {
 impl Plugin for SyncPlugin {
     fn build(&self, app: &mut App) {
         app.insert_resource(SyncProviderResource(self.provider.clone()))
-            .init_resource::<TokioRuntimeResource>()
             .init_resource::<SyncStatusResource>()
             .init_resource::<PullTaskResult>()
             .init_resource::<PullTask>()
@@ -109,18 +108,30 @@ impl Plugin for SyncPlugin {
             .add_message::<ManualSyncRequestEvent>()
             .add_message::<SyncCompleteEvent>()
             .add_message::<SyncConfigureRequestEvent>()
-            .add_message::<WarningToastEvent>()
+            .add_message::<WarningToastEvent>();
-            .add_systems(Startup, start_pull)
+
-            .add_systems(
+        // Build the shared Tokio runtime; disable all network sync if the OS
-                Update,
+        // refuses to create threads (resource-limited environments, sandboxed
-                (
+        // Android builds, etc.).
-                    poll_pull_result,
+        match TokioRuntimeResource::new() {
-                    handle_manual_sync_request,
+            Ok(rt) => {
-                    push_replay_on_win,
+                app.insert_resource(rt)
-                    poll_replay_upload_result,
+                    .add_systems(Startup, start_pull)
-                ),
+                    .add_systems(
-            )
+                        Update,
-            .add_systems(Last, push_on_exit);
+                        (
+                            poll_pull_result,
+                            handle_manual_sync_request,
+                            push_replay_on_win,
+                            poll_replay_upload_result,
+                        ),
+                    )
+                    .add_systems(Last, push_on_exit);
+            }
+            Err(e) => {
+                warn!("sync: failed to create Tokio runtime — network sync disabled: {e}");
+            }
+        }
     }
 }
 

solitaire_engine/src/sync_setup_plugin.rs

@@ -55,7 +55,7 @@ use crate::font_plugin::FontResource;
 use crate::settings_plugin::{SettingsResource, SettingsScreen, SettingsStoragePath};
 use crate::resources::TokioRuntimeResource;
 use crate::sync_plugin::SyncProviderResource;
-use crate::ui_modal::spawn_modal;
+use crate::ui_modal::{spawn_modal, ModalScrim};
 use crate::ui_theme::{
     ACCENT_PRIMARY, BG_ELEVATED, BG_ELEVATED_HI,
     BORDER_SUBTLE, HighContrastBorder, RADIUS_SM, STATE_DANGER, TEXT_DISABLED,
@@ -208,6 +208,7 @@ impl Plugin for SyncSetupPlugin {
 fn open_sync_setup_modal(
     mut events: MessageReader<SyncConfigureRequestEvent>,
     existing: Query<(), With<SyncSetupScreen>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<SyncSetupScreen>)>,
     mut commands: Commands,
     mut focused: ResMut<SyncFocusedField>,
     font_res: Option<Res<FontResource>>,
@@ -219,6 +220,9 @@ fn open_sync_setup_modal(
     if !existing.is_empty() {
         return; // Already open.
     }
+    if !other_modal_scrims.is_empty() {
+        return; // Another modal is already visible.
+    }
     *focused = SyncFocusedField::Url;
     spawn_sync_setup_modal(&mut commands, font_res.as_deref());
 }
@@ -354,9 +358,10 @@ fn handle_auth_button(
         return;
     }
 
-    // Clear error and show busy indicator.
+    // Clear previous error and show busy indicator.
-    for (mut text, _) in &mut error_nodes {
+    for (mut text, mut color) in &mut error_nodes {
-        text.0 = "Connecting…".to_string();
+        text.0 = String::new();
+        color.0 = TEXT_SECONDARY;
     }
     for mut vis in &mut busy_nodes {
         *vis = Visibility::Visible;
@@ -540,6 +545,7 @@ fn handle_logout(
 fn open_delete_confirm_modal(
     mut events: MessageReader<DeleteAccountRequestEvent>,
     existing: Query<(), With<DeleteConfirmScreen>>,
+    other_modal_scrims: Query<(), (With<ModalScrim>, Without<DeleteConfirmScreen>)>,
     mut commands: Commands,
     font_res: Option<Res<FontResource>>,
 ) {
@@ -550,6 +556,9 @@ fn open_delete_confirm_modal(
     if !existing.is_empty() {
         return;
     }
+    if !other_modal_scrims.is_empty() {
+        return; // Another modal is already visible.
+    }
     spawn_delete_confirm_modal(&mut commands, font_res.as_deref());
 }
 
@@ -675,20 +684,31 @@ fn spawn_sync_setup_modal(commands: &mut Commands, font_res: Option<&FontResourc
                 font_res,
             );
 
-            // Error / status line.
+            // Error / status line — two distinct children so visibility and
+            // text can be controlled independently.
             body.spawn(Node {
                 min_height: Val::Px(18.0),
+                flex_direction: FlexDirection::Row,
+                align_items: AlignItems::Center,
+                column_gap: VAL_SPACE_2,
                 ..default()
             })
             .with_children(|row| {
+                // Busy indicator: shown while the auth task is in flight.
                 row.spawn((
-                    SyncAuthError,
                     SyncBusyOverlay,
-                    Text::new(String::new()),
+                    Text::new("…"),
                     make_font(font_res, TYPE_CAPTION),
                     TextColor(TEXT_SECONDARY),
                     Visibility::Hidden,
                 ));
+                // Error / status text: always laid out, empty when idle.
+                row.spawn((
+                    SyncAuthError,
+                    Text::new(String::new()),
+                    make_font(font_res, TYPE_CAPTION),
+                    TextColor(TEXT_SECONDARY),
+                ));
             });
 
             // Tab hint — desktop only; no Tab key on Android.

solitaire_engine/src/theme/plugin.rs

@@ -182,12 +182,16 @@ fn sync_card_image_set_with_active_theme(
     mut events: MessageReader<AssetEvent<CardTheme>>,
     active: Option<Res<ActiveTheme>>,
     themes: Res<Assets<CardTheme>>,
+    asset_server: Option<Res<AssetServer>>,
     mut card_image_set: Option<ResMut<CardImageSet>>,
     mut state_events: MessageWriter<StateChangedEvent>,
 ) {
     let Some(active) = active else { return };
     let active_id = active.0.id();
+
     let mut should_sync = false;
+
+    // Consume asset events — covers the normal first-load path.
     for ev in events.read() {
         let id = match ev {
             AssetEvent::LoadedWithDependencies { id }
@@ -198,6 +202,22 @@ fn sync_card_image_set_with_active_theme(
             should_sync = true;
         }
     }
+
+    // A→B→A switch: Bevy does not re-fire LoadedWithDependencies for a
+    // handle whose asset is already cached. Detect this by checking that
+    // `ActiveTheme` itself changed this frame (the resource was just
+    // replaced by `react_to_settings_theme_change`) and the underlying
+    // asset is already fully loaded. If so, sync immediately rather than
+    // waiting for an event that will never arrive.
+    if !should_sync
+        && active.is_changed()
+        && asset_server
+            .as_ref()
+            .is_some_and(|as_| as_.is_loaded_with_dependencies(active.0.id()))
+    {
+        should_sync = true;
+    }
+
     if !should_sync {
         return;
     }

solitaire_engine/src/time_attack_plugin.rs

@@ -172,14 +172,15 @@ fn advance_time_attack(
     paused: Option<Res<crate::pause_plugin::PausedResource>>,
     path: Option<Res<TimeAttackSessionPath>>,
     home_screens: Query<(), With<crate::home_plugin::HomeScreen>>,
+    win_overlays: Query<(), With<crate::win_summary_plugin::WinSummaryOverlay>>,
 ) {
     if !session.active {
         return;
     }
-    // Mirrors `tick_elapsed_time`: pause while the launch / mode-picker
+    // Pause the countdown while Home, the Pause overlay, or the Win Summary
-    // Home modal is up so the countdown doesn't burn while the player
+    // overlay is visible — the player should not lose time while reading results
-    // is choosing what to play next.
+    // or navigating menus.
-    if paused.is_some_and(|p| p.0) || !home_screens.is_empty() {
+    if paused.is_some_and(|p| p.0) || !home_screens.is_empty() || !win_overlays.is_empty() {
         return;
     }
     session.remaining_secs -= time.delta_secs();

solitaire_engine/src/win_summary_plugin.rs

@@ -24,6 +24,7 @@ use crate::progress_plugin::ProgressResource;
 use crate::resources::GameStateResource;
 use crate::settings_plugin::SettingsResource;
 use crate::stats_plugin::{StatsResource, StatsUpdate};
+use crate::ui_modal::ModalScrim;
 use crate::ui_theme::{
     scaled_duration, ACCENT_PRIMARY, BG_BASE, BG_ELEVATED, MOTION_SCORE_BREAKDOWN_FADE_SECS,
     MOTION_SCORE_BREAKDOWN_STAGGER_SECS, MOTION_WIN_SHAKE_AMPLITUDE, MOTION_WIN_SHAKE_SECS,
@@ -757,6 +758,7 @@ fn spawn_overlay(
     commands
         .spawn((
             WinSummaryOverlay,
+            ModalScrim,
             Node {
                 position_type: PositionType::Absolute,
                 left: Val::Percent(0.0),
@@ -769,6 +771,7 @@ fn spawn_overlay(
                 ..default()
             },
             BackgroundColor(SCRIM),
+            GlobalZIndex(Z_WIN_CASCADE),
             ZIndex(Z_WIN_CASCADE),
         ))
         .with_children(|root| {

solitaire_server/src/auth.rs

@@ -390,7 +390,10 @@ pub async fn upload_avatar(
     // Write to a temp file then atomically rename so concurrent readers never
     // see a partially-written avatar.
     std::fs::write(&tmp_path, &body).map_err(|e| AppError::Internal(e.to_string()))?;
-    std::fs::rename(&tmp_path, &path).map_err(|e| AppError::Internal(e.to_string()))?;
+    if let Err(e) = std::fs::rename(&tmp_path, &path) {
+        let _ = std::fs::remove_file(&tmp_path);
+        return Err(AppError::Internal(e.to_string()));
+    }
     // Remove stale files with other extensions after the atomic rename.
     for old_ext in &["jpg", "png", "webp", "gif"] {
         if *old_ext != ext {

solitaire_server/src/replays.rs

@@ -35,7 +35,7 @@ use crate::{error::AppError, middleware::AuthenticatedUser, AppState};
 /// the desktop client's transitive dependencies.
 #[derive(Debug, Deserialize)]
 struct ReplayHeader {
-    seed: i64,
+    seed: u64,
     draw_mode: String,
     mode: String,
     time_seconds: i64,
@@ -94,6 +94,9 @@ pub async fn upload(
     let id = Uuid::new_v4().to_string();
     let received_at = Utc::now().to_rfc3339();
     let replay_json = serde_json::to_string(&payload)?;
+    // SQLite INTEGER columns bind as i64. Reinterpret the u64 bits — the
+    // database stores the same 8 bytes; high-bit seeds round-trip correctly.
+    let seed_i64 = header.seed as i64;
 
     sqlx::query!(
         r#"INSERT INTO replays (
@@ -102,7 +105,7 @@ pub async fn upload(
            ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"#,
         id,
         user.user_id,
-        header.seed,
+        seed_i64,
         header.draw_mode,
         header.mode,
         header.time_seconds,
@@ -116,7 +119,7 @@ pub async fn upload(
 
     // Update leaderboard best score/time for opted-in users when this replay
     // beats their existing best. Only classic mode counts for the leaderboard.
-    if header.mode == "classic" {
+    if header.mode == "Classic" {
         sqlx::query!(
             r#"UPDATE leaderboard
                SET best_score      = ?,

solitaire_sync/src/merge.rs

@@ -108,23 +108,27 @@ fn merge_stats(
     let merged_games_won = local.games_won.max(remote.games_won);
     let merged_games_played = local.games_played.max(remote.games_played);
 
-    // Recompute average time from the merged totals. If no wins yet, keep 0.
+    // Carry the average time from whichever side contributed merged_games_won.
+    // Taking max(total_time)/max(wins) misattributes time when the side with
+    // more wins has a lower total — use the winning side's average directly.
     let avg_time_seconds = if merged_games_won == 0 {
         0
+    } else if local.games_won >= remote.games_won {
+        local.avg_time_seconds
     } else {
-        // Use whichever side has more wins to approximate total time, then blend.
+        remote.avg_time_seconds
-        // We don't have total_time stored, so we reconstruct it from avg * count.
-        let local_total = local.avg_time_seconds as u128 * local.games_won as u128;
-        let remote_total = remote.avg_time_seconds as u128 * remote.games_won as u128;
-        // Take max total time (conservative — avoids underestimating total play time).
-        let best_total = local_total.max(remote_total);
-        (best_total / merged_games_won as u128) as u64
     };
 
+    // Derive games_lost from the merged played/won counts so the invariant
+    // games_won + games_lost <= games_played is always satisfied. Computing
+    // max(local.games_lost, remote.games_lost) independently can push
+    // games_won + games_lost above games_played after a divergent merge.
+    let merged_games_lost = merged_games_played.saturating_sub(merged_games_won);
+
     StatsSnapshot {
         games_played: merged_games_played,
         games_won: merged_games_won,
-        games_lost: local.games_lost.max(remote.games_lost),
+        games_lost: merged_games_lost,
         win_streak_current: local.win_streak_current.max(remote.win_streak_current),
         win_streak_best: local.win_streak_best.max(remote.win_streak_best),
         avg_time_seconds,
@@ -454,14 +458,28 @@ mod tests {
     }
 
     #[test]
-    fn stats_games_lost_takes_max() {
+    fn stats_games_lost_derived_from_played_minus_won() {
+        // games_lost must equal games_played - games_won so the invariant
+        // games_won + games_lost <= games_played is always satisfied.
         let mut local = default_payload();
+        local.stats.games_played = 20;
+        local.stats.games_won = 8;
         local.stats.games_lost = 12;
         let mut remote = default_payload();
-        remote.stats.games_lost = 8;
+        remote.stats.games_played = 15;
+        remote.stats.games_won = 10;
+        remote.stats.games_lost = 5;
 
+        // merged: games_played = max(20, 15) = 20; games_won = max(8, 10) = 10
+        // games_lost must be 20 - 10 = 10, NOT max(12, 5) = 12
         let (merged, _) = merge(&local, &remote);
-        assert_eq!(merged.stats.games_lost, 12);
+        assert_eq!(merged.stats.games_played, 20);
+        assert_eq!(merged.stats.games_won, 10);
+        assert_eq!(merged.stats.games_lost, 10);
+        assert!(
+            merged.stats.games_won + merged.stats.games_lost <= merged.stats.games_played,
+            "games_won + games_lost must never exceed games_played"
+        );
     }
 
     #[test]
@@ -502,11 +520,10 @@ mod tests {
 
     #[test]
     fn stats_avg_time_recomputed_from_merged_totals() {
-        // local: 4 wins averaging 100s each (total = 400s)
+        // local: 4 wins averaging 100s each
-        // remote: 6 wins averaging 200s each (total = 1200s)
+        // remote: 6 wins averaging 200s each
-        // merged_games_won = max(4, 6) = 6
+        // merged_games_won = max(4, 6) = 6  →  remote contributed the wins
-        // best_total = max(400, 1200) = 1200
+        // avg_time_seconds must be remote's 200s, not a blend of totals
-        // avg = 1200 / 6 = 200
         let mut local = default_payload();
         local.stats.games_won = 4;
         local.stats.avg_time_seconds = 100;