refactor(engine): ambiguity burn-down batch 4 — zero ambiguities, gate enforced

Clears the final 47 pairs and turns the ratchet into a hard gate
(AMBIGUITY_BASELINE = 0, assert_eq):

- HudButtons: the 14 HUD button/popover handlers run as one chain,
  before ui_focus::FocusKeys — Esc/keyboard consumption order is now
  defined (restore prompt → buttons/popovers → focus navigation →
  settings toggle) instead of scheduler-dependent.
- HUD text updaters (update_hud, update_selection_hud,
  update_won_previously) chained, in UiTextFx, after the new
  AutoComplete set (update_hud reads AutoCompleteState).
- restore_hud_on_modal → apply_hud_visibility chained before
  UpdateOnResize: HudVisibility writes, application, and the layout
  read happen in a fixed order.
- New writer sets UndoRequestWriters / InfoToastWriters (same
  self-ambiguous pattern as NewGameRequestWriters).
- Logic-before-paint: check_no_moves and the AutoComplete chain order
  before BoardVisuals; SettingsMutation after UpdateOnResize.
- MarkerVisuals set wraps the table painter chain; chrome fx declare
  disjointness from it.
- update_hud_typography after BoardVisuals; avatar/settings-toggle
  interaction handlers declared disjoint from HudButtons.

302 → 198 → 171 → 47 → 0 in four batches, one day. New systems now
fail CI unless they declare their ordering or their disjointness.

Closes #143

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

solitaire_engine/src/game_plugin/mod.rs

@@ -75,6 +75,17 @@ pub struct GameMutation;
 #[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
 pub struct NewGameRequestWriters;
 
+/// Self-ambiguous set for writers of `UndoRequestEvent` — same rationale as
+/// [`NewGameRequestWriters`]: consumers drain the queue, append order is
+/// meaningless (#143).
+#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct UndoRequestWriters;
+
+/// Self-ambiguous set for writers of `InfoToastEvent` — toasts queue in
+/// arrival order and any same-frame order is fine (#143).
+#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct InfoToastWriters;
+
 /// Persistence path for the in-progress game state file. `None` disables I/O.
 #[derive(Resource, Debug, Clone)]
 pub struct GameStatePath(pub Option<PathBuf>);
@@ -233,7 +244,14 @@ impl Plugin for GamePlugin {
                     .chain()
                     .in_set(GameMutation),
             )
-            .add_systems(Update, check_no_moves.after(GameMutation))
+            .add_systems(
+                Update,
+                check_no_moves
+                    .after(GameMutation)
+                    .before(crate::card_plugin::BoardVisuals)
+                    .in_set(InfoToastWriters)
+                    .ambiguous_with(InfoToastWriters),
+            )
             .add_systems(Update, record_replay_on_win.after(GameMutation))
             .add_systems(
                 Update,
@@ -244,14 +262,16 @@ impl Plugin for GamePlugin {
                     handle_game_over_button_input,
                 )
                     .after(GameMutation)
+                    .before(crate::ui_focus::FocusKeys)
                     .in_set(NewGameRequestWriters)
-                    .ambiguous_with(NewGameRequestWriters),
+                    .ambiguous_with(NewGameRequestWriters)
+                    .in_set(UndoRequestWriters)
+                    .ambiguous_with(UndoRequestWriters),
             )
             // Restore prompt: spawn the modal once the splash is gone,
             // route Continue / New Game intents back into the existing
             // GameMutation flow.
-            .add_systems(Update, spawn_restore_prompt_if_pending)
-            // All three pre-mutation game-state writers are chained: elapsed
+            // All pre-mutation game-state writers are chained: elapsed
             // time ticks first, settings sync next, then the restore prompt —
             // a deterministic spine instead of three unordered ResMut holders
             // (ambiguity burn-down, #143).
@@ -260,6 +280,7 @@ impl Plugin for GamePlugin {
                 (
                     tick_elapsed_time,
                     sync_settings_to_game,
+                    spawn_restore_prompt_if_pending,
                     handle_restore_prompt
                         .in_set(NewGameRequestWriters)
                         .ambiguous_with(NewGameRequestWriters),