refactor(engine): ambiguity burn-down batch 2 — SettingsResource cleared, 198 → 171

New SettingsMutation set: the per-frame settings mutators
(handle_volume_keys → record_window_geometry_changes →
persist_window_geometry_after_debounce) run as a deterministic chain
ordered before GameMutation, so every reader already after GameMutation
observes the current frame's settings transitively. The four readers
outside that ordering (modal enter-speed chain, focus-ring pulse, HUD
avatar, and the game plugin's pre-mutation chain) are ordered after the
set explicitly.

SettingsResource ambiguities: 21 → 0. Baseline ratchets 198 → 171.

Refs #143

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

solitaire_engine/src/settings_plugin/mod.rs

@@ -79,6 +79,14 @@ pub struct PendingWindowGeometry {
 #[derive(Message, Debug, Clone)]
 pub struct SettingsChangedEvent(pub Settings);
 
+/// System set for the systems that mutate [`SettingsResource`] every frame
+/// (hotkeys and window-geometry persistence). Ordered before
+/// [`crate::game_plugin::GameMutation`]; readers of settings should sit
+/// after this set (directly, or transitively via `.after(GameMutation)`)
+/// so they observe the current frame's settings deterministically (#143).
+#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct SettingsMutation;
+
 /// Marker on the root Settings panel entity.
 #[derive(Component, Debug)]
 pub struct SettingsPanel;
@@ -372,15 +380,31 @@ impl Plugin for SettingsPlugin {
             // also runs cleanly under `MinimalPlugins` (tests).
             .add_message::<WindowResized>()
             .add_message::<WindowMoved>()
+            // Settings changes land before game logic runs: the mutator
+            // chain (volume keys → geometry record → geometry persist) is a
+            // deterministic spine, and the whole set precedes GameMutation so
+            // every reader already ordered after GameMutation sees this
+            // frame's settings transitively (ambiguity burn-down, #143).
+            .configure_sets(
+                Update,
+                SettingsMutation.before(crate::game_plugin::GameMutation),
+            )
             .add_systems(
                 Update,
                 (
                     handle_volume_keys,
+                    record_window_geometry_changes,
+                    persist_window_geometry_after_debounce,
+                )
+                    .chain()
+                    .in_set(SettingsMutation),
+            )
+            .add_systems(
+                Update,
+                (
                     toggle_settings_screen,
                     scroll_settings_panel,
                     crate::ui_modal::touch_scroll_panel::<SettingsPanelScrollable>,
-                    record_window_geometry_changes,
-                    persist_window_geometry_after_debounce,
                 ),
             );