perf(engine): route remaining drag card→entity lookups through CardEntityIndex

Replace O(n) `Query::iter().find()` card scans with O(1) `CardEntityIndex`
lookups in the mouse and touch drag pipelines (`follow_drag`, `end_drag`,
`touch_follow_drag`, `touch_end_drag`) and `update_drag_shadow` — 7 sites
across 5 systems. Each ran per dragged card per frame during a drag.

`InputPlugin` now defensively `init_resource::<CardEntityIndex>()` (idempotent;
`CardPlugin` still owns and rebuilds it) so the plugin is self-sufficient in
tests. The lone remaining card-keyed `.find` is a `#[cfg(test)]` world-query
helper, which is the correct pattern there.

Completes the CardEntityIndex migration started in ef1efdc.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_engine/src/card_plugin.rs

@@ -1487,6 +1487,7 @@ fn update_drag_shadow(
     drag: Res<DragState>,
     layout: Option<Res<LayoutResource>>,
     card_entities: Query<(&CardEntity, &Transform)>,
+    card_index: Res<CardEntityIndex>,
     mut shadow: Local<Option<Entity>>,
 ) {
     if drag.is_idle() {
@@ -1503,9 +1504,9 @@ fn update_drag_shadow(
 
     // Find the world position of the first (top) dragged card.
     let top_pos = drag.cards.first().and_then(|first_card| {
-        card_entities
+        card_index
-            .iter()
+            .get(first_card)
-            .find(|(marker, _)| marker.card == *first_card)
+            .and_then(|entity| card_entities.get(entity).ok())
             .map(|(_, t)| t.translation)
     });
 

solitaire_engine/src/input_plugin.rs

@@ -33,7 +33,9 @@ use solitaire_core::game_state::GameState;
 use crate::auto_complete_plugin::AutoCompleteState;
 use crate::card_animation::tuning::AnimationTuning;
 use crate::card_animation::{CardAnimation, MotionCurve};
-use crate::card_plugin::{CardEntity, HintHighlight, HintHighlightTimer, STACK_FAN_FRAC};
+use crate::card_plugin::{
+    CardEntity, CardEntityIndex, HintHighlight, HintHighlightTimer, STACK_FAN_FRAC,
+};
 use crate::challenge_plugin::CHALLENGE_UNLOCK_LEVEL;
 use crate::events::{
     DrawRequestEvent, ForfeitRequestEvent, HintVisualEvent, InfoToastEvent, MoveRejectedEvent,
@@ -121,6 +123,10 @@ impl Plugin for InputPlugin {
             .init_resource::<HintSolverConfig>()
             .init_resource::<crate::pending_hint::PendingHintTask>()
             .init_resource::<GameInputConsumedResource>()
+            // The drag systems resolve cards via `CardEntityIndex`; `CardPlugin`
+            // owns and rebuilds it, but init here too so `InputPlugin` is
+            // self-sufficient in tests (idempotent if already registered).
+            .init_resource::<CardEntityIndex>()
             .add_message::<StartZenRequestEvent>()
             .add_message::<InfoToastEvent>()
             .add_message::<ForfeitRequestEvent>()
@@ -674,6 +680,7 @@ fn follow_drag(
     layout: Option<Res<LayoutResource>>,
     tuning: Res<AnimationTuning>,
     mut card_transforms: Query<(&CardEntity, &mut Transform, &mut Sprite)>,
+    card_index: Res<CardEntityIndex>,
 ) {
     // Skip if idle or if a touch drag is running.
     if drag.is_idle() || drag.active_touch_id.is_some() {
@@ -704,9 +711,8 @@ fn follow_drag(
         // Elevate cards: push to DRAG_Z and dim slightly so the board
         // beneath stays readable.
         for (i, card) in drag.cards.iter().enumerate() {
-            if let Some((_, mut transform, mut sprite)) = card_transforms
+            if let Some(entity) = card_index.get(card)
-                .iter_mut()
+                && let Ok((_, mut transform, mut sprite)) = card_transforms.get_mut(entity)
-                .find(|(ce, _, _)| ce.card == *card)
             {
                 transform.translation.z = dragged_card_z(i);
                 sprite.color.set_alpha(0.85);
@@ -719,9 +725,8 @@ fn follow_drag(
     let fan = -layout.0.card_size.y * layout.0.tableau_fan_frac;
 
     for (i, card) in drag.cards.iter().enumerate() {
-        if let Some((_, mut transform, _)) = card_transforms
+        if let Some(entity) = card_index.get(card)
-            .iter_mut()
+            && let Ok((_, mut transform, _)) = card_transforms.get_mut(entity)
-            .find(|(ce, _, _)| ce.card == *card)
         {
             transform.translation.x = bottom_pos.x;
             transform.translation.y = bottom_pos.y + fan * i as f32;
@@ -743,6 +748,7 @@ fn end_drag(
     mut changed: MessageWriter<StateChangedEvent>,
     mut commands: Commands,
     card_entities: Query<(Entity, &CardEntity, &Transform)>,
+    card_index: Res<CardEntityIndex>,
 ) {
     if paused.is_some_and(|p| p.0) {
         drag.clear();
@@ -830,9 +836,8 @@ fn end_drag(
                         continue;
                     };
                     let target_pos = card_position(&game.0, &layout.0, &origin, stack_index);
-                    if let Some((entity, _, transform)) = card_entities
+                    if let Some(entity) = card_index.get(card)
-                        .iter()
+                        && let Ok((_, _, transform)) = card_entities.get(entity)
-                        .find(|(_, ce, _)| ce.card == *card)
                     {
                         let drag_pos = transform.translation.truncate();
                         let drag_z = transform.translation.z;
@@ -930,6 +935,7 @@ fn touch_follow_drag(
     layout: Option<Res<LayoutResource>>,
     tuning: Res<AnimationTuning>,
     mut card_transforms: Query<(&CardEntity, &mut Transform, &mut Sprite)>,
+    card_index: Res<CardEntityIndex>,
 ) {
     let Some(active_id) = drag.active_touch_id else {
         return; // Mouse drag or idle.
@@ -957,9 +963,8 @@ fn touch_follow_drag(
         drag.committed = true;
 
         for (i, card) in drag.cards.iter().enumerate() {
-            if let Some((_, mut transform, mut sprite)) = card_transforms
+            if let Some(entity) = card_index.get(card)
-                .iter_mut()
+                && let Ok((_, mut transform, mut sprite)) = card_transforms.get_mut(entity)
-                .find(|(ce, _, _)| ce.card == *card)
             {
                 transform.translation.z = dragged_card_z(i);
                 sprite.color.set_alpha(0.85);
@@ -971,9 +976,8 @@ fn touch_follow_drag(
     let fan = -layout.0.card_size.y * layout.0.tableau_fan_frac;
 
     for (i, card) in drag.cards.iter().enumerate() {
-        if let Some((_, mut transform, _)) = card_transforms
+        if let Some(entity) = card_index.get(card)
-            .iter_mut()
+            && let Ok((_, mut transform, _)) = card_transforms.get_mut(entity)
-            .find(|(ce, _, _)| ce.card == *card)
         {
             transform.translation.x = bottom_pos.x;
             transform.translation.y = bottom_pos.y + fan * i as f32;
@@ -998,6 +1002,7 @@ fn touch_end_drag(
     mut changed: MessageWriter<StateChangedEvent>,
     mut commands: Commands,
     card_entities: Query<(Entity, &CardEntity, &Transform)>,
+    card_index: Res<CardEntityIndex>,
 ) {
     let Some(active_id) = drag.active_touch_id else {
         return; // Mouse drag or idle.
@@ -1070,9 +1075,8 @@ fn touch_end_drag(
                             continue;
                         };
                         let target_pos = card_position(&game.0, &layout.0, &origin, stack_index);
-                        if let Some((entity, _, transform)) = card_entities
+                        if let Some(entity) = card_index.get(card)
-                            .iter()
+                            && let Ok((_, _, transform)) = card_entities.get(entity)
-                            .find(|(_, ce, _)| ce.card == *card)
                         {
                             let drag_pos = transform.translation.truncate();
                             let drag_z = transform.translation.z;