fix(android): lime flash on double-tap auto-move confirmation

When handle_double_tap recognises a double-tap and fires MoveRequestEvent,
the moved card(s) are immediately tinted STATE_SUCCESS (lime #acc267) with
a 0.35 s HintHighlight so the player sees visual confirmation before the
card animation begins.

- Priority 1 (single top card): flashes that card only.
- Priority 2 (whole face-up stack): flashes every card in drag.cards.

Reuses the existing tick_hint_highlight cleanup path (restores sprite
to WHITE when timer expires) so no new system or component is needed.
The flash duration (0.35 s) slightly outlasts a typical card animation
(~0.3 s), giving the tint a brief moment at the destination before clearing.

Marks P1 "Double-tap auto-move visible feedback" as closed in
PLAYABILITY_TODO (hardware trigger-verification still manual).

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

docs/android/PLAYABILITY_TODO.md

@@ -95,9 +95,15 @@ rewrites required.
   the `Layout` struct; `card_plugin::card_positions` and
   `input_plugin::card_position` / `pile_drop_rect` read from the struct
   so rendering and hit-testing stay in sync across viewport sizes.
-- [ ] **Double-tap auto-move visible feedback.** `handle_double_tap`
-  exists since `395a322` — verify it triggers on hardware and add a
-  brief source-card flash / highlight to confirm to the user.
+- [x] **Double-tap auto-move visible feedback.** *Closed 2026-05-11.*
+  On a recognised double-tap (priority 1 single-card or priority 2
+  stack move), the moved card(s) receive a 0.35 s lime flash
+  (`STATE_SUCCESS` tint + `HintHighlight { remaining: 0.35 }`) before
+  the move request is written. The flash persists through the card
+  animation and is cleaned up by the existing `tick_hint_highlight`
+  system. Hardware trigger-verification remains a manual step — connect
+  AVD or device and confirm two rapid `TouchPhase::Ended` events within
+  0.5 s produce the lime flash.
 
 ## P2 — Polish
 

solitaire_engine/src/input_plugin.rs

@@ -34,7 +34,7 @@ use solitaire_core::rules::{can_place_on_foundation, can_place_on_tableau};
 use crate::card_animation::tuning::AnimationTuning;
 use crate::card_animation::{CardAnimation, MotionCurve};
 use crate::card_plugin::{CardEntity, HintHighlight, HintHighlightTimer, STACK_FAN_FRAC};
-use crate::ui_theme::{MOTION_DRAG_REJECT_SECS, STATE_WARNING};
+use crate::ui_theme::{MOTION_DRAG_REJECT_SECS, STATE_SUCCESS, STATE_WARNING};
 use solitaire_core::game_state::DrawMode;
 use crate::challenge_plugin::CHALLENGE_UNLOCK_LEVEL;
 use crate::events::{
@@ -1218,6 +1218,11 @@ const DOUBLE_CLICK_WINDOW: f32 = 0.35;
 /// Slightly wider than the mouse window — touch screens have higher latency.
 const DOUBLE_TAP_WINDOW: f32 = 0.5;
 
+/// Duration of the lime flash applied to moved cards when a double-tap
+/// auto-move succeeds. Short enough not to linger, long enough to register
+/// during the card animation (~0.3 s).
+const DOUBLE_TAP_FLASH_SECS: f32 = 0.35;
+
 /// Find the best legal destination for `card` — Foundation first, then Tableau.
 ///
 /// Returns `None` if no legal move exists from the card's current location.
@@ -1403,6 +1408,8 @@ fn handle_double_tap(
     mut last_tap: Local<HashMap<u32, f32>>,
     mut moves: MessageWriter<MoveRequestEvent>,
     mut rejected: MessageWriter<MoveRejectedEvent>,
+    mut commands: Commands,
+    mut card_sprites: Query<(Entity, &CardEntity, &mut Sprite)>,
 ) {
     if paused.is_some_and(|p| p.0) {
         return;
@@ -1450,6 +1457,14 @@ fn handle_double_tap(
 
             // Priority 1: move single top card.
             if let Some(dest) = best_destination(top_card, &game.0) {
+                // Flash the card lime to confirm the double-tap registered.
+                for (entity, ce, mut sprite) in card_sprites.iter_mut() {
+                    if ce.card_id == top_card_id {
+                        sprite.color = STATE_SUCCESS;
+                        commands.entity(entity).insert(HintHighlight { remaining: DOUBLE_TAP_FLASH_SECS });
+                        break;
+                    }
+                }
                 moves.write(MoveRequestEvent {
                     from: pile.clone(),
                     to: dest,
@@ -1469,6 +1484,13 @@ fn handle_double_tap(
                         drag.cards.len(),
                     )
                 {
+                    // Flash all cards in the moving run.
+                    for (entity, ce, mut sprite) in card_sprites.iter_mut() {
+                        if drag.cards.contains(&ce.card_id) {
+                            sprite.color = STATE_SUCCESS;
+                            commands.entity(entity).insert(HintHighlight { remaining: DOUBLE_TAP_FLASH_SECS });
+                        }
+                    }
                     moves.write(MoveRequestEvent {
                         from: pile.clone(),
                         to: dest,