feat(engine): add Android corner-label overlay for card readability

On Android, face-up cards now render a large rank+suit overlay in
the upper-left corner (FONT_SIZE_FRAC_MOBILE = 0.35 × card_width,
using Anchor::TOP_LEFT) so the rank and suit are legible at phone
scale. The baked-in SVG art corner text is only ~10–15 px physical;
the overlay is ~52 px physical — roughly 3-4× larger.

Accompanying changes:
- H_GAP_DIVISOR on Android raised 8 → 32, widening cards from
  112.5 → 124.1 logical px (135 → 149 physical px on Pixel 7 AVD).
- AndroidCornerLabel marker component tracks overlay entities so
  resize_android_corner_labels can update font-size + transform
  on orientation change without a full card respawn.
- Uses text_colour() for overlay tint so black suits render as
  near-white (BLACK_SUIT_COLOUR) on the dark Terminal card face,
  matching the existing fallback overlay behaviour.

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

solitaire_engine/src/card_plugin.rs

@@ -15,6 +15,8 @@ use std::collections::{HashMap, HashSet};
 use bevy::color::Color;
 use bevy::prelude::*;
 use bevy::window::WindowResized;
+#[cfg(target_os = "android")]
+use bevy::sprite::Anchor;
 use solitaire_core::card::{Card, Rank, Suit};
 use solitaire_core::game_state::{DrawMode, GameState};
 use solitaire_core::pile::PileType;
@@ -65,6 +67,12 @@ pub const STACK_FAN_FRAC: f32 = 0.003;
 /// Font size as a fraction of card width.
 const FONT_SIZE_FRAC: f32 = 0.28;
 
+/// Font-size fraction for the large-print readability overlay on Android.
+/// Spawned on top of PNG face cards to make the rank+suit legible at phone
+/// scale, where the baked-in PNG corner text is only ~10 px physical.
+#[cfg(target_os = "android")]
+const FONT_SIZE_FRAC_MOBILE: f32 = 0.35;
+
 /// Card-face background — Terminal `#1a1a1a` (BG_ELEVATED).
 pub const CARD_FACE_COLOUR: Color = Color::srgb(0.102, 0.102, 0.102);
 /// Suit colour for hearts + diamonds — saturated red `#e35353`.
@@ -163,6 +171,16 @@ pub struct CardEntity {
 #[derive(Component, Debug)]
 pub struct CardLabel;
 
+/// Marker for the large-print rank+suit corner overlay on Android.
+///
+/// Spawned on top of PNG face cards (face-up only) at font size
+/// [`FONT_SIZE_FRAC_MOBILE`] so the rank and suit character are
+/// readable at phone scale. Only exists when `CardImageSet` is present
+/// (the fallback solid-colour path uses a plain `CardLabel` instead).
+#[cfg(target_os = "android")]
+#[derive(Component, Debug, Clone, Copy)]
+struct AndroidCornerLabel;
+
 /// Marker component indicating the card is currently highlighted as a hint.
 /// `remaining` counts down in real seconds; the highlight is removed when it
 /// reaches zero and the card sprite colour is restored to its normal value.
@@ -429,6 +447,9 @@ impl Plugin for CardPlugin {
                     snap_cards_on_window_resize.after(collect_resize_events),
                 ),
             );
+
+        #[cfg(target_os = "android")]
+        app.add_systems(Update, resize_android_corner_labels);
     }
 }
 
@@ -761,6 +782,8 @@ fn spawn_card_entity(
     });
     // When PNG faces are loaded the rank/suit are baked into the image.
     // Only spawn the Text2d overlay in the solid-colour fallback (tests).
+    // On Android we additionally spawn a large-print corner label even in
+    // image mode so the rank/suit are legible at phone scale.
     if card_images.is_none() {
         entity.with_children(|b| {
             b.spawn((
@@ -776,6 +799,12 @@ fn spawn_card_entity(
             ));
         });
     }
+    #[cfg(target_os = "android")]
+    if card_images.is_some() {
+        entity.with_children(|b| {
+            add_android_corner_label(b, card, layout.card_size, color_blind, high_contrast);
+        });
+    }
 }
 
 #[allow(clippy::too_many_arguments)]
@@ -829,7 +858,8 @@ fn update_card_entity(
 
     // Despawn any stale children and re-add the per-card drop shadow plus,
     // in solid-colour fallback mode, the label overlay. In image mode the
-    // rank/suit are baked into the PNG, so no `Text2d` overlay is needed.
+    // rank/suit are baked into the PNG; on Android we also add a large-print
+    // corner overlay so they are legible at phone scale.
     commands.entity(entity).despawn_related::<Children>();
     commands.entity(entity).with_children(|b| {
         add_card_shadow_child(b, layout.card_size);
@@ -852,6 +882,12 @@ fn update_card_entity(
             ));
         });
     }
+    #[cfg(target_os = "android")]
+    if card_images.is_some() {
+        commands.entity(entity).with_children(|b| {
+            add_android_corner_label(b, card, layout.card_size, color_blind, high_contrast);
+        });
+    }
 }
 
 fn label_for(card: &Card) -> String {
@@ -924,6 +960,67 @@ fn label_visibility(card: &Card) -> Visibility {
     }
 }
 
+/// Rank+suit string for the Android readability overlay.
+/// Uses Unicode suit glyphs (♠♥♦♣ — U+2660–U+2666, covered by FiraMono).
+#[cfg(target_os = "android")]
+fn mobile_label_for(card: &Card) -> String {
+    let rank = match card.rank {
+        Rank::Ace => "A",
+        Rank::Two => "2",
+        Rank::Three => "3",
+        Rank::Four => "4",
+        Rank::Five => "5",
+        Rank::Six => "6",
+        Rank::Seven => "7",
+        Rank::Eight => "8",
+        Rank::Nine => "9",
+        Rank::Ten => "10",
+        Rank::Jack => "J",
+        Rank::Queen => "Q",
+        Rank::King => "K",
+    };
+    let suit = match card.suit {
+        Suit::Clubs => "♣",
+        Suit::Diamonds => "♦",
+        Suit::Hearts => "♥",
+        Suit::Spades => "♠",
+    };
+    format!("{rank}{suit}")
+}
+
+/// Spawns the [`AndroidCornerLabel`] overlay child on face-up cards.
+/// Uses [`Anchor::TopLeft`] so the transform is the inset top-left corner
+/// of the card face; the text block grows down and right from there.
+#[cfg(target_os = "android")]
+fn add_android_corner_label(
+    parent: &mut ChildSpawnerCommands,
+    card: &Card,
+    card_size: Vec2,
+    color_blind: bool,
+    high_contrast: bool,
+) {
+    if !card.face_up {
+        return;
+    }
+    let inset = 4.0_f32;
+    parent.spawn((
+        AndroidCornerLabel,
+        CardLabel,
+        Text2d::new(mobile_label_for(card)),
+        TextFont {
+            font_size: card_size.x * FONT_SIZE_FRAC_MOBILE,
+            ..default()
+        },
+        TextColor(text_colour(card, color_blind, high_contrast)),
+        Anchor::TOP_LEFT,
+        Transform::from_xyz(
+            -card_size.x / 2.0 + inset,
+            card_size.y / 2.0 - inset,
+            0.02,
+        ),
+    ));
+}
+
 // ---------------------------------------------------------------------------
 // Task #34 — Card-flip animation systems
 // ---------------------------------------------------------------------------
@@ -1832,6 +1929,31 @@ fn resize_cards_in_place(
     }
 }
 
+/// Updates font size and top-left anchor transform of every
+/// [`AndroidCornerLabel`] entity when `LayoutResource` changes (orientation
+/// change or any window resize). The full despawn/respawn path in
+/// `update_card_entity` already handles game-state changes; this system
+/// covers the resize-only path where children are mutated in place.
+#[cfg(target_os = "android")]
+fn resize_android_corner_labels(
+    layout: Res<LayoutResource>,
+    card_images: Option<Res<CardImageSet>>,
+    mut query: Query<(&mut TextFont, &mut Transform), With<AndroidCornerLabel>>,
+) {
+    if !layout.is_changed() || card_images.is_none() {
+        return;
+    }
+    let new_font_size = layout.0.card_size.x * FONT_SIZE_FRAC_MOBILE;
+    let inset = 4.0_f32;
+    let new_x = -layout.0.card_size.x / 2.0 + inset;
+    let new_y = layout.0.card_size.y / 2.0 - inset;
+    for (mut font, mut transform) in query.iter_mut() {
+        font.font_size = new_font_size;
+        transform.translation.x = new_x;
+        transform.translation.y = new_y;
+    }
+}
+
 /// Adjusts `LayoutResource.tableau_fan_frac` to match the current maximum
 /// face-up column depth. Runs after every `StateChangedEvent` so the fan
 /// expands as the player reveals cards while staying within the window.

solitaire_engine/src/layout.rs

@@ -48,6 +48,24 @@ pub const MIN_WINDOW: Vec2 = Vec2::new(320.0, 400.0);
 /// which rendered the cards ~3.6 % squashed vertically.
 const CARD_ASPECT: f32 = 1.4523;
 
+/// Divisor used to derive the horizontal gap between columns from the card
+/// width: `h_gap = card_width / H_GAP_DIVISOR`.
+///
+/// This constant also drives `card_width_width_based`:
+///   total layout width = 7*card_width + 8*h_gap = card_width*(7 + 8/H_GAP_DIVISOR)
+///   → card_width = window.x / (7 + 8/H_GAP_DIVISOR)
+///
+/// Desktop (H_GAP_DIVISOR = 4): card_width = window.x / 9  — existing behaviour.
+/// Android (H_GAP_DIVISOR = 32): card_width = window.x / 7.25  — cards are ~10 %
+///   wider than at divisor 8, with very tight gaps (~4 px) that are still visible
+///   as a faint seam between columns. The primary readability boost on Android
+///   comes from the `AndroidCornerLabel` overlay in `card_plugin`, but maximising
+///   the physical card size helps too.
+#[cfg(not(target_os = "android"))]
+const H_GAP_DIVISOR: f32 = 4.0;
+#[cfg(target_os = "android")]
+const H_GAP_DIVISOR: f32 = 32.0;
+
 /// Fraction of card height used as vertical padding between the top row and
 /// the tableau row.
 const VERTICAL_GAP_FRAC: f32 = 0.2;
@@ -149,8 +167,10 @@ pub fn compute_layout(window: Vec2, safe_area_top: f32, safe_area_bottom: f32, h
     let window = window.max(MIN_WINDOW);
     let band_h = if hud_visible { HUD_BAND_HEIGHT } else { 0.0 };
 
-    // Width-based candidate (existing behaviour): 7 cards + 8 h_gaps = 9*card_width.
-    let card_width_width_based = window.x / 9.0;
+    // Width-based candidate: 7 cards + 8 h_gaps where h_gap = card_width/H_GAP_DIVISOR.
+    // Total = card_width*(7 + 8/H_GAP_DIVISOR) = window.x  →  card_width = window.x/card_width_divisor.
+    let card_width_divisor = 7.0 + 8.0 / H_GAP_DIVISOR;
+    let card_width_width_based = window.x / card_width_divisor;
 
     // Height-based candidate. The vertical budget below the top row must hold
     // a worst-case fanned tableau column plus a bottom margin equal to h_gap.
@@ -175,13 +195,12 @@ pub fn compute_layout(window: Vec2, safe_area_top: f32, safe_area_bottom: f32, h
     let card_height = card_width * CARD_ASPECT;
     let card_size = Vec2::new(card_width, card_height);
 
-    let h_gap = card_width / 4.0;
-    // Total occupied width = 7*card_width + 8*h_gap = 9*card_width. When card
-    // sizing is height-limited (tall/narrow windows), this is smaller than
-    // window.x, so the grid is centred horizontally; otherwise side_margin
-    // collapses to h_gap and the geometry matches the original width-based
-    // layout exactly.
-    let total_grid_width = 9.0 * card_width;
+    let h_gap = card_width / H_GAP_DIVISOR;
+    // Total occupied width = 7*card_width + 8*h_gap = card_width_divisor*card_width.
+    // When card sizing is height-limited (tall/narrow windows) this is smaller than
+    // window.x and the grid is centred horizontally; otherwise side_margin collapses
+    // to h_gap and the geometry fills the window exactly.
+    let total_grid_width = card_width_divisor * card_width;
     let side_margin = (window.x - total_grid_width) / 2.0 + h_gap;
     let left_edge = -window.x / 2.0;
     let col_x = |col: usize| -> f32 {
@@ -401,11 +420,10 @@ mod tests {
     #[test]
     fn tall_narrow_window_keeps_width_based_sizing() {
         // Tall narrow window: there's plenty of vertical budget, so width is
-        // the bottleneck and card_width matches the legacy window.x / 9
-        // derivation exactly.
+        // the bottleneck and card_width matches window.x / (7 + 8/H_GAP_DIVISOR).
         let window = Vec2::new(900.0, 1600.0);
         let layout = compute_layout(window, 0.0, 0.0, true);
-        let width_based = window.x / 9.0;
+        let width_based = window.x / (7.0 + 8.0 / H_GAP_DIVISOR);
         assert!(
             (layout.card_size.x - width_based).abs() < 1e-3,
             "expected width-based sizing (card_width {} should equal {})",