Add authoritative fighter surface state

## Summary
- signal GameCube poll thread shutdown unconditionally when the snapshot is dropped
- retain and join the poll thread during resource cleanup
- add bounded, shutdown-aware backoff for recoverable parse and short-read errors
- add unit coverage for backoff capping and shutdown-aware waits

Fixes #25

Reviewed-on: #55
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/debug_tools.rs

@@ -3,11 +3,9 @@
 use std::{collections::HashMap, time::Duration};
 
 use bevy::{
-    input::InputSystems,
-    prelude::*,
-    settings::{ReflectSettingsGroup, SaveSettingsDeferred, SettingsGroup},
+    camera::{CameraOutputMode, visibility::RenderLayers}, input::InputSystems, prelude::*, render::render_resource::BlendState, settings::{ReflectSettingsGroup, SaveSettingsDeferred, SettingsGroup},
 };
-use bevy_egui::{EguiContexts, EguiPrimaryContextPass, egui};
+use bevy_egui::{EguiContexts, EguiGlobalSettings, EguiPrimaryContextPass, PrimaryEguiContext, egui};
 use bevy_ggrs::{RollbackFrameRate, RunGgrsSystems};
 use enum_cycling::EnumCycle;
 use enum_cycling_derive::EnumCycle;
@@ -397,6 +395,7 @@ impl Plugin for DebugToolsPlugin {
                     .before(RunGgrsSystems)
                     .run_if(in_state(AppState::InMatch)),
             )
+            .add_systems(Startup, spawn_egui_camera)
             .add_systems(PreUpdate, restore_frame_step_time.after(RunGgrsSystems))
             .add_systems(
                 Update,
@@ -408,6 +407,26 @@ impl Plugin for DebugToolsPlugin {
     }
 }
 
+pub fn spawn_egui_camera(mut commands: Commands, mut egui_global_settings: ResMut<EguiGlobalSettings>,) {
+    egui_global_settings.auto_create_primary_context = false;
+    commands.spawn((
+        // The `PrimaryEguiContext` component requires everything needed to render a primary context.
+        PrimaryEguiContext,
+        Camera2d,
+        // Setting RenderLayers to none makes sure we won't render anything apart from the UI.
+        RenderLayers::none(),
+        Camera {
+            order: 2,
+            output_mode: CameraOutputMode::Write {
+                blend_state: Some(BlendState::ALPHA_BLENDING),
+                clear_color: ClearColorConfig::None,
+            },
+            clear_color: ClearColorConfig::Custom(Color::NONE),
+            ..default()
+        },
+    ));
+}
+
 fn player_handles(players: &Query<&Player>) -> Vec<usize> {
     let mut handles = players
         .iter()

src/input/gamecube/poll.rs

@@ -1,6 +1,8 @@
 use std::panic::{self, AssertUnwindSafe};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
+use std::thread::JoinHandle;
+use std::time::{Duration, Instant};
 
 use bevy::prelude::*;
 use gc_adapter_neo::{Controller, GcAdapter};
@@ -55,10 +57,11 @@ impl GcPortState {
 /// Shared, `Send + Sync` handle to the latest snapshot from the poll
 /// thread. Safe to store as an ordinary [`Resource`] (no `NonSend` needed)
 /// because the `GcAdapter` itself never leaves its thread.
-#[derive(Resource, Clone)]
+#[derive(Resource)]
 pub struct GcAdapterSnapshot {
     ports: Arc<Mutex<[GcPortState; 4]>>,
     shutdown: Arc<AtomicBool>,
+    poll_thread: Option<JoinHandle<()>>,
 }
 
 impl GcAdapterSnapshot {
@@ -69,12 +72,36 @@ impl GcAdapterSnapshot {
 
 impl Drop for GcAdapterSnapshot {
     fn drop(&mut self) {
-        // Only actually signals shutdown once the last clone (this resource
-        // is never cloned in practice, but be defensive) is dropped.
-        if Arc::strong_count(&self.shutdown) <= 1 {
-            self.shutdown.store(true, Ordering::Relaxed);
+        self.shutdown.store(true, Ordering::Release);
+
+        if let Some(poll_thread) = self.poll_thread.take() {
+            if let Err(payload) = poll_thread.join() {
+                error!(
+                    "GameCube Controller Adapter poll thread panicked during shutdown: {payload:?}"
+                );
             }
         }
+    }
+}
+
+const INITIAL_ERROR_BACKOFF: Duration = Duration::from_millis(1);
+const MAX_ERROR_BACKOFF: Duration = Duration::from_millis(100);
+
+fn next_error_backoff(backoff: Duration) -> Duration {
+    backoff.saturating_mul(2).min(MAX_ERROR_BACKOFF)
+}
+
+/// Wait for a retry while still allowing the owner to shut the poll thread down promptly.
+fn wait_for_retry(shutdown: &AtomicBool, delay: Duration) -> bool {
+    let deadline = Instant::now() + delay;
+    while !shutdown.load(Ordering::Acquire) {
+        let remaining = deadline.saturating_duration_since(Instant::now());
+        if remaining.is_zero() {
+            return true;
+        }
+        std::thread::sleep(remaining.min(Duration::from_millis(10)));
+    }
+    false
 }
 
 /// Connects to the first GameCube adapter found on the USB bus and starts
@@ -94,7 +121,7 @@ pub fn spawn_poll_thread() -> Result<GcAdapterSnapshot, gc_adapter_neo::UsbError
 
     let thread_ports = ports.clone();
     let thread_shutdown = shutdown.clone();
-    std::thread::Builder::new()
+    let poll_thread = std::thread::Builder::new()
         .name("gc-adapter-poll".into())
         .spawn(move || {
             // Flush whatever the adapter had buffered before we started
@@ -107,17 +134,27 @@ pub fn spawn_poll_thread() -> Result<GcAdapterSnapshot, gc_adapter_neo::UsbError
             let mut rate_window_start = std::time::Instant::now();
             #[cfg(debug_assertions)]
             let mut rate_window_count: u32 = 0;
+            let mut error_backoff = INITIAL_ERROR_BACKOFF;
 
-            while !thread_shutdown.load(Ordering::Relaxed) {
+            while !thread_shutdown.load(Ordering::Acquire) {
                 let result = panic::catch_unwind(AssertUnwindSafe(|| adapter.read_controllers()));
 
                 let controllers = match result {
-                    Ok(Ok(controllers)) => controllers,
+                    Ok(Ok(controllers)) => {
+                        error_backoff = INITIAL_ERROR_BACKOFF;
+                        controllers
+                    }
                     // Ignore this, for some reason we get a bunch of these when we start reading
                     Ok(Err(
                         gc_adapter_neo::AdapterError::Parse(_)
                         | gc_adapter_neo::AdapterError::ShortRead(_),
-                    )) => continue,
+                    )) => {
+                        if !wait_for_retry(&thread_shutdown, error_backoff) {
+                            break;
+                        }
+                        error_backoff = next_error_backoff(error_backoff);
+                        continue;
+                    }
                     Ok(Err(gc_adapter_neo::AdapterError::Usb(err))) => {
                         error!(
                             "GameCube Controller Adapter USB read failed ({err:?}); stopping \
@@ -160,5 +197,32 @@ pub fn spawn_poll_thread() -> Result<GcAdapterSnapshot, gc_adapter_neo::UsbError
         })
         .expect("failed to spawn gc-adapter poll thread");
 
-    Ok(GcAdapterSnapshot { ports, shutdown })
+    Ok(GcAdapterSnapshot {
+        ports,
+        shutdown,
+        poll_thread: Some(poll_thread),
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn error_backoff_is_capped() {
+        let mut backoff = INITIAL_ERROR_BACKOFF;
+        for _ in 0..16 {
+            backoff = next_error_backoff(backoff);
+        }
+
+        assert_eq!(backoff, MAX_ERROR_BACKOFF);
+        assert_eq!(next_error_backoff(MAX_ERROR_BACKOFF), MAX_ERROR_BACKOFF);
+    }
+
+    #[test]
+    fn retry_wait_stops_when_shutdown_is_requested() {
+        let shutdown = AtomicBool::new(true);
+
+        assert!(!wait_for_retry(&shutdown, Duration::from_secs(1)));
+    }
 }

src/menus/character_select/mod.rs

@@ -1,19 +1,8 @@
 use bevy::{picking::pointer::PointerId, prelude::*};
 
 use crate::{
-    AppState,
-    fighter::manifest::{FighterManifest, FighterManifestRegistry},
-    game_settings::CommonAssets,
-    input::{LocalInputAssignments, LocalInputSource},
-    menus::{
-        MenuMarker,
-        button::FGUiButton,
-        character_select::{character_box::CharacterBox, token::CharacterSelectToken},
-        cursor::{FGMenuCursor, MenuCursorInputSource},
-        errors::MenuErrors::FighterManifestNotFound,
-        match_config::{MenuMatchConfig, MenuMatchPlayerSlot},
-        scaling, spawn_menu,
-        style::{FGUiButtonType, FGUiStyle},
+    AppState, fighter::manifest::{FighterManifest, FighterManifestRegistry}, game_settings::CommonAssets, input::{LocalInputAssignments, LocalInputSource}, menus::{
+        MenuCameraMarker, MenuMarker, button::FGUiButton, character_select::{character_box::CharacterBox, token::CharacterSelectToken}, cursor::{FGMenuCursor, MenuCursorInputSource}, errors::MenuErrors::FighterManifestNotFound, match_config::{MenuMatchConfig, MenuMatchPlayerSlot}, scaling, spawn_menu, style::{FGUiButtonType, FGUiStyle},
     },
 };
 
@@ -241,7 +230,7 @@ pub fn copy_cursor_transform_to_token(
     character_boxes: Query<(&CharacterBox, &ComputedNode, &UiGlobalTransform)>,
     match_config: Res<MenuMatchConfig>,
     cursors: Query<&UiGlobalTransform, With<FGMenuCursor>>,
-    cam: Single<&Camera>,
+    cam: Single<&Camera, With<MenuCameraMarker>>,
     ui_scale: Res<UiScale>,
 ) -> Result {
     let camera = cam.into_inner();

src/menus/cursor.rs

@@ -9,11 +9,8 @@ use bevy::{
 };
 
 use crate::{
-    input::{LocalInputAssignments, LocalInputSource},
-    menus::{
-        input::{MenuInput, MenuInputState},
-        scaling,
-        style::FGUiStyle,
+    input::{LocalInputAssignments, LocalInputSource}, menus::{
+        MenuCameraMarker, input::{MenuInput, MenuInputState}, scaling, style::FGUiStyle,
     },
 };
 
@@ -181,7 +178,7 @@ pub fn cursor_input(
 }
 
 pub fn update_cursor_transform(
-    camera: Single<&Camera>,
+    camera: Single<&Camera, With<MenuCameraMarker>>,
     query: Query<(&mut Node, &PointerLocation), With<FGMenuCursor>>,
     ui_scale: Res<UiScale>,
 ) {

src/menus/mod.rs

@@ -53,6 +53,7 @@ pub fn wrap_menu(menu: impl Scene) -> impl Scene {
                 #MenuCamera
                 Camera
                 Camera2d
+                MenuCameraMarker
             ),
             (
                 #MenuContainer
@@ -73,7 +74,6 @@ pub fn wrap_menu(menu: impl Scene) -> impl Scene {
 
 pub fn despawn_menu(
     existing_menu: Option<Single<Entity, With<MenuMarker>>>,
-    existing_menu_camera: Option<Single<Entity, With<MenuCameraMarker>>>,
     mut commands: Commands,
 ) {
     if let Some(entity) = existing_menu {
@@ -82,9 +82,6 @@ pub fn despawn_menu(
             .despawn();
     }
 
-    if let Some(menu_cam) = existing_menu_camera {
-        commands.entity(*menu_cam).despawn();
-    }
 }
 
 pub fn spawn_menu(