Add authoritative fighter surface state (#60)

## Summary
- add a rollback-tracked `FighterSurfaceState` as the single source of truth for stage contact
- move active stage line ownership out of individual grounded fighter states
- update landing, airborne motion, ledge departure, hit reactions, and debug save states to maintain surface contact
- add tests for contact lifecycle, connected-segment traversal, and ledge departure

Reviewed-on: #60
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/mod.rs

@@ -7,7 +7,8 @@ use bevy::prelude::*;
 
 use crate::fighter::animation::{AnimKind, FighterAnimationFrame};
 use crate::fighter::attack::{
-    FighterAttackScriptAssets, FighterKnockbackVelocity, FighterPendingHitReaction, FighterStaleMoveQueue, HitStop,
+    FighterAttackScriptAssets, FighterKnockbackVelocity, FighterPendingHitReaction,
+    FighterStaleMoveQueue, HitStop,
 };
 use crate::fighter::attributes::FighterAttributes;
 use crate::fighter::baked_animation::BakedFighterAnimations;
@@ -16,7 +17,9 @@ use crate::fighter::manifest::FighterManifest;
 use crate::fighter::state::hitstun::HitstunState;
 use crate::fighter::visual::FighterAnimations;
 use crate::fighter::{
-    Fighter, FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop, FighterHitstopShake, FighterHitstopShakeKind, FighterHitstopShakeRole, FighterPreviousTranslation, FighterTranslation, FighterVelocity,
+    Fighter, FighterECB, FighterFacingDirection, FighterHitboxes, FighterHitstop,
+    FighterHitstopShake, FighterHitstopShakeKind, FighterHitstopShakeRole,
+    FighterPreviousTranslation, FighterSurfaceState, FighterTranslation, FighterVelocity,
 };
 use crate::game_settings::GameSettings;
 use crate::input::FighterInput;
@@ -95,9 +98,7 @@ pub trait FighterStateImpl: Sized {
         None
     }
 
-    fn is_visually_grounded<'a>(
-        &'a self,
-    ) -> bool;
+    fn is_visually_grounded<'a>(&'a self) -> bool;
 }
 
 pub struct AnimationStatus {
@@ -151,6 +152,7 @@ pub struct UpdateContext<'a> {
     pub input: &'a mut FighterInput,
     pub hitboxes: &'a mut FighterHitboxes,
     pub velocity: &'a mut FighterVelocity,
+    pub surface: &'a mut FighterSurfaceState,
     pub knockback_velocity: &'a mut FighterKnockbackVelocity,
     pub game_settings: &'a GameSettings,
     pub animation_frame: u32,
@@ -170,6 +172,7 @@ pub struct CollisionContext<'a> {
     pub translation: &'a mut FighterTranslation,
     pub prev_translation: &'a FighterPreviousTranslation,
     pub velocity: &'a mut FighterVelocity,
+    pub surface: &'a mut FighterSurfaceState,
     pub ecb: &'a FighterECB,
     pub prev_ecb: &'a FighterPreviousECB,
     pub stage_collision: &'a StageCollision,
@@ -212,6 +215,7 @@ pub struct FighterFrameQuery {
     pub input: &'static mut FighterInput,
     pub hitboxes: &'static mut FighterHitboxes,
     pub velocity: &'static mut FighterVelocity,
+    pub surface: &'static mut FighterSurfaceState,
     pub knockback_velocity: &'static mut FighterKnockbackVelocity,
     pub stale_move_queue: &'static mut FighterStaleMoveQueue,
     pub ecb: &'static FighterECB,
@@ -292,13 +296,14 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             input: &mut self.input,
             hitboxes: &mut self.hitboxes,
             velocity: &mut self.velocity,
+            surface: &mut self.surface,
             knockback_velocity: &mut self.knockback_velocity,
             game_settings,
             animation_frame: self.animation_frame.frame,
             fighter_attributes: attributes,
             attack_scripts,
             attack_script_assets,
-            facing_direction: &self.facing_direction
+            facing_direction: &self.facing_direction,
         }
     }
 
@@ -310,6 +315,7 @@ impl<'w, 's> FighterFrameQueryItem<'w, 's> {
             translation: &mut self.translation,
             prev_translation: &self.prev_translation,
             velocity: &mut self.velocity,
+            surface: &mut self.surface,
             ecb: &self.ecb,
             prev_ecb: &self.prev_ecb,
             stage_collision,
@@ -400,7 +406,9 @@ pub fn state_interrupt_system(
 
         let new_state = if let Some(reaction) = pending_hit_reaction.take() {
             hitstop.remaining_frames = *reaction.hitstop_frames;
-            let shake_frames = reaction.hitstop_frames.calculate_shake_frames(&game_settings);
+            let shake_frames = reaction
+                .hitstop_frames
+                .calculate_shake_frames(&game_settings);
             hitstop_shake.role = FighterHitstopShakeRole::Receiver;
             hitstop_shake.total_frames = shake_frames;
             hitstop_shake.remaining_frames = shake_frames;
@@ -409,36 +417,26 @@ pub fn state_interrupt_system(
             } else {
                 FighterHitstopShakeKind::Vertical
             };
-            
-            let mut hitstop_kind = match &*state {
-                FighterState::Wait(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.grounded_common.clone())
-                }
-                FighterState::Walk(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.grounded_common.clone())
-                }
-                FighterState::Dash(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.ground_common.clone())
-                }
-                FighterState::Run(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.grounded_common.clone())
-                }
-                FighterState::Turn(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.grounded_common.clone())
-                }
-                FighterState::GroundAttack(value) => {
-                    hitstun::HitstopStateKind::Grounded(value.grounded_common.clone())
-                }
-                _ => hitstun::HitstopStateKind::Airborne,
+
+            let mut hitstop_kind = if frame.surface.is_grounded() {
+                hitstun::HitstopStateKind::Grounded
+            } else {
+                hitstun::HitstopStateKind::Airborne
             };
 
-            if let hitstun::HitstopStateKind::Grounded(_) = hitstop_kind {
+            if let hitstun::HitstopStateKind::Grounded = hitstop_kind {
                 let straight_up_angle = FGi32::lit("90.0");
-                if reaction.hitstop_frames >= HitStop::new(game_settings.fighter_common.tumble_bounce_hitstop_threshold) {
+                if reaction.hitstop_frames
+                    >= HitStop::new(game_settings.fighter_common.tumble_bounce_hitstop_threshold)
+                {
                     hitstop_kind = hitstun::HitstopStateKind::Airborne;
                 // TODO: Use floor normal here
-                } else if reaction.launch_angle.abs_diff(straight_up_angle) < game_settings.fighter_common.attack_ground_to_airborne_transition_vertical_angle_threshold {
-                        hitstop_kind = hitstun::HitstopStateKind::Airborne;
+                } else if reaction.launch_angle.abs_diff(straight_up_angle)
+                    < game_settings
+                        .fighter_common
+                        .attack_ground_to_airborne_transition_vertical_angle_threshold
+                {
+                    hitstop_kind = hitstun::HitstopStateKind::Airborne;
                 } else {
                     // straight down is 270
                     let straight_down_angle = FGi32::lit("270.0");
@@ -450,6 +448,10 @@ pub fn state_interrupt_system(
                 }
             }
 
+            if matches!(hitstop_kind, hitstun::HitstopStateKind::Airborne) {
+                frame.surface.leave_ground();
+            }
+
             info!("Entering hitstop kind: {:?}", hitstop_kind);
             Some(FighterState::Hitstun(HitstunState::new(
                 reaction,