Fix ledge transitions and root motion loops (#91)

## Summary

- resolve each ledge action to the walkable segment on the stage-interior side
- preserve repeating root-motion displacement across every animation cycle
- add regression coverage for left/right ledge segments and multiple root-motion wraps
- Implement ledge intangibility

Reviewed-on: #91
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/ledge_action.rs

@@ -7,7 +7,7 @@ use crate::fighter::FighterFacingDirection;
 use crate::input::FighterCommands;
 use crate::math::int::FGi32;
 use crate::math::vec::FGVec2;
-use crate::stage::line::{StageLedgeSide, StageLineID, StageVertexID};
+use crate::stage::line::{StageLedgeSide, StageVertexID};
 
 #[derive(Debug, Clone, Hash)]
 pub enum LedgeAction {
@@ -96,17 +96,15 @@ impl FighterStateImpl for LedgeActionState {
             let normalized_root_position = FGVec2::new(normalized_root_position.x * ledge_modifier, normalized_root_position.y);
             
             if normalized_root_position.x.is_positive() && normalized_root_position.y.is_positive() {
-                self.is_in_grounded_phase = true;
-                
-                let segment_id = StageLineID {
-                    polygon: self.ledge_id.polygon,
-                    segment: self.ledge_id.vertex
-                };
-                let Some(poly) = state_context.stage_collision.get_segment(segment_id) else {
+                let Some((segment_id, _)) = state_context
+                    .stage_collision
+                    .find_ledge_ground_segment(self.ledge_id)
+                else {
                     return;
                 };
-                
-                state_context.translation.0 = poly.segment.point1();
+
+                self.is_in_grounded_phase = true;
+                state_context.translation.0 = ledge.position;
                 state_context.surface.land(segment_id);
             }
         }
@@ -136,4 +134,3 @@ impl FighterStateImpl for LedgeActionState {
         self.is_in_grounded_phase
     }
 }
-

src/fighter/state/ledge_wait.rs

@@ -3,9 +3,9 @@ use crate::fighter::animation::AnimKind;
 use crate::fighter::state::air::AirborneStateCommon;
 use crate::fighter::state::fall::FallState;
 use crate::fighter::state::FighterState;
-use crate::fighter::FighterFacingDirection;
 use crate::fighter::state::jump::JumpStateInitiator;
 use crate::fighter::state::ledge_action::{LedgeActionState};
+use crate::fighter::{FighterFacingDirection, FighterInvulnerabilityState};
 use crate::input::FighterCommands;
 use crate::math::vec::FGVec2;
 use crate::stage::line::{StageLedgeSide, StageVertexID};
@@ -58,6 +58,14 @@ impl FighterStateImpl for LedgeWaitState {
     fn on_enter(&mut self, state_context: &mut EnterContext) {
         state_context.velocity.0 = FGVec2::ZERO;
         state_context.knockback_velocity.0 = FGVec2::ZERO;
+        *state_context.vulnerability = FighterInvulnerabilityState::Intangible {
+            frames_remaining: Some(
+                state_context
+                    .game_settings
+                    .fighter_common
+                    .ledge_grab_invulnerability_duration,
+            ),
+        };
         let Some(ledge) = state_context.stage_collision.find_ledge_by_vertex(self.ledge_id) else {
             return;
         };
@@ -127,4 +135,3 @@ fn is_ledge_drop_input(
 
     false
 }
-

src/fighter/state/mod.rs

@@ -195,6 +195,10 @@ impl EnterContext<'_> {
                 + animation_position_to_gameplay(position, self.facing_direction),
         )
     }
+
+    pub fn get_animation_duration(&self, kind: AnimKind) -> Option<usize> {
+        self.baked_animations.get_animation_duration(kind)
+    }
 }
 
 pub struct ExitContext<'a> {