Fix some buckling bugs (#10759)

Content.Server/Buckle/Systems/BuckleSystem.cs

@@ -85,6 +85,9 @@ namespace Content.Server.Buckle.Systems
 
         private void ContainerModifiedStrap(EntityUid uid, StrapComponent strap, ContainerModifiedMessage message)
         {
+            if (GameTiming.ApplyingState)
+                return;
+
             foreach (var buckledEntity in strap.BuckledEntities)
             {
                 if (!EntityManager.TryGetComponent(buckledEntity, out BuckleComponent? buckled))

Content.Shared/Buckle/SharedBuckleSystem.cs

@@ -5,11 +5,14 @@ using Content.Shared.Movement.Events;
 using Content.Shared.Standing;
 using Content.Shared.Throwing;
 using Robust.Shared.Physics.Dynamics;
+using Robust.Shared.Timing;
 
 namespace Content.Shared.Buckle
 {
     public abstract class SharedBuckleSystem : EntitySystem
     {
+        [Dependency] protected readonly IGameTiming GameTiming = default!;
+
         public override void Initialize()
         {
             base.Initialize();
@@ -28,6 +31,20 @@ namespace Content.Shared.Buckle
             // TODO: This looks dirty af.
             // On rotation of a strap, reattach all buckled entities.
             // This fixes buckle offsets and draw depths.
+            // This is mega cursed. Please somebody save me from Mr Buckle's wild ride.
+
+            // Consider a chair that has a player strapped to it. Then the client receives a new server state, showing
+            // that the player entity has moved elsewhere, and the chair has rotated. If the client applies the player
+            // state, then the chairs transform comp state, and then the buckle state. The transform state will
+            // forcefully teleport the player back to the chair (client-side only). This causes even more issues if the
+            // chair was teleporting in from nullspace after having left PVS.
+            //
+            // One option is to just never trigger re-buckles during state application.
+            // another is to.. just not do this? Like wtf is this code. But I CBF with buckle atm.
+
+            if (GameTiming.ApplyingState)
+                return;
+
             foreach (var buckledEntity in component.BuckledEntities)
             {
                 if (!EntityManager.TryGetComponent(buckledEntity, out SharedBuckleComponent? buckled))
@@ -35,6 +52,12 @@ namespace Content.Shared.Buckle
                     continue;
                 }
 
+                if (!buckled.Buckled || buckled.LastEntityBuckledTo != uid)
+                {
+                    Logger.Error($"A moving strap entity {ToPrettyString(uid)} attempted to re-parent an entity that does not 'belong' to it {ToPrettyString(buckledEntity)}");
+                    continue;
+                }
+
                 buckled.ReAttach(component);
                 Dirty(buckled);
             }