Prevent relay recursion (#12597)

Fixes https://github.com/space-wizards/space-station-14/issues/12562

Content.Server/CardboardBox/CardboardBoxSystem.cs

@@ -54,7 +54,7 @@ public sealed class CardboardBoxSystem : SharedCardboardBoxSystem
         foreach (var mover in mobMover)
         {
             //Set the movement relay for the box as the first mob
-            if (component.Mover == null && args.Contents.Contains(mover))
+            if (component.Mover == null)
             {
                 var relay = EnsureComp<RelayInputMoverComponent>(mover);
                 _mover.SetRelay(mover, uid, relay);

Content.Shared/Movement/Systems/SharedMoverController.Input.cs

@@ -8,6 +8,7 @@ using Robust.Shared.Input.Binding;
 using Robust.Shared.Players;
 using Robust.Shared.Serialization;
 using Robust.Shared.Timing;
+using Robust.Shared.Utility;
 
 namespace Content.Shared.Movement.Systems
 {
@@ -190,6 +191,7 @@ namespace Content.Shared.Movement.Systems
 
                 if (relayMover.RelayEntity == null) return;
 
+                DebugTools.Assert(relayMover.RelayEntity != entity);
                 HandleDirChange(relayMover.RelayEntity.Value, dir, subTick, state);
                 return;
             }

Content.Shared/Movement/Systems/SharedMoverController.Relay.cs

@@ -1,6 +1,7 @@
 using Content.Shared.Movement.Components;
 using Robust.Shared.GameStates;
 using Robust.Shared.Serialization;
+using Robust.Shared.Utility;
 
 namespace Content.Shared.Movement.Systems;
 
@@ -22,6 +23,12 @@ public abstract partial class SharedMoverController
         if (!Resolve(uid, ref component))
             return;
 
+        if (uid == relayEntity)
+        {
+            Logger.Error($"An entity attempted to relay movement to itself. Entity:{ToPrettyString(uid)}");
+            return;
+        }
+
         component.RelayEntity = relayEntity;
         Dirty(component);
     }
@@ -37,6 +44,7 @@ public abstract partial class SharedMoverController
     {
         if (args.Current is not RelayInputMoverComponentState state) return;
 
+        DebugTools.Assert(state.Entity != uid);
         component.RelayEntity = state.Entity;
     }