Fix for holoparasite's ability to attack the host through mech (#36659)

Content.Shared/Mech/EntitySystems/SharedMechSystem.Relay.cs

@@ -0,0 +1,40 @@
+using Content.Shared.Interaction.Events;
+using Content.Shared.Mech.Components;
+
+namespace Content.Shared.Mech.EntitySystems;
+
+public abstract partial class SharedMechSystem
+{
+    private void InitializeRelay()
+    {
+        SubscribeLocalEvent<MechComponent, GettingAttackedAttemptEvent>(RelayRefToPilot);
+    }
+
+    private void RelayToPilot<T>(Entity<MechComponent> uid, T args) where T : class
+    {
+        if (uid.Comp.PilotSlot.ContainedEntity is not { } pilot)
+            return;
+
+        var ev = new MechPilotRelayedEvent<T>(args);
+
+        RaiseLocalEvent(pilot, ref ev);
+    }
+
+    private void RelayRefToPilot<T>(Entity<MechComponent> uid, ref T args) where T :struct
+    {
+        if (uid.Comp.PilotSlot.ContainedEntity is not { } pilot)
+            return;
+
+        var ev = new MechPilotRelayedEvent<T>(args);
+
+        RaiseLocalEvent(pilot, ref ev);
+
+        args = ev.Args;
+    }
+}
+
+[ByRefEvent]
+public record struct MechPilotRelayedEvent<TEvent>(TEvent Args)
+{
+    public TEvent Args = Args;
+}