Fix biome marker dupes (#23500)

diff --git a/Content.Server/Parallax/BiomeSystem.cs b/Content.Server/Parallax/BiomeSystem.cs
index 09e202a76dca620625e9758f3e7ef02912527357..871373e9f8fde88477866f1a20cb147c77cda7ca 100644 (file)
--- a/Content.Server/Parallax/BiomeSystem.cs
+++ b/Content.Server/Parallax/BiomeSystem.cs
@@ -631,8 +631,12 @@ public sealed partial class BiomeSystem : SharedBiomeSystem
                 }
 
                 DebugTools.Assert(layerProto.EntityMask.Count == 0 || !string.IsNullOrEmpty(proto));
+
+                // Don't fight other layers.
+                if (!spawnSet.TryAdd(node, proto))
+                    continue;
+
                 groupSize--;
-                spawnSet.Add(node, proto);
 
                 if (existing != null)
                 {