Layering for atmospheric pipes (#36124)

Co-authored-by: ArtisticRoomba <145879011+ArtisticRoomba@users.noreply.github.com>
Co-authored-by: Kevin Zheng <kevinz5000@gmail.com>

Content.Server/NodeContainer/Nodes/PipeNode.cs

@@ -1,10 +1,8 @@
-using Content.Server.Atmos;
 using Content.Server.NodeContainer.EntitySystems;
 using Content.Server.NodeContainer.NodeGroups;
 using Content.Shared.Atmos;
+using Content.Shared.Atmos.Components;
 using Content.Shared.NodeContainer;
-using Content.Shared.NodeContainer.NodeGroups;
-using Robust.Shared.Map;
 using Robust.Shared.Map.Components;
 using Robust.Shared.Utility;
 
@@ -12,7 +10,7 @@ namespace Content.Server.NodeContainer.Nodes
 {
     /// <summary>
     ///     Connects with other <see cref="PipeNode"/>s whose <see cref="PipeDirection"/>
-    ///     correctly correspond.
+    ///     and <see cref="CurrentPipeLayer"/> correctly correspond.
     /// </summary>
     [DataDefinition]
     [Virtual]
@@ -24,6 +22,12 @@ namespace Content.Server.NodeContainer.Nodes
         [DataField("pipeDirection")]
         public PipeDirection OriginalPipeDirection;
 
+        /// <summary>
+        ///     The *current* layer to which the pipe node is assigned.
+        /// </summary>
+        [DataField("pipeLayer")]
+        public AtmosPipeLayer CurrentPipeLayer = AtmosPipeLayer.Primary;
+
         /// <summary>
         ///     The *current* pipe directions (accounting for rotation)
         ///     Used to check if this pipe can connect to another pipe in a given direction.
@@ -204,6 +208,7 @@ namespace Content.Server.NodeContainer.Nodes
             foreach (var pipe in PipesInDirection(pos, pipeDir, grid, nodeQuery))
             {
                 if (pipe.NodeGroupID == NodeGroupID
+                    && pipe.CurrentPipeLayer == CurrentPipeLayer
                     && pipe.CurrentPipeDirection.HasDirection(pipeDir.GetOpposite()))
                 {
                     yield return pipe;