diff --git a/src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs b/src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs
index 0e6e47ed..064cb264 100644
--- a/src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs
+++ b/src/AcDream.App/Rendering/Wb/EnvCellRenderer.cs
@@ -349,6 +349,12 @@ public sealed unsafe class EnvCellRenderer : IDisposable
 
         lock (lb.Lock)
         {
+            // TEMP diagnostic #105 (strip with fix): a registration landing AFTER
+            // this landblock was already finalized starts a fresh pending list that
+            // only commits if ANOTHER finalize arrives — and that one will REPLACE
+            // (not merge) the committed set. One-shot per landblock per pending list.
+            if (lb.InstancesReady && lb.PendingInstances is null)
+                Console.WriteLine($"[late-register] lb=0x{landblockId:X8} cell=0x{envCellId:X8} registered AFTER finalize — starting a new pending list ({(lb.Instances?.Count ?? 0)} already committed)");
             lb.PendingInstances ??= new List<EnvCellSceneryInstance>(capacity: 32);
             lb.PendingInstances.Add(cellInstance);
             lb.PendingEnvCellBounds ??= new Dictionary<uint, WbBoundingBox>();
@@ -403,6 +409,13 @@ public sealed unsafe class EnvCellRenderer : IDisposable
         {
             if (lb.PendingInstances is not null)
             {
+                // TEMP diagnostic #105 (strip with fix): REPLACE semantics — if a
+                // previous finalize already committed instances for this landblock,
+                // this swap DISCARDS them in favor of the new pending set. A partial
+                // pending set (finalize racing a still-registering promote job)
+                // silently loses buildings.
+                if (lb.Instances is { Count: > 0 })
+                    Console.WriteLine($"[finalize-replace] lb=0x{landblockId:X8} DISCARDING {lb.Instances.Count} committed instances, replacing with {lb.PendingInstances.Count} pending");
                 lb.Instances = lb.PendingInstances;
                 lb.PendingInstances = null;
             }