diff --git a/Assets/Scripts/ServerShared/CultCache/CultCache.cs b/Assets/Scripts/ServerShared/CultCache/CultCache.cs
index e8b494c62..0f143c586 100644
--- a/Assets/Scripts/ServerShared/CultCache/CultCache.cs
+++ b/Assets/Scripts/ServerShared/CultCache/CultCache.cs
@@ -38,7 +38,7 @@ public class CultCache
             if (type.GetCustomAttribute<GlobalSettingsAttribute>() != null)
             {
                 _globals[type] = null;
-                Add(Activator.CreateInstance(type) as DatabaseEntry);
+                AddInternal(Activator.CreateInstance(type) as DatabaseEntry);
             }
         }
     }
@@ -56,7 +56,7 @@ public class CultCache
         }
         store.EntryAdded.Subscribe(entry =>
         {
-            Add(entry, store);
+            AddInternal(entry, store);
         });
     }
 
@@ -67,6 +67,14 @@ public class CultCache
     }
 
     public void Add(DatabaseEntry entry, CacheBackingStore source = null)
+    {
+        if (ReadOnly && source == null)
+            throw new InvalidOperationException("Legacy CultCache is read-only. Durable state belongs to the Verse state spine.");
+
+        AddInternal(entry, source);
+    }
+
+    private void AddInternal(DatabaseEntry entry, CacheBackingStore source = null)
     {
         lock(addLock)
         {
@@ -102,9 +110,12 @@ public class CultCache
 
     public void AddAll(IEnumerable<DatabaseEntry> entries)
     {
+        if (ReadOnly)
+            throw new InvalidOperationException("Legacy CultCache is read-only. Durable state belongs to the Verse state spine.");
+
         foreach (var entry in entries)
         {
-            Add(entry);
+            AddInternal(entry);
         }
     }
 
@@ -144,6 +155,9 @@ public class CultCache
 
     public void Remove(DatabaseEntry entry, CacheBackingStore source = null)
     {
+        if (ReadOnly && source == null)
+            throw new InvalidOperationException("Legacy CultCache is read-only. Durable state belongs to the Verse state spine.");
+
         _entries.Remove(entry.ID);
         var type = entry.GetType();
         foreach (var parentType in type.GetParentTypes())
diff --git a/docs/aetheria-perfect-machine-map.md b/docs/aetheria-perfect-machine-map.md
index 50f4c1211..e1ede4389 100644
--- a/docs/aetheria-perfect-machine-map.md
+++ b/docs/aetheria-perfect-machine-map.md
@@ -36,7 +36,9 @@ local CultCache, and legacy UI paths should be migration-only or deleted.
   MessagePack backing stores may hydrate in-memory domain objects for the
   current Unity runtime, but this path cannot push or delete legacy files. The
   legacy backing-store abstraction is pull-only; its write and realtime
-  watcher APIs have been deleted.
+  watcher APIs have been deleted. Public `Add`, `AddAll`, and `Remove` calls
+  against the read-only cache are rejected; only backing-store pull hydration
+  can populate it.
 - `DatabaseLink<T>.Value` can resolve legacy links only after
   `LegacyCatalogBoundary` binds the read-only catalog cache. `CultCache`
   construction no longer grabs global `DatabaseLinkBase` authority.