fix: stale connection config hash and a batched entry skipped by a deregister

Both raised by the automated review on PR #4123.

GetConfig caches, and ClearConfigHash only ran on shutdown, so a GetConfig
call made before the session started cached a hash built from the default
ActiveTransformSyncMode. Initialize then captured the authored mode and the
server compared connecting clients against the stale hash, rejecting them
for a configuration mismatch. Clear the cache where the mode is captured.

RunDeltaCheck iterates by index so an instance that despawns from within its
own state update callback cannot invalidate the iteration, but Deregister
swaps the last registered instance into the vacated slot and the increment
then stepped straight over it. Its entry was already complete, so it was a
tick of delay for no reason.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Components/NetworkTransformStateManager.cs

@@ -613,12 +613,16 @@ internal void RunDeltaCheck()
                 var instance = m_Instances[i];
                 var entry = Entries[i];
                 instance.ApplyBatchedDeltaEntry(ref entry);
-                // The instance may have deregistered while applying, in which case this slot now belongs to a
-                // different instance and must not be written back.
                 if (instance.StateManagerIndex == i)
                 {
                     Entries[i] = entry;
+                    continue;
                 }
+
+                // The instance deregistered while applying, which swapped the last registered instance and
+                // its already completed entry into this slot. Hold the index so that instance is applied on
+                // the tick it was detected on as opposed to being skipped by the increment.
+                i--;
             }
         }
 

com.unity.netcode.gameobjects/Runtime/Core/NetworkManager.cs

@@ -1258,6 +1258,10 @@ internal void Initialize(bool server)
             // session UI without a mid-session write splitting a running session across both modes.
             NetworkConfig.ActiveTransformSyncMode = NetworkConfig.TransformSyncMode;
 
+            // The captured mode is part of the connection configuration hash, so drop anything GetConfig
+            // cached before the session started or the server compares connecting clients against it.
+            NetworkConfig.ClearConfigHash();
+
             // Always create a default session config when starting a NetworkManager instance
             if (DistributedAuthorityMode)
             {