update

Reverting some changes.
Adding NETCODE_UAC1001_CHECKS (for now) wrapped [Serializable] decorations to anything that is public and not already considered serializable.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Components/HalfVector3.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Runtime.CompilerServices;
 using Unity.Mathematics;
 using UnityEngine;
@@ -12,6 +13,9 @@ namespace Unity.Netcode.Components
     /// individual axis and the 16 bits of the half float are stored as <see cref="ushort"/> values since C# does not have
     /// a half float type.
     /// </remarks>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public struct HalfVector3 : INetworkSerializable
     {
         internal const int Length = 3;

com.unity.netcode.gameobjects/Runtime/Components/HalfVector4.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Runtime.CompilerServices;
 using Unity.Mathematics;
 using UnityEngine;
@@ -12,6 +13,9 @@ namespace Unity.Netcode.Components
     /// individual axis and the 16 bits of the half float are stored as <see cref="ushort"/> values since C# does not have
     /// a half float type.
     /// </remarks>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public struct HalfVector4 : INetworkSerializable
     {
         internal const int Length = 4;

com.unity.netcode.gameobjects/Runtime/Components/Interpolator/BufferedLinearInterpolator.cs

@@ -10,6 +10,9 @@ namespace Unity.Netcode
     /// Partially solves for message loss. Unclamped lerping helps hide this, but not completely
     /// </summary>
     /// <typeparam name="T">The type of interpolated value</typeparam>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif    
     public abstract class BufferedLinearInterpolator<T> where T : struct
     {
         // Constant absolute value for max buffer count instead of dynamic time based value. This is in case we have very low tick rates, so

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

@@ -1,3 +1,4 @@
+using System;
 using System.Runtime.CompilerServices;
 using Unity.Mathematics;
 using UnityEngine;
@@ -7,6 +8,9 @@ namespace Unity.Netcode.Components
     /// <summary>
     /// Used to synchromnize delta position when half float precision is enabled
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public struct NetworkDeltaPosition : INetworkSerializable
     {
         internal const float MaxDeltaBeforeAdjustment = 64f;

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

@@ -1,4 +1,5 @@
 #if COM_UNITY_MODULES_PHYSICS
+using System;
 using System.Collections.Generic;
 using Unity.Collections;
 using Unity.Jobs;
@@ -11,6 +12,9 @@ namespace Unity.Netcode.Components
     /// Information a <see cref="Rigidbody"/> returns to <see cref="RigidbodyContactEventManager"/> via <see cref="IContactEventHandlerWithInfo.GetContactEventHandlerInfo"/> <br />
     /// if the <see cref="Rigidbody"/> registers itself with <see cref="IContactEventHandlerWithInfo"/> as opposed to <see cref="IContactEventHandler"/>.
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public struct ContactEventHandlerInfo
     {
         /// <summary>

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -10,6 +10,9 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">The type for the list</typeparam>
     [GenerateSerializationForGenericParameter(0)]
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public class NetworkList<T> : NetworkVariableBase where T : unmanaged, IEquatable<T>
     {
         private NativeList<T> m_List = new NativeList<T>(64, Allocator.Persistent);

com.unity.netcode.gameobjects/Runtime/SceneManagement/NetworkSceneManager.cs

@@ -144,6 +144,9 @@ public class SceneEvent
     /// Main class for managing network scenes when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled.
     /// Uses the <see cref="SceneEventMessage"/> message to communicate <see cref="SceneEventData"/> between the server and client(s)
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public class NetworkSceneManager : IDisposable
     {
         internal const int InvalidSceneNameOrPath = -1;

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

@@ -11,6 +11,9 @@ namespace Unity.Netcode
     /// <summary>
     /// Class that handles object spawning
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public class NetworkSpawnManager
     {
         // Stores the objects that need to be shown at end-of-frame

com.unity.netcode.gameobjects/Runtime/Timing/NetworkTickSystem.cs

@@ -7,6 +7,9 @@ namespace Unity.Netcode
     /// Provides discretized time.
     /// This is useful for games that require ticks happening at regular interval on the server and clients.
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif
     public class NetworkTickSystem
     {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR

com.unity.netcode.gameobjects/Runtime/Timing/NetworkTime.cs

@@ -9,6 +9,9 @@ namespace Unity.Netcode
     /// Time is stored as a combination of amount of passed ticks + a duration offset.
     /// This struct is meant to replace the Unity <see cref="Time"/> API for multiplayer gameplay.
     /// </summary>
+#if NETCODE_UAC1001_CHECKS
+    [Serializable]
+#endif    
     public struct NetworkTime
     {
         private double m_TimeSec;