Access violation at startup — `ConstructorHelpers` in CDOs vs. the `PostConfigInit` loading phase

[M-Colley]

Describe the bug

Adding the Carla plugin to any project whose startup ordering differs from
CarlaUnreal's kills the process before a map is ever opened:

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x120
  ATrafficLightManager::ATrafficLightManager()
  ConstructorHelpers::FClassFinder<AActor>::FClassFinder<AActor>()
  StaticLoadClass() -> LoadPackage() -> FlushAsyncLoading()
  FLinkerLoad::CreateExport()
  FBlueprintCompilationManager::FlushCompilationQueue()
  UE::ProjectUtilities::FindModuleDescriptorHostType()
  FModuleManager::LoadModule()
  FLiveCodingModule::StartupModule()          <-- faults here
  UClass::CreateDefaultObject()
  UObjectLoadAllCompiledInDefaultProperties()
  ProcessNewlyLoadedUObjects()
  FEngineLoop::PreInitPostStartupScreen()

Cause

Carla.uplugin sets "LoadingPhase": "PostConfigInit", which it must: the
module registers global shaders (IMPLEMENT_SHADER_TYPE in
Util/CameraModelUtil.cpp) and those have to exist before the engine
initialises shader types — moving the module to Default instead trips
Assertion failed: !AreShaderTypesInitialized().

But that same phase means every CDO in the module is constructed inside
FEngineLoop::PreInitPostStartupScreen, and several of those constructors load
/Game/ packages:

file	what it loads
Traffic/TrafficLightManager.cpp	14 FClassFinders (traffic lights, stop/yield/speed-limit signs)
Commandlet/LoadAssetMaterialsCommandlet.cpp	RoadPainterPreset blueprint
Commandlet/PrepareAssetsForCookingCommandlet.cpp	7 material instances

Loading a Blueprint there drags the Kismet compilation manager into PreInit,
which lazily loads the LiveCoding module, whose StartupModule then creates a
CDO and dies in CastChecked<UPackage>. -NoLiveCoding does not help: it
disables the feature, not the module load.

LoadAssetMaterialsCommandlet additionally dereferences the finder result with
no null check (RoadPainterBlueprint.Object->GeneratedClass), so a genuinely
missing asset is an access violation rather than a log line.

Suggested fix

Do not load /Game/ assets from CDO constructors in a PostConfigInit module.
Resolve them on first use with LoadObject/LoadClass instead. For
ATrafficLightManager that means moving the 14 finders into a
LoadDefaultModels() called from GenerateSignalsAndTrafficLights(), which
already null-checks the models it needs. Plugin-mounted paths (/Carla/...,
as in OpenDriveActor.cpp) are fine — they mount with the module.

This is not hypothetical for other projects only: it is why the plugin cannot
currently be dropped into an existing Unreal project.

Environment

• CARLA ue58-dev-carla @ de3f38e64, CARLA fork of UE 5.8, Windows 11