fix(collision): terrain bbox proxy buried the whole street

The player never fell through - it stood on an invisible 8 m box. The
imported Terrain_DEM carried only a bounding-box simple collision proxy,
so every downward trace in the block hit Demo_Terrain_DEM at Z 819 (the
mesh bbox max) and the road/sidewalk underneath were unreachable. The
view from up there looked plausible, which is why it read as working.

- add UGigLineAssetTools (C++): set complex-as-simple collision on a
  static mesh; UE 5.8 exposes ECollisionTraceFlag, not
  bUseComplexAsSimpleCollision, and Python cannot set it at all.
- builder forces + saves the terrain asset as complex-as-simple (the flag
  lives on the asset, so saving only the .umap loses it).
- spawn (-13336, -1150, 600): inside the carved corridor; lands on the
  road at Z 456 (feet 368 on road top 366).
- HighResShot 1280x720, not "1280 720" (that is multiplier 1280).
- keep SIM + single ground-probe diagnostics (TEMP QA).

Game/GigLine/Source/GigLine/GigLineAssetTools.cpp

@@ -0,0 +1,65 @@
+#include "GigLineAssetTools.h"
+
+#include "Engine/StaticMesh.h"
+#include "PhysicsEngine/BodySetup.h"
+#include "StaticMeshResources.h"
+
+void UGigLineAssetTools::SetComplexCollisionAsSimple(UStaticMesh* Mesh, bool bEnable)
+{
+	if (!Mesh)
+	{
+		return;
+	}
+
+	UBodySetup* BodySetup = Mesh->GetBodySetup();
+	if (!BodySetup)
+	{
+		return;
+	}
+
+	BodySetup->CollisionTraceFlag = bEnable ? CTF_UseComplexAsSimple : CTF_UseSimpleAndComplex;
+	BodySetup->InvalidatePhysicsData();
+	BodySetup->CreatePhysicsMeshes();
+	Mesh->MarkPackageDirty();
+	Mesh->PostEditChange();
+}
+
+void UGigLineAssetTools::ClearSimpleCollision(UStaticMesh* Mesh)
+{
+	if (!Mesh)
+	{
+		return;
+	}
+
+	UBodySetup* BodySetup = Mesh->GetBodySetup();
+	if (!BodySetup)
+	{
+		return;
+	}
+
+	BodySetup->AggGeom.EmptyElements();
+	BodySetup->InvalidatePhysicsData();
+	BodySetup->CreatePhysicsMeshes();
+	Mesh->MarkPackageDirty();
+	Mesh->PostEditChange();
+}
+
+FString UGigLineAssetTools::GetCollisionComplexity(UStaticMesh* Mesh)
+{
+	if (!Mesh)
+	{
+		return TEXT("no mesh");
+	}
+
+	const UBodySetup* BodySetup = Mesh->GetBodySetup();
+	if (!BodySetup)
+	{
+		return TEXT("no body setup");
+	}
+
+	const int32 Flag = static_cast<int32>(BodySetup->CollisionTraceFlag.GetValue());
+	if (Flag == CTF_UseComplexAsSimple) { return TEXT("UseComplexAsSimple"); }
+	if (Flag == CTF_UseSimpleAsComplex) { return TEXT("UseSimpleAsComplex"); }
+	if (Flag == CTF_UseSimpleAndComplex) { return TEXT("UseSimpleAndComplex"); }
+	return TEXT("ProjectDefault");
+}

Game/GigLine/Source/GigLine/GigLineAssetTools.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "CoreMinimal.h"
+#include "Kismet/BlueprintFunctionLibrary.h"
+#include "GigLineAssetTools.generated.h"
+
+class UStaticMesh;
+
+/**
+ * Small editor-side helpers for the headless asset pipeline scripts.
+ *
+ * Exposed to Python so tools can fix up imported meshes that the Interchange
+ * importer gives unusable default collision. The terrain is the motivating
+ * case: without complex-as-simple it gets a bounding-box proxy, so the whole
+ * street sits under an invisible 8 m box and the player walks on the box lid.
+ */
+UCLASS()
+class GIGLINE_API UGigLineAssetTools : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+
+public:
+	/** Make collision trace against the mesh triangles instead of a proxy hull. */
+	UFUNCTION(BlueprintCallable, Category = "GigLine|Assets")
+	static void SetComplexCollisionAsSimple(UStaticMesh* Mesh, bool bEnable = true);
+
+	/** Drop any generated simple collision (hulls/boxes) from the mesh. */
+	UFUNCTION(BlueprintCallable, Category = "GigLine|Assets")
+	static void ClearSimpleCollision(UStaticMesh* Mesh);
+
+	/** Report the current collision complexity: "SimpleAndComplex", "Simple", ... */
+	UFUNCTION(BlueprintCallable, Category = "GigLine|Assets")
+	static FString GetCollisionComplexity(UStaticMesh* Mesh);
+};

Game/GigLine/Source/GigLine/GigLineCharacter.cpp

@@ -134,7 +134,7 @@ void AGigLineCharacter::BeginPlay()
 	{
 		if (APlayerController* PC = Cast<APlayerController>(GetController()))
 		{
-			PC->ConsoleCommand(TEXT("HighResShot 1280 720"));
+			PC->ConsoleCommand(TEXT("HighResShot 1280x720"));
 		}
 	}, 1.5f, false);
 
@@ -146,15 +146,26 @@ void AGigLineCharacter::BeginPlay()
 	{
 		UCharacterMovementComponent* M = GetCharacterMovement();
 		UE_LOG(LogTemp, Log,
-			TEXT("GigLine SIM: t=%.2f Z=%.0f grav=%.1f fall=%d local=%d role=%d mode=%d ctrl=%s"),
+			TEXT("GigLine SIM: t=%.2f XYZ=(%.0f,%.0f,%.0f) grav=%.1f fall=%d local=%d role=%d mode=%d ctrl=%s"),
 			GetWorld() ? GetWorld()->GetTimeSeconds() : -1.f,
-			GetActorLocation().Z,
+			GetActorLocation().X, GetActorLocation().Y, GetActorLocation().Z,
 			M ? M->GetGravityZ() : 0.f,
 			(M && M->IsFalling()) ? 1 : 0,
 			IsLocallyControlled() ? 1 : 0,
 			(int)GetLocalRole(),
 			M ? (int)M->MovementMode : -1,
 			GetController() ? *GetController()->GetName() : TEXT("NONE"));
+		if (UWorld* W = GetWorld())
+		{
+			const FVector L = GetActorLocation();
+			FHitResult Hit;
+			FCollisionQueryParams Q(TEXT("GigLineGroundProbe"), false, this);
+			const bool bHit = W->LineTraceSingleByChannel(Hit,
+				FVector(L.X, L.Y, 3000.f), FVector(L.X, L.Y, -3000.f), ECC_Visibility, Q);
+			UE_LOG(LogTemp, Log, TEXT("GigLine GROUND: top=%.0f actor=%s"),
+				bHit ? Hit.ImpactPoint.Z : -9999.f,
+				bHit && Hit.GetActor() ? *Hit.GetActor()->GetActorLabel() : TEXT("none"));
+		}
 	}, 1.0f, true);
 }