test(vehicle): clamping the velocity to zero does not stop the rise - the transform is written

The decisive clamp: zero linear and angular velocity every frame for two seconds.

  t=0.25 Z=3220 vZ=0 | t=0.75 Z=3683 vZ=0 | t=1.25 Z=4197 vZ=0

It rises at ~1200 cm/s with velocity pinned to zero, so this is not a force, an impulse, or a bad initial
state - all of those the clamp would have removed. Something calls a transform setter on the vehicle every
frame.

Our own source contains exactly one direct transform write outside the character (the shot actor's camera),
so the writer is engine-side: the Chaos vehicle component driving UpdatedComponent from a vehicle state that
was never created, or a skeletal-mesh transform update.

Also diffed the two maps, since the pawn works in ReviewMap and not in DemoMap: kill_z, gravity, lights and
partitioning are identical; DemoMap adds 593 static mesh actors, a height fog and a post-process volume,
ReviewMap adds a shot actor and the character. Nothing in either list can write a transform, so the map
difference is not in its actors or settings.

Game/GigLine/Source/GigLine/GigLineVehicle.cpp

@@ -359,6 +359,17 @@ void AGigLineVehicle::Tick(float DeltaSeconds)
 		}
 	}
 
+	// Kill any injected velocity every frame for the first two seconds. If the pawn still rises, the
+	// writer sets the transform directly; if it settles, the whole thing was one bad initial impulse.
+	if (SettleElapsed < 2.0f)
+	{
+		if (USkeletalMeshComponent* Body = GetMesh())
+		{
+			Body->SetPhysicsLinearVelocity(FVector::ZeroVector);
+			Body->SetPhysicsAngularVelocityInDegrees(FVector::ZeroVector);
+		}
+	}
+
 	// Velocity profile: an impulse shows as a spike at t=0, a force as steady growth.
 	{
 		static float NextSample = 0.0f;

TODO.md

@@ -63,6 +63,18 @@ DemoMap, 25 m above ground:    Z 2496 -> 2664 -> 3068 -> 3434    vZ +1509
 
 **So the Chaos rig is fine and `DemoMap` is what breaks it** - at any height, anywhere in that map, and not by contact (25 m in the air launches immediately). The next comparison is between the two maps' world settings and level actors: `ReviewMap` was built by `Tools/ue_build_review_map.py`, `DemoMap` by `Tools/ue_build_demo_map.py`, and the difference that matters is in what one stages and the other does not.
 
+### The transform is written directly, not moved
+
+Zeroing the body's linear and angular velocity **every frame** for two seconds changes nothing:
+
+```
+t=0.25 Z=3220 vZ=0   t=0.75 Z=3683 vZ=0   t=1.25 Z=4197 vZ=0
+```
+
+The actor keeps rising at ~1200 cm/s while its velocity is pinned to zero. **Something calls a transform setter on the vehicle every frame** - this is not a force, an impulse or a bad initial state, all of which the clamp would have removed.
+
+`Game/GigLine/Source/GigLine/*.cpp` contains exactly one direct transform write outside the character (`GigLineShotActor` moves its camera), so the writer is engine-side: the Chaos vehicle component driving `UpdatedComponent` from a vehicle state that was never created, or a skeletal-mesh transform update.
+
 ### Bisect plan for the next pass
 
 1. Spawn the same pawn in `ReviewMap` (flat 160 m floor, no slices, no UCX ground) and repeat the profile. Flies there too -> the asset/component is at fault. Settles there -> something in `DemoMap` (the UCS slabs, the terrain, or the world settings) drives it.
@@ -92,6 +104,18 @@ DemoMap, 25 m above ground:    Z 2496 -> 2664 -> 3068 -> 3434    vZ +1509
 
 **So the Chaos rig is fine and `DemoMap` is what breaks it** - at any height, anywhere in that map, and not by contact (25 m in the air launches immediately). The next comparison is between the two maps' world settings and level actors: `ReviewMap` was built by `Tools/ue_build_review_map.py`, `DemoMap` by `Tools/ue_build_demo_map.py`, and the difference that matters is in what one stages and the other does not.
 
+### The transform is written directly, not moved
+
+Zeroing the body's linear and angular velocity **every frame** for two seconds changes nothing:
+
+```
+t=0.25 Z=3220 vZ=0   t=0.75 Z=3683 vZ=0   t=1.25 Z=4197 vZ=0
+```
+
+The actor keeps rising at ~1200 cm/s while its velocity is pinned to zero. **Something calls a transform setter on the vehicle every frame** - this is not a force, an impulse or a bad initial state, all of which the clamp would have removed.
+
+`Game/GigLine/Source/GigLine/*.cpp` contains exactly one direct transform write outside the character (`GigLineShotActor` moves its camera), so the writer is engine-side: the Chaos vehicle component driving `UpdatedComponent` from a vehicle state that was never created, or a skeletal-mesh transform update.
+
 ### Bisect plan for the next pass
 
 1. Spawn the same pawn in `ReviewMap` (flat 160 m floor, no slices, no UCX ground) and repeat the profile. Flies there too -> the asset/component is at fault. Settles there -> something in `DemoMap` (the UCS slabs, the terrain, or the world settings) drives it.