Root cause: barriers were zero-thickness MeshCollider planes with no CCD on the
car. The car tunnelled through between frames. Every Python patch was trying to
catch in code what physics should enforce.
Unity (source only — build in progress):
- RoadBuilder.cs: CreateBarrier() now makes BoxCollider-per-segment with real 3D
volume (barrierThickness=1.0m default) + half-thickness overlap at corners to
seal gaps. CreateEndCap() seals open ends of non-looping tracks (generated_road).
- Car.cs: rb.collisionDetectionMode = Continuous in Awake() — prevents tunneling.
Python:
- reward_wrapper.py v7: removed CTE-patience termination, high-CTE negative
reward, solid_hit monitoring, low-speed/wedge detection. Kept: efficiency gate,
no-progress (active_node) termination, lap exploit guard. Reward = speed×CTE_quality.
- exp23_generated_road_clean.py: single track, no warm-start, 200k steps, clean
reward, MAX_EPISODE_SECONDS=120 as safety net only.
- tests: 17 tests covering clean reward properties.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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