assemble-scenelisted

# Scene assembly Represent one gameplay object with one named semantic root. Put gameplay position, heading, rigid-body, collision, and behavior on that root. Put calibrated render transforms below it. Consume the existing tuning record from `calibrate-model` exactly once. If it is missing, stop and calibrate the model; do not calculate or adjust asset tuning during assembly. ## Assembly rules - Name roots by gameplay role and use predictable names for repeated instances. - Apply model calibration once inside the visual child; never reapply scale, grounding, or authored yaw during placement. - Space neighbouring roots by their scaled footprints and pivot offsets from `calibrate-model`, not by pivot position. A non-90° authored yaw rotates a footprint, so reserve its larger horizontal extent as a conservative radius. - Put rigid-body and collision components on the same root. Size colliders from measured bounds. - Use local transforms below a parent and world transforms only for semantic roots. - Keep UI, effects, cameras, and lights outside gameplay model hierarchies. - Remove the root through its authoring surface's lifecycle. Unregister external events it owns. - Do not scale rigid-body roots or skinned bones. ## Prove placement Declare intentional support, attachment, or containment relationships between roots. After a rendered frame, measure each relationship at the supported object's actual position. Use a mount point, collision ray, or geometry sample; use a