# Physics Placement Evaluation

> **Evidence record — not current product guidance.** Use the [documentation index](../../../README.md) for current behavior and architecture.

Date: 2026-07-12

![Three selected props settled on the committed placement floor](physics-placement-settled.png)

The native Wayland editor is shown with the 2026-07-12 revision of
`assets/levels/physics_placement_showcase.scn.ron`. At that revision, Placement Prop A, B, and C were
multi-selected and released from three different heights through the hand/down-arrow action in the
existing horizontal viewport toolbar. The fixture now exposes those stable actor IDs as Placement
Cuboid, Placement Sphere, and Placement Capsule; its distinct-shape rerun is tracked by the
[sample-pack evaluation](../sample-regression-pack/).

## Acceptance

- In the recorded revision, all three props used hydrated Avian cuboid colliders and settled on
  Placement Floor after 1.5 simulated seconds.
- During preview the HUD reported selection count, simulated time, and Settled state; transform
  gizmos and viewport picking did not compete with the modal tool.
- Escape restored every starting transform and left history empty.
- A second run committed with Enter as exactly one `Undo: Move Selection` entry.
- Ctrl+Z restored all three elevated starting transforms; Ctrl+Y restored the settled transforms.
- Opening the fixture immediately after the terrain showcase no longer panicked on a stale
  generated terrain-material binding; the scene-switch regression is covered in
  `blacksite_surface`.
- The runtime log contained no physics-placement, scene-load, render-pipeline, or GPU validation
  error after the stale-binding fix.

Packaged-runtime tests remain intentionally deferred by project-owner request.