- engine-requests: a unit knocked out on its landing tile comes back there; a
retreated one still comes back home.
- robustness: the busy-tile spawnToken check uses the tile the guard stands on
after its redeploy (where it was knocked out).
- docs-consistency: SIM.md's b.snap `down` entry carries row, col; the DESIGN
check accepts the shape before and after the integrator's §8.2 update.