Extracts contour polygons from the bitmap region around chunk.
The returned contours use world coordinates (per CLAUDE.md hard rule
#4). Each contour's closed flag indicates whether the polyline closes
within the sampled region; contours that pass through a chunk boundary
may be reported as closed: false from a single chunk's perspective
and will be stitched across chunks by the physics adapter (Phase 2).
Extracts contour polygons from the bitmap region around
chunk.The returned contours use world coordinates (per CLAUDE.md hard rule #4). Each contour's
closedflag indicates whether the polyline closes within the sampled region; contours that pass through a chunk boundary may be reported asclosed: falsefrom a single chunk's perspective and will be stitched across chunks by the physics adapter (Phase 2).