Grounds the visible-cell SET in the stable per-cell PVS (stab_list) + seen_outside,
refreshed on cell entry, the way retail does (grab_visible_cells 311878, add_views
433382, DrawInside 433793). Our PortalVisibilityBuilder rebuilds the set per-frame
from a pose-brittle CameraOnInteriorSide walk, so a flipped side-test drops the exit
cell, empties OutsideView, and TerrainMode.Skip flaps terrain/shells off at the
doorway. Both stable inputs already live in-process (envCell.VisibleCells,
envCell.Flags & SeenOutside); U.4c is plumbing + grounding, not new dat parsing.
Apparatus-first: characterize the flap on a live ACDREAM_PROBE_VIS capture + port the
add_views/ClipPortals/AddToCell semantics to pseudocode before implementing; the
builder is not declared correct until a live [vis] shows non-empty + narrowing
OutsideView. No hysteresis band-aid (forbidden). Indoor rendering untouched.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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