When the chase camera roots in a thin doorway cell and the eye stands in an interior portal opening (live capture: vestibule->room portal D=0.16m, proj=0), the 2D projection degenerates and the neighbour was culled (cells=1) -> only the thin cell drew -> bluish void / transparent ceiling. Retail's 3D clip imposes no constraint for a portal the eye is inside, so the neighbour is fully visible. When the clipped region is empty but the eye stands in the opening (EyeInsidePortalOpening: within 0.5m of the portal plane AND point-in-opening), flood the neighbour with the current view. Guarded so an off-screen degenerate portal stays culled (no #95 blowup; over-include is mesh-frustum-culled at draw). Visual-verified: cellar ceiling now solid.
Band-aid for thin-cell-root coverage; likely superseded by the boom-stability + viewer-cell dead-zone + w=0 near-plane clip fix next session (reassess / maybe revert). 2 RED->GREEN tests; cyclic/hub termination guards unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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