Update() now always sets ViewerCellId: the camera-collision sweep's swept cell when collision
is on (retail viewer_cell = sphere_path.curr_cell), else the passed player cell. This is the
robust, per-frame, graph-tracked 'which cell is the camera in?' answer that V1 roots the render
on — no AABB, no grace frames (the U.4c flap source). 176 App tests green (2 new).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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