Adds a new public overload accepting an explicit IReadOnlyCollection<uint>
cellIds (the camera-buildings' EnvCellIds) instead of a BFS-derived
visibility set. Used by RR7's IndoorPass to scope indoor rendering to the
camera-buildings' cells, not the full portal BFS (which causes Issues A+C).
Pure-data test helper WalkEntitiesForTestByCellIds added alongside the
production overload, mirroring the WalkEntitiesForTest pattern.
The overload internally delegates to the existing visibleCellIds path —
the dispatcher's semantic stays the same; only the caller's intent differs
(explicit cell list vs visibility-derived).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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