Retail CEnvCell::check_building_transit (Ghidra 0x0052c5d0) opens with
`if (other_portal_id >= 0)` on the SIGNED sign-extended portal id
(CBldPortal.other_portal_id is int, acclient.h:32098). Our BldPortalInfo
carried the dat reader's raw ushort and CheckBuildingTransit had no gate
at all, so a portal whose dat value is 0xFFFF (-1, "no reciprocal
portal") could admit its interior cell. BN's pseudo-C renders the
comparison unsigned - the sign-extension is Ghidra-proven (BR-7 verified
corrections, wf1-interior-collision.md).
- BldPortalInfo.OtherPortalId: ushort -> short; GameWindow construction
reinterprets the dat ushort via unchecked((short)).
- CheckBuildingTransit: negative-id portals rejected before any sphere
test; new multi-sphere overload matching retail's per-sphere loop
(0052c5fe, first-hit admits) with the hits_interior_cell output
(0052c650) the BR-7 building channel consumes next.
- Tests: negative-id skip vs positive-id admit on a leaf-root CellBSP;
multi-sphere plumbing + zero-sphere no-op.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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