A town's outer/perimeter walls have NO collision even on a fresh login: the
player walks straight through them while houses block fine. Confirmed NOT a
frame issue — #146's bldOrigin probe showed Arwic buildings are correctly
framed (~12 m from the player, not km off), so the "#145 far-town frame"
premise was wrong here.
Root cause (dat-confirmed, Issue147ArwicBuildingsDumpTests): a perimeter wall
is stored in LandBlockInfo.Buildings as a doorless shell — 16 of Arwic's 30
buildings are PORTAL-LESS, ringing the town at 24 m intervals (x=12/132,
y=12/108). The building-collision cache loop skipped them via
`if (building.Portals.Count == 0) continue;` — a filter meant only for the
transit/entry feature (CellTransit.CheckBuildingTransit) that also dropped the
collision shell. Retail's find_building_collisions (0x006b5300) tests the shell
BSP independent of the portal list, so a doorless wall still collides.
Fix: don't skip portal-less buildings — cache them with an empty portal list
(no transit) but their collision shell (ModelId) intact. User-verified: Arwic
perimeter walls now block (Collided/Slid). Adds the dat-dump fixture test.
Suites green: Core 1569(+2 skip), App 468(+2 skip), UI 425, Net 317.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
