TDD characterisation test proving PortalVisibilityBuilder.Build correctly roots at the
outdoor cell node (OutdoorCellNode) and floods into adjacent buildings through their
entrance portals. No changes to Build or OutdoorCellNode were needed.
Key finding: the task spec's building fixture used InsideSide=0 for an exit portal whose
building interior is at Y>=5 (Normal=(0,-1,0), D=5). The correct InsideSide is 1
(interior where dot<=0 -> Y>=5); with InsideSide=0 the outdoor camera (Y=-3, dot=8)
incorrectly passes as "interior" of the building so OutdoorCellNode.Build's InsideSide
flip (0->1) puts the outdoor camera on the wrong side of the gate.
Corrected fixture uses InsideSide=1 matching OutdoorCellNodeTests geometry convention
(building interior = POSITIVE dot side, outdoor = negative dot side; flip makes outdoor
negative-dot side the traversable direction). Both tests pass; full suite 214/214.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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