Corridors carve center-to-center and pierce room walls, so the old
wall-threshold rule placed almost no doors. Detect the pierced-wall
threshold (corridor floor outside a room, room on one side, corridor on
the opposite) and mark it Door with probability door_chance (default
0.5), else leave it an open archway. Connectivity is via corridor floor,
independent of doors.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
