How can I determine which side of a RoomPlan wall surface contains the wall thickness?

I am using Apple RoomPlan and working with CapturedRoom.Surface objects representing walls.

From RoomPlan, I can get information such as:

• transform
• dimensions
• polygonCorners
• completedEdges

However, I am not sure how the returned wall surface should be interpreted geometrically.

Is the wall surface returned by RoomPlan:

• the centerline of the physical wall;
• the interior face of the wall;
• the exterior face of the wall; or
• simply an estimated 2D surface without any guarantee about wall thickness?

If I want to create a wall with thickness, for example when converting RoomPlan data to IFC or another BIM format, how can I determine which side of the returned surface the wall should be extruded toward?

Does RoomPlan provide any information such as:

• wall thickness;
• interior or exterior wall side;
• inward or outward normal;
• wall centerline;
• a full 3D wall boundary;
• or the opposite face of the wall?

I can calculate the surface normal from the third column of the wall transform and obtain the wall-face boundary using polygonCorners, but I do not know whether the positive normal points toward the room interior or exterior.

Is there an official or recommended way to determine the correct wall side, or must applications infer it from the room geometry and apply an assumed wall thickness?

Any clarification about the coordinate convention and intended geometric meaning of a RoomPlan wall surface would be appreciated.